Structure and high-temperature thermoelectric properties of SrAl_2Si_2

Abstract

Single crystals of SrAl_2Si_2 were synthesized by reaction of the elements in an aluminum flux at 1000 °C. SrAl_2Si_2 is isostructural to CaAl2Si2 and crystallizes in the hexagonal space group P–3m1 (90 K, a=4.1834 (2), c=7.4104 (2) Å, Z=1, R1=0.0156, wR2=0.0308). Thermal analysis shows that the compound melts at 1020 °C. Low-temperature resistivity on single crystals along the c-axis shows metallic behavior with room temperature resistivity value of 7.5 mΩ 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 −78 μV K^(−1) at room temperature to −34 μV K^(−1) at 1173 K. 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