ALBERT

Description: We demonstrate enhanced hydrogen generation rates at high pH using colloidal cadmium sulphide nanorods decorated with Pt nanoparticles. We introduce a simplified procedure for the decoration and subsequent hydrogen generation, reducing both the number of working steps and the materials costs. Different Pt precursor concentrations were tested to reveal the optimal conditions for the efficient hydrogen evolution. A sharp increase in hydrogen evolution rates was measured at pH 13 and above, a condition at which the surface charge transfer was efficiently mediated by the formation of hydroxyl radicals and further consumption by the sacrificial triethanolamine hole scavenger.

Description: 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.

Description: 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.

Description: 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.

Description: 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.

Description: Recently, water-gated organic field-effect transistors (WGOFET) have been intensively studied for their application in the biological field. Surprisingly, a very limited number of conjugated polymers have been reported so far. Here, we systematically explore a series of polythiophene derivatives, presenting different alkyl side chains lengths and orientation, and characterized by various morphologies: comparative evaluation of their performances allows highlighting the critical role played by alkyl side chains, which significantly affects the polymer/water interface capacitance. Reported results provide useful guidelines towards further development of WGOFETs and represent a step forward in the understanding of the polymer/water interface phenomena.

Description: Soft magnetic alloys at the nanoscale level have long generated a vivid interest as candidate materials for technological and biomedical purposes. Consequently, controlling the structure of bimetallic nanoparticles in order to optimize their magnetic properties, such as high magnetization and low coercivity, can significantly boost their potential for related applications. However, traditional synthesis methods stumble upon the long standing challenge of developing true nanoalloys with effective control over morphology and stability against oxidation. Herein, we report on a single-step approach to the gas phase synthesis of soft magnetic bimetallic iron aluminide nanoparticles, using a versatile co-sputter inert gas condensation technique. This method allowed for precise morphological control of the particles; they consisted of an alloy iron aluminide crystalline core (DO 3 phase) and an alumina shell, which reduced inter-particle interactions and also prevented further oxidation and segregation of the bimetallic core. Remarkably, the as-deposited alloy nanoparticles show interesting soft magnetic properties, in that they combine a high saturation magnetization (170 emu/g) and low coercivity (less than 20 Oe) at room temperature. Additional functionality is tenable by modifying the surface of the particles with a polymer, to ensure their good colloidal dispersion in aqueous environments.

Description: Lattice resolved and quantitative compositional characterizations of the microstructure in TiCrAlN wear resistant coatings emerging at elevated temperatures are performed to address the spinodal decomposition into nanometer-sized coherent cubic TiCr- and Al-rich domains. The domains coarsen during annealing and at 1100 °C, the Al-rich domains include a metastable cubic Al(Cr)N phase containing 9 at. % Cr and a stable hexagonal AlN phase containing less than 1 at. % Cr. The cubic and the hexagonal phases form strained semi-coherent interfaces with each other.

Description: 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).

Description: 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.

Description: 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.

Description: Nanocrystals of Mg-MOF-74 have been immobilized into the mesopores of SBA-15 rods to fabricate Mg-MOF-74@SBA-15 hybrid materials. To furnish such composites, a relatively simple synthetic strategy has been adopted by direct dispersion of the metal-organic framework (MOF) precursors in SBA-15 matrix to prepare the hybrid materials in situ . The hybrid materials have been characterized using powder X-ray diffraction and several spectroscopic and microscopic techniques, which suggest growth of the MOF nanocrystals inside the SBA-15 mesopores and the composites exhibit characteristics of both the components. N 2 adsorption isotherms at 77 K reveal that the composites contain additional mesopores, compared to only micropores of pristine MOF nanocrystals. In addition to such combination of both micro and mesoporosity, the composites also demonstrate significant CO 2 adsorption at room temperature.

Description: Transition metal ion-chelating ordered mesoporous carbon (TM-OMC) materials were recently shown to be efficient polymer electrolyte membrane fuel cell (PEMFC) catalysts. The structure and properties of these catalysts are largely different from conventional catalyst materials, thus rendering membrane electrode assembly (MEA) preparation parameters developed for conventional catalysts not useful for applications of TM-OMC catalysts. This necessitates development of a methodology to incorporate TM-OMC catalysts in the MEA. Here, an efficient method for MEA preparation using TM-OMC catalyst materials for PEMFC is developed including effects of catalyst/ionomer loading and catalyst/ionomer-mixing and application procedures. An optimized protocol for MEA preparation using TM-OMC catalysts is described.

Description: 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.

Description: 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.

Description: 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.

Description: 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.

Description: 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.

