Enhanced thermoelectric properties of p-type Ag2Te by Cu substitution

Abstract

Enhanced thermoelectric properties of p-type Ag₂Te have been achieved through partial substitution of Ag by Cu. The (Ag_0.985−xCu_x)₂Te alloy becomes a β-Ag₂Te single-phase solid solution above the structural transition temperature, which is a superionic conductor with highly mobile ions and low lattice thermal conductivity. The substitution of Cu for Ag increases the band gap and hole concentration of the solid solution, leading to not only a suppressed bipolar effect but also greatly improved electrical transport properties. Meanwhile, a periodically modulated layered nanostructure is observed in (Ag_0.985−xCu_x)₂Te alloys, which may be attributed to the Cu substitution. As a result, the electrical conductivity increases with the Cu content, and the Seebeck coefficient at high temperature is substantially improved. Both the carrier and lattice thermal conductivities are decreased because of the suppressed bipolar effect and enhanced phonon scattering, respectively. The modified electrical and thermal transport properties enable a maximum ZT value of 1.39 for the sample with x = 0.3, indicating the great potential of superionic conductors as novel thermoelectric materials.