Abstract: Near stoichiometric LiNbO₃ crystals of varied composition were grown by a double crucible Czochralski method. An etching method was applied to observe the ferroelectric domain structures
of the as-grown crystals. The results show that the congruent crystal grown along z-axis contains a domain structure consisting of concentric rings. The crystal with composition of 49.4mol% Li₂O
contains a special domain structure consisting of three fan-shape opposite domains with three-fold symmetry, which is consistent with the symmetry of the crystal structure. The crystal with composition
of 49.7mol% Li₂O has a single domain structure. The formation mechanism of the domain structures was discussed based on a thermoelectric field model. It is argued that the sign of the temperature
gradient along z-axis in the front of para- ferroelectric interface is the critical factor that determines the polarity direction of the domain in development. Finally, the technological methods to control the domain structures were discussed.

Key words: LiNbO₃ crystal, stoichiometry, ferroelectric domain structure, mechanism