Threshold concentration of MgO in near-stoichiometric LiNbO3 crystals

MgO-doped near-stoichiometric LiNbO3 crystals have been grown by the high-temperature top-seeded solution growth method from the K2O-Li2O-Nb2O5 flux. The critical threshold concentration of MgO required to minimize photorefractive damage in the crystals has been determined on the basis of the liquid-solid phase relations. The lowest MgO concentration in the melt where above-threshold crystals can be still grown with near-stoichiometric crystal composition was 0.2 mol%. At near-threshold MgO concentration, a transitional region was detected along the crystal growth axis, where two OH− absorption bands peaking at 3465 and 3534 cm−1 frequency were observed in the IR spectra at the same time.