Phase transition and compression behavior of gibbsite under high-pressure

In situ high-pressure synchrotron X-ray diffraction and infrared absorption experiments for gibbsite were performed at room temperature up to 53 and 25 GPa, respectively. A phase transition was confirmed at about 2.5 GPa. The high-pressure phase is indexed as an orthorhombic structure, rather than a triclinic structure as reported in previous studies. The compressibility of gibbsite and its high-pressure polymorph were studied, and their bulk moduli K ₀ were determined to be 49 and 75 GPa, respectively with K ₀' as 4. The in situ high-pressure infrared absorption spectra revealed the gradual disordering of hydrogen substructure above 15 GPa in quasihydrostatic compression.