“非整比化合物”概念辨析

What Is Nonstoichiometric Compound?

“非整比化合物”是固体化学和材料化学等学科领域普遍接受的概念。然而,在文献中这个概念的含义是含混的。本文通过对一些实例的组成分析,廓清了晶格缺陷、固溶体及“非整比化合物”之间的关系。通过结构分析,阐明了“道尔顿体”和“柏托雷体”的区别及“柏托雷体”与其虚拟母体化合物的关系。在此基础上对“非整比化合物”的概念给予较为全面的说明。在一定的条件下,晶态无机物质(包括金属和化合物)的晶格中可以形成高浓度(用常规化学方法可定量检测)缺陷的状态,缺陷的主要种类有空位、填隙、取代和变价等。这种含有高浓度缺陷的物质可以用固溶体的形式表示其组成。在相图中,对于母体化合物组成处于固溶区边界的固溶体其母体称为“道尔顿体”,固溶体称为“道尔顿固溶体”;而母体组成不处于固溶体边界的固溶体称为“柏托雷体”,其母体可以看成是组成处在固溶体区域外某个组成的“虚化合物”。由于其组成可变,且各元素原子个数比偏离简单整数比,广义的“非整比化合物”包含“道尔顿固溶体”和“柏托雷体”。由于不存在真实的母体化合物,狭义的“非整比化合物”仅指“柏托雷体”。

“Nonstoichiometric compound”is a widely accepted concept in solid-state chemistry and materials chemistry.However,in the literatures,the meaning of this concept is ambiguous.In this paper,based on the composition analyses for selected nonstoichiometric compounds,the relation among the defect,solid solution and the nonstoichiometric compound is built.According to the structure analyses for some examples,the essential difference between Daltonid and Berthollid,and the relation between the Berthollid and its parent compound are clarified.As a result,a comprehensive description for“nonstoichiometric compound”is given.Under certain conditions,crystalline inorganic materials(metals or compounds)may contain lattice defects(mainly vacancies,interstitials,substitutional defects,valence changed cation defects and so on)with high concentrations(quantitatively detectable by routine chemical methods),which can be considered as solid solutions.For the solid solutions with the compositions of their parent compounds at the boundaries of the solid solution ranges,the parent compounds are termed as Daltonids and the solid solutions are termed as“Daltonid solid solutions”;while no parent compounds can be found at the boundaries of the solid solution ranges,the solid solutions are named as Berthollids,their parent compounds(virtual compounds)may be located outside of the solid solution ranges.Since their compositions vary and deviate from the ratio of small natural number,as a broad concept,both Daltonid solid solutions and Berthollids are all considered as“nonstoichiometric compounds”.Since real parent compounds do not exist,as a narrow concept,only Berthollids are regarded as“nonstoichiometric compounds”.