Computational predictions of stable phase for antiperovskite Na3OCl via tilting of Na6O octahedra

Abstract

We study the structural stability of crystalline Na3OCl in terms of cohesive energies and phonon spectra through the tilting of Na6O octahedra. We prove that the crystal Na3OCl can be stabilized through octahedral tilts by comparing 14 tilted structures that are consistent with the Howard and Stokes’ group-theoretical analysis of the octahedral tilting in perovskites. We found that all the 14 tilted structures of Na3OCl have lower energies than the cubic Pm3¯m structure by about 11 to 16 meV per five-atom unit cell. The tilt angles along the pseudocubic [100], [010], and [001] directions vary in the range of 2.6°–9.3°. While the Pnma and P21/m structures of Na3OCl are found as the two most stable ones, only the P21/m phase has stable phonon vibrations with a direct band gap of 3.38 eV at the Γ point.