CRYSTAL-FIELD ENERGY-LEVELS FOR DEEP FE CENTERS AT ORTHORHOMBIC AND HIGHER SYMMETRY SITES IN BATIO3

We calculate the crystal-field energy levels for Fe3+, Fe4+, and Fe2ions in BaTiO3 by diagonalizing the complete matrices for the electros tatic term, the Trees correction, and the crystal-field interaction. W e use the superposition model to determine the crystal-field parameter s for Fe3+, Fe4+, and Fe2+ ions in each of the three phases, i.e., cub ic, tetragonal, and orthorhombic, of BaTiO3. We use a recently develop ed computer package to diagonalize the full Hamiltonian within the who le configuration 3d4(Fe4+), 3d5(Fe3+), and 3d6(Fe2+). The absorption s pectra and the charge-transfer process of deep Fe centers in BaTiO3 ar e investigated, and possible mechanisms for the photorefractive effect s in BaTiO3 are discussed.