ALBERT

Description: Dense SrLa( R 0.5 Ti 0.5 )O 4 ( R= Mg, Zn) ceramics were prepared by a standard solid-state reaction method. The single phase with complex K 2 NiF 4 -type layered perovskite structure and I 4/ mmm space group was revealed by XRD, and the refined structure was analyzed by Rietveld analysis. Significantly improved dielectric constant was obtained in SrLa( R 0.5 Ti 0.5 )O 4 ceramics compared to the analogues SrLaAlO 4 and SrLaGaO 4 , which is attributed to the increasing normalized bond lengths of Sr/La-O(1) and Sr/La-O(2a) bonds and the higher polarizability of ( R 0.5 Ti 0.5 ) 3+ than Al 3+ and Ga 3+ . In addition, τ f converts to a positive value with the increase in dielectric constant. The following microwave dielectric properties were obtained in the dense ceramics: ε r =25.5, Qf= 72 000 GHz, τ f = 29 ppm/°C for SrLa(Mg 0.5 Ti 0.5 )O 4 , and ε r =29.4, Qf= 34 000 GHz, τ f = 38 ppm/°C for SrLa(Zn 0.5 Ti 0.5 )O 4. Furthermore, the stability of K 2 NiF 4 -type structure in MLnB O 4 [ M =Ca, Sr, Ba; Ln =Y, Sm, Nd, La; B= Al, Ga, (Mg 0.5 Ti 0.5 ), (Zn 0.5 Ti 0.5 )] compounds was discussed in relation to the tolerance factor of perovskite layer and the radius ratio of M 2+ and Ln 3+ , based on which near-zero τ f values are expected to be obtained in SrLa( R 0.5 Ti 0.5 )O 4 -SrLaAlO 4 and SrLa( R 0.5 Ti 0.5 )O 4 –SrLaGaO 4 unlimited solid solutions.

Description: The oxygen nonstoichiometry of SrFeO 3−δ was determined by solid-state Coulometric titration at 750°C-1040°C and 10 −18 ≤ p O 2 (atm)≤0.5. At T ≤850°C, a hysteresis in the oxygen nonstoichiometry (δ) isotherms indicates the presence of a two-phase region corresponding to a mixture of a perovskite and an oxygen vacancy ordered phase. The variation of δ with temperature at fixed p O 2 values and the variation of log( p O 2 ) with reciprocal temperature at fixed δ are reported. The p O 2 at the p - n transition in the electrical conductivity increases as the temperature increases, and the transition in the conductivity isotherm occurs at a composition of SrFeO 2.505(1) at 950°C and SrFeO 2.508(1) at 900°C. Since strontium exclusively occupies the A-site, a simple point defect model that assumes noninteracting defects can describe the isotherms but only at 1040°C; nonideal behavior is observed at lower temperatures. The partial molar thermodynamic quantities for oxygen in SrFeO 3−δ were determined.

Description: The Ag 2 Mo 2 O 7 and Ag 6 Mo 10 O 33 ceramics for ultra-low temperature co-fired ceramic application were prepared by the solid-state reaction route. The optimized densification temperatures of Ag 2 Mo 2 O 7 and Ag 6 Mo 10 O 33 are 460°C and 500°C, respectively. The phase structures and microstructures of these ceramics were systematically studied. The Ag 2 Mo 2 O 7 ceramic sintered at 460°C/4 h exhibits excellent microwave dielectric properties with ε r =13.3, Q×f =25 300 GHz and τ f =−142 ppm/°C at 9.25 GHz. The Ag 6 Mo 10 O 33 ceramic sintered at 500°C/4 h shows the microwave dielectric properties with ε r =14.0, Q×f =8500 GHz and τ f =−50 ppm/°C at 9.00 GHz. Moreover, when Ag 2 Mo 2 O 7 samples are sintered at ultra-low sintering temperatures of 420°C-490°C, the Q×f values of them are all above 20 000 GHz. Besides, the Ag 2 Mo 2 O 7 ceramic does not react with silver powder or aluminum powder. The variation of relative permittivity, resonant frequency, and Q×f values as a function of operating temperature has been also studied. All the results indicate that the Ag 2 Mo 2 O 7 ceramic is a good candidate for ultra-low temperature co-fired microwave devices.

Description: Dielectric study over a broadband was carried out from 10 to 70 K on ceramic Gd 1− x Y x MnO 3 ( x =0.2, 0.3 and 0.4). For all the compositions, a prominent sharp peak about ~18 K was observed in the temperature dependence of both ε′( T ) and ε″( T ) at all frequencies, indicating a long-range ferroelectric (FE) transition. Using Cole-Cole fit to the permittivity data, the relaxation time τ and the dielectric strength ∆ε were estimated. Temperature variation of τ( T ) in the Arrhenius representation is found to be nonlinear (non-Debyean relaxation), with increasing barrier-activation energy over successive temperature-windows. Interestingly, for all the compositions, we witness a jump in τ( T ) about the ferroelectric transition temperature, concurred by a broad-maximum in ∆ε( T ),signifying the critical slow down of relaxations near long-range FE-correlations.

Description: The Cr/Ce-doped YAG transparent ceramic was fabricated by the solid-state reaction in vacuum. The Cr/Ce-doped YAG ceramic phosphor effectively complement the red spectral component and improve the color rendering performance when excited by blue light that is due to the effective energy transfer between Cr 3+ ion and Ce 3+ ion. However, the energy transfer from Ce 3+ to Cr 3+ ion leads to energy loss and therefore the luminous efficacy of the WLED which is composed of blue LED chip and the Cr/Ce-doped YAG ceramic phosphor decreases. The composite phase structure of ceramic phosphor is designed for improving the extraction efficacy and increasing the luminous efficacy by breaking the total internal reflection (TIR) at the interface between air and ceramic.

Description: The scheme represents the formation of cementitious hydrates from the reaction of anhydrous cement with water and how the kinetics of this reaction can be affected by different types of additives, in particular by comb-copolymers illustrated in the center of this scheme. Such polymers are widely used as dispersants in concrete to enhance its fluidity. More recently, they are playing an increasing role in enabling the production of concrete with a low environmental impact. However, the delay that they almost invariably cause to cement hydration represents a limitation to their use and to the development of alternative binding materials. The paper by Marchon et al. addresses this crucial scientific question and paves the way to the molecular design of optimized chemical admixtures. Cover Illustration by Fabian Rüdy and Stefan auf der Maur, Switzerland. The scheme represents the formation of cementitious hydrates from the reaction of anhydrous cement with water and how the kinetics of this reaction can be affected by different types of additives, in particular by comb-copolymers illustrated in the center of this scheme. Such polymers are widely used as dispersants in concrete to enhance its fluidity. More recently, they are playing an increasing role in enabling the production of concrete with a low environmental impact. However, the delay that they almost invariably cause to cement hydration represents a limitation to their use and to the development of alternative binding materials. The paper by Marchon et al. addresses this crucial scientific question and paves the way to the molecular design of optimized chemical admixtures. Cover Illustration by Fabian Rüdy and Stefan auf der Maur, Switzerland.

Description: In this work, an efficient carbothermal reduction–nitridation (CRN) strategy was rationally designed to directly synthesize β-Si 3 N 4 powders with eminent dispersity and granularity uniformity. With the aid of CaO additive, the obtained β-Si 3 N 4 particles were endowed with approximate spherical morphology and smooth surface. The size of β-Si 3 N 4 particles could be regulated in sub-micro and micro scale by altering N 2 pressures. More significantly, the underlying growth mechanism of the β-Si 3 N 4 under elevated N 2 pressure was comprehensively analyzed and tentatively put forward. Benefiting from the remarkable merits, the as-synthesized β-Si 3 N 4 powders showed great potential for alternative fillers in the application of high thermal conductivity plastic packages. This article is protected by copyright. All rights reserved.

Description: The wetting, reactivity and phase formation at the liquid Ni-Al/TiB 2 ceramic interfaces have been investigated at the temperatures close to the Ni-Al liquidus line. The wetting kinetics has been studied by the sessile drop technique utilizing liquid drop dispension and high-speed high-resolution video imaging. It is established that the wetting behavior changes from a non-reactive for the Al-rich melts to a dissolution-reactive for the Ni-rich melts. For the Ni concentration ≥40 at.%, TiB 2 precipitates are found in the solidified Ni-Al droplets after the high-temperature interaction of the melts with TiB 2 substrates. Besides, new (Al,Ti)Ni 3 and (Al,Ti) 2 Ni 21 B 6 phases are formed due to dissolution of TiB 2 ceramic in Ni-rich melts and subsequent solidification. This article is protected by copyright. All rights reserved.

Description: Searching for layered MAX phase-like materials with properties of both ceramics and metals is a topic in its infancy. Herein, through a combination of crystal structure, electronic structure, chemical bonding and elastic property investigations, we report two MAX phase-like layered materials Rh 2 YSi and Ir 2 YSi. Rh 2 YSi and Ir 2 YSi have bulk modulus B of 150 and 185 GPa, respectively, which are comparable to the typical MAX phases like Ti 2 AlC, Ti 3 AlC 2 and Ti 3 SiC 2 , but much lower shear modulus G (82 and 97 GPa for Rh 2 YSi and Ir 2 YSi, respectively) than MAX phases. The high stiffness is due to the presence of rigid Si2-M-Si3-M (M=Ir, Rh) units, while the low shear deformation resistance is due to the presence of metallic bonds and the weak bonds that link the rigid Si2-M-Si3-M (M=Ir, Rh) units. Based on the low shear deformation resistance and low Pugh's ratio, Rh 2 YSi and Ir 2 YSi are predicted as damage tolerant silicides and promising water vapor resistant interphase materials for SiC f /SiC composites if yttria or yttrium silicates are formed to protect the SiC fibers in oxygen containing environments. The possible slip systems are {0001} 〈2‾1‾10〉 and {11‾20} 〈0001〉 for both Rh 2 YSi and Ir 2 YSi. This article is protected by copyright. All rights reserved.

Description: In general, the technologically important ferrites nanoparticles, magnetite and maghemite, are converted from cubic to the more stable rhombohedral structure above 500-700 °C under air/vacuum/inert atmosphere. Here, we report, the superior thermal stability of polymer capped Fe 3 O 4 (PCIO) nanocluster (synthesized using microwave-assisted polyol approach) up to 1000 °C under vacuum and inert atmosphere. Raman spectra of post annealed PCIO nanoclusters show the Fe 3 O 4 phase with carbon signature due to the decomposition of polymer matrix. The carbon layer seems to act as a thermal shield and increases the activation energy thereby preventing the intrusion of heat, oxygen, volatiles mass into the magnetic core. The presence of carbon layer was further confirmed from the high resolution transmission electron microscopic image. After thermal annealing at 1000 °C, PCIO nanoclusters showed superparamagnetic behavior with a saturation magnetization of 89 emu/g, close to the bulk saturation magnetization of Fe 3 O 4 phase. In contrast, the uncoated Fe 3 O 4 (UCIO) nanoclusters decompose at 700 °C into α-Fe 2 O 3 and FeO phases under similar annealing conditions. Our findings open up new possibilities of stabilizing nanomaterials for high temperature applications. This article is protected by copyright. All rights reserved.

Description: Black glasses are amorphous materials based on silicon oxycarbide. The use of precursors in the form of ladder-like silsesquioxanes enables the control of the amount of carbon ions in the glass network by adjusting ratios of T to D structural units in precursors. In this study, four different sols precursors of four different layers of black glasses on titanium substrates were prepared. The materials were analysed with the use of various spectroscopic and microscopic methods. Formation of continuous and hermetic layers resistant to corrosion was proven. The black glasses layers were examined as materials for biomedical applications. Therefore, preliminary tests of their bioactivity and biocompatibility were performed. The best results were obtained for the material of lower contribution of carbon ions. This article is protected by copyright. All rights reserved.

Description: Triplex particulate composites composed of boride and carbide ceramics were found to have high strength, hardness, and fracture toughness values. Two compositions consisting of 70:15:15 and 1:1:1 volume ratios of TiB 2, SiC, and B 4 C were produced from commercially available powders by hot-pressing. The 70:15:15 ceramic exhibited a strength of ~1.3 GPa, while the 1:1:1 ceramic had a strength of ~0.9 GPa. These strengths are comparable to super-strong Y 2 O 3 -PSZ and β-SiAlON based composites. The Vickers’ hardness values of these ceramics were ~32 GPa for indent loads of 9.8 N. Hardness increased as indentation load decreased. The 1:1:1 ceramic had a hardness of ~53 GPa at an indentation load of 0.49 N, higher than values reported for so-called “super-hard” ceramics, and comparable to c-BN. This article is protected by copyright. All rights reserved.

