OBSERVATION OF 2 CHARGE STATES OF RUTHENIUM IN PBTIO3 SINGLE-CRYSTALS

Two charge states are observed for Ru in doped PbTiO3 crystals using electron paramagnetic resonance (EPR). The two paramagnetic charge states are +3 and +5. The g tensors for the Ru3+ and Ru5+ defects were found to be near axial: g∥≅1.155 and g ⊥≅2.188 for the Ru3+ center and g e∥≅2.0045 and ge ⊥≅3.959 for the Ru5+ center. Analysis of the EPR spectra by crystal field theory indicates that the Ru3+ ions are in tetragonally distorted (elongated) octahedral sites, strongly suggesting that they substitute for the central Ti4+ ions in the perovskite lattice. Analysis of the Ru5+ EPR spectra indicate that this defect is also in an octahedral site with a very large zero field splitting parameter. The results suggest that both Ru3+ and Ru5+ can substitute for Ti4+ in the perovskite lattice with self-compensation. Last, it is found that optical illumination of the crystals with band-gap light at low temperatures decreases the density of both Ru centers. © 1995 American Institute of Physics.