近化学计量比LiNbO3晶体电畴结构观察和机理探讨

采用双坩埚提拉法(DCCZ)生长了各种不同成分的近化学计量比LiNbO3晶体,并用腐蚀法观察了其电畴结构.结果表明,化学成分对未经极化处理晶体的电畴结构起决定性作用,当Li2O含量处于49.4mol%附近时,晶体z面电畴呈现特殊的三次对称反畴;当晶体中Li2O含量为49.7mol%时,晶体为完全单畴.本文对其形成机理进行了探讨,认为在由顺电相向铁电相转变时,局部铁电畴的极性方向与该处沿z轴方向的温度梯度正负密切相关,z轴生长晶体时,由于相变发生所处位置离生长界面的距离受LiNbO3晶体计量比影响,所处温场固有温梯也随之不同,在此基础上解释了不同成分晶体的电畴结构形成原因.最后讨论了控制铁电畴结构的工艺措施.

Observation of Ferroelectric Structures of Near-stoichiometric LiNbO3 Crystal and Its Mechanism

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.