Covalent dependence of octahedral rotations in orthorhombic perovskite oxides

Abstract

The compositional dependence of metal-oxygen BO6 octahedral distortions, including bond elongations and rotations, is frequently discussed in the ABO3 perovskite literature; structural distortions alleviate internal stresses driven by under- or over-coordinated bond environments. Here we identify the dependence of octahedral rotations from changes in metal-oxygen bond covalency in orthorhombic perovskites. Using density functional theory we formulate a covalency metric, which captures both the real and k-space interactions between the magnitude and sense, i.e., in-phase or out-of-phase, octahedral rotations, to explore the link between the ionic-covalent Fe-O bond and the interoctahedral Fe-O-Fe bond angles in Pbnm ferrates. Our survey finds that the covalency of the metal-oxygen bond is correlated with the rotation amplitude: We find the more covalent the Fe-O bond, the less distorted is the structure and the more important the long-range inter-octahedral (Fe-O-Fe bond angle) interactions. Finally, we show how to indirectly tune the B-O bond covalency by A-cation induced BO6 rotations independent of ionic size, facilitating design of targeted bonding interactions in complex perovskites.

Structural and magnetic phase transitions inEuTi1−xNbxO3

“…Previous studies have shown that Nb doping enhances T S of STO to higher temperatures due to the local changes in the hybridization between the (Ti, Nb)-d orbitals and O-2p orbitals [36]. Another important factor is the covalency of the transition metal-oxygen bond [37,38]. Ab initio calculations have shown that the octahedral tilting angle in KMF 3 (M = transition metal) decreases linearly with the electron occupancy of the π-bonding t 2g orbitals of the transition metal.…”

Tuning the ferroelectric polarization in AA′MnWO6double perovskites through A cation substitution

“…We understand this be- havior as follows: the magnetic moment only depends on the Mn atoms, and any small changes to it are induced by inductive effects from the A cations that weakly change the length and covalency of the Mn-O bond. 60 The electronic density of states (not shown) also primarily consists of O 2p-states at the top of the valence band and W 5d-states at the bottom of the conduction band. The A and A cations contribute states far from these band edges, and as a result their chemistry does not significantly impact the band gap.…”

Role of orbital filling on nonlinear ionic Raman scattering in perovskite titanates

“…This is because these modes mainly correspond to octahedra rotations, which are largely insensitive to the on-site electron localization at metal center. 44 On the other hand, electron correlation localizes the electron in the t 2g orbitals, reducing the Ti-O bond length, and can harden those IR modes that directly alter the Ti-O bond length [ Fig. 7(b)].…”