PMNT单晶电畴结构随组分与结构的变化

利用多种方法观察了弛豫型铁电单晶ＰＭＮＴ中电畴结构随组分与结构的演变过程与特征．观察发现，在ＰＭＮ－ＰＴ的三方相区内，随ＰＴ含量的增加，电畴结构表现出微畴一（亚微畴）－不规则宏畴一规则宏畴转变历程；在三方－四方相变中，非１８０°电畴发生７１°（或１０９°）宏畴－９０°宏畴的转化，同时电畴图像变得更为规则．根据不同组分ＰＭＮＴ电畴的显示特征，提出晶体的最大双折射率可以作为度量其弛豫性强弱的光学参数．观察到了电畴的分布不均匀与多级结构现象，前者与组分或结构的起伏有关，后者与多期式马氏体转变有关．本文还分析了偏光显微镜、ＤＩＣ、ＳＥＭ、ＳＥＡＭ等观察方法中电畴的成像特征．

Domain Configuration Changing with Composition and Structure in PMNT Single Crystals

This paper studied the evolution progress and feature of domain configuration while the composition and structure changed in relaxor ferroelectric single crystals Pb(Mg_1/3Nb_2/3)O₃-PbTiO_₃. It was found that with increasing PbTiO_3 concentration in the rhombohedral phase region of PMN-PT system, domain configuration exhibited a transition process, i.e. microdomains-(sub-microdomains)-irregular macrodomains-regular macrodomains. And then, if PbTiO₃ increased further, rhombohedral-tetragonal phase transition could take place, giving rise to the change from 71°(or 109°) domains to 90° ones. 90° domains demonstrated more regular or typical configuration than 71°(or 109°) domains. In light of the showing feature of domain configuration, it was proposed that the largest birefractive index of PMNT crystals could be taken as an optical parameter measuring their relaxor degree in ferroelectric behavior. Moreover, the phenomena of non-uniform distribution of domain structures within a plate were observed, which arose from composition heterogeneity and structure fluctuation. Domains with substructure were also visualized, which could be interpreted by multistage martensitic transformation. In addition, the paper discussed the imaging features of domain configuration under the observation means including polarizing microscopes, differential interference contrast microscopes (DIC), scanning electronic microscopes (SEM) and scanning electronic acoustic microscopes (SEAM).