Description: Hafnia (HfO 2 ) and zirconia (ZrO 2 ) are of great interest in the quest for replacing silicon oxide in semiconductor field effect transistors because of their high permittivity. Both exhibit extensive polymorphism and understanding the energetics of their transitions is of major fundamental and practical importance. In the present study, we present a systematic thermodynamic summary of the influence of particle size on thermodynamic phase stability in hafnia and zirconia using recently measured enthalpy data from the literature. The amorphous phase is found to be the most energetically stable above 165 and 363 m 2 /g of surface area for HfO 2 and ZrO 2 , respectively. Below 16 and 20.3 m 2 /g of surface area, respectively, the monoclinic phase is the most energetically stable for HfO 2 and ZrO 2 . At intermediate sizes there are closely balanced energetics among monoclinic, tetragonal, and cubic phases. The energy crossovers reflect decreasing surface enthalpy in the order monoclinic, tetragonal, cubic and amorphous for both hafnia and zirconia. This article is protected by copyright All rights reserved.

Description: The phase structure, dielectric, ferroelectric, and piezoelectric properties of (1-2 x )BiScO 3 - x PbTiO 3 - x PbMg 1/3 Nb 2/3 O 3 ceramics ( x =0.30-0.46) were studied. It was found that an increase in x leads to a structural phase transition between the rhombohedral and tetragonal phase via an intermediate monoclinic phase and to a crossover from the nonergodic relaxor state to the ferroelectric one. It was proposed that at x〉0.42 the phase transition changes from second to first order. The assumption about the existence of a tricritical point on the phase diagram at x ≈0.42 with the enhanced dielectric response has been made. The observed structure-property relationships of the studied solid solutions are discussed. It is shown that the solid solutions with x =0.42 are characterized by the high piezoelectric parameters ( d 33 = 509 pC/N, d 31 = -178 pC/N, d h = 153 pC/N), which makes possible their applications in sonar equipment. This article is protected by copyright. All rights reserved.

Description: Cr 2 AlC foams have been processed for the first time containing low (35 vol.%), intermediate (53 vol.%) and high (75 vol.%) content of porosity and three ranges of pore size, 90 – 180 μm, 180 – 250 μm and 250 - 400 μm. Sacrificial template technique was used as processing method, utilizing NH 4 HCO 3 as temporary pore former. Cr 2 AlC foams exhibited negligible oxidation up to 800 °C and excellent response up to 1300 °C due to the in-situ formation of an outer thin continuous protective layer of α-Al 2 O 3 . The in-situ α-Al 2 O 3 protective layer covered seamlessly all the external surface of the pores, even when they present sharp angles and tight corners, reducing significantly the further oxidation of the foams. The compressive strength of the foams was 73 and 13 MPa for 53 vol.% and 75 vol.% porosity, respectively, which increased up to 128 and 24 MPa after their oxidation at 1200 °C for 1 hour. The increase in the compressive strength after the oxidation was caused by the switch from inter- to transgranular fracture mode. According to the excellent high temperature response, heat exchangers and catalyst supports are the potential application of these foams. This article is protected by copyright. All rights reserved.

Description: In this work, a small amount of CaO single dopant was adopted to realize the densification and microstructure control of fine grained YAG ceramic with excellent optical quality, by a simple solid state reaction and one-step vacuum sintering method. Then, highly transparent YAG ceramics (T=84.4% at 1064 nm) were obtained just after vacuum sintering at 1820 °C for 8h. The average grain size was only 2.7 μm, when the total amount of CaO was as low as 0.045 wt.%. The effect of CaO on the microstructural evolution and optical property of the as-fabricated YAG ceramics was systematically investigated in detail. It was found that CaO dopant promoted both densification and grain growth of YAG ceramics when the sintering temperature was lower than 1660 °C, however it dramatically inhibited grain growth when the sintering temperature was further increased. This article is protected by copyright. All rights reserved.

Description: Si 3 N 4 @(TiN-Si 3 N 4 ) composites with hetero-shelled structure were designed for enhanced conductivity and successfully synthesized through the simultaneous reduction and in-situ co-coating process in liquid ammonia at around -40 °C. The hetero-shells were composed of nano-sized TiN and Si 3 N 4 particles which were amorphous with the size ranging from 10 nm to 40 nm. Using spark plasma sintering (SPS) dense bulk composite with 〉98.1% relative density of theoretical value were obtained and their electrical conductivity were increased to an adequate value (6.62×10 2 S·cm −1 ) for electrical discharge machining (EDM) by compositing 15 vol % TiN to Si 3 N 4 , which is superior to the previous reports. The excellent electric performance could be attributed to the hetero-shelled structure which guarantees the conductive network can be formed and kept with minimal TiN content. The nano-sized Si 3 N 4 powders in the shells reduce the content of conductive powders and limit the growth of TiN particles. This article is protected by copyright. All rights reserved.

Description: Porcelain stoneware was consolidated by flash sintering under DC polarization using current densities in the range 4 – 20 mA/mm 2 . The results show the applicability of this innovative sintering technology to a material whose densification occurs by vitrification, thus allowing to extend the possible application field of flash sintering to traditional ceramics. Using appropriate current density, the flash sintered samples are dense, homogeneous and well-vitrified. XRD and microstructural analysis points out the formation of primary mullite while secondary mullite is only sporadically observed. In addition, comparison between flash sintering and fast firing shows that the densification obtained in the selected ceramic system via the former route can not be reproduced just by a rapid heating process. This article is protected by copyright. All rights reserved.

Description: It has been claimed that disappearance of the {110} reflection in powder x-ray diffraction of MXene is indicative of shearing or general disorder of restacking of MXene flakes, such as in films. We correct this oversight here and provide experimental justification. Further, our methods provide a simple way to estimate a unit cell parameters when the relevant reflections are not present in most reports of MXene films. This article is protected by copyright. All rights reserved.

Description: Hi-Nicalon-S/α-Y 2 Si 2 O 7 /SiC minicomposites were formed by polymer infiltration pyrolysis (PIP) and characterized by TEM, SEM fractography, tensile testing, and fiber push-in testing. All minicomposites with α-Y 2 Si 2 O 7 fiber coatings had strengths significantly higher than the control samples without fiber coatings. Extensive fiber pullout with debonding at the coating-fiber interface or within the coating itself was observed in minicomposites with Y 2 Si 2 O 7 fiber coatings, but no debonding was observed in minicomposites without fiber coatings. Debond energies of 4.5±3, 4.6 ±3 J/m 2 and average sliding stresses of 91±40, 94±40 MPa were measured by fiber push-in tests. This article is protected by copyright. All rights reserved.

Description: A comparative study of reactive melt infiltration using Si and Si-Y alloys is presented to provide insight into the governing processes that control the effectiveness of the melt interaction with a carbonaceous preform and the temperature capability of the SiC matrix for ceramic matrix composites. Through experiments on two substantially different scales of capillaries in porous graphite tubes using Si and Si-Y alloys, the current study has characterized the phenomena that play a role in the infiltration of the melt and its reaction with the preform. It is shown that (i) the interface reaction controls wetting in both large and small capillaries and the climb rate is enhanced by the presence of Y; (ii) reaction choking occurs at critical throats within the pore network, usually behind the infiltration front; and (iii) different residual silicides can form during reaction and upon cooling. A potential mechanism for SiC growth is described, and the implications for the interplay between SiC growth and infiltration are discussed. This article is protected by copyright. All rights reserved.

Description: 〈001〉-textured 0.99(K 0.49 Na 0.49 Li 0.02 )(Nb 0.97- x Sb 0.03 Ta x )O 3 -0.01CaZrO 3 [abbreviated as 0.99KNLN 0.97- x ST x -0.01CZ, x = 0.03, 0.07, 0.10, 0.15, 0.20, 0.25] ceramics were prepared by templated grain growth (TGG) method and a two-step sintering process. Giant longitudinal piezoelectric coefficient d 33 (391 pC/N) and piezoelectric strain coefficient d 33 * (630 pm/V under an AC E-field of 20 kV/cm) can be obtained in the textured ceramics with x = 0.25. All textured ceramics display superior k p (〉 54%) and g 33 (〉 23 × 10 -3 Vm/N) which are in an order of magnitude with PZT ceramics. The maximum value of k p (~ 63.3%) obtained in textured ceramics with x = 0.15 is higher than that of famous textured LF4 ceramics. Excellent comprehensive properties suggest that 〈001〉-textured 0.99KNLN 0.97- x ST x -0.01CZ ceramics are promising candidates in the field of lead-free piezoelectric materials. This article is protected by copyright. All rights reserved.

Description: Herein, enhancement of dye-sensitized solar cell (DSC) performance is reported by combining the merits of the dye loading of TiO 2 nanoparticles and light scattering, straight carrier transport path and efficient electron collection efficiency of TiO 2 cubes. We fabricate DSC devices with various arrangement styles and compositions of the electrodes in the forms of monolayer and double layer films. For this purpose, the solvothermal synthesized TiO 2 cubic particles (100-600 nm) are employed as the scattering layer, whereas TiO 2 nanoparticles (15-30 nm) synthesized via a combination of solvothermal and sol-gel routes are used as the active layer of devices. We improve the photovoltaic characteristics of DSCs by two mechanisms. First, the light harvesting of DSC devices made of nanoparticles is improved by controlling the thickness of monolayer films, reaching the highest efficiency of 7.0%. Second, the light scattering and electron collection efficiency are enhanced by controlling the composition of double layer films composed of mixtures of TiO 2 nanoparticles and cubes, obtaining the maximum efficiency of 8.21%. The enhancements are attributed to balance between charge transfer resistance and charge recombination of photo-generated electrons as well as dye loading and light scattering. This article is protected by copyright. All rights reserved.

Description: Despite enormous interest in calcium silicate hydrate (C-S-H), its detailed atomic structure and intrinsic deformation under an external load are lacking. This study demonstrates the nanostructural deformation process of C-S-H in tricalcium silicate (C 3 S) paste as a function of applied stress by interpreting atomic pair distribution function (PDF) based on in situ X-ray scattering. Three different strains in C 3 S paste under compression were compared using a strain gauge, Bragg peak shift, and the real space PDF. PDF refinement revealed that the C-S-H phase mostly contributed to PDF from 0 to 20 Å whereas crystalline phases dominated that beyond 20 Å. The short-range atomic strains exhibited two regions for C-S-H: I) plastic deformation (0–10 MPa) and II) linear elastic deformation (〉10 MPa), whereas the long-range deformation beyond 20 Å was similar to that of Ca(OH) 2 . Below 10 MPa, the short-range strain was caused by the densification of C-S-H induced by the removal of interlayer or gel-pore water. The strains is likely to be recovered when the removed water returns to C-S-H. This article is protected by copyright. All rights reserved.

Description: Nanoparticles of Bi 2 Ti 2 O 7 pyrochlore were synthesized by a coprecipitation method. They exhibit a high visible-light photoactivity for decolourization of a methyl-orange dye solution in presence of a sacrificial agent, H 2 O 2 . The same pyrochlore system with a Ag co-catalyst showed even faster kinetics under only visible light and an unprecedentedly high photoactivity in the UV range. This article is protected by copyright. All rights reserved.

Description: A model for the fracture strength of brittle materials controlled by blunt (spherical) scratches is developed and compared with measurements on a polycrystalline alumina. The model is based on a residual stress-intensity factor for median cracks at scratches that include a localized plastic deformation zone formed by dragged spherical contacts. The stress-intensity factor depends non-linearly on the normal contact load P , resulting in a predicted strength variation of P −3/4 . The strength result validates previous claims and extends the overall indentation-strength framework. However, the result has only limited effectiveness in describing experimental measurements, pertaining only to ideal blunt scratches formed over a limited load domain. This article is protected by copyright. All rights reserved.

