Charge Transport and Thermoelectric Properties of N-type Bi2-xSbxTe3-ySey:Im Prepared by Encapsulated Melting and Hot Pressing

Iodine-doped n-type Bi2-xSbxTe3-ySey:I-m (x = 0.1-0.2, y = 0.15-0.6, and m = 0.0025-0.005) quaternary solid solutions were prepared by encapsulated melting (EM) and hot pressing (HP). The lattice constants of the resulting materials decreased with increasing Sb and Se contents, whereas the amount of I dopant was too small to significantly affect the lattice constants. An average relative density of 97% was obtained for the hot-pressed specimens. All specimens indicated n-type conductions in the temperature range of 323 to 523 K, and the electrical conductivity decreased with increasing temperature, exhibiting the typical characteristics of degenerate semiconductors. The electrical conductivity and the thermal conductivity decreased with increasing Se content, whereas they increased with I doping. This was a result of changes in the carrier concentrations due to Se substitution and I doping, and from the decreased lattice thermal conductivity due to increased alloy scattering. However, the changes in electrical and thermal conductivity caused by Sb substitution were not significant. The maximum figure of merit, ZT(max) of 0.84, was achieved at 473 K for Bi1.9Sb0.1Te2.85Se0.15:I-0.0025.