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MgO-doped stoichiometric LiNbO3 crystal has been produced using the Czochralski method and vapor transport equilibration technique. The domain reversal characteristics of the near stoichiometric single crystals with different Mg doping levels have been investigated. The switching field required for 180° ferroelectric domain reversal was compared with the near stoichiometric and congruent crystals. The near stoichiometric crystal doped with MgO shows lower switching field than the near stoichiometric and the congruent crystals. The switching field for the domain reversal in the near stoichiometric crystal doped with 2.0 mol % MgO was 1.8±0.2 KV/mm. This is about one third of the switching field for the near stoichiometric crystal, and one tenth of the switching field for the congruent crystal.

Light-induced domain reversal of near-stoichiometric Mg-doped LiNbO3 crystal was investigated with a focused 532 nm continuous laser beam. The lowest electric field applied to accomplish domain nucleation is only 30 V/mm and 1/80 of the coercive field, which is safe and convenient for us to fabricate domain structures. Under this superlow applied field, the pinning effect of domain wall is so obvious that the inverted domain reveals a gear shape contrary to the hexagon in a higher applied field. Then two-dimensional domain patterns with the smallest domain size of 4 μm have been fabricated.

Light-induced domain reversals of Mg-doped, Zr-doped, and nominally pure LiNbO3 crystals were investigated with focused 514.5 nm laser beams. It was found the light-reduced values of electric field for domain reversal are almost the same, about 3 kV/mm. Inverted domains always first nucleate on the −c surface within the illuminated region but appear at the edge of the spot on the +c surface. The light-induced inverted domains are hard to be reversed by application of a reverse electric field or by heating to temperatures as high as 600 °C. According to these experimental results, we present a qualitative model on the light-induced domain reversal process in LiNbO3.