Description: The development of devices able to detect and record ion fluxes is a crucial point in order to understand the mechanisms that regulate communication and life of organisms. Here, we take advantage of the combined electronic and ionic conduction properties of a conducting polymer to develop a hybrid organic/living device with a three-terminal configuration, using the Physarum polycephalum Cell (PPC) slime mould as a living bio-electrolyte. An over-oxidation process induces a conductivity switch in the polymer, due to the ionic flux taking place at the PPC/polymer interface. This behaviour endows a current-depending memory effect to the device.

Description: 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.

Description: 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.

Description: 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.

Description: 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.

Description: 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.

Description: 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.

Description: 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).

Description: 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.

Description: 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.

Description: 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.

Description: 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 ).

Description: 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.

Description: 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.

Description: 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.

Description: 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.

Description: 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.

Description: High-efficient ZnO-based nanorod array light-emitting diodes (LEDs) were grown by an oblique-angle deposition scheme. Due to the shadowing effect, the inclined ZnO vapor-flow was selectively deposited on the tip surfaces of pre-fabricated p-GaN nanorod arrays, resulting in the formation of nanosized heterojunctions. The LED architecture composed of the slanted n-ZnO film on p-GaN nanorod arrays exhibits a well-behaving current rectification of junction diode with low turn-on voltage of 4.7 V, and stably emits bluish-white luminescence with dominant peak of 390 nm under the operation of forward injection currents. In general, as the device fabrication does not involve passivation of using a polymer or sophisticated material growth techniques, the revealed scheme might be readily applied on other kinds of nanoscale optoelectronic devices.

Description: 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.

Description: 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.

Description: 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.

Description: Rare earth metal borides have attracted great interest due to their unusual properties, such as superconductivity and f -electron magnetism. A recent discovery attributes the tunability of magnetism in rare earth aluminoborides to the effect of so-called “building defects.” In this paper, we report data for the effect of building defects on the thermal conductivities of α -TmAlB 4 single crystals. Building defects reduce the thermal conductivity of α -TmAlB 4 by ≈30%. At room temperature, the thermal conductivity of AlB 2 is nearly a factor of 5 higher than that of α -TmAlB 4 . AlB 2 single crystals are thermally anisotropic with the c -axis thermal conductivity nearly twice the thermal conductivity of the a-b plane. Temperature dependence of the thermal conductivity near and above room temperature reveals that both electrons and phonons contribute substantially to thermal transport in AlB 2 with electrons being the dominant heat carriers.

Description: 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%.

Description: 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.

Description: 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 .

Description: 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.

Description: In this study, the mechanical performance and deformation behavior of various nano-twinned Ag foils were evaluated under two deformation modes. It was generally observed that the addition of nanotwins led to an enhanced strength, but the overall plastic flow and ductility decreased. Using a bimodal distribution of nanotwinned and non-nanotwinned grains was shown to be a possible route for overcoming this limitation. Specifically, some strengthening was observed which can be attributed to the nanotwinned grains, while the ductility was attributed to the contribution from non-nanotwinned grains. The overall deformation behavior is presented and discussed in terms of the nanotwin volume fraction.

Description: 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%).

Description: 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.

Description: 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.

Description: 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%.

Description: 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.

Description: 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.

Description: 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.

Description: 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.

Description: 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.

Description: 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.

Description: 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.

Description: 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.

Description: 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.

Description: 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.

Description: 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.

Description: 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.

Description: 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.

Description: 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.

Description: 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.

Description: 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.

Description: 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.

Description: 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.

Description: 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.

Description: 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.

Description: 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.

Description: 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.

Description: 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 .

Description: 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.

Description: In this short review, we have selected three main subjects: (i) mesoporous materials, (ii) sensing applications, and (iii) the concept of nanoarchitectonics, as examples of recent hot topics in nanomaterials research. Mesoporous materials satisfy the conditions necessary not only for a wide range of applications but also for ease of production, by a variety of simple processes, which yield bulk quantities of materials without loss of their well-defined nanometric structural features. Sensing applications are of general importance because many events arise from interaction with external stimuli. In addition to these important features, nanoarchitectonics is a concept aimed at production of novel functionality of whole units according to concerted interactions within nanostructures. For the combined subject of mesoporous sensor nanoarchitectonics, we present recent examples of research in the corresponding fields categorized according to mechanism of detection including optical, electrical, and piezoelectric sensing.

