Abstract
▸ SnX2O4 compounds have been investigated using FP-LAPW method. ▸ Direct band gap decreases from SnMg2O4 to SnZn2O4 to SnCd2O4. ▸ Zero-frequency limit ɛ1(0) increase with decreasing the energy band gap. ▸ The origin of the peaks and structures in the optical spectra is determined.
The structural, electronic and optical properties of the cubic spinels SnB2O4, with B=Mg, Zn and Cd, were studied by means of the full-potential (linear) augmented plane wave plus local orbitals method within the local density and generalized gradient approximations for the exchange-correlation potential. The Engel–Vosko form of the generalized gradient approximation (EV-GGA), which better optimizes the potential for the band structures, was also used. The results of bulk properties, including lattice constants, internal parameters, bulk moduli and their pressure derivatives are in good agreement with the literature data. The band structures show a direct band gap (Γ–Γ) for the three compounds. The computed band gaps using the EV-GGA show a significant improvement over the more common GGA. All the calculated band gaps increase with increasing pressure and fit well to a quadratic function. Analysis of the density of states revealed that the lowering of the direct gap (Γ–Γ) from SnMg2O4 to SnZn2O4 to SnCd2O4 can be attributed to the p–d mixing in the upper valence band of SnZn2O4 and SnCd2O4. We present calculations of the frequency-dependent complex dielectric function ɛ(ω). We find that the values of zero-frequency limit ɛ1(0) increase with decreasing the energy band gap. The origin of the peaks and structures in the optical spectra is determined in terms of the calculated energy band structures.