High pressure Raman spectroscopic study of H3Co(CN)6

Abstract

H3Co(CN)6 belongs to a class of flexible frame work structured cyanides that exhibit negative thermal expansion along c-axis. In-situ high-pressure Raman spectroscopic studies on H3Co(CN)6 in a diamond-anvil cell were carried out under hydrostatic conditions up to 11 GPa. From the evolution of Raman spectra, splitting of modes and discontinuous changes in the pressure dependence of mode frequencies, a phase transition is identified at 2.3 GPa. In contrast to other modes, a lattice mode at 140 cm−1 and the Co-CN deformation mode 348 cm−1 are found to be softening with increase in pressure. Mode Grüneisen parameter is obtained for the ambient trigonal phase using the pressure dependencies of Raman mode frequencies. From the spectral features, the compound has been found to undergo amorphization around 11 GPa.