Neutron powder diffraction study of phase transitions and structures of(KCN)x(KBr)1−xmixed crystals

Abstract

The structures of ${\left(\mathrm{KCN}\right)}_x{\left(\mathrm{KBr}\right)}_{1-x}$ mixed crystals for $x=0.95, 0.90, \mathrm{and} 0.80$ have been determined as a function of temperature. As the temperature is decreased from 295 K, where all of the samples are cubic (as are pure KCN and KBr), all samples measured transform to a monoclinic structure (space group $\mathrm{Cc}$). For $x=0.95\mathrm{} \mathrm{and} 0.90$, at a lower temperature there is a further transition to an orthorhombic structure similar to that found for pure KCN below 168 K. However, the samples do not transform completely, and the monoclinic and orthorhombic structures coexist down to 6 K. More of the sample transforms for $x=0.95\mathrm{}$ than for $x=0.90\mathrm{}$. In both cases, that part of the sample which goes into the orthorhombic phase orders completely at the lowest temperatures, in a structure similar to that found for pure KCN at 6 K.