Investigation of thermoelectric properties of Cu2GaxSn1 ? xSe3 diamond-like compounds by hot pressing and spark plasma sintering

P-type compounds Cu₂Ga_xSn_1 ? xSe₃ (x = 0.025, 0.05, 0.075) with a diamond-like structure were consolidated using hot pressing sintering (HP) and spark plasma sintering (SPS) techniques. High-temperature thermoelectric properties as well as low-temperature Hall data are reported. Microstructural analysis shows that the distribution of Ga is homogeneous in the samples sintered by HP but inhomogeneous in the samples sintered by SPS, even with an electrically isolating and thermally conducting BN layer during the sintering. The Seebeck coefficients of the samples sintered by HP and SPS show similar dependence on the carrier concentration and are insensitive to the composition inhomogeneity. In contrast, the composition inhomogeneity results in lower carrier mobility and thus lower electrical conductivity in the samples sintered by SPS than those sintered by HP. Lattice thermal conductivity is further reduced through Ga doping; however, this effect is weakened by the inhomogeneous distribution of Ga. Due to their larger carrier mobility and lower lattice thermal conductivity, the samples sintered by HP exhibit 15–35% higher thermoelectric figure of merits (ZT) than those SPS samples with a high Ga doping level and without the coated BN layer, in which the composition homogeneity is worse. A ZT value of 0.43 is obtained for the HP Cu₂Ga_0.075Sn_0.925Se₃ sample at 700 K.