Preferential orientation and thermoelectric properties of n-type Bi2Te2.85Se0.15 alloys by mechanical alloying and equal channel angular extrusion

Starting from elemental bismuth, tellurium and selenium powders, n-type Bi2Te2.85Se0.15 solid solution with a fine microstructure was prepared by mechanical alloying and equal channel angular extrusion (ECAE) in the present work. The effect of extrusion temperature on the microstructure and thermoelectric properties of the as-ECAEed samples was investigated. A preferentially oriented microstructure with the basal planes ( 0 0 l) in the parallel direction to extrusion was formed, and the orientation factors F of the ( 0 0 l) planes of the 703K and 753K ECAEed Bi2Te2.85Se0.15 alloys were 0.26 and 0.28, respectively. The electrical resistivity and the Seebeck coefficient decreased, and the thermal conductivity increased with increasing extrusion temperature. The electrical and thermal transmission performances were strongly affected by the preferentially oriented microstructure and the preferential orientation improved the thermoelectric properties of the ECAEed Bi2Te2.85Se0.15 alloys in the parallel direction to extrusion. The maximum dimensionless figure of merit was obtained when extruded at 753K at a testing temperature of 343 K, ZT = 0.66.