Phase transitions

Sequence of transformations during ordering of nonstoichiometric compounds with the formation of $M_3X_2$-type superstructures

A. I. Gusev, A. M. Bel’kov, T. D. Vyrodova, A. S. Kurlov

Institute of Solid State Chemistry, Urals Branch of the Russian Academy of Sciences, Ekaterinburg

Abstract: A symmetry analysis of monoclinic, orthorhombic, and trigonal $M_3X_2$-type superstructures, which can be formed in highly nonstoichiometric $MX_y$ compounds with $B1$ structure, has been performed. Channels of disorder-order transitions $MX_y$ $\to$ $M_3X_2$ have been determined. It has been shown that two physically allowed sequences of transformations associated with the formation of $M_3X_2$ superstructures are possible in nonstoichiometric $MX_y$ compounds of Group IV transition metals with decreasing temperature, i.e., "cubic (space group $Fm\bar3m$) disordered $MX_y$ phase $\to$ orthorhombic (space group $Immm$) ordered $M_3X_2$ phase $\to$ orthorhombic (space group $C222_1$) ordered $M_3X_2$ phase" and "cubic (space group $Fm\bar3m$) disordered $MX_y$ phase $\to$ orthorhombic (space group $Immm$) ordered $M_3X_2$ phase $\to$ monoclinic (space group $C2$) ordered $M_3X_2$ phase.”

Received: 02.04.2014

 English version: Physics of the Solid State, 2014, 56:10, 2092–2099

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