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

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We performed first-principles theoretical calculations to examine the interactions between oxygen vacancy (V\text{O) and rare-earth (RE) elements in barium titanate (BaTiO3), in order to clarify the mechanism of V\text{O trapping by RE dopants, which affects the insulating reliability of BaTiO3-based multilayer ceramic capacitors (MLCC). It was found that V\text{O is stabilized at the first and second nearest O sites of RE at Ba site (RE\text{Ba), and at the second nearest O site of RE at Ti site (RE\text{Ti). The structural relaxations on bond lengths of RE\text{Ba--O and RE\text{Ti--O in BaTiO3, which are brought about by the existence of V\text{O at the above sites, decrease the total energy, and thus V\text{O is stabilized. Furthermore, we revealed that the stability of V\text{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\text{O, and thus the insulation reliability of MLCC is improved.
2011-09-25