Description: The first systematic study of the BaO–B 2 O 3 system and barium orthoborate Ba 3 B 2 O 6 (3BaO·B 2 O 3 ) was reported in 1949. Thereafter, the system was repeatedly refined but the structure of Ba 3 B 2 O 6 compound has not been adequately studied yet. In our study we have, for the first time, obtained the crystalline samples of Ba 3 B 2 O 6 . The solved structure ( Pbam , a = 13.5923(4) Å, b = 13.6702(4) Å, c = 14.8894(3) Å) belongs to the class of ‘anti-zeolite’ borates with a pseudotetragonal [ Ba 12 (BO 3 ) 6 ] 6+ cation pattern which contains channels along the c axis filled with anionic clusters. The Ba 3 B 2 O 6 compound may be regarded as a fluorine-free end-member of the Ba 3 (BO 3 ) 2– x F 3 x solid solution. The BaO–B 2 O 3 phase diagram presented in our study is based on our research and literature data. This article is protected by copyright. All rights reserved.

Description: Hi-Nicalon TM -S SiC fiber was heat-treated for one hour at 1300, 1400, and 1500°C in argon with pO 2 of 3.7, 10, 20, 50, 100, and 200 ppm. Fiber strengths were measured by 30 single-filament tensile tests. Fiber microstructure and surface morphology were characterized by TEM. Active oxidation occurred in all cases except at 1500°C with 200 ppm pO 2 , 1400°C with 100 ppm pO 2 or higher, and 1300°C with 50 ppm pO 2 or higher. When active oxidation did not occur, a glass SiO 2 scale formed at 1300 and 1400°C, and a cristobalite scale formed at 1500°C. The thickness of these scales was much larger than that predicted by linear dependence of oxidation rate on pO 2 . Fiber strengths were lowest after heat-treatment at 1300°C and a pO 2 of 3.7 ppm, 1400°C and a pO 2 of 20 ppm, and 1500°C and a pO 2 of 200 ppm. Active oxidation caused fiber surface roughening, but no obvious changes to the internal fiber microstructure. Decreased fiber strength correlated with increased fiber surface roughness, but roughness magnitudes were not large enough to explain the amount by which strength was degraded. Fiber strengths, surface roughness, scale thicknesses, and the passive-active oxidation transition for SiC are compared with previous observations. Possible strength degradation mechanisms are discussed. This article is protected by copyright. All rights reserved.

Description: The interaction of fully dense 45S5-bioglass derived samples produced by Spark Plasma Sintering (SPS) with Simulated Body Fluid (SBF) solution was investigated in detail taking advantage of the Rietveld refinement method to quantitatively evidence the corresponding microstructural and compositional changes. It is observed that, when the original amorphous nature is mostly (75 wt.%) preserved in the material during sintering (550 °C, 2 min), the resulting specimens dissolve faster and determine relatively higher pH increase and ions release in the SBF solution. Correspondingly, a relatively lower amount of hydroxycarbonate apatite (HCA) is formed on their surface. In contrast, a more extensive apatite layer with trabecular structure is generated within 3 days storage on the surface of fully crystallized samples obtained at 600 °C by SPS, which only consists of Na-Ca silicate grains (20 nm). Moreover, as the sintering temperature and dwell time were increased to 700 °C and 20 min, respectively, a rhenanite-like phase was also formed (about 15 wt.%), other than crystallites growth to 90 nm. Interestingly, the presence of rhenanite provides a beneficial contribution for the production of the HCA layer, which was found the largest for this system when considering storage periods of 7 and 14 days, respectively. This article is protected by copyright All rights reserved.

Description: Niobium alkali germanate glasses were synthesized by the melt-quenching technique. The ternary system (90-x)GeO 2 -xNb 2 O 5 -10K 2 O forms homogeneous glasses with x ranging from 0 to 20mol%. Samples were investigated by DSC and XRD analysis, FTIR and Raman spectroscopy, and optical absorption. Structural and physical features are discussed in terms of Nb 2 O 5 content. The niobium content increase in the glass network strongly modifies the thermal, structural and optical properties of alkali germanate glasses. DSC, Raman and FTIR analysis suggest niobium addition promotes NbO 6 groups insertion close to GeO 4 units of the glass network. XRD analysis also pointed out that samples containing high niobium oxide contents exhibit preferential niobium oxide rich phase after crystallization after heat treatment, which is similar to orthorhombic Nb 2 O 5 . Absorption spectra revealed high transmission range between 400nm to 6.2μm, added to a considerably decreased hydroxyl group content as the addition of niobium in the alkali germanate network. The niobium oxide rich phase crystallization process was studied and activation energy was determined, as well as nucleation and crystal growth temperatures and time for obtaining transparent glass-ceramics. This article is protected by copyright. All rights reserved.

Description: The effects of fluorine and nitrogen substitution for oxygen in aluminosilicate glasses, effectively oxyfluoronitride (OFN) glasses, modified by calcium, calcium – yttrium or calcium – magnesium on thermal and physical / mechanical properties have been compared. Thus, forty-two glasses in the Ca–(Mg)–(Y)–Si–Al–O–(N)–(F) system have been prepared and characterized with respect to density (ρ), molar volume (MV), compactness (C), free volume (FV), glass transition temperatures measured by DTA (T g, DTA ) and dilatometry (T g,dil ), dilatometric softening point (T DS ), microhardness (μHv) and Young's modulus (E). Gradients of property variation with nitrogen or fluorine substitutions for oxygen are similar for all three different oxyfluoronitride glass systems and are comparable with those reported for other OFN glasses, again indicating independent and additive effects of nitrogen and fluorine. In attempting to further understand how fluorine affects the cross-link density (CLD) in OFN glasses, it becomes apparent that it is necessary to allow for a greater contribution by aluminium in a modifier role as fluorine content is increased. This modified calculation of CLD values results in good linear fits between T g and CLD values. This analysis clearly demonstrates and endorses the concepts that thermal properties are related to CLD whilst physical / mechanical properties are dependent on glass compactness. This article is protected by copyright. All rights reserved.

Description: In this paper we report for the first time synthesis of Eu 3+ doped transparent glass-ceramics (TGC) with BaBi 2 Ta 2 O 9 (BBT) as the major crystal phase using the glass system SiO 2 -K 2 O-BaO-Bi 2 O 3 -Ta 2 O 5 by melt quenching technique followed by controlled crystallization through ceramming heat-treatment. DSC studies were conducted in order to determine a novel heat-treatment protocol to attain transparent GCs by controlling crystal growth. The structural properties of the BBT GCs have been investigated using XRD, FE-SEM, TEM and FTIR reflectance spectroscopy. Optical band gap energies of the glass-ceramic samples were found to decrease with respect to the precursor glass. An increased intensity of emission along with increase in the average lifetime of Eu 3+ was observed due to incorporation of Eu 3+ ions into the low-phonon energy BBT crystal site. The local field asymmetric ratios of all the samples were observed greater than unity. The dielectric constant (ε r ), dielectric loss, and dissipation factor values of both the base glass and ceramized samples were found to decrease with increase in frequency. This article is protected by copyright. All rights reserved.

Description: We report on the materials interaction of gadolinium doped ceria (GDC) and yttria stabilized zirconia (YSZ) in the context of high temperature sintering during manufacturing of anode supported solid oxide fuel cells (AS-SOFC). While ceria-based anodes are expected to show superior electrochemical performance and enhanced sulfur and coking tolerance in comparison to zirconia-based anodes, we demonstrate that the incorporation of a Ni-GDC anode into an ASC with YSZ electrolyte decreases the performance of the ASC by approximately 50% compared to the standard Ni-YSZ cell. The performance loss is attributed to interdiffusion of ceria and zirconia during cell fabrication, which is investigated using powder mixtures and demonstrated to be more severe in the presence of NiO. We examine the physical properties of a GDC-YSZ mixed phase under reducing conditions in detail regarding ionic and electronic conductivity as well as reducibility, and discuss the expected impact of cation intermixing between anode and electrolyte. This article is protected by copyright. All rights reserved.

Description: The effect of the spark plasma sintering (SPS) process on mullite formation in porcelains was studied using X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. SPS affected the kinetics and morphology of formed mullite. After sintering at 1100°C, unlike conventional sintering, SPS promoted the formation of mullite due to the combination of vacuum and applied pressure. Mullite crystal growth was altered by the atmosphere (vacuum), dwell time (0-15 mins), and temperature (1000-1200°C). The applied pressure caused the mullite needles to orient perpendicular to the direction of the applied load. Depending on SPS dwell time, the mullite formed after sintering at 1100°C also had different crystal structure (tetragonal for short dwell time of 0-5min and orthorhombic for a long dwell time of 10-15min). Dissolution of mullite was observed at 1100°C by extending the dwell time by up to 15 minutes and the dissolved mullite re-precipitated on the small needles (~40nm) via Oswald ripening resulting in larger mullite needles (~60nm). This article is protected by copyright. All rights reserved.

Description: We explored the structure and physical properties of Ge 15 Sb 20 Se 65- x S x (with x=0, 16.25, 32.5, 48.75 and 65) glasses in order to screen the best compositions for the applications in photonics, since the laser damage thresholds in Se-based glasses are too low although their optical nonlinearities are high. We found that, linear and nonlinear refractive index of the glasses decreased, but glass transition temperature T g , optical bandgap E g and the laser damage threshold increased with increasing S content. We further employed Raman scattering and high-resolution X-ray photoelectron spectra (XPS) to probe the structure of the glasses. Through the analysis of the evolution of the different structural units in the glasses, it was concluded that, the heteropolar bonds (Ge-Se/S, Sb-Se/S) were dominated in these glasses. With the increase of chalcogen Se/S ratio, the number of the Se-related chemical bonds (Ge-Se, Sb-Se and Se-Se) increased and that of S-related chemical bond (Ge-S, Sb-S and S-S) decreased gradually, and Ge was prior to bond with S rather than Se. The elemental substitution thus had negligible effect on the glass structure. The change of the physical properties was mainly due to the difference of the strength of the chemical bonds between S-Ge(Sb) and Se-Ge(Sb). This article is protected by copyright. All rights reserved.

Description: The relaxor material Na 1/2 Bi 1/2 TiO 3 (NBT) is an important basis for the development of lead-free piezoceramics, but still many features of this material are not well understood. Here, we study the kinetics of phase transformations by octahedral tilts and A-cation displacements in NBT by means of density functional theory calculations, employing ab initio molecular dynamics and nudged elastic band calculations. Our results show that the energetic differences between the low temperature rhombohedral, intermediate orthorhombic and other metastable phases are close to the room temperature thermal energy. Therefore, it is likely that above room temperature several octahedral tilt patterns are present simultaneously on the local scale, just because of thermal vibration of the oxygen ions. Octahedral tilt transformations and A-cation displacements show similarly high energy barriers, however, since the vibrational frequency of oxygen is higher, tilt transformations occur more frequently. Further, tilt transformations in which the oxygen octahedra get deformed the least are more probable to occur. We also find that the chemical A-cation order affects energy barriers, influences the coupling between rotational and displacive modes and determines the stability of certain octahedral tilt orders. We conclude that the so-called polar nanoregions in this material result from local octahedral tilt transformations and subsequent A-cation displacements, which are driven by thermal vibration and are mediated by the underlying chemical order. This article is protected by copyright. All rights reserved.

Description: To reduce power consumption of transparent oxide-semiconductor thin film transistors, a gate dielectric material with high dielectric constant and low leakage current density is favorable. According to previous study, the bulk TiNb 2 O 7 with outstanding dielectric properties may have an interest in its thin-film form. The optical, chemical states and surface morphology of sol-gel derived TiNb 2 O 7 (TNO) thin films are investigated the effect of post-annealing temperature lower than 500°C, which is crucial to the glass transition temperature. All films possess a transmittance near 80% in the visible region. The existence of non-lattice oxygen in the TNO film is proposed. The peak area ratio of non-lattice oxygen plays an important role in the control of leakage current density of MIM capacitors. Also, the capacitance density and dissipation factor were affected by the indium tin oxide (ITO) sheet resistance at high frequencies. The sample after post-annealing at 300°C and electrode-annealing at 150°C possesses a high dielectric constant (〉30 at 1 MHz) and a low leakage current density (〈1⨯10 -6 A/cm 2 at 1V), which makes it a very promising gate dielectric material for transparent oxide-semiconductor thin film transistors. This article is protected by copyright. All rights reserved.

