No abstract

CO 2 incorporation in solids is attracting considerable interest in a range of energy-related areas. Materials degradation through CO 2 incorporation is also a critical problem with some fuel cell materials, particularly for proton conducting ceramic fuel cells. Despite this importance, the fundamental understanding of the mechanism of CO 2 incorporation is lacking. Furthermore, the growing use of lower temperature sol gel routes for the design and synthesis of new functional materials may be unwittingly introducing significant residual carbonate and hydroxyl ions into the material, and so studies such as the one reported here investigating the incorporation of carbonate and hydroxyl ions are important, to help explain how this may affect the structure and properties. This study on Ba 2 TiO 4 suggests highly unfavourable intrinsic defect formation energies, but comparatively low H 2 O and CO 2 incorporation energies in accord with experimental findings. Carbonate defects are likely to form in both pristine and undoped Ba 2 TiO 4 systems, whereas those based on H 2 O will only form in systems containing other supporting defects, such as oxygen interstitials or vacancies. However, both hydroxyl and carbonate defects will trap oxide ion defects induced through doping, and the results from both experimental and modelling studies suggest that it is primarily the presence of carbonate that is responsible for stabilising the high temperature a 0-phase at lower temperatures.

This is an Accepted Manuscript, which has been through the Royal Society of Chemistry peer review process and has been accepted for publication.Accepted Manuscripts are published online shortly after acceptance, before technical editing, formatting and proof reading. Using this free service, authors can make their results available to the community, in citable form, before we publish the edited article. We will replace this Accepted Manuscript with the edited and formatted Advance Article as soon as it is available.You can find more information about Accepted Manuscripts in the Information for Authors. Computational modelling techniques have been employed to investigate defects and ionic conductivity in Cd 2 GeO 4 . We show due to highly unfavourable intrinsic defect formation energies the ionic conducting ability of pristine Cd 2 GeO 4 is extremely limited. The modelling results suggest trivalent doping on the Cd site as a viable means of promoting the formation of the oxygen interstitial defects. However, the defect cluster calculations for the first time explicitly suggest a strong association of the oxide defects to the dopant cations and tetrahedral units. Defect clustering is a complicated phenomenon and therefore not trivial to assess. In this study the trapping energies are explicitly quantified. The trends are further confirmed by molecular dynamic simulations. Despite this, the calculated diffusion coefficients do suggest an enhanced oxide ion mobility in the doped system compared to the pristine Cd 2 GeO 4 .