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The effect of the firing conditions on the phase formation, microstructure, and electrical properties of (K0.5Na0.5)(Nb0.7Ta0.3)O3 (KNNT) ceramics synthesized by the solid-state combustion technique using glycine as fuel has been investigated. All samples were calcined at 600°C to 800°C for 2 h and sintered at 1150°C to 1190°C for 2 h to 5 h. Pure KNNT powders were produced after calcination at 600°C for 2 h. The average particle size increased when the calcination temperature was increased. The KNNT powder calcined at 600°C for 2 h showed rather square morphology with average particle size of ∼ 160 nm. The x-ray diffraction (XRD) analysis results for the ceramics revealed the presence of orthorhombic (O) and tetragonal (T) phases in all samples. When sintering at 1150°C for 4 h, the O:T ratio was 50:50, as verified by the Rietveld refinement technique. The average grain size, density values, and dielectric properties tended to increase when the dwell time was increased from 2 h to 4 h, but then degraded. The KNNT ceramic produced at the optimum firing condition (1150°C for 4 h) showed good crystalline morphology, the highest density (ρ = 5.28 g/cm3), the highest dielectric constant (eC = 5002), and good ferroelectric behavior (Pr = 18.50 μC/cm2 and Ec = 9.04 kV/cm).

Lead-free 0.94Bi0.50Na0.50TiO3–0.06Ba0.85Ca0.15Ti0.90Zr0.10O3–xmol%Bi2FeCrO6 ceramics, with x = 0–0.021 (BNT–BCTZ–xBFCO), were calcined at 650 °C for 2 h and sintered at 1150 °C for 2 h using the solid-state combustion technique. The effect of BFCO content (x) on the phase formation, microstructure, electrical and magnetic properties was studied. The sintered pellets exhibited a pure perovskite phase with the coexistence of rhombohedral (R3c) and tetragonal (P4bm) phases in all the studied compositions. The percentage of R3c increased as x increased from 0 to 0.013, before decreasing, as obtained from the Rietveld refinement analysis (Fullprof). A morphotropic phase boundary of BNT–BCTZ–xBFCO ceramics was observed at x = 0.013, and the ratio between the rhombohedral and tetragonal phases of this composition was 51.0:49.0. The scanning electron microscopy analysis showed polyhedral-shaped grains whose average size increased with increase in the BFCO content (x). The appropriate amount of BFCO doped into BNT–BCTZ ceramics enhanced the electrical, ferroelectric and piezoelectric properties. At optimum doping (x = 0.013), the sample exhibited the highest relative density (98.2%), a high dielectric constant (eR = 1572 and em = 5137), maximum remanent polarization (Pr = 42.41 µC/cm2), low coercive field (Ec = 33.57 kV/cm), maximum piezoelectric coefficient (d33 = 241 pC/N) and the highest normalized strain ($$ d_{33}^{*} $$ = Smax/Emax = 765 pm/V). These improvements to BNT–BCTZ make the ceramic a potential candidate for use in capacitors, sensors and actuators. The magnetic properties also changed with different BFCO content (x). The sample with x = 0 showed diamagnetic behavior, while the samples with 0.003 ≤ x ≤ 0.021 exhibited a paramagnetic behavior with higher magnetization at higher BFCO content.

Three tin pigmented aluminium oxide (Sn-Al 2 O 3 )films were prepared with different tin content using an anodization process, which is applied as a selective solar absorber in a new prototype of evacuated tube collector (ETC). The morphology and distribution of elements on the coatings were characterized using a Scanning Electron Microscope (SEM) equipped with an Energy Dispersive X-ray (EDX) analyzer. The spectrally selective properties, defined as the ratio of solar absorptance ( α sol ) to thermal emittance ( e therm ) were examined. In order to investigate the thermal performance of ETC using Sn-Al 2 O 3 on an Al fin as a solar receiver, thermal efficiency ( η ) of the ETC was collected under steady-state conditions, as prescribed by ISO 9806-1 standard. The results, of the Sn-Al 2 O 3 coatings reached a darker black colour with an increase in the colouring time. The samples were composed of different contents of Sn in the Al 2 O 3 layer. The solar selectivity ( α sol / e therm ) significantly increased with the increases in Sn content. The maximum thermal efficiency ( η max ) of the ETC under the nearly constant heat loss coefficient ( U L ), was obviously increased with the increasing Sn content. Therefore, the Sn-Al 2 O 3 with different Sn contents is a good candidate for selective solar absorbers in a new prototype of ETC.

Polycrystalline samples of undoped and doped indium tellurosilicate: InSiTe3 were synthesized and their thermoelectric (TE) properties were investigated in the temperature range from 323 to 723 K. Phosphorus (P) was selected as an electron dopant, i.e., the starting compositions were set as InSi1-xPxTe3 (x = 0, 0.02, 0.04, 0.06, and 0.1), The P doping increases the carrier concentration, which leads to decrease in both the electrical resistivity (ρ) and the Seebeck coefficient (S), while has little effect on the thermal conductivity (κ). As the results, the figure of merit ZT = S2ρ−1κ−1T increases with increasing the P content. The maximum ZT value is 0.14 at 723 K, obtained for InSi0.9P0.1Te3. The present results suggest that InSiTe3 can be a good TE material.

Rice kernel (RK)-like bismuth telluride (Bi2Te3) crystals were successfully synthesised by microwave-induced plasma heating of Bi and Te powders. Phase and morphology characterisation revealed the presence of the Bi2Te3 structure in the shape of RKs. The crystal orientation factor (f value) of RK Bi2Te3 powder was larger than that of the RK Bi2Te3 hot-pressed disk. A comparison of the f values of both samples suggested that the RK shape has significant influence in reducing the f value after hot processing. The Seebeck coefficient (S), electrical resistivity (ρ) and thermal conductivity (κ) of the RK Bi2Te3 disk were determined over the temperature ranging from 323 to 623 K. The S value was negative over the whole temperature range, indicating an n-type thermoelectric RK Bi2Te3 disk. The power factor (S 2 ρ −1) was the highest at about 1.07 × 10−3 W/m K2 at 323 K and decreased with increasing temperature. The maximum dimensionless figure of merit (ZT) of the RK Bi2Te3 disk was 0.26 at about 366 K.

Ni 3 GaSb and Ni 3 InSb were successfully synthesized by the direct reaction of Ni and GaSb or InSb. The XRD patterns and the lattice parameters of these compounds were in good agreement with the literature data. The Seebeck coefficient ( S ), the electrical resistivity ( ρ ), and the thermal conductivity ( κ ) of Ni 3 GaSb and Ni 3 InSb were examined in the temperature range from room temperature to 1073 K. Both compounds indicated metal-like characteristics. The power factor ( S 2 ρ −1 ) values increased with temperature and reached maximum at 1073 K. The κ and the dimensionless figure of merit ZT of both samples increased with temperature. The maximum values of the ZT of Ni 3 GaSb and Ni 3 InSb were obtained at 1073 K to be 0.022 and 0.023, respectively.