Description: InSe, In 2 Se 3 and GaSe are important III-VI semiconductors and are attractive for electronic, optical and optoelectronic applications. This paper reports a fast and cheap way called combustion synthesis to prepare InSe, In 2 Se 3 and GaSe. Bulk samples with relative densities up to 98% are directly produced in a few seconds. The samples show a high phase purity, correct stoichiometry and lamellar crystals larger than 100 μm. By optical absorption, the bandgaps of InSe, In 2 Se 3 and GaSe are determined to be 1.08, 1.24 and 1.75 eV, respectively. This article is protected by copyright. All rights reserved.

Description: Aiming on the synthesis of a water-free analogue of the mineral cryptophyllite (K 2 CaSi 4 O 10 x5H 2 O) solid-state reactions of a corresponding mixture of K 2 CO 3 , CaCO 3 and SiO 2 were carried out at 800 and 900 °C, respectively. It was possible to ascertain the existence of a previously unknown potassium calcium silicate with composition K 2 CaSi 4 O 10 . Structural investigations were based on single-crystal diffraction experiments. Basic crystallographic data are as follows: triclinic symmetry, space group P1, a = 7.0915(7) Å, b = 8.4211(9) Å, c = 10.2779(12) Å, α = 104.491(10)°, β = 100.570(9)°, γ = 113.738(9)°, V = 515.26(10) Å 3 , Z = 2. Structure solution was performed by direct methods. Subsequent refinement calculations using anisotropic displacement parameters for all atoms converged to a residual of R(|F|) = 0.0355 for 1889 independent reflections with I〉 2σ(I). From a structural point of view K 2 CaSi 4 O 10 belongs to the so-called litidionite family of A’AMSi 4 O 10 compounds for which several natural and synthetic representatives have been described in the literature. Actually, it is the first member where the A’- and A-positions are exclusively occupied by K-ions. Following the nomenclature for oxosilicates K 2 CaSi 4 O 10 can be allocated to the group of the tubular chain silicates. Fundamental building units are loop-branched dreier double chains (running parallel to [100]) which can be described using the following structural formula: {lB,2 1 ∞ }[ 3 Si 8 O 20 ]. Ca-ions are coordinated by five nearest oxygen neighbors in form of distorted trigonal bipyramids. By sharing a common edge two adjacent bipyramids are linked into [Ca 2 O 8 ]-dimers providing linkage between consecutive tubes in the direction of the c-axis. Charge compensation is achieved by the incorporation of the larger potassium ions into cavities of the heteropolyhedral network. Powder X-ray diffraction pattern of the bulk material of the synthesis products revealed that additionally to K 2 CaSi 4 O 10 the 800 °C-sample contains K 8 CaSi 10 O 25 and at least one further, yet unknown crystalline phase. This unspecified substance is also present in the 900 °C-specimen together with K 2 CaSi 4 O 10 and K 2 Ca 4 Si 8 O 21 . Our proof of the existence of K 2 CaSi 4 O 10 represents a further contribution to the description of the ternary system K 2 O-CaO-SiO 2 and corrects earlier phase-analytical studies on this system which is of relevance for applied and technical mineralogy including different types of residual materials such as slags or ashes from biomass combustion. The results of our investigation show that even comparatively simple ternary oxide systems are not as well understood as expected. This article is protected by copyright. All rights reserved.

Description: The properties of mullite-glass and mullite-mullite interfaces have been investigated at 1800K by molecular dynamics (MD) simulation and high-resolution TEM. The simulation showed that mullite-glass interfaces typically have much lower interfacial energies than mullite-mullite interfaces, which results from the structural flexibility of the glass and associated accommodation of interfacial mismatch. The (110)-glass interface has the lowest energy of all interfaces studied, which is consistent with the observed dominance of this interface in experimental mullite-glass samples examined by TEM. The simulation shows that the interfacial energies of the (100)-glass and (010)-glass interfaces are higher than that those of the (001)-glass interface, so [100] and [010] would be expected to be the dominant growth directions. However, the growth of mullite in glass occurs predominantly in the [001] direction. This apparent discrepancy can be explained by the fact that growth in the [100] and [010] directions is limited by slow growth of (110) plane ( i.e ., [110] direction), which facilitates [001] growth, which are confirmed by the TEM data. This article is protected by copyright. All rights reserved.

Description: Vitrified high-level radioactive waste that contains high concentrations of Na 2 O and Al 2 O 3 , such as the waste stored at the Hanford site, can cause nepheline to precipitate in the glass upon cooling in the canisters. Nepheline formation removes oxides such as Al 2 O 3 and SiO 2 from the host glass, which can reduce its chemical durability. Uncertainty in the extent of precipitated nepheline necessitates operating at an enhanced waste loading margin, which increases operational costs by extending the vitrification mission as well as increasing waste storage requirements. A thermodynamic evaluation of the Na 2 O-Al 2 O 3 -SiO 2 system that forms nepheline was conducted by utilizing the compound energy formalism and ionic liquid model to represent the solid solution and liquid phases, respectively. These were optimized with experimental data and used to extrapolate phase boundaries into regions of temperature and composition where measurements are unavailable. The intent is to import the determined Gibbs energies into a phase field model to more accurately predict nepheline phase formation and morphology evolution in waste glasses to allow for the design of formulations with maximum loading. This article is protected by copyright. All rights reserved.

Description: The material of choice for space applications which demand very high dimensional stability is lithium aluminosilicate (LAS) based Ultra Low thermal Expansion Glass-Ceramic (ULEGC). Generally, the controlled crystallization process recommended for the processing of transparent ULEGC involves a long soaking duration to achieve the required crystal number density. This paper brings out the process optimization procedure adopted for realizing transparent and nanocrystalline ULEGC from conventionally processed LAS glass using microwave assisted (hybrid) crystallization. The experimental strategy involves two stages (i) identification of the optimum crystallization temperature ( T c ) under a microwave field (ii) optimization of a microwave assisted crystallization process to achieve near zero CTE. Optimum heat treatment schedules for nucleation and crystallization under a microwave environment were found to be 720°C/24h and 775°C/0.3h respectively. The optimized heat treatment condition revealed the efficacy of the microwave hybrid heating, by producing nanocrystalline (35-50nm) and transparent (〉82%) ULEGC having a thermal expansion of -0.03 ×10 -6 K (0-50°C). This article is protected by copyright. All rights reserved.

Description: In the IR spectra of silica and silicate glasses, the shifts of the maximum intensity position of the ν Si-O-Si,as band upon heating or applying mechanical stress could be attributed to changes in the distribution of bond parameters such as bond length and bond angle. Upon heating, isotropic expansion occurs and the density changes; upon applying mechanical stress, anisotropic strain is induced and a significant change in the Si-O-Si bond angle is observed. From molecular dynamics simulations of silica glasses, we show that the peak position shift correlates better with the asymmetric change in the Si-O bond length distribution, rather than the Si-O-Si bridge angle, the O-Si-O tetrahedral angle, or the density change. This new finding provides an insight into how and why the ν Si-O-Si,as IR peak of soda lime silica (SLS) glass shifts upon chemical strengthening via ion exchange and thermal tempering. This article is protected by copyright. All rights reserved.

Description: Spray drying is a versatile method to perform atomization, drying, and granulation. Spray dryers enable agglomeration of particles into a spherical granule form with a nano-meter size and thus very high specific surface areas (SSA). For this, the synthesized Zn(OH) 2 precipitate should be concurrently atomized and dried under desired spray drying conditions. The drying process has many complex and critical parameters. In order to obtain ZnO nanopowders in a spherical granule form the inlet temperature and the flow rate of the hot air, the feeding rate and the solid-liquid ratio of the suspension, need to be optimized for 150°C≤ITHA≤180°C, 5 mL/min≤FRS≤15 mL/min, 50 g/L≤SLRS≤200 g/L, 0.4 m 3 /min≤FRHA≤0.6 m 3 /min and 60°C≤OTDC≤90°C respectively. The powders synthesized by these modifications have a range of 5-200 nm (TEM) and high SSA of 21-114 m 2 .g −1 (average particle size: 9-51 nm according to the SSA analyses) depending on the drying process parameters. The ZnO nanopowders have a soft granule structure according to the SSA analyses. Therefore, there is no need to grind the powders. They can be easily processed at all of the mixing and forming steps. In addition, they do not contain any contamination coming from grinding. This article is protected by copyright. All rights reserved.

Description: Effect of isovalent Zr dopant on the colossal permittivity (CP) properties was investigated in (Zr+Nb) co-doped rutile TiO 2 ceramics, i.e., Nb 0.5% Zr x Ti 1- x O 2 . Compared with those of only Nb-doped TiO 2 , the CP properties of co-doped samples showed better frequency-stability with a lower dielectric loss. Especially, a CP up to 6.4 × 10 4 and a relatively low dielectric loss (0.029) of x = 2% sample were measured at 1 kHz and room temperature. Moreover, both dielectric permittivity and loss were nearly independent of direct current bias, and measuring temperature from room temperature to around 100 °C. Based on the XPS, the formation of oxygen vacancies was suppressed due to the incorporation of Zr. Furthermore, it induced the enhancement of the conduction activation energy according to the impedance spectroscopy. The results will provide a new routine to achieve a low dielectric loss in the CP materials. This article is protected by copyright. All rights reserved.

Description: Here we study the diffusive transfer of water into silica glass in the presence of externally applied stresses, and stresses caused by water induced swelling of the glass. By considering the simultaneous action of water penetration into the surface of silica glass and the development of swelling stresses in the water-penetrated zone, several experimental findings previously published in the literature can be interpreted quantitatively. These include an apparent decrease of the diffusivity with time, an increase of water solubility in the surface region under compressive loading, the opposite effect under tensile loading and a reversal of these two effects deeper within the glass. These expectations are fully met in published experiments carried out to date. This article is protected by copyright. All rights reserved.

Description: We provide an insight into the switching of near-morphotropic composition of PZT using molecular dynamics simulations and electrical measurements. The simulations and experiments exhibit qualitatively similar hysteretic behavior of the polarization for different temperatures showing widening of the P-E loops and the decrease of the coercive field towards high T. Remarkably, we have shown that polarization switching at low temperatures occurs via polarization rotation, that is a fundamentally different mechanism from high temperature switching, which is nucleation driven. This article is protected by copyright. All rights reserved.

Description: Sodium aluminophosphate glasses were evaluated for their bone repair ability. The glasses belonging to the system 45Na 2 O-xAl 2 O 3 -(55-x)P 2 O 5 , with x=(3, 5, 7, 10 mol%) were prepared by a melt-quenching method. We assessed the effect of Al 2 O 3 content on the properties of Na 2 O-Al 2 O 3 -P 2 O 5 (NAP) glasses, which were characterized by density measurements, DSC analyses, solubility, bioactivity in simulated body fluid and cytocompatibility with MG-63 cells. To our best knowledge, this is the first investigation of calcium-free Na 2 O-Al 2 O 3 -P 2 O 5 system glasses as bioactive materials for bone tissue engineering. This article is protected by copyright. All rights reserved.

Description: Pb(In 1/2 Nb 1/2 )O 3 -Pb(Sc 1/2 Nb 1/2 )O 3 -PbTiO 3 (PIN-PSN-PT) ternary ceramics with compositions near morphotropic phase boundary (MPB) were fabricated by solid-state-sintering process. Dielectric and piezoelectric properties of xPIN-yPSN-zPT (x=0.19, 0.23 and z=0.365, 0.385) ceramics were investigated as a function of temperature, showing high T r-t and T c on the order of 160~200°C and 280~290°C, respectively. The xPIN-yPSN-0.365PT (x=0.19 and 0.23) ceramics do not depolarize at the temperature up to 200°C, showing a better thermal stability when compared to the state-of-the-art relaxor-PbTiO 3 systems. A slight variation (〈9%) of k p , k t and k 33 was observed in the temperature range of 25°C-160°C for xPIN-yPSN-0.385PT (x=0.19 and 0.23) ceramics. Rayleigh analysis was employed to quantify the contribution of domain wall motion to piezoelectric response, where the domain wall contribution was found to increase with composition approaching MPB for PIN-PSN-PT system. This article is protected by copyright. All rights reserved.

