Size and shape of oxygen vacancies and protons in acceptor-doped barium zirconate

Abstract

The defect induced chemical expansion in acceptor-doped barium zirconate is investigated using density-functional theory (DFT) calculations. The two defect species involved in the hydration reaction, the +2 charged oxygen vacancy and the proton interstitial forming a hydroxide ion, are considered both as free defects and in association with the dopants Y, In, Sc and Ga. The defect induced strain tensor λ is introduced, which provides a natural generalisation of the ordinary chemical expansion to three dimensions and to anisotropic distortions. Both the addition of a vacancy and a proton cause anisotropic distortions and a net contraction of the lattice, indicating that both the vacancy and the hydroxide ion are smaller than the oxygen ion. The contraction is considerably larger for the vacancy and the net effect in hydration, when a vacancy is filled and two protons are added, is an expansion, consistent with the experimental findings. The effect of the dopants on the chemical expansion in hydration is found to be quite small, even if it is assumed that both the vacancy and the proton are fully associated with a dopant atom in the lattice.

Gas Humidification Impact on the Properties and Performance of Perovskite‐Type Functional Materials in Proton‐Conducting Solid Oxide Cells

“…Recently, the thermo‐ and chemo‐mechanical properties based on the hydration capability have been intensively studied for the doped BaCeO 3 , BaZrO 3 , and BaCe 1− x Zr x O 3 systems. Different experimental and theoretical studies were performed by Uda et al, Løken et al, Andersson et al, Tsidilkovski et al, Jedvik et al, Bjørheim et al, and Mather et al The obtained results demonstrated that the proton formation led to a lattice expansion compared with the initial one containing oxygen vacancies ( Figure a,b) . Based on the numerical estimation, the effective ionic radii of , , and were 1.18, 1.35, and 1.40 Å, respectively .…”

Alkali metals as efficient A-site acceptor dopants in proton conducting BaZrO3

“…As shown in Table 1, the formation volume is negative for both defect complexes, with the oxygen vacancy formation leading to the largest contraction of the cell, similar to what is previously reported for the undoped and B-site acceptor doped system. 2,34,35 These formation volumes lead to a slightly positive chemical expansion upon hydration for all four dopants, which increases with increasing dopant radii. Rb displays the smallest change in 3 hydr compared to the undoped system, which can be attributed to Rb having a similar ionic radius to Ba.…”

Polaronic contributions to oxidation and hole conductivity in acceptor-dopedBaZrO3

“…The two neighboring zirconium ions relax away from the polaron similar to the relaxation of the doubly charged oxygen vacancy and the hydroxide ion in BaZrO 3 . 48 The four nearest oxygen ions in the (100) plane (see Fig. 2) are displaced toward the polaron while the four neighboring out-of-plane oxygen ions (not shown in Fig.…”