Preparation and Thermoelectric Properties of Type-VIII Single-Crystalline Sm_xBa_8−xGa₁₆Sn₃₀ Clathrate

In this study, based on the stoichiometric ratio of Sm: Ba: Ga: Sn = x: 8 − x: 16: 50 (x = 0, 0.25, 0.5, 0.75, 1, 1.5, 2), Sm-doped type-VIII single-crystalline clathrate Sm_xBa_8−xGa₁₆Sn₃₀ thermoelectric material was successfully prepared via Sn-flux method. The electrical properties were investigated by the measurement of conductivity, Seebeck coefficient and Hall coefficient. The results show that the solubility of Sm in type-VIII Ba₈Ga₁₆Sn₃₀ is very low, and the lattice constant of the samples containing Sm decreases compared with type-VIII Ba₈Ga₁₆Sn₃₀. However, for all samples containing Sm, the lattice constant increases with the increase of the initial content of Sm. Sm plays a "modulation" framework atoms ratio role in the cage compound. Moreover, the carrier mobility of the sample is greatly improved by Sm doping. The related electrical properties exhibit irregular changes with the increase of the initial content of Sm. The sample with x = 0.75 consistently shows high Seebeck coefficient and conductivity in the 300-600 K test temperature range. The maximum power factor is 2.25 × 10⁻³ W/mK² near 442 K, indicating that the energy band structure is optimized, while the conductivity is improved. The ZT value is estimated to be 1.31 at 457 K.