Crystal and defect chemistry of rare earth cations in BaTiO₃

This study revisits the issue of rare earth cation substitutions into barium titanate. Analysis based upon crystal chemistry, defect chemistry and metastable states is presented to aid interpretation of experimental data. Recent detailed and highly precise X-ray powder diffraction and Electron Paramagnetic Resonance experiments performed on samples produced with different A/B ratios and fired under different oxygen partial pressure conditions give rise to new insights into the material. Specifically, the site occupancy and the valence states for the rare-earth dopants in barium titanate are considered. Earlier work is also reviewed and compared to the studies performed here. Collectively a classification of the various types of behaviour observed for the rare-earth series in barium titanate is presented.