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Magnesium antimonide (Mg3Sb2) is a promising thermoelectric compound utilized for thermoelectric power generation. We have found out that the Mg3Sb2 compound can be made from Mg and Sb powder mixture via the combustion synthesizing reaction. In this study, we manufactured the compounds from the compacted bodies with a different Mg fraction between 60.0 and 75.0 at% in an argon gas flow at 650°C for 1 hour via the combustion synthesis process. Morphology, porosity, phases and thermoelectric properties (electrical resistivity and Seebeck coefficient at room temperature to 500°C) were investigated for the manufactured samples. All samples manufactured with different Mg fractions were mainly consisted of Mg3Sb2 and became foamed bodies with a porosity between 50 and 70%. The thermoelectric properties changed with the Mg fraction. The maximum power factor of 42.1 μW/mK² at 488°C was obtained in the foamed body with the Mg fraction of 64 at%. The dimensionless figure of merit (ZT) of the sample was also estimated using the thermal conductivity, which was calculated considering its large porosity. The maximum dimensionless figure of merit (ZTmax) would be 0.13 at 488°C. [ABSTRACT FROM AUTHOR]

From the viewpoints of grain refinement and preferred orientation, a mechanical alloying (MA) and hot-extrusion technique has been proposed to fabricate Bi2Te3-based bulk materials. In this paper, the MA and hot-extrusion process, microstructure and texture, thermoelectric and mechanical properties of extruded samples, and the effect of Cu-doping in n-type samples have been reviewed. The extruded samples exhibited fine-grained microstructure, and their basal planes were predominantly oriented parallel to the extrusion direction. The p-type Bi0.4Sb1.6Te3 samples showed significant enhancements in both thermoelectric and mechanical properties. For example, the sample extruded at 400°C had a maximum value of ZT = 1.2 at room temperature and a much higher hardness than unidirectionally solidified samples. However, the n-type Bi2Te2.85Se0.15 samples showed lower thermoelectric properties due to their higher carrier concentrations and smaller fractions of twin boundaries. Cu-doping in n-type samples resulted in a reduction in carrier concentration, and thus increases in related Seebeck coefficient and electrical resistivity and decrease in carrier thermal conductivity. The resulting ZT value of 0.86 for Cu0.05Bi2Te2.85Se0.15 sample was obtained. [ABSTRACT FROM AUTHOR]

Although numerous papers are published each year, most of the experimental data reported in those papers are only available as two-dimensional plot images. Data-driven materials science using the machine learning technologies will be accelerated by gathering those published experimental data into a database. By taking thermoelectric materials as a test case, we attempted to optimize the processes of collection of papers, extraction of numeric data from plot images, and sample-based data storage into a database. By searching with a keyword “thermoelectric”, we obtained a list of 47,936 papers. Among these papers, we selected 18,471 papers as possible papers with thermoelectric properties, and succeeded to download 14,835 full-text PDF files. We developed a web system named “Starry data”, to assist the sequential data extraction from the images contained in those PDF files. This system also assists materials scientists to annotate experimental samples efficiently, to develop a descriptive database that can be used for machine-learning of the complex, sample-dependent materials properties. [ABSTRACT FROM AUTHOR]

Development of thermoelectric materials based on iron-sulfide minerals is reviewed with focusing on n-type doped CuFeS2. It is found that the thermoelectric properties of Zn-doped CuFeS2 strongly depend on the synthesis method, especially on the cooling rate and heat treatment conditions after spark-plasma sintering (SPS). A high power factor exceeding 1 mW/K2m is achieved around room temperature for samples annealed and slowly cooled after SPS. With aiming at reducing thermal conductivity, several methods are applied including the high-pressure torsion technique and nano-structuring by ball milling. These experiments successfully yield reduced thermal conductivity, though experimental conditions needs to be optimized to reduce electrical resistivity simultaneously. [ABSTRACT FROM AUTHOR]

Ca3(Co1−xAlx)4O9+δ, Ca3(Co1−yCuy)4O9+δ, Ca3(Co1−x−yAlxCuy)4O9+δ thin-films and sintered bodies were prepared using the electrostatic spray deposition method. Electrical conductivity of Ca3(Co0.95Al0.025Cu0.025)4O9 showed large values compared with Ca9Co12O28. Power factor of Ca3(Co0.95Al0.025Cu0.025)4O9 also showed approximately same values as those of single phase compounds of Ca9Co12O28. It was considered that the phenomenon was due to the increase of hole concentration and its mobility. [ABSTRACT FROM AUTHOR]