Microstructural Features And Deformation-induced Lattice Defects In Hot-extruded Bi_2te_3 Thermoelectric Compound

摘要

Bismuth telluride (Bi_2Te_3) bulk material was prepared by a powder hot-extrusion technique. The microstructure, texture evolution, and deformation-induced lattice defects, as well as the effect of heat treatment on its microstructure and thermoelectric properties were investigated. As-extruded Bi_2Te_3 compound was found to be characterized by a dynamically and statically recrystallized microstructure with fine-equiaxed grains and low dislocation density. The majority of boundaries in the extruded specimens were large-angle boundaries with average misorientation angles of more than 30°. There was no significant change in dislocation configuration, even after heat treatment at a temperature higher than the extrusion temperature. Moreover, the Seebeck coefficient and electrical resistivity of the extruded specimens could not be improved by annealing. Microstructural examinations indicated the existence of a deformation-induced stacking disorder with local atomic shift, which we term "phase disorder," on the basal plane in the extruded Bi_2Te_3 compound. The presence of this structural defect may be one of the main reasons for the slightly lower values of thermoelectric properties for the hot-extruded Bi_2Te_3 compound, compared with a unidirectionally solidified specimen.