CHARACTERIZATION OF STOICHIOMETRIC LINBO3 GROWN FROM MELTS CONTAINING K2O

The growth of LiNbO3 single crystals from a melt with the Li/Nb ratio of 0.946, to which 6wt.% K2O has been added, leads to stoichiometric specimens, essentially free of potassium, with (50 +/- 0.15)mol% Li2O in the crystal. This is established by studying the composition dependence of the following properties: linewidths of the electron paramagnetic resonance (EPR) of Fe3+, energy of the fundamental absorption edge, Raman linewidths of phonon modes, and dispersion of the optical birefringence. Comparison of the results with relevant calibration scales leads to the above composition. In all cases the Li2O content was found to be closer to 50% than that of a LiNbO3 crystal vapor-phase equilibrated to 49.9 mol% Li2O. The photorefractive effect at light intensities I greater-than-or-equal-to 10(7) W/m2 is suppressed in this stoichiometric material. The features of the ternary system K2O-Li2O-Nb2O5, which are possibly responsible for the unexpected growth of stoichiometric LiNbO3 from the indicated melts, are discussed.