Crystal structure and proton conductivity of BaSn0.6Sc0.4O3- δ : insights from neutron powder diffraction and solid-state NMR spectroscopy

Francis G Kinyanjui; Stefan T Norberg; Christopher S Knee; Istaq Ahmed; Stephen Hull; Lucienne Buannic; Ivan Hung; Zhehong Gan; Frédéric Blanc; Clare P Grey; Sten G Eriksson

doi:10.1039/c5ta09744d

Crystal structure and proton conductivity of BaSn_0.6Sc_0.4O_{3- δ} : insights from neutron powder diffraction and solid-state NMR spectroscopy

J Mater Chem A Mater. 2016 Apr 14;4(14):5088-5101. doi: 10.1039/c5ta09744d. Epub 2016 Mar 16.

Authors

Affiliations

¹ Department of Chemical and Biological Engineering , Chalmers University of Technology , SE-412 96 Gothenburg , Sweden.
² The ISIS Facility , STFC Rutherford Appleton Laboratory , Didcot , Oxfordshire OX11 0QX , UK.
³ Department of Chemistry , State University of New York , Stony Brook , NY 11790-3400 , USA.
⁴ Center of Interdisciplinary Magnetic Resonance , National High Magnetic Field Laboratory , 1800 East Paul Dirac Drive , Tallahassee , Florida 32310 , USA.
⁵ Department of Chemistry , University of Cambridge , Lensfield Road , Cambridge , CB2 1EW , UK ; Department of Chemistry and Stephenson Institute for Renewable Energy , University of Liverpool , Crown Street , Liverpool , L69 7ZD , UK.
⁶ Department of Chemistry , State University of New York , Stony Brook , NY 11790-3400 , USA ; Department of Chemistry , University of Cambridge , Lensfield Road , Cambridge , CB2 1EW , UK.

Abstract

The solid-state synthesis and structural characterisation of perovskite BaSn_1-x Sc _x O_3-δ (x = 0.0, 0.1, 0.2, 0.3, 0.4) and its corresponding hydrated ceramics are reported. Powder and neutron X-ray diffractions reveal the presence of cubic perovskites (space group Pm3m) with an increasing cell parameter as a function of scandium concentration along with some indication of phase segregation. ¹¹⁹Sn and ⁴⁵Sc solid-state NMR spectroscopy data highlight the existence of oxygen vacancies in the dry materials, and their filling upon hydrothermal treatment with D₂O. It also indicates that the Sn⁴⁺ and Sc³⁺ local distribution at the B-site of the perovskite is inhomogeneous and suggests that the oxygen vacancies are located in the scandium dopant coordination shell at low concentrations (x ≤ 0.2) and in the tin coordination shell at high concentrations (x ≥ 0.3). ¹⁷O NMR spectra on ¹⁷O enriched BaSn_1-x Sc _x O_3-δ materials show the existence of Sn-O-Sn, Sn-O-Sc and Sc-O-Sc bridging oxygen environments. A further room temperature neutron powder diffraction study on deuterated BaSn_0.6Sc_0.4O_3-δ refines the deuteron position at the 24k crystallographic site (x, y, 0) with x = 0.579(3) and y = 0.217(3) which leads to an O-D bond distance of 0.96(1) Å and suggests tilting of the proton towards the next nearest oxygen. Proton conduction was found to dominate in wet argon below 700 °C with total conductivity values in the range 1.8 × 10^-4 to 1.1 × 10^-3 S cm^-1 between 300 and 600 °C. Electron holes govern the conduction process in dry oxidizing conditions, whilst in wet oxygen they compete with protonic defects leading to a wide mixed conduction region in the 200 to 600 °C temperature region, and a suppression of the conductivity at higher temperature.