Preparation and characterization of nonstoichiometric Te-deficient and Te-rich thermoelectric Bi2-Gd Te3± compounds

The Gd-doped Bi2Te3 compounds were prepared by solvothermal synthesis and spark plasma sintering. It was found that for the Bi2-xGdxTe3±y with x = 0.01; 0.05; 0.1; 0.15 0.2, Gd doping results in relevant changing Te content, y, i.e. y are inter-dependent. Governing Te-deficient Bi2-xGdxTe3-y compositions 0; 0.05 0.018; 0.011; 0.003, Te-rich Bi2-xGdxTe3+y 0.15; 0.2 0.013; 0.023; 0.04, successfully prepared. Te-vacancies anti-site BiTe defects specific compositions, whereas interstitial atoms TeBi characteristic compositions. Deviation from Te-stoichiometry is originated high-temperature evaporation under Te-enriched starting Bi2-xGdxTe3 powders applied to tune desired manner. A rate of decreases increasing related difference electronegativites Bi atoms, which, turn, strength polar covalent Gd-Te bond as compared Bi-Te bond. Crystal lattice parameters, concentration mobility electrons, thermoelectric properties, grain ordering degree different nonstoichiometric Highest figure-of-merit Bi1.99Gd0.01Te2.989 composition (ZT?0.7 at ~400 K).