Raman Study of Structural Phase Transition in K3Co(CN)6

Raman spectra of K 3 Co(CN) 6 crystals have been observed at temperatures down to 30 K. The lowest frequency band in the low temperature phase, ∼13 cm -1 at 30 K, softens to 5 cm -1 near the transition temperature (∼63 K). This soft mode behavior shows that the phase transition is displacive one. Since no soft optically active modes arc found in the high temperature phase, the instability of the high temperature lattice is ascribed to the zone boundary phonon.