Random Strains and the Structure of(KBr)1−x(KCN)xMixed Crystals

Constant-pressure molecular dynamics has been used to study the effect of random strains on the low-temperature structure of ${\left(\mathrm{KBr}\right)}_{1-x}{\left(\mathrm{KCN}\right)}_x$ mixed crystals with $x\approx 0.75$. In accord with experiment, systems with a random arrangement of ${\mathrm{Br}}^{-}$ ions transform on cooling from a cubic phase to either a rhombohedral or a monoclinic structure. For an ordered $A_{3}B$ anion sublattice, however, the ground-state structure is similar to that of pure KCN, namely orthorhombic. It is concluded that strain-rotation coupling plays a critical role in the destabilization of the orthorhombic phase.