High-pressure behavior of &#946;-Ni (OH)<SUB>2</SUB>- a Raman scattering study

The existence of very short non-bonded H-H distances in &#946;-Ni(OH)<SUB>2</SUB> at ambient conditions, predisposes this compound towards a structural change at very low pressures. To investigate this, we have now carried out a high-pressure Raman scattering investigation on &#946;-Ni(OH)<SUB>2</SUB> up to 25 GPa. Our results show a monotonic stiffening of all the lattice modes and a small softening of hydroxyl symmetric stretch mode under pressure. Absence of any signature of a phase transformation up to 25 GPa and a reversible intrinsic broadening of the OH mode suggest that, even at the ambient conditions, &#946;-Ni(OH)<SUB>2</SUB> may be in the non-ideal CdI<SUB>2</SUB> structure in which H-lattice is disordered