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Bi 2 Sr 2 Co 2 O y is a thermoelectric material with low thermal conductivity. The Bi 2 Sr 2 Co 2 O y /Si 80 Ge 20 composite samples were prepared by solid phase sintering at high temperature to investigate the effects of Si 80 Ge 20 alloys as the second phase on the microstructure and thermoelectric properties of the fabricated composites. An appropriate amount of the dispersed Si 80 Ge 20 in the Bi 2 Sr 2 Co 2 O y matrix can reduce the resistivity of the composite successfully. In particular, the increase in phonon scattering caused by the second phase leads to a significant decrease in thermal conductivity, which improves the thermoelectric properties of the material significantly. At 923 K, the thermal conductivity of the Bi 2 Sr 2 Co 2 O y + 0.2 wt% Si 80 Ge 20 sample achieves an ultralow value of 0.58 W/K·m. Its corresponding optimal dimensionless thermoelectric figure of merit value is 0.36, which is 56% higher than that of the pure Bi 2 Sr 2 Co 2 O y sample. [ABSTRACT FROM AUTHOR]

Misfit-layered oxides Ca 3 Co 4 O 9+δ + z wt% SiC (z = 0.00, 0.025, 0.05, 0.1, 0.2) samples were synthesized using solid-state sintering method and the effects of SiC nanoparticles diapersion on the thermoelectric properties were investigated. Thermoelectric properties of Ca 3 Co 4 O 9+δ + z wt% SiC (z = 0.00, 0.025, 0.05, 0.1, 0.2) were investigated up to 923 K. Compared with pure sample, the electrical resistivity of SiC-added samples reduces, for Ca 3 Co 4 O 9+δ + z wt% SiC (z = 0.00, 0.025, 0.05, 0.1, 0.2) ceramic samples with x ≤ 0.05, the electrical resistivity decreases with increasing SiC nanoparticles adding amounts. And, the electrical resistivity exists transition from semiconductor to metal conduction mechanism. While, the thermal conductivity also decreases due to the addition of SiC nanoparticles. As a result, the Ca 3 Co 4 O 9+δ + 0.2 wt% SiC sample had the lowest thermal conductivity of 1.47 W/Km at 923 K, which was 18.4% lower than that of the Ca 3 Co 4 O 9+δ sample. The ZT value of Ca 3 Co 4 O 9+δ + 0.05 wt% SiC can reach 0.218, which is 40.9% higher than the pure Ca 3 Co 4 O 9+δ sample. [ABSTRACT FROM AUTHOR]

Abstract: Nanopowders of elements doped Bi2Te3 thermoelectric alloy R0.2Bi1.8Te3 (R=Ce, Y and Sm) were synthesized by the hydrothermal method. The nanopowders were hot-pressed into pellets and their thermoelectric properties were investigated. The results show that Ce, Y, and Sm doping has significant effects on the morphologies of the synthesized nanopowders and thermoelectric properties. Among the doping elements, Ce doping is a superiority dopant. Although the electrical conductivity and Seebeck coefficient are not improved much by Ce doping, the thermal conductivity is supressed greatly. As a result the figure of merit (ZT) of Ce0.2Bi1.8Te3 is improved and reaches 1.29 at 398K, which is higher than the Bi2Te3 ingots made by the traditional zone-melting method [Copyright &y& Elsevier]

Abstract: RBaCo2O5+δ (R=Sm, Eu, Dy, Gd, and Y) thick films were prepared by the solid state reaction followed by the spin-coating method. The oxygen resistivity sensor properties of these films were investigated in switching O2/N2 atmosphere. The results show that the RBaCo2O5+δ films are promising as oxygen resistance sensors at elevated temperature. Especially, DyBaCo2O5+δ film shows a fast response speed, high sensitivity and good repeatability at 600°C. The correlation between the sensor properties of RBaCo2O5+δ thick films and their oxygen intake/release properties is also discussed. [Copyright &y& Elsevier]

Abstract: Oxygen permeability of dense perovskite-type Y1−x La x Ba2Cu3O7−δ (x =0.1, 0.3, 0.5, 0.8 and 1.0) and Y1−y Ca y Ba2Cu3O7−δ (y =0.1, 0.2, 0.3 and 0.4) membranes were investigated under an air/He gradient in a temperature range from 750 to 950°C. The results indicate that doping of La or Ca has great effects on the oxygen permeability. Oxygen permeation flux of Y1−x M x Ba2Cu3O7−δ (M=La, Ca) membrane increases with M substitution for Y in YBa2Cu3O7−δ , and has an obvious increase at about 900°C due to an order–disorder transition of the oxygen vacancies in the membrane material. Maximum oxygen fluxes of 0.92 and 0.77μmol/scm2 are obtained for LaBa2Cu3O7−δ (x =1.0) and Y0.8Ca0.2Ba2Cu3O7−δ (y =0.2) membranes with thickness 1.0mm at 950°C, respectively. [Copyright &y& Elsevier]

