ALBERT

Beschreibung: Glass–ceramic tubes were developed from Bayan Obo tailings and fly ash by the centrifugal method. This paper investigates the corrosion rate of the glass–ceramics exposed to hydrochloric acid solution. The leaching concentration of cations into the solution is analyzed by ICP. XRD analysis and Raman spectra were used for identifying the phase transformation of corrosion reactions. The changes in morphological and chemical composition were investigated using SEM combined with EDS. The results revealed that the formed corrosion layer was amorphous phase. It was also indicated that Fe 2 O 3 and CaF 2 exerted some negative effect on the corrosion resistance in HCl solution.

Beschreibung: Herein, we report on the crystal structures of Nb 2 AlC and TiNbAlC—actual composition (Ti 0.45 ,Nb 0.55 ) 2 AlC—compounds determined from Rietveld analysis of neutron diffraction patterns in the 300–1173 K temperature range. The average linear thermal expansion coefficients of a Nb 2 AlC sample in the a and c directions are, respectively, 7.9(5) × 10 −6 and 7.7(5) × 10 −6  K −1 on one neutron diffractometer and 7.3(3) × 10 −6 and 7.0(2) × 10 −6  K −1 on a second diffractometer. The respective values for the (Ti 0.45 ,Nb 0.55 ) 2 AlC composition—only tested on one diffractometer—are 8.5(3) × 10 −6 and 7.5(5) × 10 −6  K −1 . These values are relatively low compared to other MAX phases. Like other MAX phases, however, the atomic displacement parameters (APDs) show that the Al atoms vibrate with higher amplitudes than the Ti and C atoms, and more along the basal planes than normal to them. When the predictions of the APDs obtained from density functional theory are compared to the experimental results, good quantitative agreement is found for the Al atoms. In case of the Nb and C atoms, the agreement was more qualitative.

Beschreibung: In this study, lithium disilicate (LS 2 ) glass samples with different particle sizes ranging from less than 105 to 850 μm were prepared. These specimens were inserted in a Pt-Rh DSC crucible and heated to 850°C at different rates (ϕ = 0.5–30 K/min) to identify their crystallization peaks. The activation energies for the overall crystallization ( E ) and the Avrami coefficient ( n ) were evaluated using different nonisothermal models. Specifically, n was evaluated using the Augis–Benett model and the Ozawa method, and E was evaluated using the Kissinger and Ligero methods. As expected, the coarse particles mainly crystallized in the volume, while surface crystallization was predominant in the samples with particle sizes of less than 350 μm. This result was confirmed through SEM analysis of the double stage heat-treated samples. In contrast with previous studies, our results demonstrated that the activation energy decreased as the particle size increased. In addition, no clear correlation between the peak intensity (δ T p ) and the particle size was observed.

Beschreibung: Selective Laser Melting (SLM) is a candidate for on-site manufacturing as its characteristics of energy source and powder-based fabrication process are suitable for use with in situ material. The feasibility of using lunar regolith simulant to create objects with SLM process is investigated in this study. The process parameters are optimized and multiple objects are fabricated. A qualitative chemical analysis is carried out with scanning electron microscopy using energy-dispersive X-ray emission. Lastly, properties such as particle size distribution, particle shape, and crystal structure of the lunar simulant powder as well as the crystallinity and hardness of the fabricated objects are investigated.

Beschreibung: SrLn 2 Al 2 O 7 (Ln = La, Nd, Sm) ceramics belonging to Ruddlesden–Popper phase with n  =   2 in space group I 4 /mmm have been prepared by a standard solid-state reaction process. Their crystal structure refinement and infrared reflection spectra analysis have been carried out to investigate the correlations among the crystal structure, polar phonon modes, and microwave dielectric characteristics. Heavy deviations of cation–oxygen bonds in (Sr,Ln)O 12 , (Sr,Ln)O 9 , and AlO 6 polyhedra are observed, and the deviations significantly affect the microwave dielectric characteristics of the present ceramics. The polar phonon modes with lower frequencies due to translation vibration of Sr/La ions against the AlO 6 octahedron give the primary contribution to dielectric constant and intrinsic dielectric loss at microwave frequencies. The calculated Q  ×  f value is significantly larger than the measured one, and this result is very obvious for SrLa 2 Al 2 O 7 ceramics where the calculated one (130,300 GHz) is about 2 times of the measured one (68,800 GHz).

Beschreibung: In this letter, 2-μm Pb 0.97 La 0.02 (Zr 0.75 Sn 0.18 Ti 0.07 )O 3 antiferroelectric thick film with tetragonal structure was prepared. The effects of operating electric field, temperature, and frequency on the thermal–electrical energy harvesting capacity of the film were studied by using the Olsen cycle. The results demonstrated that giant energy harvesting effect could be realized in the antiferroelectric thick film. The maximum harvestable energy density per cycle of the film was about 7.8 J/cm 3 at 1 kHz, which was the largest reported value to date. The corresponding energy harvesting efficiency was 0.53%. Moreover, the film had a low leakage current density (about 7.3 × 10 −7 and 3.9 × 10 −5  A/cm 2 at 25 and 200°C, respectively), which was favorable for its application in the devices of the thermal–electrical energy harvesting.

Beschreibung: Discharged energy properties of PbO–SrO–Na 2 O–Nb 2 O 5 –SiO 2 glass-ceramics with crystallization time from 1 to 1000 min were investigated by measuring their hysteresis loops (described as quasi-static measuring method) and pulse-discharge current-time curves (described as dynamic measuring method). The results show the same trend for both measuring methods: With the increment of crystallization time, the discharged energy density increases gradually, while the energy efficiency decreases. The highest energy efficiencies were obtained in the sample with crystallization time of 1 min, which are 96.3% and 82.4%, corresponding quasi-static and dynamic measurement, respectively. The reduction of energy efficiency with crystallization time is attributed to combined effect of ferroelectric polarization and interfacial polarization, and part of the corresponding energy could not release in the pulse-discharge process.

Beschreibung: A Ba 0.6 Sr 0.4 TiO 3 –ZnO–B 2 O 3 composite ink was prepared and used for the manufacturing of fully inkjet-printed metal-insulator-metal varactors. The dielectric thick films were co-fired with printed silver electrodes at 850°C and show a fine grained microstructure. The films have a relative permittivity of ε r  = 129 and a dielectric loss of tan δ = 0.043 at f  =   3 GHz. Printed varactors with different dielectric film thickness were prepared. The characterization of the printed structures and 3D electromagnetic simulations of the layout reveal the strong influence of electrode inductance and fringing effects on the properties of the components. The printed varactors reach tunabilities between 14.4% and 16.4% by applying a tuning field of 5 V/μm. To demonstrate the capability of the inkjet printing process for the preparation of tunable microwave devices, a fully inkjet-printed phase shifter was fabricated. It is based on seven pairs of the printed varactors and reaches a phase shift of 180° and a figure of merit of 19°/dB at 3.4 GHz.

Beschreibung: New lead-free perovskite solid solution ceramics of (1  − x )( Bi 1/2 Na 1/2 ) TiO 3 – x Ba ( Ni 1/2 Nb 1/2 ) O 3 [(1− x )BNT– x BNN, x  =   0.02–0.06) were prepared and their dielectric, ferroelectric, piezoelectric, and electromechanical properties were investigated as a function of the BNN content. The X-ray diffraction results indicated that the addition of BNN has induced a morphotropic phase transformation from rhombohedral to pseudocubic symmetry approximately at x  =   0.045, accompanying an evolution of dielectric relaxor behavior as characterized by enhanced dielectric diffuseness and frequency dispersion. In the proximity of the ferroelectric rhombohedral and pseudocubic phase coexistence zone, the x  =   0.045 ceramics exhibited optimal piezoelectric and electromechanical coupling properties of d 33 ~121 pC/N and k p ~0.27 owing to decreased energy barriers for polarization switching. However, further addition of BNN could cause a decrease in freezing temperatures of polar nanoregions till the coexistence of nonergodic and ergodic relaxor phases occurred near room temperature, especially for the x  =   0.05 sample which has negligible negative strains and thus show the maximum electrostrain of 0.3% under an external electric field of 7 kV/mm, but almost vanished piezoelectric properties. This was attributed to the fact that the induced long-range ferroelectric order could reversibly switch back to its original ergodic state upon removal of external electric fields.

Beschreibung: Light transmission in polycrystalline magnesium fluoride was studied as a function of the mean grain size at different wavelengths. The mean grain size was varied by annealing hot-pressed billets in argon atmosphere at temperatures ranging from 600°C to 800°C for 1 h. The grain-size and grain-orientation distributions were characterized by electron back scatter diffraction. The scattering coefficients were calculated from the in-line transmittance measured at various wavelengths. The scattering coefficient of polycrystalline magnesium fluoride increased linearly with the mean grain size and inversely with the square of the wavelength of light. It is shown that these trends are consistent with theoretical models based on both a limiting form of the Raleigh–Gans–Debye (RGD) theory of particle scattering and light retardation theories that take refractive index variations along the light path. Quantitative predictions of the theories are, however, subject to uncertainly due to the restrictive assumptions made in the theories and difficulties in representing the microstructure in the theoretical models. In particular, grain-size distribution has a significant influence on the scattering coefficient calculated using particle scattering models.

Beschreibung: Determining the absolute chronology of ceramic artifacts has significant implications for archeological and historical research. Wilson, Hall et al . recently suggested a new technique for direct absolute dating of archeological ceramics based on a moisture-induced chemical reaction, called rehydroxylation (RHX) dating. RHX dating proceeds by measuring the mass of chemically combined water in the ceramics in the form of OH hydroxyls, and the mass gain rate at the Effective Lifetime Temperature (ELT) that the ceramics experienced over its lifetime. To date, ELT determinations have been based on estimates of the ceramic's lifetime temperature history; taking into account weather and climate data and the depth at which the artifact was found. The uncertainty in determining the ELT can be a major component of the overall dating uncertainty. Here, we propose an alternative method which relies minimally on weather and climate data, and provides more precise determinations of the ELT and the ceramic age . The proposed method (SAS: Same Age Samples) involves a minimum of four measurements of the RHX mass gain rate constant for two ceramic samples of the same age at two temperatures. We show via simulations that the proposed SAS method can determine the ELT with a precision of 0.2 K which is comparable to the best ELT determination based on lifetime temperature history, and also comparable to available microbalance temperature resolutions of around 0.1 K. The corresponding percent age error is then 1.4%, or 43 yr for a 3000-yr-old ceramic. The proposed SAS method should be tested with ceramic samples of different ages, whose ELT are well-known.

Beschreibung: Glasses in the Na 2 O–CaO–SrO–ZnO–SiO 2 system have previously been investigated for suitability as a reagent in Al-free glass polyalkenoate cements (GPCs). These materials have many properties that offer potential in orthopedics. However, their applicability has been limited, to date, because of their poor strength. This study was undertaken with the aim of increasing the mechanical properties of a series of these Zn-based GPC glasses by doping with nitrogen to give overall compositions of: 10Na 2 O–10CaO–20SrO–20ZnO–(40−3 x )SiO 2 – x Si 3 N 4 ( x is the no. of moles of Si 3 N 4 ). The density, glass-transition temperature, hardness, and elastic modulus of each glass were found to increase fairly linearly with nitrogen content. Indentation fracture resistance also increases with nitrogen content according to a power law relationship. These increases are consistent with the incorporation of N into the glass structure in threefold coordination with silicon resulting in extra cross-linking of the glass network. This was confirmed using 29 Si MAS-NMR which showed that an increasing number of Q 2 units and some Q 3 units with extra bridging anions are formed as nitrogen content increases at the expense of Q 1 units. A small proportion of Zn ions are found to be in tetrahedral coordination in the base oxide glass and the proportion of these increases with the presence of nitrogen.

