Probing Cation and Vacancy Ordering in the Dry and Hydrated Yttrium-Substituted BaSnO3 Perovskite by NMR Spectroscopy and First Principles Calculations: Implications for Proton Mobility

作者：Buannic Lucienne; Blanc Frederic; Middlemiss Derek S; Grey Clare P^*

来源：Journal of the American Chemical Society, 2012, 134(35): 14483-14498.

DOI：10.1021/ja304712v

Hydrated BaSn1-xYxO3-x/2 is a protonic conductor that, unlike many other related perovskites, shows high conductivity even at high substitution levels. A joint multinuclear NMR spectroscopy and density functional theory (total energy and GIPAW NMR calculations) investigation of BaSn1-xYxO3-x/2 (0.10 <= x <= 0.50) was performed to investigate cation ordering and the location of the oxygen vacancies in the dry material. The DFT energetics show that Y doping on the Sn site is favored over doping on the Ba site. The Sn-119 chemical shifts are sensitive to the number of neighboring Sn and Y cations, an experimental observation that is supported by the GIPAW calculations and that allows clustering to be monitored: Y substitution on the Sn sublattice is close to random up to x = 0.20, while at higher substitution levels, Y-O-Y linkages are avoided, leading, at x = 0.50, to strict Y-O-Sn alternation of B-site cations. These results are confirmed by the absence of a "Y-O-Y" O-17 resonance and supported by the O-17 NMR shift calculations. Although resonances due to six-coordinate Y cations were observed by Y-89 NMR, the agreement between the experimental and. calculated shifts was poor. Five-coordinate Sn and Y sites (i.e., sites next to the vacancy) were observed by Sn-119 and Y-89 NMR, respectively, these sites disappearing on hydration. More five-coordinated Sn than five-coordinated Y sites are seen, even at x = 0.50, which is ascribed to the presence of residual Sn-O-Sn defects in the cation-ordered material and their ability to accommodate O vacancies. High-temperature Sn-119 NMR reveals that the O ions are mobile above 400 degrees C, oxygen mobility being required to hydrate these materials. The high protonic mobility, even in the high Y-content materials, is ascribed to the Y-O-Sn cation ordering, which prevents proton trapping on the more basic Y-O-Y sites.

• 出版日期2012-9-5