Study of systematic trends in electronic and optical properties within ZnM2O4 (M = Co, Rh, Ir) family by FPLAPW method with PBE and TB-mBJ potentials

Abstract

The systematic trends for electronic and optical properties for the family of spinel oxides ZnM2O4 depending on the type of M element (M=Co, Rh, Ir) have been investigated using full potential linearized augmented plane wave (FPLAPW) method based on the density functional theory. Calculations have been performed by alternative form of generalized gradient approximation proposed by Perdew, Berke and Erzzehof (GGA-PBE) and by orbital independent Tran–Blaha modified Becke-Johnson (TB-mBJ) potentials as coupled with GGA. The optimized unit cell length, a0, and internal parameter, u, calculated are in agreement with experimental data. TB-mBJ scheme shows a significant improvement in bandgaps over PBE value and are closer to the experimental data. By analyzing density of states (DOS), we find that more pronounced splitting of M-d states splitting is responsible for larger band gap in TB-mBJ scheme for ZnM2O4 compounds. It also shows valence band dispersion is reduced in the TB-mBJ scheme compared to the PBE. Optical properties have been calculated for the energy range 0–14eV. The values of calculated reflectivity stays low till 3.5eV which is consistent with energy gap. The results are analyzed on the basis of band to band transitions. We also present the analysis of frequency dependent refractive index, n (ω), and extinction coefficient, k (ω), of ZnM2O4 using PBE and TB-mBJ schemes.