Phases of anionic ordering in elpasolite structures (ordered perovskites)

The 108 dissymmetric phases were obtained as a result of $X$ anions ordering in elpasolite structure $A_2BB'X_6$ (ordered perovskite) using group theoretical methods. The critical order parameters which transform according to the irreducible representations of $\Gamma$ and $\mathrm{X}$ points of Brillouin zone of $O_h^5$— $Fm\bar 3m$ space group were considered only. Polyhedral structures showed for dissymmetric phases which are accompanied by appearing of ferroelectricity at phase transition. All results are summarized in convenient tables.