Comparison of proton conduction in KTaO3 and SrZrO3

Abstract

In the present paper, the authors focus on proton conduction pathways in a cubic perovskite KTaO(3) and an orthorhombic perovskite SrZrO(3). Density functional theory with a generalized gradient approximation is used to find proton binding sites. The nudged elastic band method is used to find transition states between minima. With this potential energy map of binding and transition states, adjacency matrices and their analogs identify four types of conduction paths in KTaO(3). Distortions from these paths are seen in SrZrO(3). In both cases, the lowest energy path has an intraoctahedral transfer rate-limiting barrier. A Fourier analysis of the OH stretch in ab initio molecular dynamics simulations revealed a strongly redshifted OH stretch in SrZrO(3) relative to KTaO(3). Hence, an orthorhombic system with a lowest energy conduction path limited by an intraoctahedral barrier can exhibit a redshifted OH stretch.

The effect of dopant at the Zr site on the proton conduction pathways of SrZrO3: An orthorhombic perovskite

“…Bilić and Gale 5,6 found pathways for proton conduction in another orthorhombic perovskite, CaZrO 3 , by considering low energy paths and exploring kinetic Monte Carlo pathways. These pathways are consistent with those we have found for orthorhombic systems without a dopant 7,8 and pseudocubic systems with a dopant. 2 Recently, we showed that vertex coding can enumerate all possible simple N-step periodic proton conduction pathways and used it to find pathways for Y / BaZrO 3 .…”

“…This is the same shortest optimum pathway found in the undoped system. 8 It is also similar to the lowest energy path in In/ CaZrO 3 path. 6 However, the single C → B rotation in that work maps to two rotations here since four differently oriented binding sites per oxygen are considered.…”

“…2 The same optimum undoped orthorhombic lattice parameters of 5.84, 5.91, and 8.29 Å were found as in earlier work. 8 Glazer showed that a system of 2 ϫ 2 ϫ 2 cubic unit cells can represent an orthorhombic system when octahedral tilting is allowed. 18 As highlighted in Fig.…”

Effects on the Proton Conduction Limiting Barriers and Trajectories in BaZr0.875Y0.125O3 Due to the Presence of Other Protons

“…Since the mechanism suggests a 1 : 1 ratio of protons to trivalent dopant ions, previous proton conduction simulations in perovskites have considered only one proton and one dopant simulations. [4][5][6][7][8][9][10][11][12][13][15][16][17][18][19][20][21][22][23][24][25][26] However, one study 28) on a different perovskite system finds low energy minima in a perovskite with protons only 2.3 Å apart due to lattice relaxation as well as pathways for moving the two protons together. The same study uses a simplified model to show that the two proton motion may in fact be the dominant diffusing defect.…”

“…25) In principle, both the excess proton and the probe proton move through the lattice. Since a proton can bind to an oxygen in a perovskite with four possible hydroxyl orientations, [23][24][25][26] after one proton is added to the system, there are only N − 4 possible sites for the second proton where N is the total number of binding sites. As a result, there are N (N − 4) / 2 combinations of two protonated sites when two protons are in the system.…”