Spin Transition in BiCoO3 Correlated with Large Polar Distortion and Its Applications

Perovskite oxide BiCoO3 belongs to the class of compounds that show the spin transition of the Co ion. The spin state of Co3+ in BiCoO3 is closely correlated with its crystal structure. The application of high pressure induces structural transition accompanied by spin transition. This chapter describes the correlation between the large structural distortion and the spin state of Co3+ in BiCoO3. In addition, negative thermal expansion, which is observed in the BiCoO3-BaTiO3 system, and polarization rotation in the BiCo1−xFexO3 solid solution system are introduced.