Beschreibung: Hercynite nanoparticles were obtained by pulsed laser ablation of hercynite in liquid media technique. Colloidal solutions of hercynite nanoparticles were synthesized in three different liquids by ablation using 532-nm output of a pulsed Nd:YAG laser with three laser fluencies. Transmission electron microscopy, selected area electron diffraction, energy-dispersive X-ray analysis, and X-ray photoelectron spectroscopy were used for the characterization of these nanoparticles. The nanoparticles obtained were of spherical shapes with cubic crystalline structure. It was observed that the laser fluence and liquid media could affect the morphology and size of hercynite nanoparticles.

Beschreibung: This study presents a thermodynamic analysis to predict the type of initial, amorphous oxide overgrowth (i.e., am - Al 2 O 3 or am - SiO 2 ) on bare Al – Si alloy substrates. This analysis have taken into account the energies associated with both its interfaces (interface between the Al – Si alloy substrate and the thin oxide film and interface between the thin oxide film and vacuum) along with the bulk Gibbs free energy of oxide formation. This developed analysis is then applied for various parameters, such as, Si alloying element content at the substrate/oxide interface, the growth temperature, the oxide film thickness (up to 1 nm), and various low-index crystallographic surfaces of the substrate. It is found that am - SiO 2 overgrowth is thermodynamically preferred for a combination of lower oxide film thickness, lower growth temperature, and lower Si alloying content at the alloy/oxide interface. This is because of the overcompensation of the lower energies of both the interfaces over the bulk Gibbs free energy. Furthermore, it is found that for all cases, am - Al 2 O 3 forms a more stable interface with Al – Si alloy than am - SiO 2.

Beschreibung: In this study, translucent CeF 3 ceramics was firstly fabricated by hot-pressing, aiming to develop an economical, radiation hard scintillation material. After sintering at 950°C and pressure exertion of 300MPa for 2 h, a transmittance of 10–25% was achieved in the visible region, through a thickness of 0.75 mm. Microstructure investigations indicated the average grain size was around 42.7 μm, with no obvious pores observed on the fracture surface. The X-ray luminescence spectra, decay time, and thermoluminescence spectra were measured, and the results of the ceramics were similar to its corresponding single crystals, which proved it to be a promising scintillation material.

Beschreibung: The effect of direct integration of PZT into LTCC by sintering on its polarization behavior is studied. Due to the typically small thermal expansion of PZT, compressive stresses are expected after cooling, which should promote poling. However, measurements show a strongly reduced remanent polarization compared to free PZT. Analysis of thermal expansion reveals that thermal shrinkage of the PZT is larger than that of LTCC. The impact of this finding on the poling behavior is simulated for the LTCC/PZT module, confirming the experimental observations and allowing for conclusions concerning the suitability of the PZT for integration into LTCC structures.

Beschreibung: Sintered nanoceramics of Pr -doped lanthanum hafnate, La 2 Hf 2 O 7 : Pr , were prepared by means of a high-pressure sintering technique using nanopowders made by Pechini method. Structure, morphology, and spectroscopic properties of the ceramics compared to the starting powder are presented and discussed. Emission and excitation spectra recorded at room temperature as well as at 7 K using synchrotron radiation are presented together with results of luminescence kinetics measurements. In ceramics, at 7 K, the Pr 3+ luminescence from 3 P 0 (blue-green, green, and red region) and 1 D 2 (red) levels is accompanied by a broad-band emission located in the 380–530 nm range of wavelengths, whereas powders gives only the Pr 3+ -related luminescence. Depending on the excitation wavelength, the broad-band emission maximum moves between 430 and 470 nm indicating superposition of at least two components. In sintered nanoceramics, the lifetimes of Pr 3+ emissions from 3 P 0 and 1 D 2 levels were by 10%–20% shorter compared to the powder. The existence of different luminescence centers was proved by the selective emission decays examination. The fast 5 d → 4 f luminescence of Pr 3+ was not observed from either of the two types of La 2 Hf 2 O 7 :Pr materials.

Beschreibung: TiO 2 -doped NiFe 2 O 4 samples were prepared via ball-milling and two-step sintering processes. Besides NiFe 2 O 4 phase, two new phases, NiTiO 3 and Fe 2 TiO 5 , formed in TiO 2 -doped samples. The temperature of sintering onset for 1.0 wt% TiO 2 -doped samples is 230°C lower than that of undoped samples. Early-stage synthesis process of TiO 2 -doped NiFe 2 O 4 ceramics is controlled by grain boundary diffusion mechanism. Increasing TiO 2 content from 0 to 1.0 wt%, the apparent activation energy decreased from 813.919 KJ/mol to 639.361 KJ/mol. The values of relative density and bending strength reached their maximum value with 1.0 wt% TiO 2 . Saturation magnetization, residual magnetization ratio and coercivity decrease with increasing TiO 2 content.

Beschreibung: This article demonstrates the energy harvesting capabilities of bulk lead-free ferroelectric materials using Olsen cycle. Lead-free compositions K[(Nb 0.90 Ta 0.10 ) 0.99 Mn 0.01 ]O 3 (KNTM) and 0.5Ba(Zr 0.2 Ti 0 . 8 )O 3 -0.5(Ba 0.7 Ca 0.3 )TiO 3 (BZT-50BCT) have been explored for their energy harvesting capabilities. Further, we studied the variation in energy density over wide range of applied temperature and electric field. The maximum harness-able energy density for KNTM and BZT-50BCT compositions are found to be 629 J/L (629 kJ/m 3 ) and 87 J/L (87 kJ/m 3 ), respectively. This estimated energy density, obtained for the bulk samples, is comparable with the highest energy density reported to-date (888 J/L for lanthanum-doped lead zirconate titanate (8/65/35 PLZT) thick films).

Beschreibung: Zirconium diboride–based ceramics were studied to explore the effects of high secondary phase content and the relative merits of silicon carbide and zirconium carbide. Densification and grain growth were not influenced by heating rate or composition. Hardness increased with silicon carbide or zirconium carbide content from 18 to 26GPa and 18 to 21.5GPa respectively. Flexural strength was controlled by grain size and mode of crack propagation, and maximized at 380MPa at 20wt% silicon carbide and 590 MPa at 50wt% zirconium carbide. Zirconium carbide enhanced flexural strength better, due to its smaller coefficient of thermal expansion mismatch with zirconium diboride.

Beschreibung: Using the association of low-cost screen-printing technology with the sacrificial layer method, the feasibility of totally released piezoelectric thick-film microceramics of gold-electroded PZT type is studied. After the deposition of the sacrificial layer on an alumina substrate and subsequent printing and drying of gold/PZT/gold layers, the final firing is performed at low temperature. This is followed by the releasing step of the Au/PZT/Au in a diluted acidic solution. Impedance analysis shows that the electrical properties and electromechanical coefficients of poled PZT thick films are still lower than those of PZT ceramics. This result is correlated with the high porosity rate of the PZT layer. However, these piezoelectric microceramics present desirable electromechanical behavior and can therefore be used as dynamic-mode sensors or as actuators to generate vibrations in a structure on which they are bonded. Moreover, the successful fabrication and the electromechanical impedance (EMI) levels obtained on a metallic structure suggest possible structural health monitoring applications of these screen-printed PZT microceramics.

Beschreibung: We have investigated the electromechanical response of potassium sodium niobate ( K 0.5 Na 0.5 NbO 3 or KNN) thick films. The high-field strain hysteresis loops and weak-field converse piezoelectric d 33 coefficient of the films were measured and compared with those of KNN bulk ceramics under the same electric field conditions. The converse d 33 values of the thick films and bulk ceramics were equal to 82.5 and 138 pm/V, respectively, at 0.4 kV/mm. The fundamental difference between the piezoelectric response of the KNN films and the ceramics was studied in terms of the effective (“clamped”) piezoelectric d 33 coefficient. The reduction in the piezoelectric d 33 coefficient of the KNN films, resulting from the clamping by the substrate, was compared to lead-based ferroelectric thick films, including Pb ( Zr , Ti ) O 3 (PZT) and (1 −  x ) Pb ( Mg 1/3 Nb 2/3 ) O 3 − x PbTiO 3 (PMN-PT). We propose a possible explanation, based on the particular elastic properties of KNN, for the small relative difference observed between the “clamped” and “unclamped” (“bulk”) d 33 of KNN, in comparison with lead-based systems.

Beschreibung: Lead zirconate titanate (PbZr 1 −  x Ti x O 3 , PZT)/epoxy composites with one- dimensional epoxy in PZT matrix (called 3-1 type piezocomposites) have been fabricated by tert-butyl alcohol (TBA)-based directional freeze casting of PZT matrix and afterward infiltration of epoxy. The composites with PZT volume fraction ranging from 0.36 to 0.69 were obtained by adjusting initial solid loading in freeze-casting slurry. The effect of poling voltage on piezoelectric properties of the composites was studied for various volume fraction of PZT phase. With the increasing of PZT volume fraction, relative permittivity (ε r ) increased linearly and piezoelectric coefficient ( d 33 and d 31 ) increased step by step. The resultant composites with 0.57 PZT volume fraction possessed the highest hydrostatic piezoelectric strain coefficient ( d h ) value (184 pC/N), voltage coefficient ( g h ) value (13.6 × 10 −3  V/m Pa), and hydrostatic figure of merit (HFOM) value (2168 × 10 −15  Pa −1 ).

Beschreibung: Multiphase borosilicate glass-ceramics represent one candidate to contain radioactive nuclear waste separated from used nuclear fuel. In this work, the thermophysical properties from room temperature to 1273 K were investigated for four different borosilicate glass-ceramic compositions containing waste loadings from 42 to 60 wt% to determine the sensitivity of these properties to waste loading, as-fabricated microstructure, and potential evolutions in microstructure brought about by temperature transients. The thermal expansion, specific heat capacity, thermal diffusivity, and thermal conductivity are presented. The impact of increasing waste loading is shown to have a small but measurable effect on the thermophysical properties between the four compositions, contrasted to a much greater impact observed when transitioning from predominantly crystalline to amorphous systems. Thermal cycling below 1273 K was not found to measurably impact the thermophysical properties of the compositions investigated here.

Beschreibung: The thermal cycling reliability of ceramic/metal laminates is critical for their applications in microelectronic modules. A eutectic bonding process is used to prepare copper/sapphire bilayers in this study. Due to elastic and thermal mismatches between alumina and copper, the Cu/sapphire bilayer cannot pass a thermal cycling test. The thermal cycling reliability can be improved through the use of a metallic nickel interlayer. During the bonding process, the nickel interlayer was oxidized first, reacted with alumina to form a NiAl 2 O 4 spinel phase. The thermal diffusivity of the bilayer with spinel interphase remains high after the temperature cycling test.

Beschreibung: Nano-sized (i) N-doped sodium trititanate and (ii) N and Cu 2+ (Ag + ) co-doped sodium trititanates CuTi 3 NO 6−x (Ag 2 Ti 3 NO 6−x ) were prepared by a solid-state and ion-exchange methods, respectively. The materials were characterized by EDS, PXRD, XPS, FESEM, TEM, UV–visible DRS, and Raman spectroscopy. All the materials were crystallized in monoclinic lattice with P21/m space group. The bandgap energy of all the samples was deduced from their UV–visible DRS profiles. Visible-light-induced photocatalytic oxidation of the methylene blue (MB) and methyl orange (MO), cyclohexene and phenol, was examined. The Ag + co-doped trititanate exhibited the highest photocatalytic activity among the materials investigated.

