First Principles Calculation Study of the Origin of the Tetragonal Structure of BiCoO3

We have investigated the electric state of BiCoO3 in various crystal and magnetic structures by first-principles calculation method to clarify the origin of the tetragonal structure of BiCoO3. The ferroelectric displacement of Co in the tetragonal crystal is larger than that in the rhombohedral one. Because of the large ferroelectric displacement, the energy levels of the Co's d(6) localized electrons are lowered and the crystal tends to be tetragonal. Moreover, we calculated the electric state of BiCo0.5Fe0.5O3, BiCoO3-BiFeO3 solid solution. In this solid solution, the effect of Co's d6 localized electron is effective and the crystal also tends to be tetragonal. (C) 2010 The Japan Society of Applied Physics