Theoretical calculations of the effect of nitrogen substitution on the structural, vibrational, and electronic properties of wolframite-type ScTaO4 at ambient conditions

Abstract

In this study, the effect of nitrogen substitution in wolframite-type ScTaO₄ was investigated using density-functional theory calculations. First, structural and mechanical properties, as well as the dynamical stability of ScTaO₄ were examined deeply for the ambient-pressure structure. Subsequently, we studied how lattice vibrations are affected by hydrostatic pressure and determined the elastic moduli of ScTaO₄. The results of our study show that the monoclinic structure of ScTaO₄ is rigid and non-compressible. In addition, band-structure calculations show that ScTaO₄ has a wide direct band-gap of 4.04 eV, which in turn leads to a possible tuning of electronic properties. We have found that this task can be conducted by partially substituting oxygen atoms in the unit cell with nitrogen atoms. Both band-structure calculations and charge-density analyses revealed a narrowing in the band gap caused by the presence of nitrogen atoms, which act as a shallow acceptor state, resulting in weak repulsive interactions and structural distortions in both Sc and Ta coordination polyhedra; reducing the crystal symmetry from monoclinic to triclinic.