The Bi 2 Sr 2 Co 2 O y ceramic, known for its stability as a p-type thermoelectric material, has limited thermoelectric performance that necessitates enhancement. In this study, Bi 2- x Cu x Sr 2 Co 2 O y (x = 0, 0.025, 0.05, 0.1, 0.2) ceramic samples were synthesized using the conventional solid-state reaction method. Substitution of Cu2+ for Bi3+ in the samples increased carrier concentration, significantly reducing electrical resistivity. Utilizing the single parabolic band (SPB) model, it was determined that Cu incorporation led to an increased effective mass, thereby enhancing the Seebeck coefficient. Additionally, fine grains and lattice defects induced by Cu2+ substitution effectively scattered phonons, resulting in an ultra-low thermal conductivity of 0.59 Wm−1K−1 at 923 K for the Bi 1.8 Cu 0.2 Sr 2 Co 2 O y sample. Consequently, Cu substitution optimized both the electrical and thermal transport properties of Bi 2-x Cu x Sr 2 Co 2 O y samples. The dimensionless thermoelectric figure of merit (ZT) for Bi 1.95 Cu 0.05 Sr 2 Co 2 O y reached 0.31 at 923 K, representing a 63 % increase over the pristine Bi 2 Sr 2 Co 2 O y sample. [ABSTRACT FROM AUTHOR]

Ca 3 Co 4 O 9+δ is a typical p -type thermoelectric oxide material with a low thermal conductivity. In this study, double-layered oxide samples Ca(Ba,Sr) 3 Co 4 O 9+δ dispersed with different SiC contents were obtained via the traditional solid phase reaction method. The effects of different elemental substitutions and SiC dispersion contents on the microstructure and thermoelectric properties of the samples were studied. The double optimisation of partial substitution of Ca-site atoms and SiC dispersion considerably improved the thermoelectric properties of Ca 3 Co 4 O 9+δ. Through the elemental substitution, the resistivity of the Ca 3 Co 4 O 9+δ material was reduced. Conversely, introducing an appropriate amount of SiC nanoparticles enhanced phonon scattering and was crucial in reducing its thermal conductivity. After double optimisations, the dimensionless thermoelectric figure of merit (ZT) values of both Ca 2.93 Sr 0.07 Co 4 O 9+δ + 0.1 wt% SiC and Ca 2.9 Ba 0.1 Co 4 O 9+δ + 0.1 wt% SiC achieved an optimum value of 0.25 at 923 K. [ABSTRACT FROM AUTHOR]

Abstract: When the Y0.5Tb0.5BaCo4O7+δ ceramic powder is heated to 200–380°C in oxygen atmosphere, it can adsorb oxygen remarkably. The adsorbed oxygen could be released by raising temperature over 420°C or by switching the atmosphere from oxygen to nitrogen. In a temperature cycle between 360°C and 440°C, the relative mass change of the Y0.5Tb0.5BaCo4O7+δ sample can reach 4.4% of its original mass, and shows high efficiency and stable oxygen adsorption/desorption reproducibility. However, the oxygen adsorption/desorption efficiency in the cycles switched between oxygen and nitrogen atmosphere is poor. The large adsorption capacity, the fast adsorption/desorption speeds, and the easy regeneration of Y0.5Tb0.5BaCo4O7+δ absorbent under temperature cycles make it to be a highly potential candidate in air separation and oxygen removal. [Copyright &y& Elsevier]

Currently, bismuth telluride-based zone-melted ingots dominate the commercial thermoelectric (TE) market. However, bismuth telluride-based zone-melted ingots with a layered lattice structure are brittle, posing challenges for their application in miniature devices. Their polycrystalline alloys have robust mechanical strength. However, the electrical conductivity of a p -type polycrystalline BiSbTe alloy bulk deteriorates. In the current study, the Bi 0.46 Sb 1.54 Te 3 powder was from crushed zone-melted ingots. Large-sized polycrystalline (CuO) x Bi 0.46 Sb 1.54 Te 3 (x = 0, 0.003, 0.01, 0.03 and 0.1) bulks were prepared via the hot-pressing method under 65 MPa at 510°C for 15 min. The electrical conductivity was improved remarkably by the acceptor doping effect. The bipolar effect of the Seebeck coefficient and thermal conductivity at high temperatures was suppressed significantly due to increased majority carrier centration and enlarged bandgaps. Consequently, their TE performance (the dimensionless TE figure of merit, ZT) was significantly improved and the ZT max and ZT ave reached 1.4 and 1.27, respectively. [ABSTRACT FROM AUTHOR]