Description: We report the growth of crystalline Al 2 O 3 thin films deposited by thermal Atomic Layer Deposition (ALD) at 200 °C, which up to now has always resulted in the amorphous phase. The 5 nm thick films were deposited on Ga 2 O 3 , ZnO, and Si nanowire substrates 100 nm or less in diameter. The crystalline nature of the Al 2 O 3 thin film coating was confirmed using Transmission Electron Microscopy (TEM), including high-resolution TEM lattice imaging, selected area diffraction, and energy filtered TEM. Al 2 O 3 coatings on nanowires with diameters of 10 nm or less formed a fully crystalline phase, while those with diameters in the 20–25 nm range resulted in a partially crystalline coating, and those with diameters in excess of 50 nm were fully amorphous. We suggest that the amorphous Al 2 O 3 phase becomes metastable with respect to a crystalline alumina polymorph, due to the nanometer size scale of the film/substrate combination. Since ALD Al 2 O 3 films are widely used as protective barriers, dielectric layers, as well as potential coatings in energy materials, these findings may have important implications.

Description: Epitaxial CeO 2 films with different thickness were grown on Y 2 O 3 stabilised Zirconia substrates. Reduction of cerium ions at the interface between CeO 2 films and yttria stabilised zirconia substrates is demonstrated using aberration-corrected scanning transmission electron microscopy combined with electron energy-loss spectroscopy. It is revealed that most of the Ce ions were reduced from Ce 4+ to Ce 3+ at the interface region with a decay of several nanometers. Several possibilities of charge compensations are discussed. Irrespective of the details, such local non-stoichiometries are crucial not only for understanding charge transport in such hetero-structures but also for understanding ceria catalytic properties.

Description: Low-temperature MnBi (hexagonal NiAs phase) exhibits anomalies in the lattice constants ( a ,  c ) and bulk elastic modulus (B) below 100 K, spin reorientation and magnetic susceptibility maximum near 90 K, and, importantly for high-temperature magnetic applications, an increasing coercivity (unique to MnBi) above 180  K. We calculate the total energy and magneto-anisotropy energy (MAE) versus ( a ,  c ) using DFT+U methods. We reproduce and explain all the above anomalies. We predict that coercivity and MAE increase due to increasing a , suggesting means to improve MnBi permanent magnets.

Description: We developed an on-chip microfabricated architecture for high-accuracy gate voltage modulated Seebeck coefficient measurements on an organic field-effect transistor (FET). The microfabricated device comprises integrated heaters and temperature sensors that enable simultaneous Seebeck and FET measurements on devices with practical channel lengths on the order of 50 μ m. We exemplify the capabilities of this architecture by investigating the transition from conduction in the semiconductor bulk to conduction in the accumulation layer of a conjugated polymer FET.

Description: The pyrochlore compounds Ho 2 Ti 2 O 7 and Dy 2 Ti 2 O 7 show an exotic form of magnetism called the spin ice state, resulting from the interplay between geometrical frustration and ferromagnetic coupling. A fascinating feature of this state is the appearance of magnetic monopoles as emergent excitations above the degenerate ground state. Over the past years, strong effort has been devoted to the investigation of these monopoles and other properties of the spin ice state in bulk crystals. Here, we report the fabrication of Ho 2 Ti 2 O 7 thin films using pulsed laser deposition on yttria-stabilized ZrO 2 substrates. We investigated the structural properties of these films by X-ray diffraction, scanning transmission electron microscopy, and atomic force microscopy, and the magnetic properties by vibrating sample magnetometry at 2 K. The films not only show a high crystalline quality, but also exhibit the hallmarks of a spin ice: a pronounced magnetic anisotropy and an intermediate plateau in the magnetization along the [111] crystal direction.

Description: An unexpected, strong deterioration of crystal quality is observed in epitaxial perovskite BiFeO 3 films in which microscale features have been patterned by focused-ion-beam (FIB) milling. Specifically, synchrotron x-ray microdiffraction shows that the damaged region extends to tens of μ m, but does not result in measureable changes to morphology or stoichiometry. Therefore, this change would go undetected with standard laboratory equipment, but can significantly influence local material properties and must be taken into account when using a FIB to manufacture nanostructures. The damage is significantly reduced when a thin metallic layer is present on top of the film during the milling process, clearly indicating that the reduced crystallinity is caused by ion beam induced charging.

Description: A dramatically enhanced self-assembly of GeSi quantum dots (QDs) is disclosed on slightly miscut Si (001) substrates, leading to extremely dense QDs and even a growth mode transition. The inherent mechanism is addressed in combination of the thermodynamics and the growth kinetics both affected by steps on the vicinal surface. Moreover, temperature-dependent photoluminescence spectra from dense GeSi QDs on the miscut substrate demonstrate a rather strong peak persistent up to 300 K, which is attributed to the well confinement of excitons in the dense GeSi QDs due to the absence of the wetting layer on the miscut substrate.