Description: Schematic image showing the preparation of ZnO nanorods and ZnO/ZnS core-shell nanorods on the FTO substrate. “Sonochemical Synthesis of ZnO-ZnS Core-Shell Nanorods for Enhanced Photoelectrochemical Water Oxidation” by Se Young Cheon, Jae-Sik Yoon, Kyung Hee Oh, Kyu Yeon Jang, Jong Hyeok Seo, Joon Yong Park, Sang-Il Choi, Won Seok Seo, Gaehang Lee, and Ki Min Nam. Cover image courtesy of Kyung Hee Oh. Schematic image showing the preparation of ZnO nanorods and ZnO/ZnS core-shell nanorods on the FTO substrate. “Sonochemical Synthesis of ZnO-ZnS Core-Shell Nanorods for Enhanced Photoelectrochemical Water Oxidation” by Se Young Cheon, Jae-Sik Yoon, Kyung Hee Oh, Kyu Yeon Jang, Jong Hyeok Seo, Joon Yong Park, Sang-Il Choi, Won Seok Seo, Gaehang Lee, and Ki Min Nam. Cover image courtesy of Kyung Hee Oh.

Description: ReB 2 -type hexagonal Osmium diboride (OsB 2 ) has been predicted to exhibit higher hardness than its orthorhombic phase, but hexagonal-orthorhombic phase transformation occurs at temperature higher than 600°C, resulting in the decrease of its hardness. Therefore, ReB 2 -type hexagonal OsB 2 samples with Re addition were produced by a combination of mechanochemical method and pressureless sintering technique, and the effects of Rhenium (Re) addition on phase composition, thermal stability and mechanical properties of OsB 2 were investigated in this study. X-ray diffraction (XRD) analysis of the as-synthesized powders by high energy ball milling indicates the formation of hexagonal Os 1- x Re x B 2 solid solution with Re concentration of 5 and 10 at. % without forming a second phase. After being sintered at 1700 °C, part of the hexagonal phase in OsB 2 transformed to orthorhombic structure, while Os 0.95 Re 0.05 B 2 and Os 0.9 Re 0.1 B 2 maintained their hexagonal structure. This suggests that the thermal stability of the hexagonal OsB 2 was significantly improved with by the addition of Re.. Scanning electron microscopy (SEM) photographs show that all of the as-sintered samples exhibit a homogeneous microstructure with some pores and cracks formed throughout the samples with the relative density 〉 90%. The measurements of micro-hardness, nano-hardness, and Young's modulus of the OsB 2 increased with Re addition, and these properties of the sample with 5 at. % addition of Re is higher than that with 10 at. % Re. This article is protected by copyright. All rights reserved.

Description: For fiber-optic mid-infrared bio- and chemical-sensing, Ge-Sb-Se glass optical fibers are more attractive than Ge-As-Se because of: (i) lowered toxicity and (ii) lower phonon energy and hence transmission to longer wavelengths, with potential to reach the spectral ‘fingerprint region’ for molecular sensing. There is little previous work on Ge-Sb-Se fibers. Here, fibers are fabricated from two glass compositions in the Ge x Sb 10 Se 90-x atomic (at.) % series. Both glass compositions are of similar mean-coordination-number, lying in the overconstrained region, yet of different chemical composition: stoichiometric Ge 25 Sb 10 Se 65 at. % and non-stoichiometric Ge 20 Sb 10 Se 70 at. %. Thermal analysis on bulk glasses has previously shown that the former exhibited the maximum glass stability of the series. However, during fiber-drawing of Ge 25 Sb 10 Se 65 at. %, the preform tip is found to undergo surface-devitrification to monoclinic GeSe 2 alone, the primary phase, no matter if the preform is an annealed, as-melted rod or annealed, extruded rod. The heating rate of the preform-tip to the fiber-drawing temperature is estimated to be up to ~ 100 °C min −1 to ~ 490 °C. Lower heating rates of 10 °C min −1 using thermal analysis, in contrast, encourage crystallization of both Sb 2 Se 3 and GeSe 2 . The non-stoichiometric: Ge 20 Sb 10 Se 70 at. % composition drew successfully to low optical loss fiber, no matter whether the preform was an annealed, as-melted rod or annealed, extruded rod. This article is protected by copyright. All rights reserved.

Description: With the objective of incorporating some divalent transition metal ions in thoria and to comprehend its effect on the crystal structure, electronic as well as catalytic properties, Ni 2+ , Cu 2+ and Cd 2+ substituted thoria samples were synthesized by the epoxide gel method. Of the two concentrations investigated, 10 mol% of Ni 2+ , Cu 2+ and Cd 2+ could be substituted retaining the fluorite structure and phase separation into individual oxides was noticed for 15 mol %. The average crystallite size of thoria and 10 mol % substituted samples was 14 nm. Le-Bail structural refinements of PXRD patterns indicated marginal increase in unit cell constant for the Cd 2+ substituted sample and a decrease for Ni 2+ and Cu 2+ substituted samples. In addition to broadening of the band at around 460 cm −1 (F 2g vibration of the fluorite), less intense band near 560-590 cm −1 emerged for all the transition metal ion containing samples in the Raman spectra implying the formation of oxygen defects. The absorption edge in the UV-visible spectra moved toward higher wavelength for the Cd 2+ , Ni 2+ and Cu 2+ containing samples as compared to pure thoria. In addition, d-d transition was observable for Ni 2+ and Cu 2+ containing samples. By virtue of these changes in the electronic structure of transition metal ion containing samples, they were examined as catalysts for the degradation of aqueous Rhodamine-6G (Rh-6G) dye solutions under visible radiation. This article is protected by copyright. All rights reserved.

Description: In this work, the Ag or Au nanoparticle single-existing and co-existing tellurite glasses doped with Eu 3+ were prepared, and the influence of gold or silver nanoparticles on the photoluminescence of tellurite glasses doped with Eu 3+ were investigated. The photoluminescence of tellurite glasses doped with Eu 3+ was enhanced by the surface plasmon absorption of gold or silver nanoparticles, and the maximum luminescence enhancement factors caused by the silver and gold nanoparticles are 4.8 and 3.5 factors, respectively. The differentiation of luminescence enhancement mechanisms caused by the gold or silver nanoparticles was demonstrated. The enhanced luminescence mechanism of the Au nanoparticle single-existing tellurite glasses doped with Eu 3+ was from the increasing of radiative decays rate caused by the Au nanoparticles. The excitation field enhancement caused by the Ag nanoparticles was responsible for the luminescence enhancement of the Ag single-existing tellurite glasses doped with Eu 3+ . About 4.2-factors luminescence enhancement was observed in the Ag and Au nanoparticle co-existing tellurite glasses doped with Eu 3+ , which is attributed to the increasing of radiative decays rate and excitation field enhancement caused by the Au and Ag nanoparticles. This article is protected by copyright. All rights reserved.

Description: Strontium plays important physicochemical and biological roles in the applications of bone repair materials. And the available methods of Sr doping in bone cements were believed to make a key effect on the biodegradation and Sr ion release behaviors of cements. In this work, Sr-doped octacalcium phosphate (Sr-OCP), Sr-doped α-tricalcium phosphate (Sr-α-TCP), SrCO 3 and SrCl 2 with different actual availability of Sr 2+ were imported into α-TCP bone cements; and their effects on the biodegradation and ions release of cements were comparatively investigated. Incorporation of different Sr carriers had led to distinct hydration morphologies, crystal evolutions, degradation rates and microenvironments of bone cements during their in vitro biodegradation. Compared with other Sr carriers, Sr-OCP facilitated the hydration reaction of α-TCP, which induced the enhanced degradation and Sr ion release behaviors. In conclusion, Sr-OCP was supposed to be a more potential Sr carrier applied in the synthesis of biodegradable Sr doped calcium phosphate bone cements. This article is protected by copyright. All rights reserved.

Description: The present study investigated the relationship between sulfide capacity and the average non-bridging oxygens to tetrahedral cations (NBO/T) of CaO–SiO 2 –Al 2 O 3 –MgO slags. The sulfide capacity and NBO/T increase with increasing Al 2 O 3 /SiO 2 ratio and X C aO due to increasing basicity. The inflected dependence of sulfide capacity and NBO/T observed at a eutectic composition. Thermodynamic investigations revealed that the inflected dependence is caused by the effects of mixing enthalpy and entropy components in eutectic composition. Quantitative analysis of sulfide capacity and NBO/T revealed a proportional linear relationship between the two variables. Based on these experimental results, the corresponding structure-property relationships concerning sulfide capacity, viscosity, and stability are discussed in detail. This article is protected by copyright. All rights reserved.

Description: This work demonstrates the critical role of orbital hybridizations in the FeO 6 octahedral distortion, composition-driven phase transition, and bonding covalency in multiferroic (Bi 1- x Sm x )FeO 3 ( x =0.10-0.20) ceramics in the vicinity of the morphotropic phase boundary (MPB). Sequential composition-driven transitions from the polar rhombohedral R 3 c to antipolar orthorhombic Pbam and then Pnma phases were revealed as the system crosses the MPB with increasing Sm. A coexistence of ferroelectric (FE) rhombohedral R 3 c and antiferroelectric (AFE) PbZrO 3 -like orthorhombic Pbam symmetries was identified by the 1/2{000}, 1/4{000}, 1/4{110}, 1/4{111}, and 1/4{121}, superlattice diffractions at x =0.12-0.16. In addition to R 3 c and Pbam space groups, the nonpolar SmFeO 3 -like orthorhombic Pnma space group becomes the predominant phase at x =0.20 confirmed by the 1/2{100} superlattice diffractions. The Fe L 3 -edge and oxygen K-edge synchrotron X-ray absorptions indicate that the O 2 p –Fe 3 d and O 2 p –Bi 6 s /6 p orbital hybridizations were decreased as the system approaches the MPB. This article is protected by copyright. All rights reserved.

Description: Molecular dynamics simulations of seven compositionally different sodium calcium alumino-borosilicate glasses showed formation of 4 B and 5 Al more consistent with experimental data without compromising the other structural features that match experimental results observed in recent simulations of these glasses. Analysis of the dry surfaces of these glasses show a lack of 4 B in the top 5-6Å of the surface in comparison to the bulk concentration for all glasses and no 5 Al. Upon exposure to water, the simulations show that the 3 B in the top 5-6Å of the glasses are preferentially attacked, decreasing the number of B bonds to O originally from the glass, indicating a change in the glass network. Inclusion of all B-O bonds in the top 5-6Å (i.e. including O from water) shows a decrease in 3 B but an increase in 4 B that is consistent with NEXAFS analysis, which the simulations show are hydroxylated. There is an increase in the concentration of 3 Al in the dry surface in comparison to the bulk, but exposure to water converts almost all of these 3 Al to 4 Al. Hydroxyl concentrations vary from 2.6/nm 2 to 4.1/nm 2 , with SiOH and BOH dominating these surface hydroxyls. Upon exposure to water, network linkages to B are preferentially ruptured. This, and the preferential loss of the non-bridging oxygen sites attached to Na, provide atomistic evidence of the initial stages of removal of B and Na from glass surfaces exposed to water. This article is protected by copyright. All rights reserved.

Description: A novel family of Ga 2 S 3 –Sb 2 S 3 –XI (XI= PbI 2 , CsI, AgI) was investigated to understand the role of metal halides and exploit new chalco-halide glasses for infrared optics. The dependence of the thermal properties, infrared optical properties, and structural information of the novel family on different metal–iodines was investigated. Results showed that metal halides increase the glass stability but decrease the glass network connectivity. The compositional dependence of the short-wave cut-off edge is associated with the electronegativity difference between the cations and anions of the metal halides. Raman study showed that the metal–iodine modified the glass structure mainly through the iodide content, and the cations dissolved in the glass network mostly as charge compensators for the aperiodic network. For the glasses in the series Ga 2 S 3 –Sb 2 S 3 –XI–Dy 3+ , Dy 3+ emission increased in the PbI 2 - and CsI-doped glasses but decreased in the AgI-doped glass due to the combined effect of dysprosium and oxygen. For all that, these novel glasses are highly promised for use in infrared optics. This article is protected by copyright. All rights reserved.

Description: Hexagonal tungsten nitrides were synthesized by the metathesis reaction between WCl 6 and NaN 3 under high pressure and temperature. As well as tungsten mononitride (WN), which is isostructural with hexagonal tungsten carbide (WC), a nitrogen-rich hexagonal compound was also confirmed in the product. The ratio of nitrogen to tungsten was determined to be 1.34 by the quantitative combustion method. The composition was estimated to be W 2.25 N 3 by considering the crystal structure that is best explained by the X-ray diffraction profile. Volume compression measurements under hydrostatic pressure revealed that the WC-type WN has a higher bulk modulus ( K 0 = 342 ± 1 GPa) than that of hexagonal W 2.25 N 3 ( K 0 = 291 ± 2 GPa). This article is protected by copyright. All rights reserved.

