First-Principles Calculations of Structural, Electronic, Optical, Vibrational, Dielectric, and Elastic Properties of Tetragonal Mg2TiO4 and Mg2TiO4:Mn4.

In this study, first-principles simulations of inverse spinel Mg2TiO4 (MTO) and MTO:Mn4+ on the base of the tetragonal phase were performed within the linear combination of atomic orbitals (LCAO) approximation of density functional theory (DFT), as implemented in CRYSTAL23 computer code. The effect of Mn doping on the MTO band gap structure was studied for the first time. Lattice relaxation around Mn4+ ions upon substitution was considered. Two possible spin configurations of the Mn4+ ion (3d3) in MTO:Mn4+ (total spin of system S = 3/2 and 1/2) were considered in the framework of the unrestricted (open shell) DFT-LCAO calculations. The structural, electronic, vibrational, dielectric and elastic properties of materials were investigated, compared and discussed. It has been shown that dopant atoms create new defect states within the band gap and modify the conduction band and the valence band, which is one of the most important results in the present study. The effect of isotopic substitution on the vibrational properties was analyzed. Based on the calculated elastic moduli, the Debye temperature for MTO was estimated. This study provides a basis for the assessment of the optical and luminescent properties of the doped material and its use in LED applications.