Realizing High Thermoelectric Performance in BaCu_2–xAg_xTe₂ through Enhanced Carrier Effective Mass and Point-Defect Scattering

With the aim of realizing mid-temperature thermoelectric materials, the electrical and thermal transport properties of the Zintl phase compound BaCu2Te2 with a channel structure (Pnma) were systematically investigated. BaCu2Te2 exhibits moderate electrical transport properties and low intrinsic thermal conductivity, which contribute to its high thermoelectric figure of merit (zT = 0.72 at 823 K). The partial substitution of Cu with Ag led to a significant enhancement of the Seebeck coefficient, as the carrier effective mass increased from 1.0m0 for BaCu2Te2 to 1.5m0 for BaCu1.9Ag0.1Te2 at room temperature, and reduction of the Hall carrier concentration. In addition, at higher temperature, a lower thermal conductivity of ∼0.5 W m–1 K–1 was achieved for BaCu1.9Ag0.1Te2; this reduced thermal conductivity resulted from the point-defect scattering arising from the Ag/Cu isovalent substitution. Together, these integrated effects led to a significant improvement of the quality factor β with a peak thermoelectric figure of merit zT of 1.08 for BaCu1.9Ag0.1Te2 at 823 K. The average zT of BaCu1.9Ag0.1Te2 over the temperature range of 323–823 K was 0.68, demonstrating its potential as a promising thermoelectric Zintl compound in the mid-temperature range.