First Principles Study of Electronic and Crystallographic Structure and Elastic Properties of RbNiF[sub 3

Abstract

First principles calculations, based on density functional theory (DFT) with ultra‐soft pseudo potentials were performed to simulate the electronic, magnetic and crystallographic structure and elastic properties of RbNiF3, a candidate for magneto optical applications. The transparent magnetodielectric RbNiF3 is of interest because in contrast to the majority of other ABF3 compounds, which are orthorhombic perovskites, it is a representative of a much smaller group of chalcogenides with hexagonal crystal symmetry. In fact, this is the structural phase at normal pressure and it is isomorphous with the hexagonal modification of BaTiO3. The compound becomes ferrimagnetically ordered below a Néel temperature reported as 135 K. Synthesis at elevated temperature and pressure yields another phase that is a cubic perovskite (a0 = 4.077 Ǻ), reported as antiferromagnetic. Computer simulations were performed using the generalized gradient approximation exchange‐correlation functional with included Hubbard correction term; (GGA+U) approach. The relative stabilities of the hexagonal and cubic phases versus applied pressure were investigated. The stability of different magnetic structures available from theoretical calculations and experimental results has been studied. The elastic constants have been evaluated via the Birch‐Murnaghan equation of state. According to the DFT calculations RbNiF3 is an insulator in both phase structures. The present results for calculated electronic band structure, magnetic structures, lattice parameters, atomic positions and elastic constants can reproduce reasonably well the available own and literature data. For the cubic phase G type antiferromagnetic ordering with magnetization collinear to axis 〈111〉 was predicted.