Preparation and thermoelectric properties of quaternary bismuth telluride–indium selenide compound

Quaternary In–Se–Bi–Te compounds (7.5Bi2Te3–In2Se3 and 7.5Bi2Te3–In4Se3) were prepared by water quenching and annealing, and the microstructures and thermoelectric properties were investigated. These materials were solidified to near-eutectic compositions in order to obtain micro-scale heterointerfaces. The formation of sub-micrometer-scale lamellae layers of Bi2Te3 and In–Se–Te compounds was observed. Through quenching, the 7.5Bi2Te3–In2Se3 consisted of a Bi2Te3 and In–Se–Te compound, while the 7.5Bi2Te3–In4Se3 was composed of Bi2Te3, BiTe, and In4Se3 and In–Se–Te. Both the microstructure and the constituent phases changed after annealing. The reduction of thermal conductivities, as compared to that of bulk Bi2Te3, was confirmed. This result can be attributed to the increased number of phase boundary areas. The size of the decomposed phase could be controlled by changing the parameters of the annealing process, which could further decrease the thermal conductivity.