We evaluated Bi-substitution effects of Ge 2 Sb 2−x Bi x Te 5 (x=0, 0.1, 0.3, 0.5) bulk materials on the crystal structures and low-temperature thermoelectric properties in the temperature range of 100-300 K. When the substitution amount of Bi increased from x=0 to 0.5, the ratio of cubic to hexagonal structure changed from 79: 21 to 67:33 in wt%, resulting in increase in the ratio of hexagonal structure in the sample. With increasing x, Seebeck coefficient S would be mainly influenced by the

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... crease in the phase fraction of the hexagonal structure, and electrical resistivity ρ and thermal conductivity κ would be affected by the alloy scattering. As a result, the maximum dimensionless figure of merit zT at 300 K decreased from 0.07 (x=0) to 0.02 (x=0.5) because decrease in S 2 ρ −1 exceeded decrease in κ.