Pressure-induced isostructural phase transition in α-Ni(OH)2 nanowires**Project supported by the National Key Research and Development Program of China (Grant No. 2018YFA0305900), the National Natural Science Foundation of China (Grant Nos. 11874172, 11374120, 11634004, and 51320105007), and the Fund from Jilin University for Science and Technology Innovative Research Team (Grant No. 2017TD-01).

Abstract

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.