Description: Using in situ scanning transmission electron microscopy heating experiments, we observed the formation of a 3-dimensional (3D) epitaxial Cu-core and Ag-shell equilibrium structure of a Cu-Ag nanoalloy. The structure was formed during the thermal interaction of Cu(∼12 nm) and Ag NPs(∼6 nm) at elevated temperatures (150–300 °C) by the Ag NPs initially wetting the Cu NP along its {111} surfaces at one or multiple locations forming epitaxial Ag/Cu (111) interfaces, followed by Ag atoms diffusing along the Cu surface. This phenomenon was confirmed through Monte Carlo simulations to be a nanoscale effect related to the large surface-to-volume ratio of the NPs.

Description: We have investigated the Mn-site substitution effect in Nd 0.45 Sr 0.55 MnO 3 single crystal, which has an A -type layered antiferromagnetic ( A -AFM) phase with the 3 d x 2 − y 2 -type orbital-order. Substitution of Fe or Ga for Mn-site suppresses both the A -AFM order and competing ferromagnetic (FM) correlation, whereas Cr substitution suppresses only the A -AFM order but reactivates the underlying FM correlation via double-exchange mechanism along the AFM coupled c -direction. In Nd 0.45 Sr 0.55 Mn 0.95 Cr 0.05 O 3 , the A -AFM state with the orbital-order is changed into the orbital-disordered three-dimensional FM metallic state by applying magnetic field of μ 0 H = 12 T, which is much smaller than that of the parent compound Nd 0.45 Sr 0.55 MnO 3 .

Description: Cuprous oxide (Cu 2 O) is actively studied as a prototypical material for energy conversion and electronic applications. Here we reduce the growth temperature of phase pure Cu 2 O thin films to 300 °C by intentionally controlling solely the kinetic parameter (total chamber pressure, P tot ) at fixed thermodynamic condition (0.25 mTorr pO 2 ). A strong non-monotonic effect of P tot on Cu-O phase formation is found using high-throughput combinatorial-pulsed laser deposition. This discovery creates new opportunities for the growth of Cu 2 O devices with low thermal budget and illustrates the importance of kinetic effects for the synthesis of metastable materials with useful properties.

Description: Alloyed silicon-germanium (SiGe) nanostructures are the topic of renewed research due to applications in modern optoelectronics and high-temperature thermoelectric materials. However, common techniques for producing nanostructured SiGe focus on bulk processing; therefore little is known of the physical properties of SiGe nanocrystals (NCs) synthesized from molecular precursors. In this letter, we synthesize and deposit thin films of doped SiGe NCs using a single, flow-through nonthermal plasma reactor and inertial impaction. Using x-ray and vibrational analysis, we show that the SiGe NC structure appears truly alloyed for Si 1−x Ge x for 0.16 〈 x 〈 0.24, and quantify the atomic dopant incorporation within the SiGe NC films.

Description: In this study, we developed a new neutron-detection device using a boron gallium nitride (BGaN) semiconductor in which the B atom acts as a neutron converter. BGaN and gallium nitride (GaN) samples were grown by metal organic vapor phase epitaxy, and their radiation detection properties were evaluated. GaN exhibited good sensitivity to α-rays but poor sensitivity to γ-rays. Moreover, we confirmed that electrons were generated in the depletion layer under neutron irradiation. This resulted in a neutron-detection signal after α-rays were generated by the capture of neutrons by the B atoms. These results prove that BGaN is useful as a neutron-detecting semiconductor material.

Description: Many complex oxides display an array of structural instabilities often tied to altered electronic behavior. For oxide heterostructures, several different interfacial effects can dramatically change the nature of these instabilities. Here, we investigate LaAlO 3 /SrTiO 3 (001) heterostructures using synchrotron x-ray scattering. We find that when cooling from high temperature, LaAlO 3 transforms from the to the Imma phase due to strain. Furthermore, the first 4 unit cells of the film adjacent to the substrate exhibit a gradient in rotation angle that can couple with polar displacements in films thinner than that necessary for 2D electron gas formation. P m 3 ¯ m

Description: We report on real time-resolved Reflectance-difference (RD) spectroscopy of GaAs(001) grown by molecular beam epitaxy, with a time-resolution of 500 ms per spectrum within the 2.3–4.0 eV photon energy range. Through the analysis of transient RD spectra we demonstrated that RD line shapes are comprised of two components with different physical origins and determined their evolution during growth. Such components were ascribed to the subsurface strain induced by surface reconstruction and to surface stoichiometry. Results reported in this paper render RD spectroscopy as a powerful tool for the study of fundamental processes during the epitaxial growth of zincblende semiconductors.

