Discovery of a New Cu‐Based Chalcogenide with High <i>zT</i> Near Room Temperature: Low‐Cost Alternative for the Bi<sub>2</sub>Te<sub>3</sub>‐Based Thermoelectrics
Oleksandr Cherniushok, Taras Parashchuk, G. Jeffrey Snyder, Krzysztof T. Wojciechowski
Abstract
Abstract Copper‐based chalcogenides are cost‐effective and environmentally friendly thermoelectric (TE) materials for waste heat recovery. Despite demonstrating excellent thermoelectric performance, binary Cu 2 X ( X = S, Se, and Te) chalcogenides undergo superionic phase transitions above room temperature, leading to microstructural evolution and unstable properties. In this work, a new γ‐phase of Cu 6 Te 3‐ x S 1+ x (0 < x ≤ 1) is discovered, a narrow‐bandgap semiconductor with outstanding thermoelectric performance and high stability. By substituting Te with S in metallic Cu 6 Te 3 S, the crystal symmetry is modified and structural phase transitions are eliminated. The γ‐phase exhibits a significantly higher Seebeck coefficient of up to 200 µVK −1 compared to 8.8 µVK −1 for Cu 6 Te 3 S at room temperature due to optimized carrier concentration and increased effective mass. Cu 6 Te 3‐ x S 1+ x materials also demonstrate ultralow thermal conductivity (≈0.25 Wm −1 K −1 ), which, in concert with improved power factors, enables a high zT of ≈1.1 at a relatively low temperature of 500 K. Unlike most Cu‐based chalcogenides, the γ‐phase exhibits excellent transport property stability across multiple thermal cycles, making it a cost‐effective and eco‐friendly alternative to Bi 2 Te 3 ‐based materials. The developed Cu 6 Te 3‐ x S 1+ x is a promising candidate for thermoelectric converters in waste heat recovery, and its potential can be further extended to cooling applications through carrier concentration tuning.