Beschreibung: We report a novel oscillatory pressure-assisted hot-pressing process for preparing high-quality ceramics. Compared with the samples prepared by conventional pressureless sintering (PS) and hot-pressing (HP), the zirconia ceramic prepared by oscillatory pressure-assisted hot-pressing (OPAHP) exhibited a higher density, smaller grain size, and more homogeneous structure. More remarkably, the strength of the OPAHP sample reached 1556 MPa, which is much higher than the samples prepared by other two techniques. The results suggest that OPAHP is a more effective technique for preparing high-quality zirconia, which is likely applicable to other material systems.

Beschreibung: The formation of a homogeneous Bi 8 TiO 14 phase was successfully achieved in a specimen calcined at 600°C. However, a Bi 4 Ti 3 O 12 secondary phase also developed in specimens calcined at temperatures higher than 600°C, probably because of Bi 2 O 3 evaporation. For specimens sintered above 800°C, a small amount of the Bi 8 TiO 14 phase melted during sintering, with the liquid phase contributing to the densification of the specimens; however, Bi 4 Ti 3 O 12 and Bi 12 TiO 20 secondary phases were still formed in these specimens. The microwave dielectric properties of the Bi 8 TiO 14 phase were considerably affected by variations in the microstructure of the specimens. When the sintering temperature exceeded 825°C, the amount of secondary phases increased, and this decreased the density and Q×f values of the specimens. Bi 8 TiO 14 ceramics sintered at 825°C exhibited promising microwave dielectric properties, with ε r = 47.4, Q×f  =   5370 GHz, and τ f = −16.01 ppm/°C.

Beschreibung: Sensing of low concentrations of two nitroaromatic compounds, 1,2-dinitrotoluene and 2-nitrophenol, is presented. The sensing mechanism is based on surface-enhanced Raman scattering (SERS) using nanostructured tin oxide as the SERS-active substrate. The SnO x nanostructures are synthesized by a simple solgel method and doped with Ag and Au. The Raman signal of a low concentration of the analyte, otherwise extremely weak, becomes significant when the analytes are attached to these substrates. Doping of SnO x nanopowders with Ag and Au leads to a further increase in the Raman intensities. This study demonstrates the scope of ceramic–metal nanocomposites as convenient solid-state SERS sensors for low-level detection.

Beschreibung: Isostatically pressed dense reaction-sintered zirconia–mullite composites were prepared from zircon flour and reactive alumina with different proportions of MgO and CaO additives. The pressed compacts were sintered at elevated temperatures with variable soaking times. Development of different phases and microstructures of the sintered compacts were analyzed to assess the relative influence of the additives on the formation of the zirconia–mullite.

Beschreibung: A new solid solution of (1− x ) Pb ( Mg 1/2 W 1/2 ) O 3 – x Pb ( Zn 1/2 W 1/2 )O 3 has been prepared in the form of ceramics by solid-state reaction with composition x up to 30%. It is found that with the substitution of Zn 2+ for Mg 2+ on the B site of the of complex perovskite structure the antiferroelectric (AFE) Curie temperature T C of PMW increases from 40°C ( x  = 0) to 67°C ( x  = 30%), indicating an enhancement of antiferroelectric order, whereas, at the same time, the phase transition becomes more diffuse due to a higher degree of chemical inhomogeneity. X-ray diffraction analysis indicates that the crystal structure adopts an orthorhombic space group ( Pmcn ) with a decrease in lattice parameter a, but an increase in b and c as the Zn 2+ concentration increases. The low dielectric constant (~ 10 2 ), low dielectric loss (tanδ ≈ 10 −3 ), linear-field-induced polarization, and significantly high breakdown field (~ 125 kV/cm) at room temperature make this family of dielectric materials a promising candidate for ceramic insulators.

Beschreibung: To study the improvement in solid particle impact erosion wear resistances of 3 mol% yttria-stabilized zirconia (3YSZ) ceramic at elevated temperatures up to 1400°C, 2 wt% LaMgA1 11 O 19 was added into 3YSZ to prepare LaMgA1 11 O 19 -3YSZ ceramic for erosion resistance tests with angular corundum abrasive particles. The testing results show that the volume erosion rates of 3YSZ and LaMgA1 11 O 19 -3YSZ ceramic were similar in the temperature range from room temperature to 600°C, then exhibited a sharp increase from 600°C to 1200°C, and dropped again at 1400°C. It was mainly caused by the change in material removal mechanisms from plastic deformation below 600°C to the interaction of transverse cracks in the temperature range from 600°C to 1400°C. The solid particle impact erosion wear properties of 3YSZ ceramic in the temperature range from 600°C to 1400°C were successfully improved by the addition 2 wt% LaMgA1 11 O 19 platelets. Comparing with the volume erosion rate of pure 3YSZ ceramic (0.687 mm 3 /g) at 1200°C, the value of LaMgA1 11 O 19 -3YSZ ceramic (0.551 mm 3 /g) has been decreased by 20%.

Beschreibung: The study presents a ferroelectric–ferromagnetic composite based on a doped PZT-type and ferrite powders. Ferroelectric powder (in amount of 90 wt-%) was based on multicomponent PZT-type materials, while nickel–zinc ferrite Ni 1–x Zn x Fe 2 O 4 (in amount of 10 wt-%) served as the magnetic component of the composite. The syntheses of the ferroelectric–ferromagnetic composite's components were performed using solid-phase sintering, while final densification of the synthesized powder was achieved using free sintering. X-ray analysis of the composite confirmed the presence of strong maxima originating from particular PZT-type material phases, as well as weak peaks from the Ni 0.64 Zn 0.36 Fe 2 O 4 ferrite , without foreign phases. The microstructure of the fracture of the ferroelectric–ferromagnetic composites shows that the ferrite grains on the surface of the ferroelectric component are distributed heterogeneously. Magnetic studies have characterized composite as a soft ferromagnetic material. The study indicated the influence of the magnetic subsystem on the electrical properties. In the two-phase PBZTMC–NZF ceramic composite, the magnetic component causes the decrease in electric permittivity and increased value of the dielectric losses.

Beschreibung: A nearly pure, dense Ti 3 Al 0.8 Sn 0.4 C 2 solid solution bulk has been prepared by two-time hot-pressing sintering a purity Ti 3 Al 0.8 Sn 0.4 C 2 powders at 1450°C with 30 MPa for 30 min in Ar atmosphere. The Ti 3 Al 0.8 Sn 0.4 C 2 powders have been synthesized by sintering a mixture of Ti, Al, Sn, and TiC powders with a molar ratio of 1:0.8:0.4:1.85 at 1450°C for 5 min. The Vickers microhardness and flexural strength of the Ti 3 Al 0.8 Sn 0.4 C 2 have been measured to be 3.51 GPa and 620 MPa, respectively. Buckling and kinking of the layered structure as well as grain delamination crack deflection have been extensively observed around indentations and on the fracture surfaces. The tribological behaviors have been investigated by dry sliding a low-carbon steel disk. Ti 3 Al 0.8 Sn 0.4 C 2 bulk has a friction coefficient of 0.3–0.48 and a very low wear rate of 0.4–4.3 × 10 −6  mm 3 /Nm for the test conditions. These tribological properties are attributed to the presence of a compact self-generating film, which covers uniformly over the friction surface of Ti 3 Al 0.8 Sn 0.4 C 2 .

Beschreibung: Yttrium (Y)-based bioceramics are important materials in radiation therapy and biomedical applications. This paper describes a low-temperature method to prepare yttrium phosphate (YPO 4 ) and Y-doped calcium phosphate (Y-CaP) microspheres using CaP microspheres as template. The as-formed microspheres were characterized using X-ray diffraction, fourier transform infrared spectroscopy, scanning electron microscope, and energy dispersive X-ray spectroscopy, confirming the formation of YPO 4 and Y-CaP microspheres. The process was based on the dehydration effect of ethanol to CaP materials and hydrated ions transportation in amorphous CaP microspheres. The procedure, owing to its simplicity, may provide a new sight for the preparation of Y or rare earth elements-based bioceramic materials.

Beschreibung: Laser machining technique has emerged as an innovative tool to effectively machine the structural ceramics, which previously was nearly impossible using various conventional machining techniques. However, obtaining a desired surface finish via laser machining is still a critical issue. As many physical phenomena act simultaneously during laser machining, it is very difficult to understand their influence in real time and predict the surface topography. To address this issue, a multiphysics-based finite-element modeling approach was implemented to understand the influence of moving laser beam (with lateral overlap) on the generation of corresponding surface topography/profile/roughness during laser machining of structural alumina. A computation model that coupled heat transfer and computational fluid dynamics was designed to understand the combined influence of Marangoni convection, recoil pressure, cooling rates, and surface tension on the evolving surface topography during laser machining of structural alumina under various machining conditions. Both computational and experimental results evidently showed the systematic increase in surface roughness parameters with the increase in lateral overlap (0, 17, 33, 50, 67, and 83%). The results of the computational model are also validated by experimental observations with reasonably close agreement (±3.5%).

Beschreibung: Reverse-flow reactors achieve the desired hydropyrolysis reaction of natural gas and other hydrocarbon feeds at very high temperatures of up to 2000°C, which enables the production of many high-value chemicals. To identify refractory ceramic materials suitable for constructing key components of the reactor, the full range of solid solutions between zirconia and yttria having 18 to 100 mol% yttria have been tested in a laboratory reactor. Conventional yttria-stabilized zirconia (YSZ) materials having 8 mol% Y 2 O 3 appear to accommodate reactor thermal severity, but are prone to a new form of corrosion termed ceramic dusting that is observed when pyrolysis and oxidation cycles are alternated under reverse-flow conditions. Yttria and high yttria–zirconia ceramics having ~80 mol% or more yttria suppress ceramic dusting corrosion in steam-free pyrolysis environments. The addition of low levels of steam of ~5% to the pyrolysis gas stream increases the stability of YSZ materials substantially, so that the stability threshold is closer to 40 mol% Y 2 O 3 in the yttria–zirconia system. The two approaches can be combined to optimize reactor performance. Key experimental results are presented and discussed taking into account the thermodynamic phase stability of the different phases.

Beschreibung: Mullite is one of the popular ceramic materials for different engineering applications due to some of its important properties which include good thermal and chemical stability, high creep resistance, etc. Mullite synthesized by solgel process generally requires lower temperature for processing and generate product with better homogeneity and more purity compared with other conventional processes. Coating of solgel-derived mullite film on surface of a ceramic substrate can improve its thermomechanical properties, making it suitable for applications in different aggravated conditions. This study embarks a comprehensive review on synthesis, characterization and applications of solgel-derived mullite coating.

Beschreibung: Direct coagulation casting of alumina suspension via controlled release of high valence counter ions (DCC–HVCI) using calcium citrate as coagulating agent was reported. Hydrolysis of glycerol diacetate shifts the pH of suspension to weakly acidic region which helps to decompose calcium citrate and release calcium ions. The effect of concentration of glycerol diacetate and calcium citrate on the pH and viscosity of alumina suspension was investigated at 25°C and 60°C, respectively. The pH of suspensions with glycerol diacetate and calcium citrate decreases to 8.6 and 7.5 treated at 25°C and 60°C, respectively. It is indicated that high viscosity is achieved by adding 2 vol% glycerol diacetate and 0.5 wt% calcium citrate which is enough to coagulate the suspension. Green body with compressive strength of 1.0 MPa is obtained by treating the alumina suspension with 2 vol% glycerol diacetate and 0.5 wt% calcium citrate at 60°C for 1 h. The alumina ceramics sintered at 1550°C have homogeneous microstructure with relative density above 99.0%.