Description: Domain engineering via oxygen vacancy, V O •• , loading achieved by A/B modification as well as quenching treatment, was utilized for Ba 0.8 Sr 0.2 TiO 3 (0.8 BSTs) in an attempt to enhance the microwave tunable characteristics. For similar grain sizes, the domain sizes were notably reduced for all non-stoichiometric BSTs, indicating that the loaded V O •• (as a consequence of Ti defects, V Ti ′′′′ ) played a role in the nuclei for new domain walls. The tunability T at 100 MHz under a direct current field of 30 V/20 μm increased steadily as the domain size ( d.s .) declined for all BSTs, regardless of the A/B ratio, due to the d.s . effect. The tunable characteristics in non-stoichiometric BSTs having a similar d.s . of ˜ 190 nm were then compared. The tunability and tan δ decreased for A/B = 1.002 (0.2 mol% Ti defects). The introduced V O •• formed pinning centers that restricted domain wall motion, leading directly to lower tunability and smaller dielectric loss. However, V O •• -overloaded samples (i.e., A/B ≥ 1.005) exhibited increased values for tan δ due to V O •• conduction in the domains. The quench treatment of 0.8 BST (with A/B = 1.002) samples resulted in a d.s . reduction from 191 to 170 nm. These quenched specimens showed greater tunability, T total , originating from the strengthened dipole contribution, T dipole , as a consequence of the d.s . effect. The tan δ of the quenched specimens was essentially unchanged, indicating a homogenous V O •• distribution via the quench, effectively reducing the mobile V O •• (which contributes to electrical conduction) in the domains. Consequently, the achieved figure of merit via domain engineering was 2.25 at 100 MHz for the quenched BST with A/B = 1.002, which was 1.54 times larger than that of unmodified BST. This article is protected by copyright. All rights reserved.

Description: 2016 ACerS Ceramographic Exhibit & Competition Category: SEM 2016 ACerS Ceramographic Exhibit & Competition Category: SEM

Description: The thermal effects of Er / Yb doped NaYF 4 phosphor induced by 980 / 1510 nm laser diode irradiation were intuitively and contrastively investigated using an infrared thermal imaging technology with real-time online monitoring. The Yb 3+ / Er 3+ codoped materials have strong thermal effects and high temperature elevation under 980 nm irradiation. However, the severe thermal effects of materials with higher Er 3+ ion doping concentration is remarkably attributed to the cross relaxation between the Er 3+ ions under 980 nm irradiation. The energy transfer between Er 3+ and Yb 3+ ions in Er 3+ / Yb 3+ codoped materials also contributes to the thermal effects under 1510 nm laser diode irradiation. Under the same testing conditions, the temperature elevation ∆T of samples induced by 1510 nm laser diode irradiation is lower than that induced by 980 nm laser diode irradiation. The temperature rising rate and elevation ∆T value of samples depend on the ion doping concentration and power density of the laser diode excitation. The internal temperature of the samples exhibits deep temperature gradient under 980 / 1510 nm laser diode irradiation. By comparing the two kinds of thermometry methods, the temperature value calculated by fluorescence intensity ratio is almost similar to that obtained through infrared thermal imaging technology under higher excitation power pumping. This article is protected by copyright. All rights reserved.

Description: In this research, series of Ag nanoclusters (Ag NCs) contained oxyfluoride glasses were prepared by using the melt quenching method, in which the REF 3 (RE= Y, La and Gd) were selected as dopants to control their size distribution. The absorption, steady and time-resolved PL spectra were carried to investigate the size dependent luminescence properties of Ag NCs. The spectral results indicated that the super broadband emission of Ag NCs is contributed by the spin-allowed (blue side) and the spin-forbidden (red side) transitions, respectively. Besides, the introduction of REF 3 (RE= Y, La and Gd) can promote the formation of Ag NCs with different sizes and therefore modulated their luminescence properties. The maximum external quantum yields of Ag NCs with emissions at 430, 510, 520 and 570 nm were evaluated to be 24.6%, 40.7%, 56.3% and 30.7%, respectively, which can be obtained in SAg, SAgLa, SAgGd, and SAgY. This article is protected by copyright. All rights reserved.

Description: Bulk niobium diboride ceramics were consolidated by spark plasma sintering (SPS) at 1900 °C. SPS resulted in dense specimens with a density of 98% of the theoretical density and a mean grain size of 6 μm. During the SPS consolidation, the hexagonal boron nitride (h-BN) was formed from B 2 O 3 on the powder particle surface and residual adsorbed nitrogen in the raw diboride powder. The room-temperature strength of these NbB 2 bulks was 420 MPa. The flexural strength of the NbB 2 ceramics remained unchanged up to 1600 °C. At 1700 °C an increase in strength to 450 MPa was observed, which was accompanied by the disappearance of the secondary h-BN phase. Finally, at 1800 °C signs of plastic deformation were observed. Fractographic analysis revealed a number of etching pits and steplike surfaces suggestive of high-temperature deformation. The temperature dependence of the flexural strength of NbB 2 bulks prepared by SPS was compared with data for monolithic TiB 2 , HfB 2 and ZrB 2 . Our analysis suggested that the thermal stresses accumulated during SPS consolidation may lead to additional strengthening at elevated temperatures. This article is protected by copyright. All rights reserved.

Description: Nd 3+ -doped silicate glass (Nd-glass) was employed as a color filter for a white LED based on red and green phosphor (RG-LED), to manipulate the photoluminescence spectral shape and thus to provide a wider color gamut. The hypersenstive transition of Nd 3+ : 4 I 9/2 4 G 5/2 , 2 G 7/2 was adjusted via glass composition and Nd concentration, and improved absorbance as well as reduced the absorption bandwidth. The effective absorption of the Nd-glass at ~580 nm reduced the spectral linewidth of the green and red emissions, improving the color reproduction range. The color gamut of the RG-LED was improved from 75.3 to 81.6% NTSC by the introduction of Nd-glass as a color filter. Reliability under high operating current and high temperature were also examined and discussed. This article is protected by copyright. All rights reserved.

Description: TaB 2 powders were synthesized by a molten-salt assisted borothermal reduction method at 900–1000 °C in flowing argon using Ta 2 O 5 and amorphous B as starting materials. The results indicated that the presence of liquid phase, such as B 2 O 3 and NaCl/KCl, accelerated the mass transfer of reactant species and resulted in the complete finish of the reaction at low temperatures. The obtained TaB 2 powders exhibited a flow-like shape assembled from nanorods grow along [001] direction or c-axis. The morphology of the synthesized TaB 2 powders could be tailored by the amount of B 2 O 3 or NaCl/KCl. This article is protected by copyright. All rights reserved.

Description: Conventional ceramic processing techniques do not produce ultrafine grained materials. However, since the mechanical and optical properties are highly dependent on the grain size, advanced processing techniques are needed to obtain ceramics with a grain size smaller than the wavelength of visible light for new laser sources. As an empirical study for lasing from an ultrafine grained ceramics, transparent Yb 3+ :Y 2 O 3 ceramics with several doping concentrations were fabricated by spark plasma sintering (SPS) and their microstructures were analyzed, along with optical and spectroscopic properties. Laser oscillation was verified for 10 at.% Yb 3+ :Y 2 O 3 ceramics. The laser ceramics in our study were sintered without sintering additives, and the SPS produced an ultrafine microstructure with an average grain size of 261 nm, which is about one order of magnitude smaller than that of ceramics sintered by conventional techniques. A load was applied during heating to enhance densification, and an in-line transmittance near the theoretical value was obtained. An analysis of the crystal structure confirmed that the Yb 3+ :Y 2 O 3 ceramics were in a solid solution. To the best of our knowledge, the present study is the first report verifying the lasing properties of not only ultrafine grained but also Yb-doped ceramics obtained by SPS. This article is protected by copyright. All rights reserved.

Description: Bismuth-doped (Bi) glasses and fibers have raised considerable attention for broadband emission and tunable fiber lasers in the near infrared (NIR) region. However, they suffer from low efficiency and it remains challenging to enhance Bi NIR emission. Here, we propose a facile way to enhance and tune the Bi NIR emission by adjusting optical basicity and modulating the boron and aluminium coordination in borate glasses. We find that BO 4 and AlO 5 species favor Bi NIR emission, right followed by the analyses of static emission specra, the fourier transform infrared (FT-IR) and nuclear magnetic resonance (NMR) spectroscopy. Furthermore, abnormal Bi NIR luminescence phenomenon and boron anomaly were observed, which are attributed to the synthetic effect of B and Al coordination transformation. Besides, we find that BO 4 tetrahedron plays a major role in enhancing Bi NIR emission at low Al content, while AlO 5 hexahedron group will dominate at high Al concentration. Our investigation may give an insight into the luminescent behaviors of Bi in borate glasses and contribute to improving the performance of Bi-doped fiber and fiber lasers in future. This article is protected by copyright. All rights reserved.

Description: The effect of glass composition on surface layers formed through reaction between strong acid and several silicate and aluminosilicate glasses was studied through transmission-IR, ATR- IR, XPS, SIMS and nano-indentation analyses. It was shown that aluminum is depleted from the surface while molecular water is diffused into the surface layer of glasses with high levels of aluminum. Nano-indentation experiments indicated that the hardness of the surface layers were decreased compared with that of the bulk region and the degree of the softening was more significant in the high aluminum glass. This article is protected by copyright. All rights reserved.

Description: Si 3 N 4 ceramics with different amount of Fe 5 Si 3 were prepared by adding FeSi 2 . Residual thermal stress distribution and elastic energy around Fe 5 Si 3 particles in various depths were calculated. Interface status between second phase particles and matrix was analyzed in terms of stress and energy. High tangential compressive stresses and low radial tensile stresses are generated along the surface of the ceramics. Elastic strain energy caused by unit interface is high around big particles in deep area of the ceramics. Microcracks around the interface preferentially tend to be generated in different area according to the relationship of thermal expansion coefficient. Residual stresses and microcracks around Fe 5 Si 3 particles have great influence on mechanical properties. Fracture toughness of Si 3 N 4 ceramics with similar Si 3 N 4 particle size distribution increases with amount of Fe 5 Si 3 , and fine Fe 5 Si 3 particles could enhance the strength of Si 3 N 4 ceramics. Si 3 N 4 ceramics with exceed 1.2GPa strength were prepared. This article is protected by copyright. All rights reserved.

Description: Polymer-derived SiC and SiOC aerogels have been synthesized and characterized both from the microstructural point of view and as sorbent materials for removing organic dyes (Methylene Blue, MB, and Rhodamine B, RB) from water solutions. Their adsorbent behavior has been compared with a polymer-derived SiC foam and a commercial mesoporous silica. The aerogels can efficiently remove MB and RB from water solution and their capacity is higher compared to the SiC foams due to the higher surface area. The SiOC aerogel remains monolithic after the water treatment (allowing for an easy removal without the need of a filtration step) and its maximum capacity for removing MB is 42.2 mg/g, which is higher compared to the studied mesoporous silica and many C-based porous adsorbents reported in the literature. The reason for this high adsorption capacity has been related to the unique structure of the polymer-derived SiOC, which consists of an amorphous silicon oxycarbide network and a free carbon phase. This article is protected by copyright. All rights reserved.

Description: We present a novel and effective method for sintering ceramic coatings onto metallic substrates. This new technique, called Flame-assisted flash sintering (FAFS), utilizes a flame as both a heating source and a conformal, current-carrying top electrode to facilitate flash sintering. Using this method, Yttria-stabilized Zirconia (8 mol% Y, 8YSZ) coatings are sintered onto stainless steel substrates to controlled degrees of porosity in rapid fashion. Flame-assisted flash sintering utilizes a dynamic soft electrode for flash sintering and has commercial potential to sinter ceramic coatings on complex-shaped substrates for a variety of applications including tribological or thermal protection coatings.

Description: Cylindrical DCDC glass specimen for crack extension study - Courtesy Fabrice Célarié, Patrick Houizot, Clément Roux-Langlois, Theany To (Glass Engineering Team, MV Dept, IPR UMR 6251, Univ. Rennes 1, France). Cylindrical DCDC glass specimen for crack extension study - Courtesy Fabrice Célarié, Patrick Houizot, Clément Roux-Langlois, Theany To (Glass Engineering Team, MV Dept, IPR UMR 6251, Univ. Rennes 1, France).

