X-ray diffraction study of the structural phase transition in NaCN under high pressure

Pressure-induced structural phase transition in NaCN was studied by X-ray d iffraction. A single crystal sample was loaded in a miniature diamond-anvil cell and diffraction patterns were recorded at room temperature by the pre cession method on a laboratory radiation source. It was confirmed that the cubic B1-type structure stable under atmospheric pressure is transformed in to the orthorhombic structure with the preferential alignment of the CN- mo lecules in the [110] direction of the cubic lattice. The orientation relati onship is such that the (001) plane of the orthorhombic lattice is formed p arallel to the (100) and equivalent planes of the cubic lattice and each or ientation variant contains twin. Compression experiments were performed up to 5.0 GPa, but no clear indication was obtained of the occurrence of the p reviously suggested second transition at 4.0 GPa. Discussion is given on th e structural phase transition in the alkali cyanides taking into account th e repulsive interaction between ion cores. (C) 2001 Elsevier Science B.V. A ll rights reserved.