Beschreibung: A series of lead-free perovskite solid solutions of (1 −  x ) Na 0.5 Bi 0.5 TiO 3 (NBT)— x BaSnO 3 (BSN), for 0.0 ≤  x  ≤ 0.15 have been synthesized using a high-temperature solid-state reaction route. The phase transition behaviors are studied using dielectric and Raman spectroscopic techniques. The ferroelectric to relaxor phase transition temperature ( T FR ) and the temperature corresponding to maximum dielectric permittivity ( T m ) are estimated from the temperature-dependent dielectric data. Dielectric studies show diffuse phase transition around ~335°C in pure NBT and this transition temperature decreases with increase in x . The disappearance of x -dependence of A 1 mode frequency at ~134 cm −1 for x  ≥ 0.1 is consistent with rhombohedral-orthorhombic transition. In situ temperature dependence Raman spectroscopic studies show disappearance and discontinuous changes in the phonon mode frequencies across rhombohedral ( x  〈 0.1)/orthorhombic ( x  ≥ 0.1) to tetragonal transition.

Beschreibung: Two mole percentage Er -doped ( K 0.5 Na 0.5 ) 1 −  x Li x NbO 3 ceramics have been prepared and their dielectric, ferroelectric, and photoluminescence (PL) properties have been investigated. Under an excitation of 980 nm, the ceramics exhibit intense up-conversion luminescent emission at 548 nm (green), weak emission at 660 nm (red) as well as strong down-conversion luminescent emission in near-infrared (NIR) (1.40–1.65 μm) and mid-infrared (2.60–2.85 μm) regions. Probably due to the induced structure distortion and reduced local symmetry, the PL intensities of the green, red as well as mid-infrared emissions are enhanced by the doping of Li + . Our results show that the Li-doping is effective in establishing a dynamic circulatory energy process to further enhance the PL intensity of the mid-infrared emission at the expense of the NIR emission. At the optimum doping level of Li + (~6 mol%), the full bandwidth at half maximum of the mid-infrared emission reaches a very large value of ~250 nm. The ceramics also exhibit good ferroelectric properties, and thus they should have great potential for multifunctional optoelectronic applications.

Beschreibung: We report a power conversion efficiency of ~0.01% in multistacking of BiFeO 3 /BiCrO 3 bilayer thin films used as active layers in a photovoltaic (PV) device. The films were epitaxially deposited by pulse laser deposition onto (100) oriented CaRuO 3 -coated LaAlO 3 substrates and were subsequently illuminated with 1 sun (AM 1.5). The fill factor is determined to be 0.31%, a remarkable value for ferroelectric- and multiferroic-based PV devices. Our results demonstrate that photocurrent density and photovoltage can be tuned by varying the thickness and number of respective bilayers in the improvement of PV properties of multiferroic heterostructures. The maximum photocurrent is generated at an optimal multilayer thickness of 60 nm, with its origin being mainly ascribed to the contribution of ferroelectric polarization.

Beschreibung: Temperature dependences of thermal and elastic properties, such as the Grüneisen parameters, thermal expansion, bulk modulus, and heat capacity of Ti 2 AlC and Cr 2 AlC , are studied by combining first-principles method and lattice dynamic calculation based on the quasi-harmonic model. Experimental thermal expansion coefficient is also measured for comparison. Thermal expansion coefficients of Ti 2 AlC and Cr 2 AlC show different trends: Ti 2 AlC exhibits anisotropic thermal expansion while Cr 2 AlC shows generally isotropic character. The mechanism is explored by investigating the isotropy or anisotropy of Grüneisen parameters (phonon anharmonicity and thermal pressure) and elastic stiffness (response to thermal pressure) of Ti 2 AlC and Cr 2 AlC . In addition, the calculated bulk modulus of Cr 2 AlC is higher at ambient temperature but decreases faster than the value of Ti 2 AlC as temperature increasing.

Beschreibung: The effects of process parameters on thermal barrier coating (TBC) formation and microstructural properties have been studied. Further understanding of the evolution of properties such as porosity and hardness is an important aspect in the design of efficient TBCs. Plasma-sprayed yttria-stabilized zirconia was coated onto mild steel substrates. The torch was held perpendicular to the substrate to form cone-shaped deposits. Standoff distance (SOD) (80, 90, and 120 mm) and time (15, 30, and 60 s) were altered to investigate the microstructural property relationships of the coatings. Shape characteristics of the coatings were measured via a coordinate measuring machine, and surface roughness measurements were acquired using a 3D optical profiler. The deposition efficiency and coating roughness were affected by SOD and the evolving contour of the underlying surface. Hardness and porosity profiles were mapped to display the effect of process parameters. Dynamic parameters such as particle trajectory, evolving impact angle and dwell time affected changes in porosity, hardness, and density for each coating profile.

Beschreibung: Wear resistance of ceramics can be improved by suppressing fracture, which can be accomplished either by decreasing the grain size or by reducing the size of the deformation zone. We have combined these two strategies with the goal of understanding the atomistic mechanisms underlying the plasticity-controlled friction and wear in nanocrystalline (nc) silicon carbide ( SiC ). We have performed molecular dynamics simulations of nanoscale wear on nc- SiC with 5 nm grain diameter with a nanoscale cutting tool. We find that grain-boundary (GB) sliding is the primary deformation mechanism during wear and that it is accommodated by heterogeneous nucleation of partial dislocations, formation of voids at the triple junctions, and grain pull-out. We estimate the stresses required for heterogeneous nucleation of partial dislocations at triple junctions and shear strength of GBs. Pile up in nc- SiC consists of grains that were pulled out during deformation. We compare the wear response of nc- SiC to single-crystal (sc) SiC and show that scratch hardness of nc- SiC is lower than that of sc- SiC . Our results demonstrate that the higher scratch hardness in sc- SiC originates from nucleation and motion of dislocations, whereas nc- SiC is more pliable due to additional mechanism of deformation via GB sliding.

Beschreibung: A composite geopolymeric material was synthesized from Bayer red mud combined with granulated blast-furnace slag. Thermal pretreatment was applied to improve the solubility of red mud in alkaline solution to promote geopolymerization. The dissolution efficiencies of alumina and silica reached a maximum when red mud was calcined at 800°C, resulting in the highest compressive strength of binders. It was demonstrated that a higher solubility of calcined red mud led to a higher strength of the composite binders. The characteristic microstructures of hydration products were studied to illustrate the geopolymerization process by XRD, FTIR and SEM. The results showed that aluminosilicates were dissolved in the alkaline solution to form nanostructural particulates during the early dissolution process, and then accumulated to form highly dense geopolymeric matrices through solidification reaction. The coexistence of geopolymer and C–(A)–S–H is suggested to contribute to the good performance of the composite binders.

Beschreibung: The crystals Gd 2 SiO 5 and Yb -doped Gd 2 SiO 5 were grown by Czochralski method successfully. Dielectric properties of the two crystals were investigated in the temperature range from 100 to 1100 K and the frequency range from 20 Hz to 10 MHz. Our results revealed that these crystals show intrinsic dielectric behavior in the temperature below room temperature, whereas in above room temperature, a relaxor-like dielectric anomaly and a metal–insulator transition were observed. It was found that the relaxor-like anomaly contains two dielectric relaxations. Impedance analysis showed that the low- and high-temperature relaxations are dipolar- and Maxwell–Wagner-type relaxation, respectively. The transition was found to be strongly related to oxygen vacancies, which leads to positive temperature coefficient of resistance and an abnormal dielectric behavior contrary to the conventional thermally activated behavior at temperatures near the transition temperature.

Beschreibung: Sol–gel-derived TiO 2 films were prepared by dip-coating from Ti (OC 3 H 7 i ) 4 –CH 3 COCH 2 COCH 3 –HNO 3 – H 2 O – C 2 H 5 OH solutions, and the effect of the H 2 O content in solutions on the crystallization of TiO 2 films during the heat treatment at 800°C was discussed. The crystalline phase, crystallite size, grain size, and refractive index of the TiO 2 films depended on the H 2 O / Ti (OC 3 H 7 i ) 4 mole ratios ( x ) in the coating solutions. Highly dense and crystalline rutile films were obtained at x  = 0.5–10, where the crystallites and grains became larger with increasing x . The further increase in x from 10 to 50 reduced the crystallite size and refractive index of the films, where anatase phase appeared at x  = 30–50.

Beschreibung: Dy 3+ -doped Li 8 Bi 2 ( MoO 4 ) 7 (LBM: Dy 3+ ) white-emitting phosphors have been prepared by sol-gel method at about 400~550°C low temperature. The electronic structure of Li 8 Bi 2 ( MoO 4 ) 7 is also calculated using density functional theory. The calculation results show that Li 8 Bi 2 ( MoO 4 ) 7 has a direct band gap with 2.63 eV, the top of the valence band and the bottom of the conduction band are dominated by O 2 p and Mo 4 d , respectively. The effect from Bi 3+ ions is so weak that it could be neglected, which is also be proved by the experimental results. The crystal structure and luminescent properties of the obtained phosphors are characterized by powder X-ray diffraction and photoluminescence spectrum, respectively. Photoluminescence results showed that the obtained phosphors can be excited efficiently by near-UV 387 nm and generated white light emission. The yellow/blue ratio and Commission International de I'Eclairage color coordinates could be tuned by adjusting the concentration of Dy 3+ . Results demonstrated that Li 8 Bi 2 ( MoO 4 ) 7 : Dy 3+ was a potential white light-emitting phosphor candidate for NUV-based w-LEDs.

Beschreibung: In this paper, the phase compositions and the dielectric properties of 3 ZnO –2 B 2 O 3 glass-ceramic prepared by solid-state method were investigated. The X-ray diffraction patterns show that all sintered samples consist of Zn 3 B 2 O 6 and α- Zn (BO 2 ) 2 . The dielectric properties changed significantly with the sintering temperature. After sintering at 650°C for 30 min, the glass-ceramic exhibits optimum dielectric properties: a dielectric constant of 7.5 and a dielectric loss of 0.6 × 10 −3 at 10 MHz. The chemical compatibility with Ag electrode under the co-fired process illustrates a potential application in low temperature co-fired ceramic field for the glass-ceramic.

Beschreibung: A novel technique was utilized to fabricate fine-scaled piezoelectric ceramic/polymer 2-2 composites for high-frequency ultrasonic transducers. Lead zirconate titanate (PZT) was used as raw material. Tape-casted acetylene black tapes were used to define kerfs after sintering. A one-directional supporter was utilized to avoid distortion of PZT elements. PZT elements with 20 ± 2 μm width exhibited good consistency in longitudinal direction. A resonant method was utilized to evaluate the piezoelectric and dielectric properties of the composites. A 72-μm-thick composite with an aspect ratio of ~3.6 exhibited a k t of 0.61 with satisfied piezoelectric and dielectric properties. A prototype high-frequency ultrasonic transducer was fabricated and evaluated by an underwater pulse-echo test. The center frequency was found to be 23.75 MHz, with −6 dB bandwidth of 5.5 MHz.

