Electron Paramagnetic Resonance, Optical, and Electronic Structure Studies of Photorefractive Barium Titanate

Barium titanate (BaTiO 3 ) is an important electrooptic ferroelectric oxide material which exhibits the unusual optical nonlinearity of photorefractivity. There is evidence that the photorefractive effect, which refers to the change in the index of refraction of the crystal by the action of light, is related to the presence of defects/impurities such as transition metal ions and/or cation or anion vacancies. This paper will review our electron paramagnetic resonance, optical, and theoretical eletronic structure studies aimed at probing the nature of the defects/impurities in BaTiO 3 and their role in the photorefractive effect.