Enhanced thermoelectric performance of variable-valence element Sm-doped BiCuSeO oxyselenides

Here, the effects of variable-valence element Sm doping on the thermoelectric performance of BiCuSeO are studied. The Bi 1- x Sm x CuSeO ( x  = 0, 0.025, 0.05, and 0.10) oxyselenides were prepared by a two-step solid state reaction and spark plasma sintering. Experimental measurements and first-principles calculations indicated that Sm 2+ and Sm 3+ coexisted in the samples. The electrical conductivity of the Sm-doped samples was greater than that of pristine BiCuSeO mainly because the holes introduced by Sm 2+ doping increased the carrier concentration, and the shift of the Fermi level by Sm 3+ substitution changed the band gap. The combination of a moderate Seebeck coefficient and relativity low thermal conductivity, gave a maximum ZT value of 0.65 at 823 K for Bi 0.975 Sm 0.025 CuSeO, which is approximately 25 % higher than that of the pristine sample. This study indicates that doping with rare-earth variable-valence elements is an efficient approach to designing high-performance thermoelectric materials.