Structural, elastic and optoelectronic properties of Sr-based perovskite-type oxides SrXO3 (M = Th, Zr) via first-principles calculations

In this paper, we present a detailed theoretical investigation on the structural, elastic, electronic and optical properties of the perovskite oxides SrThO3 and SrZrO3 by using the pseudo-potential plane wave (PP-PW) method. The computed lattice constants of SrXO3 (X = Th and Zr) are in excellent agreement with the available experimental data. SrThO3 and SrZrO3 are direct (Γ-Γ) and indirect (Γ-R) band gap semiconductors, respectively. Under pressure effect a crossover between the indirect band gap (R-Γ) and the direct band gap (Γ-Γ) curves occurs at about 35 GPa for SrZrO3, resulting in the energy minimum of direct gap (Γ-Γ) for this compound. The covalence in the Zr-O and Th-O bonds arises due to the hybridization between O-p and Zr-d (Th-d) states. Under pressure effect, the threshold energy becomes slightly greater (smaller) for SrZrO3 (SrTO3) for 3.21 (2.28) eV and the main peaks are shifted towards higher energies. Although the positions of all peaks shifted under pressure, they still have the same type as those at zero pressure, with decreasing the intensity of the main peaks.