New High-Pressure Phase Transitions in Potassium Cyanide
Potassium Cyanide, KCN, is an ionic crystal of cubic symmetry at room temperature which is very similar to potassium chloride. In contrast, the ellipsoidal-shaped CN− molecules rotate more or less freely and independently in their octahedral lattice cells and because of their different orientation from cell to cell the KCN crystal is orientationally disordered. At 168 K the CN− molecules freeze in with a uniform orientation over the entire crystal, and KCN undergoes an order-disorder phase transition to an ordered orthorhombic phase . There still remains the disorder in the C-N-sequence of the CN− molecules and it requires another phase transition at 83 K to establish complete order. The CN dumbbells order antiparallel in this low temperature phase of space group Pmmn .
KeywordsMolecular Axis Phase Line Potassium Cyanide Sapphire Window Complete Order
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