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采用常规高分辨透射电镜(HRTEM)在层状共生化合物Bi7Ti4NbO21中可经常观察到大量生长缺陷:比如插入额外的Bi3TiNbO9或Bi4Ti3O12层而产生的无序共生结构,以及由共生相Bi7Ti4NbO21和母相Bi4Ti3O12在同一晶粒内形成的共相体[1]。为了给先前提出的共生结构重组生长模型提供更充分的依据,采用低/中分辨率下的高角环暗场像(HAADF)配合X射线能谱(EDXS)定量分析来研究共生缺陷的产生原因。观察到一种共生缺陷可以从共生相到Bi4Ti3O12母相发生结构渐变。用空间分辨的能谱测量可以排除相邻Bi3TiNbO9层所带来的干扰,其结果表明Bi4Ti3O12层中固溶了相当含量的Nb。一定量Nb的固溶进一步表明,在形成共生结构的过程中两种亚结构层之间发生了普遍的阳离子互换过程,而这一过程应该通过重组模型中的部分溶解液相来实现[1]。
A large number of growth defects are often observed in the layered commensal compound Bi7Ti4NbO21 using conventional high-resolution transmission electron microscopy (HRTEM): disordered intergrowth structures such as intercalated Bi7Ti4NbO21 and parent Bi4Ti3O12 The same grain formed within the co-phase [1]. In order to provide a more adequate basis for the recombination growth model proposed previously, HAADF and EDXS quantitative analysis were used to study the causes of the symbiotic defects. A symbiotic defect was observed to change the structure from the intergrowth phase to the Bi4Ti3O12 parent phase. The spatially resolved energy spectrum measurement can eliminate the interference caused by the adjacent Bi3TiNbO9 layer. The results show that a considerable amount of Nb is solid-solved in the Bi4Ti3O12 layer. The solid solution of a certain amount of Nb further indicates that a common cation exchange process occurs between the two sub-structure layers during the formation of the symbiotic structure, and this process should be achieved by partial dissolution of the liquid phase in the recombination model [1 ].