二元铌镥酸铅-钛酸铅晶体的相变特性机理研究及室温相图完善

On the previous work, a T–x phase diagram of the PLN–xPT binary system is established from the rhombohedral to tetragonal phase transition, which also confirm the exists of the MPB region. By investigating the binary ferroelectric/antiferroelectric crystal PLN-PT system, it is found that in the phase diagram the Curie temperature of some component does not display in the dielectric spectrum and deviate from the linear relationship near the antiferroelectric-ferroelectric phase transition region. We think that the possible mechanisms behind this deviation might include: the structure competition of the antiferroelectric and ferroelectric, and the competition of long range ordering and short-range ordering of B-site cations. In order to explore the real physics in this process, more crystal compositions in the area of antiferroelectric-ferroelectric phase transition region would be grown to further improve the phase diagram of the system using more component data from research. Furthermore, through the analysis of the crystal structure among the components that deviates from the linear relationship, lattice structure, electric domain configuration, order -disorder distribution and interaction relations can be found. Through the analysis of the relationship among the structure, electric domain and dielectric response behavior, the physical mechanism that causes the .second-order phase transition of the Curie temperature can be figured out, thus to provide scientific basis for the division of phase diagram. Based on this mechanism, new materials with different Curie point and properties can be developed.

在二元铁电/反铁电晶体铌镥酸铅-钛酸铅（PLN-PT）体系的研究中，发现该体系相图中部分组分对应的居里温度在介温谱图中无法测得，且在反铁电-铁电交界的相区附近，居里温度偏离了线性关系。我们认为导致这一关系的原因包括：反铁电-铁电结构的竞争，B位长程有序和短程有序的竞争。针对这一现象，我们在早期研究三方-四方相变区相图的基础上，通过反铁电-铁电交界相区附近组分的单晶生长工作，从而可以利用更多组分研究得到的数据，进一步完善整个体系的相图。进而，通过偏离线性关系组分的晶体的结构分析，得到晶体的晶格结构、电畴组态、有序无序分布规律和相互作用关系。通过阐明结构、电畴与介电响应行为的关系，来研究二级相变居里温度的物理机制，从而为相图的划分提供科学依据。利用这种机制，可以更好的通过组分调控和开发不同居里点、不同性能的新材料。

铁电晶体是一类重要的功能晶体材料，它具有压电性、热释电性、铁电性及非线性光学效应等重要特性，可用于制作压电换能器、红外探测器、能量存储器和集成光电器件等新型元器件，在国防及民用等领域具有广泛的应用前景。本项目以二元PLN-PT体系为研究对象，生长了部分组分的晶体，晶体组分主要分布在反铁电相区、铁电与反铁电混合相区及铁电相区。通过XRD粉末衍射确定了相区各个组分的晶体结构，通过介电分析仪和铁电分析仪测试了各个组分晶体的电学性质，通过偏光显微镜研究了晶体的宏观畴结构特征，通过高分辨透射电镜标记了反铁电体的两套超晶格衍射点阵及铁电体的B位有序超晶格点阵。研究居里温度偏离线性关系的物理机制，研究PLN-PT晶体的畴结构和组态以及畴结构在温度、电场等下的变化规律。根据PLN-PT晶体的相结构、电畴结构以及宏观铁电、反铁电、介电响应行为和微观结构演化之间的关联，揭示PLN-PT晶体异常介电响应行为的物理机制，从而对形成的相图提供科学的论据。对一系列晶体性能及结构数据的汇总，系统分析了PLN-PT晶体的结构随组分、温度、电场等的变化规律，研究晶体的相结构分布情况，形成了较为完善的PLN-PT二元相图。