Bi 2 Te 3 -based crystal ingots produced by zone melting (ZM) are the most widely used materials to manufacture commercial thermoelectric (TE) devices. However, the poor mechanical properties of such crystalline materials limit the production of small-scale devices. While processability can be improved by powder metallurgy (PM), it also leads to the deterioration of the TE properties due to the donor-like effect of the introduced defects and grain boundaries. Thus, additional efforts towards re-optimizing doping are required. Here, we report a PM method to improve the mechanical properties of Bi 2 Te 3 -based TE materials through the crushing and hot pressing of Bi 2 Te 3 ingots obtained by ZM. Besides, we demonstrate the TE properties of n-type Bi 2 Te 2.7 Se 0.3 (BTS) to be remarkably improved by Cu doping, which enables optimization of the carrier concentration and enhances phonon scattering at heterointerphases thus increasing the Seebeck coefficient and reducing thermal conductivity. Overall, optimized materials reach dimensionless TE figures of merit (ZT) up to 1.16 at 408 K, i.e. 45% higher than that of state-of-the-art BTS, and an average ZT value of 1.08 in the temperature range of 300–473 K. [ABSTRACT FROM AUTHOR]

Abstract: Cu-coated Al2O3 composite powders were synthesized by using the electroless plating method. The influence of the components proportion and the pH value of the plating solution on the Cu layer were analyzed with XRD and SEM. The results showed that the proportion of the plating solution components plays an important role for synthesizing the Al2O3/Cu composite powders. The content of copper in the composite powders could be effectively controlled by adjusting the content of copper sulfate and formaldehyde in the plating solution. Furthermore, the pretreatment of the Al2O3 powders is also a key factor to form a uniform Cu layer coating Al2O3 particles. The optimum technical parameters for producing Al2O3/Cu composite powders with uniform Cu coat were obtained. [Copyright &y& Elsevier]

The oxygen in-diffusion, out-diffusion, and permeability of layered perovskite-type-like YBa2Cu3O7−x (YBCO) were investigated by thermogravimetry, oxygen static adsorption, and oxygen permeability experiment. The results show that the oxygen in-diffusion at higher oxygen partial pressure is very faster, while the oxygen out-diffusion at lower oxygen partial pressure is relatively slow due to the formation of surface barrier. Oxygen permeation rate increases with temperature and arrives at 3.36×10−7 mol/s cm2 at 900 °C for a YBCO membrane with thickness 1.00 mm. [Copyright &y& Elsevier]

Bi 2 Sr 2 Co 2 O y with excellent thermoelectric properties has received extensive attention from scientific researchers. In this study, Bi 2 Sr 2 Co 2 O y ceramic samples were prepared using the solid-phase sintering method. By Ag + substitution for Bi3+, the hole concentration and electrical conductivity were optimised. On this basis, nano-SiC particles were introduced to increase grain boundaries, improve phonon scattering, reduce the mean free path of phonons, and reduce the lattice thermal conductivity. A sample with a nominal composition of Bi 1.8 Ag 0.2 Sr 2 Co 2 O y + 0.025 wt% SiC had a maximum ZT value of 0.35 at 923 K, which was approximately 67 % higher than the ZT value of pure Bi 2 Sr 2 Co 2 O y. These results confirmed that under the combined action of Ag substitution and SiC doping, the thermoelectric performance of Bi 2 Sr 2 Co 2 O y was significantly improved. [ABSTRACT FROM AUTHOR]

As a new type of clean and environmentally friendly energy material that can mutually transform thermal energy and electric energy, thermoelectric materials have received extensive attention from researchers. In this study, the traditional high-temperature solid-phase reaction method was used to prepare Bi 1.9 Ba 0.1 Sr 2 Co 2 O y + g wt% SiC (g = 0, 0.025, 0.05, 0.1 and 0.15) polycrystalline samples. Ba element was used to substitute the Bi site of Bi 1.9 Ba 0.1 Sr 2 Co 2 O y , in an attempt to change the carrier concentration and raise its electrical transport performance. Then, based on Ba substituting, nano-SiC was introduced as the second phase to increase the grain boundary number, which would enhance phonon scattering and reduce its heat transport performance. Finally, the ZT value of Bi 1.9 Ba 0.1 Sr 2 Co 2 O y + 0.025 wt% SiC reaches 0.35 at 923 K, which is approximately 35 % higher than that of the pure sample Bi 2 Sr 2 Co 2 O y. [ABSTRACT FROM AUTHOR]

