Transport properties of the doped thermoelectric material β-K₂Bi₈Se₁₃

The synthesis, physicochemical, spectroscopic, and structural characterization of the compounds β-K₂Bi₈Se₁₃, K₂Sb₈Se₁₃, K_2.5Bi_8.5Se₁₄, and K_2.5Sb_8.5Se₁₄ have been previously reported and show promising properties for thermoelectric applications. While β-K₂Bi₈Se₁₃ is isostructural with K₂Bi₈Se₁₃, the isostructural K_2.5Bi_8.5Se₁₄ and K_2.5Sb_8.5Se₁₄ are different but have similar structural features to β-K₂Bi₈Se₁₃. Compared with α-K₂Bi₈Se₁₃, which has a room temperature electrical conductivity of 2 S/cm and a Seebeck coefficient ranging from -210 to -260 μV/K, β-K₂Bi₈Se₁₃ shows excellent electrical conductivity values at room temperature while maintaining high Seebeck coefficients. In this work the doping of the homologous compound β-K₂Bi₈Se₁₃ was explored by employing varying concentrations of different dopants. Where possible, transport measurements were carried out on both single crystal and polycrystalline ingot material. From these data the trends in the key parameters were identified for optimizing the power factor and figure of merit.