The role of nonstoichiometry in 180° domain switching of LiNbO3 crystals

We show here conclusively that the internal field originates from nonstoichiometric point defects in LiNbO3 crystals. The switching fields required for 180 degrees domain reversal in congruent crystals [C =Li2O/(Li2O+Nb2O5)=0.484] are similar to 4-5 times larger than the switching fields for near-stoichiometric crystals (C=0.498). An internal field of similar to 2.5 k (V) over bar/mm observed in congruent crystals disappears in stoichiometric crystals. The concentration of hydrogen incorporated during crystal growth has no effect on the switching or internal fields. The measured spontaneous polarization, P-s=80+/-5 mu C/cm(2) is relatively insensitive to the crystal nonstoichiometry and the hydrogen content. (C) 1998 American Institute of Physics.