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A‑Site Cation Bulk and Surface Diffusion in A‑Site-Deficient BaZrO3 and SrZrO3 Perovskites
journal contribution
posted on 2017-05-11, 00:00 authored by Akira Yoko, Junjie Wang, Naoto Umezawa, Takahisa Ohno, Yoshito OshimaDiffusion of A-site
cations in A-site-deficient BaZrO3 and SrZrO3 perovskite oxides was investigated by first-principles
nudged elastic band calculations. We found an energy barrier for surface
diffusion that was significantly lower than that for bulk diffusion
(3.41 eV vs 2.41 eV for Ba diffusion in Ba-deficient BaZrO3 and 3.07 eV vs 1.44 eV for Sr diffusion in Sr-deficient SrZrO3), which suggests unusually rapid cation diffusion at low
temperatures in nanomaterials with a large proportion of surface-exposed
atoms. The lower mobility of Ba in BaZrO3 compared to that
of Sr in SrZrO3 explains why the proportion of A-site vacancies
in BaZrO3 nanoparticles is much greater than that in SrZrO3 nanoparticles, as previously observed during nanoparticle
formation in which an A-site-deficient nucleus gradually incorporated
A-site cations. Finally, thermal and nanoscale effects on the lattice
parameter were studied by carrying out high-temperature X-ray diffraction
measurements on BaZrO3 nanoparticles synthesized in supercritical
water. The data derived from this experimental investigation and subsequent
Rietveld analyses were included in our calculations. We showed that
lattice expansion lowered the calculated energy barrier for Ba bulk
diffusion from 3.41 to 3.28 eV.