Theoretical insight into the solar thermal absorption property of ultra-high temperature ceramics TMB2 (TM = Ti, Zr, and Hf)

Abstract

TMB2 (TM = Ti, Zr, and Hf) ultra-high temperature ceramics have experimentally been proved as efficient sunlight absorbers operating at elevated temperatures. However, few have been known on the origination and factors that control the absorption performance. In this manuscript, the electronic structure and optical properties of TMB2 (TM = Ti, Zr, and Hf) were investigated by first principles calculations. Quasiparticle correction is introduced in the calculation of electronic structure. The theoretical dielectric function and optical constants are in good agreement with experiments. The reflectance spectra of TMB2 demonstrate they are typical spectrally selective materials. The spectral selectivity of these borides at high temperature is weakened when effect of temperature is considered. The anisotropy in solar absorption of TMB2 is rather weak. Discussion on the solar absorbance and thermal emittance reveals that plasma frequency acts on the solar absorbance and high temperature thermal emittance contradictorily. Our theoretical results demonstrate that it is feasible to tune the spectral selectivity of diborides by regulating the plasma frequency through cation doping.