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Understanding the defect chemistry of alkali metal strontium silicate solid solutions: insights from experiment and theory

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journal contribution
posted on 08.01.2017 by R.D. Bayliss, S.N. Cook, D.O. Scanlon, S. Fearn, J. Cabana, C. Greaves, J.A. Kilner, S.J. Skinner
Recent reports of remarkably high oxide ion conduction in a new family of strontium silicates have been challenged. It has recently been demonstrated that, in the nominally potassium substituted strontium germanium silicate material, the dominant charge carrier was not the oxygen ion, and furthermore that the material was not single phase (R. D. Bayliss et. al., Energy Environ. Sci., 2014, DOI: 10.1039/ c4ee00734d). In this work we re-investigate the sodium-doped strontium silicate material that was reported to exhibit the highest oxide ion conductivity in the solid solution, nominally Sr0.55Na0.45SiO2.775. The results show lower levels of total conductivity than previously reported and sub-micron elemental mapping demonstrates, in a similar manner to that reported for the Sr0.8K0.2Si0.5Ge0.5O2.9 composition, an inhomogeneous chemical distribution correlating with a multiphase material. It is also shown that the conductivity is not related to protonic mobility. A density functional theory computational approach provides a theoretical justification for these new results, related to the high energetic costs associated with oxygen vacancy formation.

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RDB would like to thank the King Abdullah University of Science and Technology for providing resources to complete the work. The UCL/Diamond work presented here made use of the UCL Legion HPC Facility, the IRIDIS cluster provided by the EPSRC funded Centre for Innovation (EP/K000144/1 and EP/ K000136/1), and the ARCHER supercomputer through membership of the UK's HPC Materials Chemistry Consortium, which is funded by EPSRC grant EP/L000202.

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Publisher Statement

This is a copy of an article published in the Journal of Materials Chemistry A © 2014 Royal Society of Chemistry Publications.

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Royal Society of Chemistry

issn

2050-7488

Issue date

24/09/2014

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