MnGa的晶体结构与有序度

本文叙述了用德拜·谢乐的方法探讨Mn-Ga二元系中γ₃相的晶体结构,并进一步研究了在这个相区内原子排列的有序度随Ga含量的变迁。γ₃相属四方晶系,空间群为D_4h¹—P4/mmm,其理想配比成分为MnGa,每晶胞含1个化合式量,Mn原子和Ga原子分别占据着(0,0,0)和(1/2,1/2,1/2)等效位置。这是一种畸变型的B2结构,如果原晶胞沿c轴转动π/4,则变换后的晶胞就是LI₀型结构,与CuAu-1同型。在室温,原晶胞在42.9at.％Ga成分处的点阵常数为a=2.7475?,c=3.6756?。这个相可看作是γ-Mn的替代式固溶体,由于Ga原子替代了部分Mn原子而在室温稳定存在为四方面心有序结构。在整个相区内,有序度随Ga含量的增加而增加。 关键词：

THE CRYSTAL STRUCTURE OF MnGa AND THE DEGREE OF ORDER

The crystal structure of the γ₃ phase in the Mn-Ga system has been determined by the Debye-Scherrer method, and thence the degree of order in the atomic arrangement in this phase region has been estimated as a function of the gallium content.The structure of the γ₃ phase belongs to the tetragonal system, the space group being D_4h¹-P4/mmm. The ideal stoichiometric composition is MnGa, and each unit cell contains one formula weight, the manganese and gallium atom occupying (000) and 1/2 1/2 1/2) positions respectively. It is a distorted form of the B structure, and if it is rotated π/4 about the c-axis, the transformed unit cell can be shown to be of the type LI₀, isomorphous with CuAu-I. At room temperature, the lattice spaeings of the original cell at 42.9 at.% Ga are α=2.7475? and c=3.6756?.This phase may be considered as a substitutional solid solution of γ-Mn, stabilized at room temperature due to the partial substitution of manganese atoms by gallium atoms as a tetragonal face-centred ordered structure. In this entire phase region, the degree of order increases with the gallium content.
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