Enhanced thermoelectric properties of β-Cu2Se by incorporating CuGaSe2

(Cu2Se)1−x(CuGaSe2)x alloys with x = 0, 0.005, 0.0075, 0.01, 0.015, 0.025 and 0.03 were prepared by melting and ball milling, followed by spark plasma sintering. The X-ray powder diffraction analysis results indicated that there was a very low amount of CuGaSe2 in a solid solution of crystalline β-Cu2Se. However, a small amount of dissolved Ga atoms significantly decreased the electrical resistivity and thermal conductivity and drastically decreased the lattice thermal conductivity of β-Cu2Se, thereby improving the power factor and the figure of merit of the system. When the second phase of CuGaSe2 was present, its high electrical resistivity and thermal conductivity had an opposing effect, which lowered the thermoelectric performance of the system. A high figure of merit (zT) of 1.4 was obtained for the (Cu2Se)0.9925(CuGaSe2)0.0075 samples at 823 K.