Theoretical Study on Interactions between Oxygen Vacancy and Doped Rare-Earth Elements in Barium Titanate

We performed first-principles theoretical calculations to examine the interactions between oxygen vacancy (V-O) and rare-earth (RE) elements in barium titanate (BaTiO3), in order to clarify the mechanism of V-O trapping by RE dopants, which affects the insulating reliability of BaTiO3-based multilayer ceramic capacitors (MLCC). It was found that V-O is stabilized at the first and second nearest O sites of RE at Ba site (REBa), and at the second nearest O site of RE at Ti site (RETi). The structural relaxations on bond lengths of REBa-O and RETi-O in BaTiO3, which are brought about by the existence of V-O at the above sites, decrease the total energy, and thus V-O is stabilized. Furthermore, we revealed that the stability of V-O increases with decreasing solution stability of RE dopants in BaTiO3. Accordingly, we concluded that RE dopants with higher solution energy in BaTiO3 efficiently trap V-O, and thus the insulation reliability of MLCC is improved. (C) 2011 The Japan Society of Applied Physics