Beschreibung: The 0.45 Bi ( Mg 0.5 Ti 0.5 ) O 3 –(0.55 −  x ) PbTiO 3 – x ( Bi 0.5 Na 0.5 ) TiO 3 (BMT–PT– x BNT) ternary solid solution ceramics were prepared via a conventional solid-state reaction method; the evolution of dielectric relaxor behavior and the electrostrain features were investigated. The XRD and dielectric measurements showed that all studied compositions own a single pseudocubic perovskite structure and undergo a diffuse-to-relaxor phase transition owing to the evolution of the domain from a frozen state to a dynamic state. The formation of the above dielectric relaxor behavior was further confirmed by a couple of measurements such as polarization loops, polarization current density curves, as well as bipolar strain loops. A large strain value of ~0.41% at a driving field of 7 kV/mm (normalized strain d 33 * of ~590 pm/V) was obtained at room temperature for the composition with x  = 0.32, which is located near the boundary between ergodic and nonergodic relaxor. Moreover, this electric field-induced large strain was found to own a frequency-insensitive characteristic.

Beschreibung: AgNbO 3 is a weak ferroelectric with antiferroelectricity due to Ag displacements at room temperature. A dielectric anomaly at 250 K, which has not been observed previously, reveals a transition between the weak ferroelectric phase (M1 phase) at the higher temperature and a new ferroelectric phase (M0 phase) at the lower temperature in AgNbO 3 . This transition was further verified by the pyroelectric current and differential scanning calorimetry measurements. The spontaneous polarization value is found to be much larger in the M0 phase than that of the M1 phase. A well-defined saturating ferroelectric hysteresis loop can also be observed at 77 K, showing a remnant polarization value of 2.4 μC/cm 2 and a coercive field of 25 kV/cm. All the above results indicate that the larger polarization of the M0 phase mainly comes from the alignment of the antiferroelectric displacements of the Ag atoms.

Beschreibung: In this study, effects of the molar ratio of acetylacetone to aluminum precursor on crystallization and morphology of yttrium aluminum garnet (YAG) were investigated. YAG nanopowders were synthesized by a sol–gel process incorporating different amounts of acetylacetone as a chelating agent and fuels. The dry gels and powders were characterized using FTIR, SDT, XRD, and FESEM. The results showed the lowest YAG crystallization temperature at 800°C when the ratio of acetylacetone/aluminum precursor was two. This is 150°C lower than that without acetylacetone. The crystallite size of YAG powders was about the same, around 20–30 nm.

Beschreibung: The oxidation kinetics of ZrB 2 -30 vol% SiC were analyzed statistically with the goal of understanding the underlying mechanisms for observed variability. A box furnace was used to oxidize specimens for times between 30 s and 100 h at temperatures of 1300°C–1550°C in air. The specimens were characterized to determine weight change, scale thickness, and scale composition to quantify the oxidation behavior. Weight gain measurements of different specimens after 100 min of exposure showed differences of up to 2 mg/cm 2 for the same testing conditions where the average weight gain was 2.54 mg/cm 2 . Variation of 30%–80% was observed in the average thickness of each layer of the oxide within a single specimen. Viscous glass flow was ruled out as a potential mechanism. Glass bubble formation was proposed as the main cause for oxidation kinetics variability.

Beschreibung: Phase equilibria in the La 1− x Ca x FeO 3−δ (LCF) system were assessed at temperatures below 1350°C in both simulated air and argon atmospheres using a combination of differential scanning calorimetry, thermogravimetric analysis, scanning electron microscopy, and high-temperature X-ray diffraction. The solubility limit of Ca in the perovskite structure was determined to be 38% A-site substitution. A high-temperature orthorhombic to rhombohedral transition was identified and the dependence on oxygen partial pressure and effect on thermal expansion were characterized. A partial, pseudobinary LaFeO 3 –CaFeO 2.5 phase diagram is presented that is based on these analyses combined with data available in the open literature.

Beschreibung: TiB 2 powders were synthesized by borothermal reduction in nanoscale TiO 2 with boron under vacuum. Reaction processes were investigated, and the effect of by-product B 2 O 3 was evaluated. Results showed that TiO 2 was firstly reduced by boron to form TiBO 3 and Ti 2 O 3 , and then to produce TiB 2 and B 2 O 3 with increasing temperature. The reaction processes of TiB 2 powders synthesis included two-step reduction in TiO 2 by boron and the removal of B 2 O 3 . The presence of B 2 O 3 , which was previously reported as the most important factor in promoting the coarsening of ZrB 2 and HfB 2 powders by borothermal reduction, did not lead to significant coarsening of TiB 2 powders. Due to the minor effect of B 2 O 3 , TiB 2 powders with small particle size and low oxygen content could be prepared by direct heat treatment of TiO 2 and boron at 1550°C under vacuum for 1 h. The particle size and oxygen content of synthesized TiB 2 powders were ~0.9 μm and ~1.7 wt%, respectively.

Beschreibung: In this work, a low-firing microwave dielectric ceramic PbMoO 4 with tetragonal structure was prepared via a solid-state reaction method. The sintering temperature ranges from 570°C to 670°C. Ceramic samples with relative densities above 97% were obtained when sintering temperature was around 600°C. The best microwave dielectric properties were obtained in the ceramic sintered at 650°C for 2 h with a permittivity ~26.7, a Q  ×  f value about 42 830 GHz (at 6.2 GHz) and a temperature coefficient value of 6.2 ppm/°C. From the X-ray diffraction, backscattered electron imaging results of the cofired sample with 30 wt% silver and aluminum additive, the PbMoO 4 ceramic was found not to react with Ag and Al at 630°C. The microwave dielectric properties and low sintering temperature of PbMoO 4 ceramic make it a candidate for low-temperature cofired ceramic applications.

Beschreibung: Commercial EIA-Y5V base-metal-electrode multilayer ceramic capacitors (BME-MLCCs) made of ( CaO + ZrO 2 )-doped BaTiO 3 are analyzed for the microstructure and investigated for its relation to dielectric properties. The characteristic diffuse scattering (DS) intensities observed in BaTiO 3 ceramics and the featureless “solid-solution” grains in Y5V capacitor chips are originated from multiple Ti sites in the dynamic BaTiO 3 structure. The pseudo-cubic ( PC )-grains retaining the overall cubic ( C -) symmetry metastably at room temperature are embedded with polar nanoregions (PNRs) in the ferroelectric (FE) tetragonal ( T -), and rhombohedral ( R -) phases, as revealed by high-resolution transmission electron microscopy (HRTEM). The presence of PNRs contributes effectively to large relative permittivity ε r  ≈ 13 200 at 25°C. The FE T -domains grow from within PC -grains at the expense of embedded PNRs after prolonged annealing by extending “oxidizing firing” at 950°C in p O 2  = 10 −7  atm. These domains contain less Zr with otherwise homogeneously distributed solutes in PNR-dispersed PC -grains. Although preserving the relaxors characteristics, ε r is reduced to ~11 000 after 12 h, and then to ~9000 after 24 h annealing. The reduction in ε r is attributed to the annealing-induced FE T -domains grown at the expense of PNRs in PC -grains. The Vögel–Fulcher analysis indicates that Y5V ceramics are in the relaxor FE category, containing PNRs derived from polarization frustration.

Beschreibung: The progresses of the relative density, average grain size (GS), and maximum pore size entering into the final sintering stage are investigated in 3 mol% yttria-stabilized tetragonal zirconia polycrystals (3Y-TZP) compacts in the range of 87%~99% theoretical density. It is found that during conventional pressureless sintering, the pores in the compact enlarged dramatically, which appears to be the major obstacle for preparing fully dense nanoceramics. Transparent 3Y-TZP nanoceramics with an average GS of 87 nm were prepared by exploiting microstructural refinement on nanoscale. The yields a maximal optical transmittance of 67% and shows no noticeable low-temperature degradation after 100 h aging at 134°C under a hydrothermal pressure of two bars.

Beschreibung: Porous β- Si 3 N 4 ceramics are sintered at 1600°C in N 2 and postheat treated at 1500°C under vacuum using Li 2 O and Y 2 O 3 as the sintering additives. The partial sintering and phase transformation are promoted at low temperature by the addition of Li 2 O . The addition of Y 2 O 3 is advantageous for the formation of high aspect ratio β- Si 3 N 4 grains. After postheat treatment, a large amount of intergranular glassy phase is removed, and the Li content in the samples is decreased. By this method, the β- Si 3 N 4 porous ceramic with a porosity of 54.1% and high flexural strength of 110 ± 8.1 MPa can be prepared with a small amount of sintering additives, 0.66 wt% Li 2 O and 0.33 wt% Y 2 O 3 , and it is suitable for high-temperature applications.

Beschreibung: To solve the heavy mass problem of the traditional spinel ferrite using as the microwave absorber, the Co x Zn (1− x ) Fe 2 O 4 ( x  =   0.2, 0.4, 0.6, 0.8) ferrite nanofibres were synthesized by electrospinning method. The phase composition, morphology, and electromagnetic properties were analyzed. The results showed that all the as-prepared Co x Zn (1− x ) Fe 2 O 4 ferrites exhibited the homogeneous nanofibrous shape. The saturation magnetization and coercivity were enhanced by tuning the Co 2+ content. The electromagnetic loss analysis indicated that the Co 0.6 Zn 0.4 Fe 2 O 4 ferrite nanofiber performed the strongest microwave attenuation ability. The microwave absorbing coating containing 15 wt% of Co 0.6 Zn 0.4 Fe 2 O 4 ferrite nanofiber showed the reflection loss less than −10 dB in the whole X -band and 80% of the Ku -band frequencies. Meanwhile, the surface density was only 2.4 Kg/m 2 .

Beschreibung: The kinetics of the cristobalite transformation are reported for sintered silica glass from 1200°C to 1650°C and plotted as a time–temperature–transformation diagram. The 1200°C–1350°C transformation data were fit to the Johnson–Mehl–Avrami–Kolmogorov expression with an time exponent of 3.0 ± 0.6 and an apparent activation energy of 555 ± 24 kJ/mol for the kinetic constant. The temperature of maximum transformation rate was found to fall between 1500°C and 1600°C. Seeding amorphous silica powder with cristobalite resulted in accelerated transformation kinetics. Silica glass powder containing residual quartz had faster transformation kinetics than fully amorphous powder seeded with cristobalite.

Beschreibung: The morphology and crystal growth of devitrite crystals nucleated heterogeneously on glass surfaces have been studied. The crystals grow as fans of needles, with each needle having a characteristic [100] growth direction with respect to the centrosymmetric triclinic unit cell. An analysis of crystal growth data reported here and a reappraisal of crystal growth data reported in prior studies suggests a best estimate of 260 kJ/mol for the activation enthalpy for the crystal growth of devitrite along [100], higher than the values previously reported.

Beschreibung: Single crystal (1  − x ) Pb ( Mg 1 / 3 Nb 2 / 3 ) O 3 – x PbTiO 3 [ PMN – x PT] ( x  = 0.32) is a relaxor-ferroelectric material known to exhibit ‘giant’ piezoelectric behavior, with achievable strains in excess of 1% for samples of certain particular crystallographic orientations and chemical compositions close to the morphotropic phase boundary. In this study, we investigate the electric field-induced structural phase transitions in single crystal PMN –0.32 PT with time-of-flight neutron diffraction and macroscopic electrical polarization measurements, and show that both the frequency of the applied ac field and the temperature of the sample are critical factors in determining these phase transition fields.

Beschreibung: Glass nanocomposites, fabricated using borosilicate glass microspheres and antimony tin oxide (ATO) nanoparticles, were previously reported to have formed segregated networks at the boundaries of the glass particles. This resulted in an electrically conducting composite at low volume fractions (~0.5–0.8 vol%) of ATO nanoparticles. The wide range of electrical response in these borosilicate glass composites containing networks of varying concentration of ATO was examined using impedance spectroscopy. The electrical resistance of these composites varied over a range of around 12 orders of magnitude and exhibited several different types of insulator and conductor behavior. The formation of the ATO network was identified and tracked by scanning electron microscopy images and energy dispersive X-ray spectroscopy (EDS) scans. Detailed impedance spectroscopy analysis using all of the dielectric functions (impedance, permittivity, electric modulus, and admittance) was found to be an excellent method for detecting the development of the network and the effect that processing variables can have on its formation and the overall electrical properties of the nanocomposites.