Description: Dissolution of Al 2 O 3 particles into a MgAl 2 O 4 (spinel) matrix is accompanied by a volumetric expansion that is predicted to lead to a compressive stress field upon cooling, resulting in a promising microstructure for enhanced toughening of transparent spinel. The present study explores the conditions to form such a microstructure by hot pressing powders of Al 2 O 3 particles and at temperatures that promote dissolution of the Al 2 O 3 . Tough, particulate-reinforced composites were formed under lower temperatures and shorter times, but single phase, cubic spinel was formed at 1700°C for 10 hours. The single phase spinel made in this way exhibited a toughness of 2.26 ± 0.17 MPa√m, higher than the equivalent non-stoichiometric spinel made by traditional methods, 1.72 ± 0.06 MPa√m. X-ray diffraction measurements revealed lattice parameter changes consistent with the dissolution of Al 2 O 3 into spinel. Mechanics modeling reveals that toughening arises due to the volume expansion as Al 2 O 3 dissolves into the spinel matrix. This article is protected by copyright. All rights reserved.

Description: Nano-multilayered TiAlN/CrAlN coatings combining advantages of Ti-Al-N and Cr-Al-N are considered to be promising candidates for advanced machining processes. Here, the structure and thermal properties of Ti 1- x Al x N/CrAlN (x = 0.48, 0.58 and 0.66) multilayered coatings as well as referential Ti 1- x Al x N and Cr 0.32 Al 0.68 N monolithic coatings were investigated. Ti 1- x Al x N coatings show a structural transformation from cubic (c) structure for x = 0.48 to mixed cubic and wurtzite (c/w) structure for x = 0.58 and 0.66, and Cr 0.32 Al 0.68 N coating exhibits a single cubic structure. Through a multilayer arrangement with Cr 0.32 Al 0.68 N layers, the Ti 0.52 Al 0.48 N and Ti 0.42 Al 0.58 N layers can be stabilized in their metastable cubic structure, but the Ti 0.34 Al 0.66 N layer still tends to crystallize in the mixed cubic and wurtzite structure. The hardness of Ti 0.52 Al 0.48 N/CrAlN and Ti 0.42 Al 0.58 N/CrAlN coatings is higher than that of corresponding monolithic coatings regardless of as-deposited and annealed states. Especially, after annealing at 800 °C, the Ti 0.52 Al 0.48 N/CrAlN and Ti 0.42 Al 0.58 N/CrAlN coatings reach their peak hardness of ~34.2 and 32.8 GPa due to the spinodal decomposition of Ti 1- x Al x N layers. However, the oxidation resistance of Ti 1- x Al x N/CrAlN coatings is mainly up to the Al content of Ti 1- x Al x N layers, where only the Ti 0.34 Al 0.66 N/CrAlN coating can survive the 10 h exposure to air at 1000 °C. This article is protected by copyright. All rights reserved.

Description: Citric acid-based sol-gel method has been used to synthesize metal oxides widely. Iron-based one-dimensional nanostructured materials, including Fe 2 O 3 nanotubes and Fe 3 O 4 nanofibers, have been successfully prepared by directly annealing electrospun citric acid-based precursor fibers under different atmospheres in this study. Thermo-gravimetric and differential thermal analyses were carried out from room temperature to 800 °C under air and argon atmospheres, respectively. The results reveal the formation mechanisms for Fe 2 O 3 nanotube and Fe 3 O 4 nanofiber. Fe 2 O 3 tubular structures with average inner diameter about 500 nm and wall thickness about 20 nm were obtained. Fe 3 O 4 nanoparticles were self-assembled along the one dimensional orientation to form Fe 3 O 4 nanofibers with average diameter around 500 nm. The reflection losses as a function of frequency for the samples with 23 and 33 wt% Fe 3 O 4 nanofibers in paraffin were examined. The frequency dependence of reflection losses under various matching thicknesses (2, 3, 4, 6 and 8mm) was simulated. The as-fabricated Fe 3 O 4 nanofibers can be believed to be promising candidates as highly effective microwave absorbers. This article is protected by copyright. All rights reserved.

Description: A series of SnO x -Sb 2 O 3 thin film varistors were fabricated through hot-dipping tin oxide films deposited by radio frequency magnetron sputtering in Sb 2 O 3 powder at varied temperatures in air. With the hot-dipping temperature (HDT) increased from 200 to 600 °C, the nonlinear coefficient (α) of the samples increased first and then decreased, reaching the maximum at 500 °C, which was mainly determined by the completeness of high-resistant Sb 2 O 3 layer at tin oxide grain boundary and the chemical composition of tin oxide films. Correspondingly, the leakage current ( I L ) decreased first and increased later. The breakdown electric field ( E 100mA ) decreased constantly with increasing HDT. The SnO x -Sb 2 O 3 film varistors prepared at 500 °C exhibited the optimum nonlinear properties with the maximum α of 10.88, the minimum I L of 36.3 mA/cm 2 , and an E 100mA of 0.0188 V/nm. The obtained nanoscaled film varistors would be promising in electrical/electronic devices working in low-voltage. This article is protected by copyright. All rights reserved.

Description: A reversible electrochromic effect has been observed for the first time in flame spray pyrolysis (FSP) processed ε-WO 3 thin films without the use of an ion storage layer and an electrolytic layer. The dark coloration that appears upon the application of a voltage in films deposited on top of interdigitated gold electrodes is localized to the low voltage (-) electrode arm and it switches to the opposite arm upon a reversal of the polarity. Raman spectroscopy indicated that the coloration was not due to intercalation. It is argued here that the coloration is driven by the asymmetric ferroelectric properties of the ε-WO 3 crystals and that this electrochromic reversibility is intrinsically coupled with the polarization switching of the device. This article is protected by copyright. All rights reserved.

Description: While it is well established that ionic conduction in lithium aluminosilicates proceeds via hopping of Li ions, the nature of the various hoping-based mechanisms in different temperature regimes has not been fully elucidated. The difficulties associated with investigating the conduction have to do with the presence of grains and grain boundaries of different orientations in these usually polycrystalline materials. Herein, we use electrochemical impedance spectroscopy (EIS) to investigate the ion conduction mechanisms in β-eucryptite, which is a prototypical lithium aluminosilicate. In the absence of significant structural transitions in grain boundaries, we find that there are three conduction regimes for the one-dimensional ionic motion along the c axis channels in the grains, and determine the activation energies for each of these temperature regimes. Activation energies computed from molecular statics calculations of the potential energy landscape encountered by Li ions suggest that at temperatures below 440 °C conduction proceeds via cooperative or correlated motion, in agreement with established literature. Between 440 °C and 500°C, the activation barriers extracted from EIS measurements are large and consistent with those from atomistic calculations for uncorrelated Li ion hopping. Above 500 °C the activation barriers decrease significantly, which indicates that after the transition to the Li-disordered phase of β-eucryptite, the Li ion motion largely regains the correlated character. This article is protected by copyright. All rights reserved.

Description: Control of the chemical state and local environment of Cr dopant in glass through self-limited nanocrystallization is presented. Interesting wavelength-tunable and ultra-broadband near-infrared (NIR) luminescence with the full width at half maximum (FWHM) of about 380 nm in obtained Cr-activated glass-ceramics are demonstrated. The results indicate that the presented method may be an effective means of fabricating multifunctional optical gain materials and wideband fiber light sources. This article is protected by copyright. All rights reserved.

Description: The Y 3 MgAl 3 SiO 12 ceramics with pure phase were successfully synthesized by solid state sintering reaction method for the first time. Their microwave dielectric properties were investigated as a function of sintering temperature. Their microstructure characteristics and ionic occupation sites of tetrahedral and octahedral units were characterized and analyzed by SEM&EDS and Rietveld refinement of X-ray powder diffraction data. Crystal structure of Y 3 MgAl 3 SiO 12 is isostructural to Y 3 Al 5 O 12 with a cubic garnet structure and space group of Ia-3d, which contains YO 8 dodecahedra, (Mg/Al oct )O 6 octahedral and (Si/Al tet )O 4 tetrahedral units. The Qf and ε r values of different samples are strongly dependent on the distribution of grain sizes, grain sizes, and porosity. The samples sintered at 1550°C exhibit optimized microwave dielectric properties with relative permittivity (ε r ) of 10.1, Qf values of 57,340GHz (at 9.5 GHz), and τ f values of -32 ppm/°C. Such properties indicate potential application of Y 3 MgAl 3 SiO 12 as microwave substrates. This article is protected by copyright. All rights reserved.

Description: In this study, we have investigated the effect of planar defect on thermal and electron transport as compared to point defect in the rutile TiO 2- x . Two series of bulk TiO 2- x (2- x = 2.000, 1.992, 1.985, 1.972, and 1.934) samples were prepared using different heat treatment procedures to clearly identify the presence of point and planar defects via powder X-ray diffraction. The charge carrier density and mobility were determined from Hall effect measurements using van der Pauw method. The elastic properties of the studied materials such as bulk modulus, shear modulus, Young's modulus, compressibility, and Debye temperature were evaluated from the measured sound velocities, while their thermal conductivities were determined from the thermal diffusivities, heat capacities, and densities measured in the temperature range between 300 and 1073 K. The theoretical calculation based on Klemens-Callaway model have been performed to analyze the thermal conductivity. As a result, the effect of planar defects on the carrier mobility was almost equivalent to the effect produced by point defects. On the other hand, the presence of planar defects significantly reduced the thermal conductivity of TiO 2- x as compared to point defect due to strong phonon scattering induced by planar defects. This article is protected by copyright. All rights reserved.

Description: Nanoindentations with a Berkovich type indenter were performed on (001) strontium titanate (STO) single crystal at 25 °C and 350 °C, analyzing the influence of temperature on the indentation size effect (ISE) and dislocation structure around the residual impression. It is found that the STO exhibits an ISE, which is strongly reduced at 350 °C compared to 25 °C. The dislocation structure around the residual impression has been resolved using an etch-pit technique. At 25 °C, the extension of the dislocation pile-ups were found to be shorter as compared to 350 °C. This also correlates with the smaller size effects at 350 °C. Peach-Koehler forces and the elastic-plastic indentation stress field were used to model the influence of the lattice frictional stress on the dislocation pile-ups. Based on an equilibrium position of the outermost dislocations, the average lattice frictional stresses were calculated to be 89 MPa and 46 MPa at 25 °C and 350 °C, respectively. This article is protected by copyright. All rights reserved.

Description: The proton conductivity in functional oxides is crucial in determining electrochemistry and transport phenomena in a number of applications such as catalytic devices and fuel cells. However, single characterization techniques are usually limited in detecting the ionic dynamics at the full range of environmental conditions. In this report, we probe and uncover the links between the microstructure of nanostructured ceria (NC) and parameters that govern its electrochemical reaction and proton transport, by coupling experimental data obtained with time-resolved Kelvin probe force microscopy (tr-KPFM), electrochemical impedance spectroscopy (EIS), and finite element analysis. It is found that surface morphology determines the water splitting rate and proton conductivity at 25 °C and wet conditions, where protons are mainly generated and transported within surface physisorbed water layers. However, at higher temperature (i.e., ≥ 125 °C) and dry conditions, when physisorbed water evaporates, grain size and crystallographic orientation become significant factors. Specifically, the proton generation rate is negatively correlated with the grain size, whereas proton diffusivity is facilitated by surface {111} planes and additional conduction pathways offered by cracks and open pores connected to the surface. This article is protected by copyright. All rights reserved.

Description: A small quantity of Eu 3+ ions was doped in the lead-free ferroelectric K 0.5 Na 0.5 NbO 3 - x LiNbO 3 (KNN- x LN, 0≤ x ≤0.08) ceramics to investigate the NbO 6 octahedral distortion induced by the increasing LN content. In addition, the phase structure, ferroelectric and photoluminescence properties of K 0.5 Na 0.5 NbO 3 - x LiNbO 3 :0.006Eu 3+ (KNN- x LN:0.006Eu 3+ ) lead-free piezoelectric ceramics were characterized. All the X-ray diffraction, Raman spectra, dielectric constant versus temperature measurements and the photoluminescence of Eu 3+ ions demonstrated that the prepared ceramics undergo a polymorphic phase transition (PPT, from orthorhombic to tetragonal phase transformation) with the rising LN content, and the PPT region locates at 0.05≤ x ≤0.06. The ferroelectric properties, Raman intensity ratios and photoluminescence intensity ratios show similar variations with the increasing LN content, all with a maximum value achieved at the PPT region. We believe that the close relationship among the ferroelectric properties, Raman intensity ratios and photoluminescence intensity ratios is caused by the NbO 6 octahedral distortion. The photoluminescence of Eu 3+ ion was discussed basing on the crystal-symmetry principle and Judd-Ofelt theory. This article is protected by copyright. All rights reserved.

