Phase transitions of Zn(OH)2 under high pressure and high temperature

High-pressure and high-temperature behavior of Zn(OH)2 with a peculiar orthorhombic structure was examined using the in-situ X-ray powder diffraction method. Two high-pressure phases were observed by elevating temperature up to 400 ∘C at ca. 15 GPa. One was a new high-pressure and high-temperature phase discovered at 14.5 GPa and 300 ∘C, and the X-ray diffraction pattern could be indexed on an orthorhombic cell. The other was observed at 14.2 GPa and 400 ∘C and it had the hexagonal CdI2-type structure. The phase was finally quenchable to the ambient condition. The volume of the CdI2-type phase was 22.8% smaller than that of the peculiar orthorhombic phase at ambient condition. The bulk modulus was determined to be K0=46.7K0=46.7 (2.6) GPa and K′=8.6K′=8.6 (1.1). The cc-axis was more compressive than the aa-axis. The anisotropic behavior of Zn(OH)2 with the CdI2-type structure was consistent with that of other hydroxides.