Beschreibung: By combining the concept of defect chemistry and the small-polaron hopping conduction model, the present work takes an intensively considering of the electron conduction mechanism in the nonstoichiometric SnO 2 nanocrystalline film. The temperature-dependent and atmosphere-dependent relationship between the electrical conductivity and the defect reaction is outlined. To investigate the influence of temperature and atmosphere on the electrical properties of the SnO 2 nanocrystalline film, a temperature-programmed system integrated with the high-throughput screening platform of gas-sensing materials (HTSP-GM) is developed as the test tool in this work. With this platform, the temperature-dependent conductivity of SnO 2 nanocrystalline film in different atmosphere (dry air, nitrogen, and formaldehyde) was conducted. A good fit between the theoretical deductions and experimental results is achieved.

Beschreibung: We demonstrate a facile synthesis of monodisperse magnetite ( Fe 3 O 4 ) nanoparticles (NPs) via a simple wet chemical route at 180°C using oleylamine ( C 18 H 37 N ), which serves as a solvent, ligand, and surfactant. The particles have a narrow size distribution centered at about 10 nm. To provide better electron conductivity and structural stability, the as-synthesized particles are given a carbon nanocoating by pyrolysis of the residual surfactant on their surface. This pyrolysis forms a uniform thin nanocoating on each particle, and a core/shell Fe 3 O 4 /carbon NP network was thus obtained. The core/shell Fe 3 O 4 /carbon electrode shows better reversible capacity, cycle life, and rate capability than a bare Fe 3 O 4 NP electrode because of its efficient electron transport and stress relaxation provided by the thin carbon layer.

Beschreibung: Nickel ferrite (NiFe 2 O 4 ) is a major constituent of the corrosion deposits formed on the exterior of nuclear fuel cladding tubes during operation. NiFe 2 O 4 has attracted much recent interest, mainly due to the impact of these deposits, known as CRUD, on the operation of commercial nuclear reactors. Although advances have been made in modeling CRUD nucleation and growth under a wide range of conditions, the thermophysical properties of NiFe 2 O 4 at high temperatures have only been approximated, thereby limiting the accuracy of such models. In this study, samples of NiFe 2 O 4 were synthesized to provide the thermal diffusivity, specific heat capacity, and thermal expansion data from room temperature to 1300 K. These results were then used to determine thermal conductivity. Numerical fits are provided to facilitate ongoing modeling efforts. The Curie temperature determined through these measurements was in slight disagreement with literature values. Transmission electron microscopy investigation of multiple NiFe 2 O 4 samples revealed that minor nonstoichiometry was likely responsible for variations in the Curie temperature. However, these small changes in composition did not impact the thermal conductivity of NiFe 2 O 4 , and thus are not expected to play a large role in governing reactor performance.

Beschreibung: Boron carbide thin films have been synthesized via pulsed laser deposition process using Spark Plasma Sintered (SPSed) and dual-targets, respectively. Two kinds of structural evolutions have been found by investigation of bonding environments in as-deposited thin films via X-ray photoelectron spectroscopy study. With decreasing of B/C ratio, films deposited from SPSed-target show the transformation of B 11 C -CBB → B 11 C -CBC. In contrast, the films deposited from dual-target present the B 11 C -CBB → B 10 C 2 -CBB structural change.

Beschreibung: The SrTiO 3 (STO) thin films were directly grown on Si (111) substrates without buffer layer by an electron-cyclotron-resonance ion beam sputter deposition. The growth temperature was varied from 700°C to 850°C, while other parameters were kept unchanged. X-ray structural analysis demonstrates that the growth temperature has a strong influence in tuning degree of (100) orientation. The STO film grown at 800°C is found to be the highest degree of (100) orientation (98%) and a strong (100) fiber texture. For the surface morphology, the development of plate-shaped grains reveals a good correlation with the change in the degree of (100) orientation. Moreover, the leakage current–voltage characteristics of the Au /STO/ Si (111) metal-insulator-semiconductor capacitors are investigated and discussed in considerable detail.

Beschreibung: The effect of combined substitution of Sm 3+ and O 2− with Ca 2+ and F − , respectively, on the structural and superconducting properties of SmFeAsO system is investigated. It is observed that the binary doping using CaF 2 causes considerable structural as well as microstructural changes wherein the preferred orientation of (00  l ) planes and enhancement of grain size are quite interesting. Moreover, a maximum T C of 53.8 K and a transport J C of 880 A/cm 2 (12 K) are achieved in the codoped samples. The achievement of preferred orientation, enhanced T C , and the subsequent increase in J C of the modified SmFeAsO system are particularly significant for high current conductor development.

Beschreibung: Lead free piezoelectric ceramics of Y 3+ -doped Ba 1− x Ca x Zr 0.07 Ti 0.93 O 3 with x  = 0.05, 0.10, and 0.15 were prepared. Composition and temperature-dependent structural phase evolution and electrical properties of as-prepared ceramics were studied systematically by X-ray diffraction, Raman spectroscopy, impedance analyzer, ferroelectric test system, and unipolar strain measurement. Composition with x  = 0.10 performs a good piezoelectric constant d 33 of 363 pC/N, coercive field E c of 257 V/mm, remanent polarization P r of 14.5 μC/cm 2 , and a Curie temperature T m of 109°C. High-resolution X-ray diffraction was introduced to indicate presence of orthorhombic phase. Converse piezoelectric constant d 33 * of x  = 0.10 composition performed better temperature stability in the range from 50°C to 110°C. That means decreasing orthorhombic–tetragonal phase transition temperature could be an effective way to enlarge its operating temperature range.

Beschreibung: TiO 2 -doped Y 2 O 3 -stabilized ZrO 2 compounds with low thermal conductivity have been considered as a promising thermal barrier coating material. In the present research, a series of TiO 2 -doped Y 2 O 3 -stabilized ZrO 2 compounds have been synthesized and investigated. Lattice distortion and disordering caused by TiO 2 doping were observed and their effects on mechanical properties, such as fracture toughness, elastic modulus, and coefficient of thermal expansion (CTE), were also investigated. Lattice distortion enhanced the ferroelastic toughening and the fracture toughness, whereas the variation in elastic modulus and CTE is due to the lattice disordering. The combination of thermal and mechanical properties bodes well for the potential application as thermal barrier coating materials.

Beschreibung: The influence of second phase zirconia particles on the electrical properties and fracture behavior of various polycrystalline soft Pb ( Zr 1− x Ti x ) O 3 (PZT) compositions was investigated. PZT composites with yttria-stabilized tetragonal zirconia particles exhibited enhanced crack resistance in comparison to monolithic compositions, regardless of the PZT composition. The addition of zirconia, however, was found to change the PZT composition through the diffusion of zirconium, resulting in variations in the observed piezoelectric and ferroelectric responses. Through the tailoring of the PZT matrix composition, the large electromechanical response and enhanced fracture toughness could be retained. The variation in both small and large signal properties is contrasted to fracture results and crystal structure changes, as determined by X-ray diffraction.

Beschreibung: A novel method is employed for the formation of rare earth phosphate solid solution compounds with unique mesoscopic structures. Europium- and lanthanum-doped sodium borate glass microspheres and particles, ranging in sizes from 50 to 300 μm, were reacted in 0.25 M K 2 HPO 4 solution to form hollow spheres of nanocrystalline rare earth phosphate compounds by dissolution–precipitation reactions. The initially X-ray amorphous precipitated rare earth phosphate materials were heat-treated at 700°C for 2 h to form nanocrystalline compounds. Differential thermal analysis (DTA) experiments yield an average activation energy for crystallization of 394 ± 26 kJ/mol. X-ray diffraction (XRD) data indicate that samples crystallized to the monazite structure (monoclinic P2 1 /n) with unit cell volumes ranging from 306.5 Å 3 for LaPO 4 to 282.5 Å 3 for EuPO 4 and with crystallite grain sizes of 56 ± 14 nm. Compositions containing both rare earth elements formed solid solutions with the composition La (1− x ) Eu x PO 4 . Raman spectroscopy indicates that the P–O symmetric stretching vibrations (ν 1 ) change systematically from 963 cm −1 for LaPO 4 to 986 cm −1 for EuPO 4 , consistent with a systematic decrease in average P–O bond length. Photoluminescence measurements show maximum emission intensity for the La 0.65 Eu 0.35 PO 4 composition.

Beschreibung: A single crystal of α- Ca 2 [ HSiO 4 ](OH) (α- C 2 SH) was repeatedly imaged at room temperature with synchrotron mid-infrared microscopy after heating to 310°C, 340°C, 370°C, and 400°C respectively. The mechanisms of the observed phase transformations are discussed on the basis of a modular concept of the crystal structures. All images show domains of dellaite, Ca 6 [ Si 2 O 7 ][ SiO 4 ](OH) 2 , which are predominantly formed in the core of the crystal. In the crystal rim area α- C 2 SH persists in higher abundance. The mechanism of the phase transformation of α- C 2 SH into dellaite includes the following: (1) Partial formation of killalaite ( Ca 3 [ HSi 2 O 7 ](OH)) as nuclei according to the isochemical reaction 2 Ca 2 [ HSiO 4 ](OH) → Ca 3 [ HSi 2 O 7 ](OH) +  Ca (OH) 2 probably induced by anisotropic thermal expansion, local chemical fluctuations, structural (proton) disorder, and different bond strengths of the OH groups in the α- C 2 SH structure. (2) Further dehydration of killalaite and α- C 2 SH domains results in the formation of dellaite according to Ca 3 [ HSi 2 O 7 ](OH) + Ca(OH) 2  + Ca 2 [ HSiO 4 ](OH) – 2 H 2 O → Ca 6 [ Si 2 O 7 ][ SiO 4 ](OH) 2 . The results suggest that the polymerization of two isolated [ HSiO 4 ] tetrahedra takes place without dehydration according to reaction (1) rather than through condensation with simultaneous H 2 O release: 2[ HSiO 4 ] → [ Si 2 O 7 ] +  H 2 O . We suggest that reaction (1) cannot be completed at ambient pressure. Thus in the regions close to the rim of the crystals we expect the formation of x - C 2 S , which starts along the crystal edges according to Ca 2 [ HSiO 4 ](OH) → Ca 2 SiO 4  +  H 2 O . Based on a modular concept, a structural relationship between α- C 2 SH, killalaite, dellaite, and x - C 2 S has been established. Similarities and differences in the thermal behavior of α- C 2 SH and afwillite have been highlighted.

Beschreibung: The oxygen permeability of polycrystalline α-alumina wafers, which served as models for alumina scales on alumina-forming alloys, under steep oxygen potential gradients ( ) was evaluated at 1873 K. Oxygen permeation occurred by the grain-boundary (GB) diffusion of oxygen from the higher-oxygen-partial-pressure ( ) surface to the lower- surface, along with the simultaneous GB diffusion of aluminum in the opposite direction. The fluxes of oxygen and aluminum at the outflow side of the wafer were significantly larger than at the inflow side. Furthermore, Lu and Hf segregation at the GBs selectively reduced the mobility of oxygen and aluminum, respectively. A wafer with a bilayer structure, in which a Lu-doped layer was exposed to a lower and an Hf-doped layer was exposed to a higher , decreased the oxygen permeability. When the sign of was reversed, however, the oxygen permeability of the wafer was comparable to that of a nondoped wafer. Co-doping with both Lu and Hf markedly increased the oxygen permeation, presumably because the Lu-stabilized HfO 2 particles that were segregated at the GBs acted as extremely fast diffusion paths for oxygen through the large number of oxygen vacancies introduced by the solid solution of Lu in the particles.

