Is ReO₃ a mixed ionic–electronic conductor? A DFT study of defect formation and migration in a B^VIO₃ perovskite-type oxide

Abstract

Density-functional-theory (DFT) calculations within the generalised gradient approximation (GGA) were used to examine the behaviour of point defects in the cubic BO perovskite-type oxide, ReO. Energies of reduction and of hydration were calculated, and the results are compared with literature data for ABO perovskite oxides. The activation energies of migration were determined for O, H, Li, Na, K and HO. An occupied A site in ReO is found to be beneficial to oxide-ion migration by a vacancy mechanism as well as to proton migration by a Grotthuss mechanism. Na, K and HO exhibit activation energies of migration higher than 2 eV, whereas Li is characterised by a very low migration barrier of 0.1 eV. Reasons for this behaviour are discussed. Our results suggest that H, O, and especially Li, are highly mobile ions in ReO.

Perovskite crystal symmetry and oxygen-ion transport: a molecular-dynamics study of perovskite

“…And at present it is still not clear. A detailed study based on the working hypothesis that Coulomb interactions play the key role in determining the migration barrier for X moieties in ABX 3 perovskites 13,92,93 is underway.…”

Fast lithium-ion conductivity in the ‘empty-perovskite’ n = 2 Ruddlesden–Popper-type oxysulphide Y2Ti2S2O5

“…Similar four-coordinate distorted square-planar-like Li + insertion geometry in 'window' positions has been reported from DFT calculations for selected sites within the Wadsley-Roth-type Nb-W-O bronzes 29,53 and TiNb 2 O 7 , 30 as well as in cubic ReO 3 under dilute conditions. 22 It is notable that a squareor rectangular-planar-like arrangement is an unusual geometry for Li + . An ideal four-fold coordination for the stabilisation of an ion from a set of point charges is tetrahedral geometry, and whilst three-coordinate trigonal-planar Li + is described in KLiO, 54 and a range of ve-fold coordination environments are know, four-fold geometry such as square-planar is not discussed in reviews of Li + coordination chemistry in crystals.…”

“…Liions can be introduced into the open cavities of ReO 3 and under dilute conditions they move with low activation barriers, leaving the framework relatively undisturbed. 22 However, progressive intercalation of Li + causes correlated rotations of the cornersharing octahedra (Fig. 1c) and a loss of the cubic framework, greatly increasing activation barriers and eventually leading to structural degradation on cycling.…”

Superionic Lithium Intercalation through 2 × 2 nm2 Columns in the Crystallographic Shear Phase Nb18W8O69

“…'central' tunnels). Bond valence sum maps (Figure 6) and calculations on related systems indicate that lithium moves through both types of tunnel 42,34. It is not known how the dynamics differ at central vs. edge tunnels; this is an interesting question requiring computational insights, though it is non-trivial as diffusion barriers are highly sensitive to the specific transition metal cation ordering in Wadsley-Roth TiNb2O7 34.…”