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Piezoelectric devices such as piezoelectric speaker, motor, and actuator have been actively researched. Accordingly, for developing the ceramics capable of being sintered at low temperature for piezoelectric devices, 0.97(Na0.52K0.443Li0.037)(Nb0.923Sb0.04 Ta0.037)O3 − 0.03(Bi0.5Na0.5)0.9(Sr)0.1ZrO3 ceramics were manufactured according to x (=sintering time) and their piezoelectric and dielectric properties were systematically investigated. At the x = 9 h, the best piezoelectric properties of d33 = 244.33pC/N εr = 1475, and kp = 0.441 were appeared, respectively, for piezoelectric devices. [ABSTRACT FROM AUTHOR]

Recent developments have seen breakthroughs in zero-, one-, two-, and three-dimensional AlN micro- and nanostructures, such as nanoparticles, nanowires, nanotubes, thin films and 3D multifold symmetry crystals. The attractive electrical, optical, and thermal properties of AlN make these materials irreplaceable for microelectrochemical systems (MEMS), surface acoustic waves (SAWs) and light emitting diodes (LED). The significant interest in the field of AlN nanostructure synthesis and application encouraged us to summarise the reported data to better understand the physical and chemical aspects of AlN crystal growth processes. Four main topics are covered in this review article: (1) the morphological diversity of AlN nano- and microstructures; (2) formation mechanisms and growth dynamics; (3) theoretical simulation of growth processes based on density functional theory (DFT) and phase field (PF) modelling approaches; (4) application and devices. This article also provides a perspective on future research relevant to AlN micro- and nanostructures. [ABSTRACT FROM AUTHOR]

The fabrication of high-quality metallic powders has been attracted considerable attention in terms of producing advanced materials through additive manufacturing (AM) technology. The efficiency of AM products mainly dependent on the initial powder, therefore, characterisation of pre-alloyed powders become important. In this study, we explored the fabrication of Al0.5CoCrFeMnNi high-entropy alloy (HEA) powders by gas atomisation process and investigated their powder characteristics according to particle size distribution. X-ray diffraction results revealed the formation of major face-centred cubic and minor body-centred cubic phase by the addition of Al content. The detailed characterisations such as scanning electron microscopy, Auger electron spectroscopy and XPS analysis was carried out to examine the chemical composition of HEA powders. The relationship between secondary dendrite arm spacing and cooling rate was evaluated. The results demonstrated that produced alloy powders are spherical in shape with smooth surfaces, compositional homogeneity, indicating the gas-atomised powders are widely acceptable for additive manufacturing applications. [ABSTRACT FROM AUTHOR]

The importance of ZT in thermoelectric (TE) materials is critical for green power generation and cooling applications. Therefore, tremendous efforts were underway to improve ZT, in which we proposed a layer structured approach by successively arranging of coarse Bi 0.5 Sb 1.5 Te 3 (BST) and fine BST/0.07Cu microstructure materials and investigated their transportation mechanism. The dual bulk microstructure was well-bonded and confirmed by analyzing the microstructure through scanning electron microscope (SEM), electron backscatter diffraction analysis (EBSD) and simulated the electrical potential and temperature distribution during spark plasma sintering with COMSOL software. The results indicate that the highest power factor of 3.8 mW/m-K2 was attained in the layer structured sample, which is significantly higher than other samples due to its synergistically optimized electrical conductivity and Seebeck coefficient. Through the varied microstructure, the κ was decreased at 400 K and consequently the ZT was improved to 1.25 at 400 K for the layer structure samples. Therefore, it is suggested that layered arrangement of different microstructure material could improve the thermoelectric properties of materials. [Display omitted] • Novel fabrication of hierarchical structured material with successive arrangement of two different microstructures. • Successful consolidation of well-bonded hierarchical material and confirming by simulating results from COMSOL software. • Highest power factor of 3.8 * 10−3 W/m-K2 obtained by transportation of charge carriers through two different energy levels. • Hierarchical structured sample show highest figure of merit of 1.25 at 400 K which is highest among all reported samples. [ABSTRACT FROM AUTHOR]

The analyses of phase composition, microstructure and the mechanical properties were conducted for as-cast Ta x Al 0.7 CoCrFeNi 2.1 (x = 0.3, 0.5, 0.6 and 0.7) eutectic high entropy composites (EHECs). With the x value increases from 0.3 to 0.6, the phases of dendrite changed from L1 2 to B2 and volume fraction of ultrafine-eutectic matrix consisting of Face-centered cubic and Laves phases increased. When x = 0.7, the Laves phase appears as the primary dendrite and the matrix region changed into the bimodal eutectic structure (L1 2 + Laves and B2 + Laves). Thermo-physical parameters could be used for understanding phase formation in EHECs. Experimental and theoretical comparison using thermo-physical parameters shows a reasonable consistency. Depending on the microstructural variation, the yield strength increased from 1304 MPa (x = 0.3) to 2154 MPa (x = 0.6) and plasticity decreased from 17% (x = 0.5) to 4% (x = 0.6). In order to understand the nano-to-micronscale deformation mechanisms depending on the microstructural variations, the systematic investigations of post-deformed samples (x = 0.5 and 0.6) were carried out by multi-scale SEM, TEM, and AFM analyses. [Display omitted] [ABSTRACT FROM AUTHOR]

• Produced large-scale (3 Kg/batch) of 75%Sb 2 Te 3 -25%Bi 2 Te 3 powder by gas atomization. • The hot isostatic pressed bulk displays random distribution of grains. • Higher electrical conductivity achieved for 450 °C sample due to high mobility. • Peak ZT of 1.15 obtained for HIPed at 450 °C sample due to high conductivity values. For economic viability of thermoelectric modules, issues of scalability and sturdiness to drive down production and manufacturing cost must be adequately addressed. In this study, we report a large-scale production of 3 Kg/batch of 75%Sb 2 Te 3 -25%Bi 2 Te 3 powder by gas atomization. The as-produced large-scale atomized powder was subsequently sintered by hot isostatic pressing (HIP) at two different temperatures. The microstructure of the HIPed fracture surface reveals a transgranular mode of fracture in the basal plane of the grains perpendicular to the contact surface. The texture analysis showed that grains were randomly distributed and indicating no preferred alignment in any direction. The sample HIPed at 450 °C shows the highest electrical conductivity of 1350 Ω−1 cm−1 at room temperature due to their high carrier mobility. The highest ZT of 1.15 at 375 K was observed for the sample HIPed at 450 °C owing to their high electrical conductivity, and reasonable low thermal conductivity. [ABSTRACT FROM AUTHOR]