Structural, elastic, thermodynamic, electronic, magnetic, thermoelectric and optical investigation of chromate spinels TCr2O4 [T = V2+, Mn2+, Fe2+] for optoelectronic applications

Spinel oxides (TM2O4) containing transition metals are gaining vast momentum not only for advanced exploration of fundamental properties but also because of their potential as promising materials for various technological applications, such as microwaves, fuel cells, sensors, information storage, supercapacitors, magnetic fluids, photocatalysis and biomedical devices. In this regard, the structural, elastic, thermodynamic, electronic, magnetic, thermoelectric and optical properties of three related chromate spinels (TCr2O4) with 3d transition metals (T2+ = V, Mn, Fe) have been systematically investigated. The Perdew-Burke-Ernzerh (PBE) functional and the exchange-correlation method (PBE + U) based on the generalized gradient approximation were used to investigate these properties. The elastic parameters confirm that TCr2O4 compounds are mechanically stable and possess stiffness and anisotropic properties. The calculated band structures, DOSs and magnetic moments show that the cubic TCr2O4 (Fd-3m) are half-metallic (HM) ferromagnetic compounds due to strong hybridization between their T-3d, Cr-3d and O-2p states. The thermodynamic properties are explained by calculating the melting temperature (Tm), average sound velocity (vm) and Debye temperature (ƟD). High values of these parameters, Tm, νm and ƟD, indicate the high thermodynamic stability of TCr2O4, which allows them to maintain their ground state structures at high temperatures. The thermoelectric properties as a function of temperature illustrate the stability of the current spinel structures. We have also calculated the optical properties, including real ε1(ω) and imaginary ε2(ω) parts of dielectric function ε(ω), conductivity σ(ω), absorption coefficient α(ω), reflectivity R(ω), refractive index n(ω), extinctive index k(ω) and energy loss function L(ω). TCr2O4 exhibits high dielectric constants; low reflectivity and minimal energy loss in the range VL-UV, making these FM-HM compounds promising materials for many optoelectronics devices.