Pressure-induced isostructural phase transition in α-Ni(OH)₂ nanowires

High pressure structural phase transition of monoclinic paraotwayite type α-Ni(OH)₂ nanowires with a diameter of 15 nm-20 nm and a length of several micrometers were studied by synchrotron x-ray diffraction (XRD) and Raman spectra. It is found that the α-Ni(OH)₂ nanowires experience an isostructural phase transition associated with the amorphization of the H-sublattice of hydroxide in the interlayer spaces of the two-dimensional crystal structure at 6.3 GPa-9.3 GPa. We suggest that the isostructural phase transition can be attributed to the amorphization of the H-sublattice. The bulk moduli for the low pressure phase and the high pressure phase are 41.2 (4.2) GPa and 94.4 (5.6) GPa, respectively. Both the pressure-induced isostructural phase transition and the amorphization of the H-sublattice in the α-Ni(OH)₂ nanowires are reversible upon decompression. Our results show that the foreign anions intercalated between the α-Ni(OH)₂ layers play important roles in their structural phase transition.