EPR study of two Cr3+ defect centers in LiTaO3 single crystals

Paramagnetic defect centers due to Cr3+ ions in LiTaO3 single crystals doped with 0.05 mole% of chromium and grown by the Czochralski method have been investigated by employing a Bruker Q-band spectrometer. The observed electron paramagnetic resonance lines can be classified into two sets of the fine structure lines. One set (C1) with a stronger intensity agrees with the center established by previous investigators, while the other set (C2) with a comparatively weaker intensity is newly identified in this study. It is proposed that both the C1 and the C2 centers originate from Cr3+ ions located at Li+ sites in the normal and from Cr3+ ions located at Li+ sites in one of three possible ilmenite ordering structures of LiTaO3, respectively. Two lithium vacancies, V-Li, play the role of a divalent charge compensator for both centers.