Carrier Doping in the Type VIII Clathrate Ba<Subscript>8</Subscript>Ga<Subscript>16</Subscript>Sn<Subscript>30</Subscript> Through Sb Substitution

The type VIII clathrate Ba₈Ga₁₆Sn₃₀ has a relatively high figure of merit (ZT) from 200°C to 400°C. Our previous calculations showed that the optimum carrier concentration for high ZT is on the order of 10²⁰/cm³ for both p- and n-type samples. The ZT value exceeds unity for the n-type material. However, actual carrier concentrations for synthesized samples were on the order of 10¹⁹/cm³. With the aim of increasing the carrier concentration, we have synthesized single crystals of Sb-doped Ba₈Ga₁₆Sn₃₀. Contrary to our expectation, the Ga content in the crystal increased with the increase in Sb content. In both p- and n-type samples, the carrier concentration was increased, and the power factor for the p-type samples was improved to 1.4 × 10⁻² W/mK². These results are discussed in relation to the change in the band structure.