Anisotropic n-Type Bi2Te3–In2Te3 Thermoelectric Material Produced by Seeding Zone Melting and Solid State Transformation

Seeding zone melting is applied to produce bulk Bi1.625In0.375Te3 with 7.5 atom % In in solid solution. The concentration distribution is markedly homogeneous and exhibits pronounced anisotropic electrical and thermal conductivity. Subsequent precipitation from the solid solution leads to the formation of a highly anisotropic composite thermoelectric material consisting of aligned microscaled Bi2Te3 and extended micro- to nanoscaled In2Te3 plates. By the precipitation, an increase of zT by a factor of 6 compared with the parent supersaturated solid solution crystal is achieved. This is attributed to the combination of a decrease of In concentration from 7.5 to 3 atom % in the Bi2Te3 layer and an increasing interface density due to the precipitation of In2Te3. The Bi2Te3/In2Te3 interface is determined as coherent, and the crystallographic orientation between the two phases is determined as ⟨211⟩In2Te3//⟨1100⟩Bi2Te3, {111}In2Te3//{0001}Bi2Te3.