Structural, electronic, optical and elastic properties of Mg3TH7 (T=Mn, Tc and Re) complex hydrides: First-principles calculations

The structural, electronic, optical and elastic properties of Mg3TH7 (T=Mn, Tc, Re) complex hydrides have been investigated by using the density functional theory ‘DFT’ within the generalized gradient approximation ‘GGA’ parameterized by the Perdew, Burke and Ernzerhof ‘PBE’. The optimized lattice constants, atomic positions and interatomic distance are in good agreement with both theoretical results and experimental data available in the literature. Band structure, densities of states ‘DOS’, optical properties, and elastic constants have been calculated. The obtained results of elastic properties were compared with those of the simplest Mg-based hydride MgH2. More importantly, it is found that, the energy band gap is highly augmented when Mn atom is replaced by Re, but it is less pronounced when Re atom is replaced by Tc. From elastic constants calculations, it is noted that MgH2, Mg3MnH7, Mg3TcH7 and Mg3ReH7 compounds are mechanically stable and are brittle. In addition, the polycrystalline elastic properties such as bulk modulus, shear modulus, Young modulus and Poisson’s ratio were also determined by the Voigt-Reuss-Hill, ‘VRH’ approximation. It was found that the bulk modulus of complex hydrides Mg3TH7 (T=Mn, Tc and Re) are higher than that of MgH2 and increases with increasing atomic number of element (Mn, Tc, Re) in the sequence (B) Mg3MnH7 < (B) Mg3TcH7 < (B) Mg3ReH7. The shear anisotropy, linear bulk modulus and percentage anisotropy in compressibility and shear were also determined and discussed in details. Finally, Debye temperatures were calculated and discussed.