Description: The microstructural, in vitro and in vivo properties of the microwave-synthesized samples were investigated using the optical microscope, scanning electron microscope, X-ray diffraction, differential scanning calorimeter, contact angle goniometer, cell cytotoxicity assay and chick chorioallantoic membrane (CAM) model in the study. When the calcium sulfate dihydrate (CSD) precursor underwent microwave irradiation treatment at temperatures between 100°C and 160°C, the crystal morphologies and crystalline structures were transformed from (tablet-like CSD (monoclinic)) (tablet-like CSD (monoclinic) + long column α-calcium sulfate hemihydrate (α-CSH, hexagonal)) (long column CSD (monoclinic) + short column α-CSH (hexagonal)) (uniform short column α-CSH (hexagonal)). The high-purity α-CSH with uniform short column crystals around 10 μm in length can be synthesized at 160°C for 10 min and exhibits a higher hydrophilic feature in blood. Moreover, the cell cytotoxicity assay indicated that the microwave-synthesized samples possessed well biocompatibility. In vivo results also demonstrated that the microwave-synthesized α-CSH not only induces angiogenesis formation but also facilitates osteogenesis. Therefore, the microwave-synthesized α-CSH is a promising bone graft substitute that can be applied in dental and orthopedic fields. This article is protected by copyright. All rights reserved.

Description: x Pb(Zn 0.5 Te 0.5 )O 3 -(1- x )Pb(Zr 0.5 Ti 0.5 )O 3 (PZnTe-PZT) ceramics were prepared by the solid state reaction method. The phase structure, microstructure, ferroelectric and dielectric properties and thermal expansion properties were systematically investigated. X-ray diffraction analysis showed the morphotropic phase boundary (MPB) existed at the composition of x =0.08, which was the coexistence of the rhombohedral phase and the tetragonal phase. The grain size of ceramics decreased rapidly from 10~20μm to 1~3μm when the PZnTe was added in. The PZnTe-PZT ceramics at the MPB composition showed the largest high field effective piezoelectric coefficient d 33 * and the lowest strain hysteresis H . The dielectric permittivity and phase transition temperature exhibited strongly compositional dependence. A good linear relation was shown in T m temperature versus x content and a DPT behavior was found in x PZnTe-(1- x )PZT ( x =0.02~0.08). The thermal expansion properties showed a low thermal expansion coefficient in the low temperature while a high thermal expansion coefficient in the high temperature. Besides, the thermal expansion curve also showed the characteristic of DPT in PZnTe-PZT ceramics. This article is protected by copyright. All rights reserved.

Description: Phase relations in the ZrO 2 –TiO 2 system were studied experimentally using X-ray diffraction (XRD), scanning electron microscopy combined with dispersive X-ray spectrometry (SEM/EDX) and differential thermal analysis (DTA). The homogeneity ranges of ZrO 2 and TiO 2 , as well as high temperature disordered β-(Zr x Ti 1-x ) 2 O 4 compound were defined in the temperature range of 1700-2040 K. Temperature and composition of eutectic reaction were measured. The standard enthalpy of formation of the β-ZrTiO 4 compound was obtained by using high-temperature oxide-melt solution calorimetry. High temperature heat capacity measurement for the β-ZrTiO 4 compound was performed in the temperature range from 250 K to 1200 K. Thermodynamic description of ZrO 2 –TiO 2 system has been derived based on obtained experimental results and data from literature. This article is protected by copyright. All rights reserved.

Description: Due to poor mechanical properties and anti-oxidation properties, etc of single phase ultra-high temperature ceramics (UHTCs), the second phase such as SiC was usually introduced for improving those properties. Herein, a novel stratage for synthesis of binary HfC-SiC ceramics has been presented. A Hf-O-Hf polymer as HfO 2 precursor has been synthesized for preparing soluble HfC-SiC precursors owing high solid content and low viscosity solutions without additional organic solvents. The structure of PHO was characterized by FTIR and 1 H-NMR, The crystalline behavior and morphlogies of polymer-derived ceramics were identified by XRD, SEM-EDS and TEM. It was shown that PHO firstly transformed into HfO 2 , and then reacted with in-situ carbon derived from DVB and PCS thus producing cubic HfC through carbothermal reduction. In addition, the obtained HfC–SiC nanopowders exhibited spherical morphology with diameter less than 100nm, while the Hf, Si and C are homogeneously distributed. This article is protected by copyright. All rights reserved.

Description: Surface chemistry and topo-physical properties determine the interactions of biomaterials with their physiological environment. Ferroelectrics hold great promise as the next generation of scaffolds for tissue repair since they feature tunable surface electrical charges, piezoelectricity, and sensing capabilities. We investigate the topography, wettability, chemical stability, and cytotoxicity in salient ferroelectric systems such as (1-x) (Na 1/2 Bi 1/2 )TiO 3 -xBaTiO 3 , (1−x)Ba(Zr 0.2 Ti 0.8 )O 3 –x(Ba 0.7 Ca 0.3 )TiO 3 , and Pb(Zr,Ti)O 3 to test their suitability as biomaterials. The lead-free ferroelectrics promote in vitro cell viability and proliferation to a considerably high extent. 0.94 mol (Na 1/2 Bi 1/2 )TiO3- 0.06 mol BaTiO 3 showed the greatest potential leading to a cell viability of (149 ± 30) % and DNA synthesis of (299 ± 85) % in comparison to the reference. Lead leaching from Pb(Zr,Ti)O 3 negatively affected the cultured cells. Wettability and chemical stability are key factors that determine the cytotoxicity of ferroelectrics. These variables have to be considered in the design of novel electroactive scaffolds based on ferroelectric ceramics. This article is protected by copyright. All rights reserved.

Description: Bi 2 O 2 Se oxyselenides, characterized with intrinsically low lattice thermal conductivity and large Seebeck coefficient, are potential n -type thermoelectric material in the mediate temperature range. Given the low carrier concentration of ~10 15 cm −3 at 300 K, the intrinsically low electrical conductivity actually hinders further enhancement of their thermoelectric performance. In this work, the isovalent Te substitution of Se plays an effective role in narrowing the band gap, which notably increases the carrier concentration to ~10 18 cm −3 at 300 K and the electron conduction activation energy has been lowered significantly from 0.33 eV to 0.14 eV. As a consequence, the power factor has been improved from 104 μW·K −2 ·m −1 for pristine Bi 2 O 2 Se to 297 μW·K −2 ·m −1 for Bi 2 O 2 Se 0.96 Te 0.04 at 823K. Meanwhile, the suppressed lattice thermal conductivity derives from the introduced point defects by heavier Te atoms. The gradually decreased phonon mean free path reflects the increasingly intense phonon scattering. Ultimately, the ZT value attains 0.28 for Bi 2 O 2 Se 0.96 Te 0.04 at 823K, an enhancement by a factor of ~2 as compared to that of pristine Bi 2 O 2 Se. This study has demonstrated that Te-substitution of Se could synergistically optimize the electrical and thermal properties thus effectively enhancing the thermoelectric performance of Bi 2 O 2 Se. This article is protected by copyright. All rights reserved.

Description: Ba 1+1/ M [Si 2 O 5+1/ M ] low-permittivity microwave dielectric ceramics are prepared using the conventional solid-state method. Pure phases are obtained in barium silicates with M =1, 3, 4, 5, and ∞, except for M =7, in which two phases, Ba 5 Si 8 O 21 and BaSi 2 O 5 , are observed. As the complexity of the crystal structure described by the Shannon information per reduced unit cell increases, the τ f value tends to change from a negative to a positive value, except for M =5, which has the highest complexity. A single Ba 5 Si 8 O 21 phase with ε r anomaly peak at −180 °C exhibits a rare positive τ f value (+25 ppm/°C), which is a novel temperature compensator. This article is protected by copyright. All rights reserved.

Description: Phase equilibria of the PbO-SiO 2 system have been established for a wide range of compositions: (a) liquid in equilibrium with silica polymorphs (quartz, tridymite and cristobalite) between 740°C and 1580°C, at 60-90 mol.% SiO 2 ; (b) with lead silicates (PbSiO 3 , Pb 2 SiO 4 and Pb 11 Si 3 O 17 ) and lead oxide (PbO) between 700°C and 810°C. A high-temperature equilibration/quenching/electron probe X-ray microanalysis (EPMA) technique has been used to accurately determine the compositions of the phases in equilibrium in the system. Significantly, no liquid immiscibility has been found in the high-silica range, and the liquidus in this high-silica region has been accurately measured. The phase equilibria information in the PbO-SiO 2 system is of practical importance for the improvement of the existing thermodynamic database of lead-containing slag systems (Pb-Zn-Fe-Cu-Si-Ca-Al-Mg-O). This article is protected by copyright. All rights reserved.

Description: Sintering reactions of clay bodies have previously been studied by numerous experiments that involve quenching of the sintered ceramic bodies to room temperature and analyzing the reaction product by different analytical techniques. In this study, green bodies containing quartz, alkali feldspar, kaolinite, and calcite, were progressively fired in air at various temperatures from room temperature to about 1060°C. For the first time, mineral reactions and textural relationships were studied in situ as a function of temperature and time with a spatial resolution of a few micrometers by confocal hyperspectral Raman imaging. Gehlenite, wollastonite, and pseudowollastonite could unambiguously be identified as newly formed phases during sintering, and their textural evolution could be followed with temperature and time. From 800°C onwards wollastonite formed at the direct contact to gehlenite, whereby at temperatures higher than 990°C wollastonite seems to be gradually replacing gehlenite. The crystallization of pseudowollastonite was observed already ~290°C below the accepted critical temperature (~1125°C) for the wollastonite-to-pseudowollastonite transformation, suggesting that pseudowollastonite can form metastably. The results of this study demonstrate that hyperspectral Raman imaging is a powerful method to study in situ phase transitions and recrystallization processes at grain boundaries during high-temperature sintering of ceramic materials. This article is protected by copyright. All rights reserved.

Description: For solid specimens, Young's modulus is commonly determined from straightforward uniaxial tension experiments. However, honeycomb specimens are far more challenging to test in tension, and it is therefore desirable to conduct bending experiments to determine Young's modulus. The premise of this work is that the bending response of honeycomb specimens may be significantly different from that of solid specimens, and therefore it is necessary to establish a sound protocol for the determination of the axial Young's modulus of honeycomb specimens under bending. Toward this goal, we present results of a study that combines experimental, finite element simulation, and classical beam theory approaches. These results confirm that accurate measurements of Young's modulus of honeycombs require careful consideration of the specimen geometry and analysis of the data. We demonstrate that the use of conventional Bernoulli-Euler's beam theory to interpret the data requires very slender specimens. We also show that less slender specimens can be used if the experimental data is interpreted on the basis of three-dimensional elasticity theory and numerical simulations. A third option is to use a combination of moderately slender specimens and Timoshenko's beam theory.

Description: 2016 ACerS Ceramographic Exhibit & Competition Category: Microanalysis/Combined Techniques, 3rd Place 2016 ACerS Ceramographic Exhibit & Competition Category: Microanalysis/Combined Techniques, 3rd Place

Description: This basic research deals with the microstructure evolution of a W-doped ZrB 2 ceramic, as-sintered and upon oxidation at 1650°C. Transmission electron microscopy enabled to disclose microstructural features occurred during oxidation never observed before. In the pristine material, (Zr,W)B 2 solid solutions surround the original ZrB 2 nuclei, whereas refractory W-compounds at triple junctions and clean grain boundaries are distinctive of this ceramic. After oxidation, the microstructure is typified by intragranular nanostructures, in which nanosized W inclusions remained trapped within ZrO 2 grains, or decorate their surfaces. The understanding of the oxidation reactions occurring in the system as a function of the oxygen partial pressure was fundamental to conclude that W-based compounds do not notably suppress or retard the oxidation of ZrB 2 ceramics.