Description: The internal architecture of polymeric self-assembled chiral micro-particles is studied by exploring the effect of the chirality, of the particle sizes, and of the interface/surface properties in the ordering of the helicoidal planes. The experimental investigations, performed by means of different microscopy techniques, show that the polymeric beads, resulting from light induced polymerization of cholesteric liquid crystal droplets, preserve both the spherical shape and the internal self-organized structures. The method used to create the micro-particles with controlled internal chiral architectures presents great flexibility providing several advantages connected to the acquired optical and photonics capabilities and allowing to envisage novel strategies for the development of chiral colloidal systems and materials.

Description: Iron sulfide thin films were fabricated by the electrochemical deposition method from an aqueous solution containing FeSO 4 and Na 2 S 2 O 3 . The composition ratio obtained was Fe:S:O = 36:56:8. In the photoelectrochemical measurement, a weak negative photo-current was observed for the iron sulfide films, which indicates that its conduction type is p-type. No peaks were observed in X-ray diffraction pattern, and thus the deposited films were considered to be amorphous. For a heterojunction with ZnO, rectification properties were confirmed in the current-voltage characteristics. Moreover, the current was clearly enhanced under AM1.5 illumination.

Description: We have performed high field magnetotransport measurements to investigate the interface electron gas in a high mobility SrTiO 3 /SrCuO 2 /LaAlO 3 /SrTiO 3 heterostructure. Shubnikov-de Haas oscillations reveal several 2D conduction subbands with carrier effective masses of 0.9 m e and 2 m e , quantum mobilities of order 2000 cm 2 /V s, and band edges only a few millielectronvolts below the Fermi energy. Measurements in tilted magnetic fields confirm the 2D character of the electron gas, and show evidence of inter-subband scattering.

Description: To enlighten microscopic origin of visible-light absorption in transparent amorphous semiconducting oxides, the intrinsic optical property of amorphous InGaZnO 4 is investigated by considering dipole transitions within the quasiparticle band structure. In comparison with the crystalline InGaZnO 4 with the optical gap of 3.6 eV, the amorphous InGaZnO 4 has two distinct features developed in the band structure that contribute to significant visible-light absorption. First, the conduction bands are down-shifted by 0.55 eV mainly due to the undercoordinated In atoms, reducing the optical gap between extended states to 2.8 eV. Second, tail states formed by localized oxygen p orbitals are distributed over ∼0.5 eV near the valence edge, which give rise to substantial subgap absorption. The fundamental understanding on the optical property of amorphous semiconducting oxides based on underlying electronic structure will pave the way for resolving instability issues in recent display devices incorporating the semiconducting oxides.

Description: Nickel oxide (NiO) nanocrystals epitaxially grown on (001) strontium titanate (SrTiO 3 ) single crystal substrates were characterized to investigate interface morphology and chemistry. Aberration corrected high angle annular dark field scanning transmission electron microscopy reveals the interface between the NiO nanocrystals and the underlying SrTiO 3 substrate to be rough, irregular, and have a lower average atomic number than the substrate or the nanocrystal. Energy dispersive x-ray spectroscopy and electron energy loss spectroscopy confirm both chemical disorder and a shift of the energy of the Ti L 2,3 peaks. Analysis of the O K edge profiles in conjunction with this shift, implies the presence of oxygen vacancies at the interface. This sheds light into the origin of the previously postulated minority carriers’ model to explain resistive switching in NiO [J. Sullaphen, K. Bogle, X. Cheng, J. M. Gregg, and N. Valanoor, Appl. Phys. Lett.100, 203115 (2012)].

Description: 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.

Description: Using density functional theory-based calculations, we explore the effects of oxygen vacancies and epitaxial layering on the atomic, magnetic, and electronic structure of (SrTiO 3 ) n (SrFeO 3− x ) 1 superlattices. While structures without oxygen vacancies ( x = 0) possess small or non-existent band gaps and ferromagnetic ordering in their iron layers, those with large vacancy concentrations ( x = 0.5) have much larger gaps and antiferromagnetic ordering. Though the computed gaps depend numerically on the delicate energetic balance of vacancy ordering and on the value of Hubbard U eff used in the calculations, we demonstrate that changes in layering can tune the band gaps of these superlattices below that of SrTiO 3 (3.2 eV) by raising their valence band maxima. This suggests the possibility that these superlattices could absorb in the solar spectrum, and could serve as water-splitting photocatalysts.

Description: 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.

Description: 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.

Description: 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.

Description: 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.