Beschreibung: Scandium fluoride ( ScF 3 ) belongs to one of the rare compounds which exhibit isotropic negative thermal expansion. Here, a facile and environmentally friendly hydrothermal synthesis method has been presented. High-quality single-crystalline ScF 3 cubes, with an average size of 200 nm, can be easily fabricated in a large scale. Sc (NO 3 ) 3 and NH 4 HF 2 were used as precursors. The as-prepared ScF 3 demonstrates cubic symmetry ( Pm -3  m ), which was confirmed by X-ray diffraction and selected-area electron diffraction. Its uniform morphology and size were characterized by high-resolution transmission electron microscopy. Furthermore, thermal analysis was also performed in argon gas atmosphere to investigate its thermal stability.

Beschreibung: Results of the spectroscopic characteristics and upconversion luminescence in Er 3+ doped yttria ( Y 2 O 3 ) transparent ceramics prepared by a modified two-step sintering method are presented. The near-infrared (1.5 μm) luminescence properties were evaluated as a function of Er 3+ concentration. Judd–Ofelt intensity parameters, radiative rates, branching ratios, and emission lifetimes were determined and compared with results reported for Er 3+ -doped Y 2 O 3 single crystal and nanocrystals. Following pumping at 1.532 μm, weak blue (~0.41 μm, 2 H 9/2 → 4 I 15/2 ), strong green (~0.56 μm, 2 H 11/2 , 4 S 3/2 → 4 I 15/2 ), and red (~0.67 μm, 4 F 9/2 → 4 I 15/2 ) emission bands were observed as well as weak near-infrared emissions at 0.8 μm ( 4 I 9/2 → 4 I 15/2 ) and 0.85 μm ( 4 S 3/2 → 4 I 13/2 ) at room temperature. The upconversion luminescence properties under ~1.5 μm pumping were further investigated through pump power dependence and decay time studies. Sequential two-photon absorption leads to the 4 I 9/2 upconversion emission, whereas energy-transfer upconversion is responsible for the emission from the higher excited states 2 H 9/2 , 2 H 11/2 , 4 S 3/2 , and 4 F 9/2 . The enhanced red emission with increasing Er 3+ concentration most likely occurred via the cross-relaxation process between ( 4 F 7/2 → 4 F 9/2 ) and ( 4 I 11/2 → 4 F 9/2 ) transitions, which increased the population of the 4 F 9/2 level.

Beschreibung: Zirconia phase transformation is usually studied on surface. For in-depth study, three methods were proposed using Raman microspectroscopy quantitative evaluation: direct measurement on sample cross section, confocal Raman spectroscopy (CRS), and progressive pinhole aperture enlargement (PPAE). The aim of this study was to compare transformation profiles obtained with these three methods on the same sample. Three 3Y-TZP samples were aged, respectively, for 25, 72, and 90 h in artificial saliva. Transformation profiles were determined with cross-sectional measurement, CRS and PPAE. A transformation profile simulation model based on PPAE measurements is proposed, using the convolution of the excitation intensity profile and the Beer–Lambert law (optical properties of zirconia). The simulation model was validated with the determination of 3Y-TZP transformation factor, T  = 1.15 μm −1 , identical for the three aging durations. Both cross section and PPAE measured similar in-depth transformation decrease, but with a 10 μm-shift: transformed zirconia layer is more important in cross-sectional protocol (36 μm with PPAE and 46 μm with cross-sectional after 90 h aging). Complementary measurements on a 10 h aged sample, where transformation is initiated by Low-Temperature Degradation, showed that sample preparation and polishing, necessary in the cross-sectional method, were responsible for the higher transformation. PPAE method enables noninvasive in-depth measurements with limited optical and mechanical biases.

Beschreibung: New cementitious materials based on calcium hydrosilicate hydrates were recently developed as potential substitutes for ordinary portland cement, but with a reduced CO 2 footprint. The materials are produced by hydrothermal processing of SiO 2 and Ca ( OH ) 2 , giving rise to calcium silicate hydrates, followed by mechanical activation of the latter via cogrinding with various siliceous materials. Thus, the chemical composition in terms of C/S ratio could be adjusted over a broad range (1–3). In this study the synthesis of a previously unknown cementitious material produced via the combination of mechanical activation in a laboratory mill and thermal treatment of a mixture of quartz and hydrothermally synthesized calcium silicate hydrates: α- Ca 2 [ HSiO 4 ]( OH ) (α- C 2 SH ) and Ca 6 [ Si 2 O 7 ]( OH ) 6 (jaffeite) are reported. It forms independently of the type of mill used (eccentric vibrating mill, vibration grinding mill) after thermal treatment of the ground materials at 360°C–420°C. The new material is X-ray amorphous and possesses a CaO / SiO 2 ratio of 2. A characteristic feature in regards to the silicate anionic structure is the increased silicate polymerization (up to 27% Si 2 O 7 dimers) as revealed by the trimethylsilylation method. Infrared (IR) spectra show a very broad absorption band centered at about 935 cm −1 . Another characteristic feature is the presence of ~2.5 wt% H 2 O as shown by thermogravimetry (TG) coupled with IR spectroscopy. As this water is bound mostly as hydroxyl to Ca, we refer to this new cementitious material as calcium-oxide–hydroxide–silicate ( C – CH – S ). Calorimetric measurements point to a very high hydraulic reactivity which is beyond that for typical C 2 S materials. The influence of the type of grinding on the thermal behavior of α- C 2 SH upon its transformation into water-free Ca 2 SiO 4 modifications is discussed.

Beschreibung: A series of Ce 3+ , Tb 3+ , Eu 3+ tri-doped Ba 2 Y (BO 3 ) 2 Cl red-emitting phosphor have been synthesized by solid-state method. The Ce 3+ → Tb 3+ → Eu 3+ energy-transfer scheme has been proposed to realize the sensitization of Eu 3+ ion emission by Ce 3+ ions. Following this energy-transfer model, near-UV convertible Eu 3+ -activated red phosphors have been obtained in Ba 2 Y (BO 3 ) 2 Cl : Ce 3+ , Tb 3+ , Eu 3+ phosphors. Energy transfers from Ce 3+ to Tb 3+ , and Tb 3+ to Eu 3+ , as well as corresponding energy-transfer efficiencies are investigated. The combination of narrow-line red emission and near-UV broadband excitation makes Ba 2 Y (BO 3 ) 2 Cl : Ce 3+ , Tb 3+ , Eu 3+ as a novel and efficient red phosphor for NUV LED applications.

Beschreibung: Computational simulations of glass extrusion are performed to quantify the effects of material behavior and slip at the die/glass interface on the die swell. Experimental data for three glass types are used to guide the computational study, which considers glass material to be viscous with and without shear thinning and viscoelastic using the Maxwell upper-convected model. The study starts with assuming no-slip at the glass/die interface to see if material behavior alone can explain the die swell results, and then considers slip using the Navier model where interface shear is directly proportional to the relative slip speed at the interface. Consistent with the possibility of slip and intended high viscosity applications, viscosity ranging from 10 7.4 –10 8.8  Pa·s was used. Based on optimization of the various input parameters required to achieve the measured die swell and ram force values, the study concludes that interface slip occurred as only extreme values of the shear thinning parameters provided an alternative.

Beschreibung: A bilayer concept was proposed to adjust the electrical properties of NTC thermistors. The conventional NTC material Ni 0.75 Mn 2.25 O 4 was chosen as the sensitive layer, and high conductive LaMnO 3 – Ni 0.75 Mn 2.25 O 4 composite was chosen as the support layer. The bilayer NTC thermistors were successfully fabricated by classical uniaxial pressing method. After cosintering at 1235°C for 4 h, the two layers adhered well to each other without any cracking or delamination. The resistance decreased linearly with the decrease in the thickness of Ni 0.75 Mn 2.25 O 4 layer, and the B values varied between 3868 and 3901 K. After annealing at 150°C in air for 500 h, the resistance shifts at 25°C were less than 1%, which mean that the bilayer NTC thermistors had high stability.

Beschreibung: Easy sinterable Ti 3 SiC 2 powder was synthesized from a powder mixture with a molar ratio of 1.0 Ti , 0.3 Al , 1.2 Si , and 2.0 TiC by heating at 1200°C in the flowing Ar. Here, the Al powder acts as a deoxidation agent and provides a liquid phase for the reaction. The powder compacts subjected to pressureless sintering at 1300°C in Ar had a relative density up to 99%. The results of chemical analysis and the measured lattice constant suggest that the Al–Si liquid phase was formed at approximately 1200°C and that liquid-phase sintering was promoted by the 0.1 molar ratio of Al and the 0.2 molar ratio of Si remaining in excess. The three-point bending strength, fracture toughness, and electrical resistivity of the sintered samples were 380 MPa, 4.1 MPa m 1/2 , and 0.34μΩm, respectively.

Beschreibung: Dense nanocrystalline barium strontium titanate Ba 0.6 Sr 0.4 TiO 3 (BST) ceramics with an average grain size around 40 nm and very small dispersion were obtained by spark plasma sintering at 950°C and 1050°C starting from nonagglomerated nanopowders (~20 nm). The powders were synthesized by a modified “Organosol” process. X-ray diffraction (XRD) and dielectric measurements in the temperature range 173–313 K were used to investigate the evolution of crystal structure and the ferroelectric to paraelectric phase transformation behavior for the sintered BST ceramics with different grain sizes. The Curie temperature T C decreases, whereas the phase transition becomes diffuse for the particle size decreasing from about 190 to 40 nm with matching XRD and permittivity data. Even the ceramics with an average grain size as small as 40 nm show the transition into the ferroelectric state. The dielectric permittivity ε shows relatively good thermal stability over a wide temperature range. The dielectric losses are smaller than 2%–4% in the frequency range of 100 Hz–1 MHz and temperature interval 160–320 K. A decrease in the dielectric permittivity in nanocrystalline ceramics was observed compared to submicrometer-sized ceramics.

Beschreibung: Very few studies have been directed at the compositional dependence of the intrinsic photostability of the Ge x Se 1− x binary ChG films especially for the Ge-rich films with the mean coordination number (MCN) larger than 2.67. Here, by measuring the in-situ transmission changes, it shows that the photosensitivity (e.g., photobleaching, PB) of the Ge-rich films (as compared to the GeSe 2 film) is attenuated, in fact almost completely eliminated in the film with the largest MCN. A straightforward technique, in-situ Raman spectroscopy, is used to record the time-resolved intrinsic structural changes during the irradiation of the films. The result indicates a transition from PB towards photostability occurs at the critical composition of GeSe 2 corresponding to the structural phase transition. The stressed rigid structures of the Ge-rich films inhibit any significant photo-structural changes.

