Anomalous transport and thermoelectric performances of CuAgSe compounds

•b-CuAgSe exhibits low thermal conductivity.•b-CuAgSe has low resistivity and high seebeck coefficient.•The zT of b-CuAgSe nearly approaches unity at 623 K.

Copper silver selenide has two phases: low-temperature semimetal phase (α-CuAgSe) and high-temperature phonon-glass superionic phase (β-CuAgSe). In this work, the electric transport and thermoelectric properties of the two phases are investigated. It is revealed that β-CuAgSe is a p-type semiconductor and exhibits low thermal conductivity while α-CuAgSe shows metallic conduction with dominant n-type carriers and low electrical resistivity. The thermoelectric figure of merit zT of the polycrystalline β-CuAgSe at 623 K is ~ 0.95, suggesting that superionic CuAgSe can be a promising thermoelectric candidate in the intermediate temperature range.