The Effect of Cu Addition on the System Stability and Thermoelectric Properties of Bi2Te3

Cu-doped Bi2Te3 nanopowders with nominal composition CuxBi2Te3 (x = 0, 0.01, 0.025, and 0.05) were synthesized by a gas-induced-reduction method using TeO2, Bi(NO3)3·5H2O and Cu(NO3)2·3H2O as raw materials and then hot-pressed into bulk materials. x-Ray diffraction (XRD) analysis indicates that, when x ≠ 0, pure CuxBi2Te3 phase was obtained, and that when x = 0, Bi2Te3 mixed with a small amount of Bi2TeO5 was obtained. Field emission scanning electron microscopy observation reveals that Cu addition significantly reduces the grain sizes of the materials. First-principle calculations show that the order of the free energies of the materials is: Cu-doped Bi2Te3 (substitution of Cu for Bi) < Cu intercalated Bi2Te3 < Bi2Te3. The electrical and thermal conductivities decrease and the Seebeck coefficient increases with Cu addition. The maximum figure of merit, ZT, reaches 0.67 at 500 K for a Cu0.05Bi2Te3 sample.