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 °C. SrAl2Si2 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.

Single crystals of SrAl2Si2 have been prepared via an Al flux reaction and are of the CaAl2Si2 structure type. The melting point is approximately 1020°C. Low temperature resistivity curve is similar to that observed for single crystals of CaAl2Si2 High temperature Seebeck coefficient is negative, indicating n-type carriers.Figure optionsDownload full-size imageDownload as PowerPoint slide