Owing to the fact of the AB$_2$O$_4$ spinel oxide’s chemical and thermal stability, and other intriguing properties make them suitable candidate materials for many applications, including chemical looping and catalytic reactions. To do our investigations, a short-range non-Coulomb potential theoretical model is used to calculate the zone-centre, elastic constants, infrared phonon mode frequencies, Raman phonon mode frequencies, velocities of the sound wave along the highly symmetric three crystallographic-axes and Debye temperature of the vanadium spinel oxides AV$_2$O$_4$ (A $=$ Mn, Fe and Zn). The preliminary results of our calculations show that the interaction inthe second neighbour (V–O) is much stronger than the interaction of the first neighbour (A–O). Moreover, from the analysis of the obtained results of elastic constants, the nature of the studied vanadium spinels are found to beductile.

In this study, an analysis of the effect of Na substitution on the electronic, structural and thermoelectric (TE) properties of the Li$_2$CuAs material is presented. The study is performed by employing the full-potential linearized augmented plane wave plus local orbital method designed within the density functional theory. To carry out the calculations related to the band structure, generalized gradient approximation by Wu-Cohen (WC-GGA) in combination with Trans Blaha-modified Becke-Johanson mBJ (TB-mBJ) potential is employed. Our results at the level of the WC-GGA approach show that there is no bandgap, whereas, at the level of the TB-mBJ approximation, the material displays bandgap with Na substitution, which is found to be further increased with the increasing Na concentration. To understand the role of different electronic states on the bandgap structure, the total and partial densities of states are also analysed. Furthermore, the temperature effect on the Seebeck coefficient, electronic thermal conductivity, electrical conductivity, power factor and figure of merit are computed. Our obtained results of the TE properties of Li$_2$CuAs at different Na compositions suggest that this compound is a potential candidate for thermoelectricity.

With widespread physical properties from electrical to catalytic and optical to magnetic, etc., pyrochlore materials have attracted a lot more attention in the application field. In this study, we report the interatomic interactions, frequencies of Raman, and infrared phonon modes at the zone centre of mixed pyrochlore-structured compounds A$_2$GaSbO$_7$ (Y, Dy and Gd). The mechanical and elastic properties of these compounds are also reported. The obtained results show that the interatomic interaction between the atoms A–O is the strongest one as compared to the other interatomic interactions. Born’s stability conditions are found to be satisfied for all the examined compounds, showing their mechanical stability. Further analysis shows the ductile and anisotropic nature of the elastic properties for title compounds. The 3D picture of the elastic properties, such as Young’s modulus, shear modulus, linear compressibility and the Poisson ratio, is also presented and analysed. Furthermore, the obtained results are compared with previously reported theoretical and experimental results, which are found to be in good agreement where available.