In this work, Bi 2 Ba 2 Co 2 O y + v wt% SiC (v = 0.00, 0.025, 0.05, 0.1, 0.2) and Bi 1.975 Na 0.025 Ba 2 Co 2 O y + w wt% SiC (w = 0.00, 0.025, 0.05, 0.1, 0.2) ceramic samples were synthesised. The increase in the carrier concentration caused by a small amount of Na element doping leads to a decrease in the resistivity and Seebeck coefficients. The lattice distortion caused by Na element doping decrease the sample thermal conductivity. After adding SiC nanoparticles, the resistivity can be reduced further. Especially more phonons are scattered by more grain boundaries, which leads to reduced thermal conductivity. The Seebeck coefficients increase slightly due to the low energy carrier scattering effect. Considering the influence of these two factors, dispersing SiC particles on the basis of Na element doping can effectively improve the thermoelectric performance of Bi 2 Ba 2 Co 2 O y -based samples. The ZT value of the Bi 1.975 Na 0.025 Ba 2 Co 2 O y + 0.1 wt% SiC sample reaches a maximum value of 0.21 at 923 K, 26.6% higher than the Bi 1.975 Na 0.025 Ba 2 Co 2 O y sample and 93% higher than the pure Bi 2 Ba 2 Co 2 O y sample. [ABSTRACT FROM AUTHOR]

Bi 2 Sr 2 Co 2 O y (BSCO) is a layered cobalt-based oxide whose thermoelectric properties have been extensively studied recently because its layer structure of CoO 2 gives good electrical conductivity. SiC, with larger Seebeck coefficients and higher electrical conductivity, is also widely concerned in the field of thermoelectricity. In this paper, the effects of alkali metal element doping and SiC dispersion on thermoelectric properties of BSCO are studied for two series samples of Bi 1·85 Na 0·15 Sr 2 Co 2 O y + m wt% SiC (m = 0, 0.025, 0.05, 0.1, and 0.15) and Bi 1·9 K 0·1 Sr 2 Co 2 O y + z wt% SiC (z = 0, 0.025, 0.05, 0.1, and 0.15). After Na+ and K+ replacing Bi3+ sites, the electrical resistivity of BSCO is reduced by the increased hole concentration. On the basis of the optimized Na+ and K+ doping, nano-SiC particles are dispersed on the BSCO matrix, which increases the phonon scattering at the interface and greatly reduces the thermal conductivity. Meanwhile, the Seebeck coefficients of Bi 2 Sr 2 Co 2 O y materials are basically unchanged under the combined action of cation doping and SiC dispersion. The maximum ZT values of 0.26 and 0.24 at 923 K are obtained for m = 0.025 and z = 0.05 Bi 2 Sr 2 Co 2 O y -based samples, respectively. [ABSTRACT FROM AUTHOR]

Abstract: La-doped NiO nanofibers were synthesized by the electrospinning method. The X-ray diffraction (XRD) pattern showed that La doping does not change the crystal structure up to the doping ratio of La/Ni=1.5%. Electrochemical properties of La-doped NiO nanofibers were investigated using cyclic voltammetry and galvanostatic charge/discharge. The results showed that the La doping can enhance the charge/discharge specific capacitance and electrochemical stability of the NiO nanofibers. Especially, the sample with doping ratio of La/Ni=1.5% could reach a discharge specific capacitance of 94.85Fg−1 at a constant current density of 5mAcm−2. [Copyright &y& Elsevier]

Abstract: The solid–gas phase oxygen ions exchange of the superconducting material YBa2Cu3O7−δ (YBCO) powder at high temperature subject to an instantaneous change of surrounding gas between pure oxygen and nitrogen was studied by a transient thermogravimetric analysis (TGA) method. The dependence of equilibrium oxygen vacancy of YBCO sample on surrounding partial oxygen pressure at temperature region 500–800 °C was measured by a homemade static oxygen absorption instrument. A rapid weight gain in the oxygen absorption period and a slow weight loss in the oxygen desorption period were observed in the transient experiment. The surface reaction rate constants both for the oxygen absorption and desorption periods were calculated by considering the surface reaction as the rate-limiting step. The result shows that rate constant for the oxygen desorption period is much smaller than that of the oxygen absorption period. [Copyright &y& Elsevier]