Synthesis and thermoelectric properties of type-I clathrate compounds Si46-xPxTe8

Tellurium-containing cationic clathrates Si46-xPxTe8 (x = 11-17) were synthesized using powder metallurgy. This study crystallized the Pm3n (No. 223) structure and showed a p-type conductivity; their band gap energy is estimated to be 1.24 eV. Although the Si46-xPxTe8 samples with x = 16 and 17 were intrinsic, the samples with x = 11-15 were degenerated semiconductors; their electrical conductivity a increased and their Seebeck coefficient S almost decreased with decreasing x. A power factor S-2 sigma of 12 mu W cm(-1) K-2 at 1000 K and a dimensionless figure of merit ZT of 0.45 at 900 K were achieved for a p-type silicon clathrate Si33P13Te8.