Haozhe Liu1, Jingzhu Hu2, Zhenxian Liu2, Yue Meng2, Jian Xu2, Ho-kwang Mao2, Jiuhua Chen1, Donald J. Weidner1
1Mineral Physics Institute, State University of New York at Stony Brook, NY, 11794,
2Geophysical Laboratory, Carnegie Institution of Washing
NSLS-X17C (DAC)
Facilities: NSLS-X17C, NSLS-U2A, APS-HPCAT
The aluminum trihydroxide has been studied over hundred years and so far four
polymorphs have been found in nature, i.e. gibbsite (á-Al(OH)3),
bayerite (â-Al(OH)3), nordstrandite (ã-Al(OH)3),
and doyleite. Among them, gibbsite is one of the most abundant minerals in aluminum
hydroxide and oxide family, and has attracted experimental and theoretical attention
from point of view of mineralogical and industrial applications. The in
situ high pressure energy dispersive and angular dispersive XRD, as well
as IR experiments for gibbsite were carried out recently, and a phase transition
was observed starting from 2.2 GPa and completed above 5 GPa. The orthorhombic
new phase of Al(OH)3 has the highest symmetry structure in aluminum trihydroxide
family with layer stacked sequence similar to gibbsite. Its molar volume is
about 2% smaller than that of gibbsite phase at ambient condition. Three unique
O positions exist in its unit cell, supported by its OH stretching modes in
IR and Raman spectra. Gradual disorder of hydrogen sublattice above 15GPa was
observed, but the Al-O sublattice still remained at crystalline structure even
compressing above 50GPa. The quenchable new phase keeps stable at ambient condition
for at least 6 months.