Spectroscopic study of β-Ni(OH)₂ under pressure

Abstract

Infrared absorption and Raman study of β-Ni(OH)₂ has been carried out up to 25 GPa and 33 GPa, respectively. The frequency of A_2u internal antisymmetric stretching O-H mode decreases linearly with pressure at a rate of −0.7 cm⁻¹/GPa. The FWHM of this mode increases continuously with pressure and reaches a value of ~ 20 cm⁻¹ around 25 GPa. There was no discernible change observed in the frequency and width of the symmetric stretching A_1g O-H Raman mode up to 33 GPa. The constancy of the Raman mode is taken as a signature of the repulsion produced by H-H contacts in this material under pressure. Lack of any discontinuity in these modes suggests that there is no phase transition in this material in the measured pressure range.