Thermoelectric Properties of Chalcopyrite-Type CuGaTe2 with Ag Substituted into the Cu Sites

CuGaTe2 has recently been reported to have a high thermoelectric (TE) figure of merit (Z T) of 1.4 at 950 K [T. Plirdpring et al.: Adv. Mater. 24 (2012) 3622]. However, the Z T values of CuGaTe2 in the low and middle temperature ranges are not high, due to high lattice thermal conductivity (κlat) in those temperature ranges. We have attempted to reduce the κlat of CuGaTe2 by the substituting Ag into the Cu sites. Polycrystalline samples of Cu1-x Ag x GaTe2 (x = 0, 0.25, 0.5, 0.75, and 1) were prepared and the TE properties were examined. Ag substituted reduced κlat and changed the carrier concentration and mobility, which improved Z T in the low and middle temperature ranges; a Z T value of 0.7 was obtained at 700 K for Cu1-x Ag x GaTe2 with x = 0.5, which is 40% higher than that of CuGaTe2.