The influence of cation ordering, oxygen vacancy distribution and proton siting on observed properties in ceramic electrolytes: the case of scandium substituted barium titanate
Journal article, 2017

The origin of the 2-order of magnitude difference in the proton conductivity of the hydrated forms of hexagonal and cubic oxygen deficient BaScxTi1-xO3-delta (x = 0.2 and x = 0.7) was probed using a combination of neutron diffraction and density functional theory techniques to support published X-ray diffraction, conductivity, thermogravimetric and differential scanning calorimetry studies. Cation ordering is found in the 6H structure type (space group P6(3)/mmc) adopted by BaSc0.2Ti0.8O3-delta with scandium preferentially substituting in the vertex sharing octahedra (2a crystallographic site) and avoiding the facesharing octahedra (4f site). This is coupled with oxygen vacancy ordering in the central plane of the facesharing octahedra (O1 site). In BaSc0.7Ti0.3O3-delta a simple cubic perovskite (space group Pm3m) best represents the average structure from Rietveld analysis with no evidence of either cation ordering or oxygen vacancy ordering. Significant diffuse scattering is observed, indicative of local order. Hydration in both cases leads to complete filling of the available oxygen vacancies and permits definition of the proton sites. We suggest that the more localised nature of the proton sites in the 6H structure is responsible for the significantly lower proton conduction observed in the literature. Within the 6H structure type final model, proton diffusion requires a 3-step process via higher energy proton sites that are unoccupied at room temperature and is also likely to be anisotropic whereas the highly disordered cubic perovskite proton position allows 3-dimensional diffusion by well-described modes. Finally, we propose how this knowledge can be used to further materials design for ceramic electrolytes for proton conducting fuel cells.

Author

Nico Torino

Chalmers, Chemistry and Chemical Engineering, Energy and Material

Paul Henry

Chalmers, Chemistry and Chemical Engineering, Energy and Material

Christopher Knee

Chalmers, Chemistry and Chemical Engineering, Energy and Material

T. S. Bjorheim

University of Oslo

Habibur Seikh Mohammad Rahman

Chalmers, Chemistry and Chemical Engineering, Energy and Material

E. Suard

Institut Laue-Langevin

C. Giacobbe

European Synchrotron Radiation Facility (ESRF)

Sten Eriksson

Chalmers, Chemistry and Chemical Engineering, Energy and Material

Dalton Transactions

1477-9226 (ISSN) 1477-9234 (eISSN)

Vol. 46 26 8387-8398

Subject Categories

Inorganic Chemistry

DOI

10.1039/c7dt01559c

More information

Latest update

5/8/2018 6