The electron paramagnetic resonance spectra of Cr3+ in LiNbO3 co-doped
with ZnO or CaO (approximate to 6%) have been studied. Both impuritie
s give rise to the same effect as that observed in MgO-doped samples:
a strong diminution of the anisotropic (axial) spectrum reported for L
iNbO3:Cr and the appearance of an intense and isotropic line. The orig
in of this line in the co-doped samples is discussed.