Dopant substitution and oxygen migration in the complex perovskite oxide Ba3CaNb2O9: A computational study

Atomistic simulation methods have been used to study the defect chemistry of the complex perovskite oxide Ba3CaNb2O9. Calculations were carried out for the hexagonal (P-3m1) phase and the cubic (Fm-3m) phase. The hexagonal structure is predicted to be energetically more stable at room temperature. In both structures the most favourable dopant for Nb5+ is found to be Ca2+ rather than Mg2+, in contrast to the generally accepted rule that size similarities govern such processes. The diffusion of oxygen vacancies in the hexagonal and cubic phases occurs within different networks of corner-sharing NbO6 and CaO6 octahedra. Irrespective of the arrangement of octahedra, however, migration of oxygen vacancies around NbO6 octahedra takes place with lower activation energies than around the CaO6 octahedra.