Cation vacancy related crystal structure and bandgap and their effects on the thermoelectric performance of Cu-ternary systems Cu3+δIn5Te9 (δ = 0–0.175)

Abstract

In this work the crystal structure and bandgap in the Cu_3+δIn₅Te₉ material system were engineered through modifying the copper vacancy concentration (V_c). The results reveal that the crystal distortion parameter (ψ) increases as the V_c value decreases, which plays a fundamental role in enhancing the phonon scattering, thereby reducing the lattice part (κ_L) to the minimum value 0.21 W K⁻¹ m⁻¹ at ∼830 K. Although the electrical properties degrade due to the reduced Hall carrier concentration (n_H) caused by the widened bandgap (E_g) as the V_c value increases, the mobility (μ) increases. As a consequence, the thermoelectric performance remarkably improves with a highest ZT value of ∼1.0 for the sample Cu_3+δIn₅Te₉ (δ = 0.1). This value doubles that of the pristine Cu₃In₅Te₉. The work gives insight into the potential phonon scattering in the distorted crystal structure in Cu-ternary systems and sheds some light on the design of high performance thermoelectric materials.