A DFT study of the perovskite and hexagonal phases of BaTiO3

A geometry optimisation of the perovskite and hexagonal phases of BaTiO3 has been conducted using Density Functional Theory (DFT) within the Local Density Approximation (LDA) and Generalised Gradient Approximation (GGA) schemes. The LDA was found to give lattice parameters closer to experiment than the GGA. A study of oxygen vacancies in the hexagonal phase has been performed and the results suggest an O(1) type (face sharing) vacancy is more stable than an O(2) type (corner sharing) vacancy in the octahedral structure. In addition, the effect of different Ru doping concentrations on the structure and stability of the hexagonal phase has been investigated.