Structure and high-temperature thermoelectric properties of SrAl2Si2

Single crystals of SrAl2Si2 were synthesized by reaction of the elements in an aluminum flux at 1000 degrees C. SrAl2Si2 is isostructural to CaAl2Si2 and crystallizes in the hexagonal space group P-3m1 (90K, a = 4.1834 (2), c = 7.4104 (2) angstrom, Z = 1, R1 = 0.0156, wR2 = 0.0308). Thermal analysis shows that the compound melts at similar to 1020 degrees C. Low-temperature resistivity on single crystals along the c-axis shows metallic behavior with room temperature resistivity value of similar to 7.5 m Omega cm. High-temperature Seebeck, resistivity, and thermal conductivity measurements were made on hot-pressed pellets. The Seebeck coefficient shows negative values in entire temperature range decreasing from similar to-78 mu V K-1 at room temperature to -34 mu V K-1 at 1173K. Seebeck coefficients are negative indicating n-type behavior; however, the temperature dependence is consistent with contribution from minority p-type carriers as well. The lattice contribution to the thermal conductivity is higher than for clathrate structures containing Al and Si, approximately 50 mW cm(-1) K, and contributes to the overall low zT for this compound. (C) 2008 Elsevier Inc. All rights reserved.