Thermoelectric properties of single crystalline Ba₈Al _xSi_46-x clathrate

We have synthesized single- and poly-crystalline Ba₈Al _xSi_46-x clathrates to compare their thermoelectric properties. Single-crystal sample was prepared by Czochralski(CZ) method in an argon atmosphere. Poly-crystal sample was prepared by arc melting and annealed at 850°C for l00h in an argon atmosphere. The Seebeck coefficients of single- and poly-crystalline Ba₈Al₁₂Si₃₄ at 500°C were 44.5 μV/K and 53.0 μV/K, respectively. The Seebeck coefficients of both samples were almost the same because the Seebeck coefficient depends on carrier concentration, which is related to the aluminum content. The specific electric resistance of the single-crystal sample with 0.49 mΩcm was lower than that of the poly-crystal with 0.95 mΩcm due to the reduction of electron scattering. Therefore, the power factor of the single-crystal sample with 4.0×10^-4V²/K ²Ωm was higher than that of the poly-crystal sample with 3.0×l0^-4V²/K²Ωm at 500°C. It is suggested that single-crystallization is efficient for the thermoelectric property in the Ba₈Al_xSi_46-x system.