Interconnected effects of direct Gd doping and accompanying indirect Te-stoichiometry destroying on the thermoelectric properties of Te-rich Bi₂₋ₓGdₓTe₃₊y compounds

Abstract

Solvothermal synthesis and spark plasma sintering were applied to prepare Te-rich Bi₂₋ₓGdₓTe₃₊y compounds with 1; 2; 3 and 4 at. % Gd. To synthesize the Te-rich compositions, 3 at. % Te excess was introduced into all the starting powders with different x. Under sintering, high-temperature Te evaporation occurred. Owing to difference in electronegativity of Bi and Gd, resulting in increasing of ionicity degree and relevant strengthen of polar covalent Bi(Gd)-Te bond, a rate of the Te evaporation is remarkably decreasing with increasing x