The influence of a material microstructure on the behaviour of dopants

Dopants, when introduced into a host lattice, can influence profoundly the properties of a material. It is therefore desirable in the design of new materials with improved or indeed optimised properties to understand the behaviour of such dopants. Most previous simulations have explored the structure and segregation of dopants in a 'perfect' host lattice, or, more recently, within a host lattice comprising a single additional structural feature such as a vacancy or dislocation. However, real materials are likely to comprise a complex microstructure. Here, we present simulations which explore the behaviour and segregation of dopant ions within a material which comprises such a complex microstructure. Specifically, we consider Ca-doped SrO thin films supported on MgO. Microstructural features of the host SrO lattice include: heterointerfaces, dislocation networks, defects (vacancies, substitutionals, and interstitials) and defect clusters, interfacial and epitaxial configurations, low interfacial densities, surface structures and morphologies. Our simulations suggest that the dopant Ca ions segregate to the surface of the SrO thin film, accommodate lattice positions within dislocation cores and migrate across the SrO/MgO heterointerfacial boundary. Such models can then be used as realistic starting configurations to calculate pertinent physical properties as performed previously ('Synthesis, structure and ionic conductivity in nanopolycrystalline BaF2/CaF2 heterolayers': D.C. Sayle et al., Chem. Commun., 2003, 1804 [ref. 11]). The strategy provides therefore a framework for using simulation techniques predictively to design systems with tailored properties.