Charge Transport and Thermoelectric Properties of Ge-Doped Famatinites Cu₃Sb_1−yGe_yS₄

Abstract

Ge-doped famatinites Cu₃Sb_1−yGe_yS₄ (0 ≤ y ≤ 0.1) were prepared by mechanical alloying and hot pressing. The phase transition, microstructure, charge transport properties and thermoelectric properties were examined in accordance with the Ge content. The famatinites were maintained as a single phase with a tetragonal structure at temperatures below their melting point without secondary phases. The melting points of Cu₃SbS₄ and Cu₃Sb_0.92Ge_0.08S₄ were 817 and 819 K, respectively. The hot-pressed specimens exhibited high relative densities of 98.3–99.5%. The a-axis and c-axis were decreased from 0.5386 to 0.5378 nm and from 1.0744 to 1.0719 nm, respectively, by doping Sb sites with Ge. Both intrinsic and Ge-doped famatinites exhibited positive Hall and Seebeck coefficients. The carrier concentration and mobility of Cu₃SbS₄ were 2.2 × 10¹⁸ cm⁻³ and 1.6 cm² V⁻¹ s⁻¹, but those of Ge-doped specimens increased to (0.4–3.3) × 10¹⁹ cm⁻³ and 29–71 cm²V⁻¹ s⁻¹, respectively. Cu₃SbS₄ exhibited non-degenerate semiconductor characteristics and demonstrated a dimensionless figure of merit, ZT, of 0.1 at 623 K owing to a power factor of 0.14 m Wm⁻¹ K⁻² and a thermal conductivity of 0.62 Wm⁻¹ K⁻¹. However, the Ge-doped specimens exhibited degenerate semiconductor behaviors, and Cu₃Sb_0.92Ge_0.08S₄ exhibited the highest ZT of 0.55 at 623 K owing to a power factor of 0.64 m W m⁻¹ K⁻² and a thermal conductivity of 0.72 Wm⁻¹ K⁻¹.

Graphic abstract