THE ROLE OF NONSTOICHIOMETRY IN 180-DEGREES DOMAIN SWITCHING OF LINBO3 CRYSTALS

We show here conclusively that the internal field originates from nons toichiometric point defects in LiNbO3 crystals. The switching fields r equired for 180 degrees domain reversal in congruent crystals [C =Li2O /(Li2O+Nb2O5)=0.484] are similar to 4-5 times larger than the switchin g 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 di sappears in stoichiometric crystals. The concentration of hydrogen inc orporated during crystal growth has no effect on the switching or inte rnal 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.