title: Jahn-Teller effect in BaTiO(3):Cr(5+): an electron paramagnetic resonance study.
abstract: Electron paramagnetic resonance (EPR) spectra of Cr(I)(5+) defects incorporated on Ti(4+) sites in single-crystal and powdered ceramics of BaTiO(3) were investigated in the temperature range 50-220 K at 34 GHz (Q band). Single-crystal and powder measurements allow the unambiguous determination of the full g tensor in the ferroelectric rhombohedral phase whereas in the orthorhombic phase only the determination of the principal values of the Cr(I)(5+) g tensor was successful. The [Formula: see text] Jahn-Teller effect stabilizes the vibronic ground state of the 3d(1) electron of the Cr(I)(5+) ion and leads to a tetragonally compressed defect-O(6) octahedron with the point symmetry D(4h). The spontaneous electrical polarization present in the ferroelectric phases of BaTiO(3) appears as a further perturbation. The quadratic field effect reduces the D(4h) symmetry of the Cr(I)(5+) defect centre and produces an additional g tensor breaking the tetragonal symmetry of the Zeeman term. For symmetry reasons one of the principal axes of the rhombic g tensor must be directed along one [Formula: see text] direction. The angles of the other two principal axes with respect to the [Formula: see text] axes are dependent on the absolute value of the spontaneous polarization. The difference in the temperature behaviour of the single-crystal and powder spectra can be explained by the presence of internal stress in the grains of the ceramic samples which increases the JT energy of the 3d(1) electron.
authors.affiliation: Fakultät für Physik und Geowissenschaften, Universität Leipzig, Linnéstraße 5, D-04103 Leipzig, Germany.
authors.forename: R
authors.initials: R
authors.lastname: Böttcher
authors.forename: H T
authors.initials: HT
authors.lastname: Langhammer
authors.forename: T
authors.initials: T
authors.lastname: Müller