Beschreibung: Although chemically inert nanosize mineral fillers have been shown to modify early cement hydration kinetics, with the effects dependent upon usage rate, particle size, and dispersibility, the effects of such fillers on the “apparent activation energy” ( E a ) of cement has not been previously examined. Here, cement E a was calculated from isothermal calorimetry performed at different temperatures with two different types of fillers (i.e., titanium dioxide and limestone) using a linear method as well as a modified ASTM C1074 method. The use of both types of nanoparticles increased the rate of cement hydration as well as accelerated the reaction rate, due to heterogeneous nucleation effect, as previously demonstrated. E a increased in the presence of nanosized fillers, demonstrating an increased temperature sensitivity of the filler-cement composites relative to ordinary cement. These results show that chemically inert nanoparticles behave fundamentally differently compared with supplementary cementitious materials such as fly ash and silica fume which instead decrease temperature sensitivity. The increased temperature sensitivity could thus be used to modify and optimize the reaction mechanism and kinetics of cement hydration, especially to increase the rate of cement hydration, to decrease setting time, and to achieve faster strength gain accounting for higher or lower temperatures during curing.

Beschreibung: The growing demand of reliable high-performance membrane materials for separation processes requires new simple, straightforward, environmental friendly, sustainable approaches for membrane fabrication. In this study, we present an environmentally friendly gel-casting, one-pot process based on ionotropic-gelation for obtaining alumina membranes. A slurry of alumina particles and the biopolymer alginate, which acts in combination with calcium iodate like a resin, was gelled in a controllable temperature dependent manner. Alumina membranes are obtained by three different shaping routes (extrusion, free-forming, casting). The suitability of extruded capillaries in a polymer-ceramic hybrid state (green body) and after sintering (1150°C for 2 h) for potential application in micro- and ultrafiltration is evaluated by monitoring the chemical and mechanical stability, permeability and separation behavior. Varying the initial alumina particle size from 200 to 900 nm, membranes with a narrow pore size distribution, predictable and tunable average pore diameters from 70 up to 480 nm and a constant open porosity of ~40%, are obtained. The permeability behavior is tested with fluorescence labeled submicron- and nano-particles. Our novel colloidal processing route represents a very versatile tool for designing and manufacturing ceramic membranes with complex shapes for micro- (〉0.1 μm) and ultrafiltration (0.1–0.01 μm).

Beschreibung: Amorphous thin films of Ti 1− y Si y (N,O) with y  ≥ 0.38 were prepared by reactive sputter deposition in a nitrogen atmosphere. Thermal annealing of the films in an ammonia flow above 800°C yielded Si (N,O) amorphous thin films dispersed with precipitated TiN nanosized particles. The film color changed with Si content y and the annealing conditions, from carrot orange to cream yellow in the as-deposited films due to their oxynitride nature, and from dark green to canary yellow and from iron blue to horizon blue at respective annealing temperatures of 800°C and 900°C due to metallic nature of the TiN nanosized particles precipitated in the annealing.

Beschreibung: A series of phosphors Ca 12(0.97− x ) Al 14 O 32 F 2 : 0.03 Ce 3+ , x Tb 3+ have been prepared by a hightemperature solid-state reaction using boric acid as flux. These oxyfluorides crystallize in cubic structure, space group. Under the near ultraviolet excitation within wavelength range 310–390 nm, Ca 12(0.97− x ) Al 14 O 32 F 2 : 0.03 Ce 3+ , x Tb 3+ phosphors exhibit an intense emission covering a broad band of 370–500 nm derived from the 5 d →4 f transitions of Ce 3+ and a characteristic emission at 544 nm of Tb 3+ . The emission can be tuned from blue to green by altering the relative ratio of Ce 3+ to Tb 3+ in the composition. The energy-transfer mechanism from Ce 3+ to Tb 3+ is investigated based on the site occupancy of the luminescence center in the crystal structure of the Ca 12 Al 14 O 32 F 2 host. More importantly, when a certain amount of boric acid is added as flux in the synthesis, the fluorescence intensity of the phosphors increases about 65%. Because of its broad excitation and efficiently tunable blue to green luminescence, the Ca 12(0.97− x ) Al 14 O 32 F 2 : 0.03 Ce 3+ , x Tb 3+ phosphors may find promising application as a near UV-convertible phosphor for white-light-emitting diodes.

Beschreibung: Ti , TiC , Al and AlN powders were mixed to synthesize Ti 2 Al ( C x N y ) ( x  +  y  〈 1) solid solutions, Ti 2 AlC x ( x  〈 1) and Ti 2 AlN -related end-members by hot isostatic pressing at 1400°C/80 MPa for 4 h. For the pure carbides, it is demonstrated that single-phased samples can only be obtained when about 15% of substoichiometry on the carbon site is applied. Such a result likely implies that Ti 2 AlC x can only exist in a narrow range of carbon composition. Ti 2 AlN nitride can be synthesized with y  = 1. Assuming that vacancy content varies linearly from 0 to 0.15 going from Ti 2 AlN to Ti 2 AlC 0.85 in the solid solutions, element concentrations have been calculated to synthesize different solid solutions. Thus, it is demonstrated that single-phased and fully dense Ti 2 Al ( C 0.23 N 0.71 ), Ti 2 Al ( C 0.45 N 0.45 ), and Ti 2 Al ( C 0.66 N 0.22 ) carbonitrides can be synthesized.

Beschreibung: The dielectric and electromechanical properties of 0.75 Bi 1/2 Na 1/2 TiO 3 –0.25 SrTiO 3 (25 ST ) as a function of temperature and frequency were studied. It is shown that the 25 ST is a relaxor ferroelectric as evidenced by the temperature-dependent dielectric relaxations with an incipient piezoelectricity featured by the presence of a reversible electric-field-induced phase transformation at room temperature. The transition occurs on a broad electric field strength range depending on field amplitude and frequency. It is also accompanied by a huge strain that is attributed to repetitive poling and depoling originating due to the reversibility of the phase transition. The 25 ST makes an attractive lead-free candidate for stack actuators as it presents a high normalized d 33 * of ~600 pm/V at a low electric field of 4 kV/mm for frequencies ranging from 0.1 up to 100 Hz.

Beschreibung: Mullite ceramics were fabricated with fly ash, clay, and Al 2 O 3 as raw materials. The effects of Al 2 O 3 content, the sintering temperature and the pickling process on the crystalline phases, sintering characteristics and microstructures were studied. With more addition amount of Al 2 O 3 and higher sintering temperature, the peak intensity of the mullite crystalline phase increased. By pickling process, mullite instead of anorthite became the main phase with little corundum. Moreover, the required sintering temperature had reduced to 1300°C and the Al 2 O 3 content also decreased to 30 wt%. The pickling process also enlarged the sintering range of the green bodies.

Beschreibung: Laminated (SiC w +SiC p )/SiC ceramic composites were fabricated by tape casting and chemical vapor infiltration (CVI), and the effect of SiC particles on strengthening/toughening of the composites was investigated. When the SiC particle content was constant, the mechanical properties of (SiC w +SiC p )/SiC composites were increased with increasing SiC whisker content. When the SiC particle content was varied, the mechanical properties of (SiC w +SiC p )/SiC composites were dependent on SiC particle content. The addition of SiC particles can increase the strength of the matrix and the crack propagation resistance, the former increased the strength and the latter increased the toughness.

Beschreibung: Sodium-doped ZnO (ZnO:Na) nanowires were grown with a high-pressure pulsed-laser deposition process on silicon substrates using sputtered gold particles as catalysts. The introduction of sodium dopants into ZnO nanowires was confirmed by both X-ray diffraction spectrum and X-ray photoelectron spectroscopy. The morphology and microstructural changes in ZnO nanowires due to sodium doping were investigated with scanning electron microscope, high-resolution transmission electron microscope, and Raman spectrum. Detailed photoluminescence studies of ZnO:Na nanowires revealed characteristic sodium acceptor-related peaks, for example, neutral acceptor-bound exciton emission (A 0 X, 3.356 eV), free-to-neutral-acceptor emission (e, A 0 , 3.314 eV), and donor-to-acceptor pair emission (DAP, 3.241 eV). This indicated that sodium doping induces stable acceptor level with a binding energy of 133 meV in ZnO:Na nanowires.

Beschreibung: Multiferroic Bi 1− x La x FeO 3 [ BLFO ( x )] ceramics with x  = 0.10–0.50 and Mn-doped BLFO ( x  = 0.30) ceramics with different doping contents (0.1–1.0 mol%) were prepared by solid-state reaction method. They were crystallized in a perovskite phase with rhombohedral symmetry. In the BLFO ( x ) system, a composition ( x )-driven structural transformation ( R 3 c → C 222) was observed at x  = 0.30. The formation of Bi 2 Fe 4 O 9 impure phase was effectively suppressed with increasing the x value, and the rhombohedral distortion in the BLFO ceramics was decreased, leading to some Raman active modes disappeared. A significant red frequency shift (~13 cm −1 ) of the Raman mode of 232 cm −1 in the BLFO ceramics was observed, which strongly perceived a significant destabilization in the octahedral oxygen chains, and in turn affected the local FeO 6 octahedral environment. In the Mn-doped BLFO ( x  = 0.30) ceramics, the intensity of the Raman mode near 628 cm −1 was increased with increasing the Mn-doping content, which was resulted from an enhanced local Jahn–Teller distortions of the ( Mn,Fe ) O 6 octahedra. Electron microscopy images revealed some changes in the ceramic grain sizes and their morphologies in the Mn-doped samples at different contents. Wedge-shaped 71° ferroelectric domains with domain walls lying on the {110} planes were observed in the BLFO ( x  = 0.30) ceramics, whereas in the 1.0 mol% Mn-doped BLFO ( x  = 0.30) samples, 71° ferroelectric domains exhibited a parallel band-shaped morphology with average domain width of 95 nm. Dielectric studies revealed that high dielectric loss of the BLFO ( x  = 0.30) ceramics was drastically reduced from 0.8 to 0.01 (measured @ 10 4  Hz) via 1.0 mol% Mn-doping. The underlying mechanisms can be understood by a charge disproportion between the Mn 4+ and Fe 2+ in the Mn-doped samples, where a reaction of Mn 4+  + Fe 2+ →Mn 3+  + Fe 3+ is taken place, resulting in the reduction in the oxygen vacancies and a suppression of the electron hopping from Fe 3+ to Fe 2+ ions effectively.

Beschreibung: There is a growing requirement for high-temperature piezoelectric materials in the petrochemical, automotive, and aerospace industries. Here, the piezoelectric materials of Fe and Mn comodified 0.36 BiScO 3 –0.64 PbTiO 3 (BS-PTFMn) ceramics with high Curie temperature ( T c ), large mechanical quality factor ( Q m ), and reduced strain hysteresis were presented. XRD results revealed that all the BS- PTFMn ceramics have a pure perovskite structure with tetragonal symmetry, and the ratio of c/a is insensitive to the contents of Fe . With the modifications of Fe, the dielectric loss tanδ and strain hysteresis decrease clearly, while the mechanical quality factor improves significantly. The Curie temperature, piezoelectric constant, planar electromechanical coupling factor, dielectric loss, and mechanical quality factor of the BS- PTFMn with 3% Fe content are 492°C, 235 pC/N, 0.38, 0.6%, and 280, respectively. BS-PTFMn ceramics show 50°C higher T c than BS-PT morphotropic phase boundary composition. The figure of merit (product of Q m , and k ij ) of BS-PTFMn ceramics is about five times than that of pure BS-PT ceramics. Furthermore, for the BS- PTFMn ceramics with Fe content of 3 mol%, the high field strain coefficient value calculated from the electric-field-induced strain curves ( S max / E max ) is 320 pm/V, while the strain hysteresis (under 40 kV/cm) is reduced to one fifth that of unmodified BS-PT ceramics. Moreover, the temperature-dependent electromechanical coupling coefficient and dielectric constant are very stable in the temperature range from room temperature (RT) to 450°C. These results indicated that BS- PTFMn ceramics are promising for high-temperature piezoelectric applications.