The solvothermal synthesis of γ-AlOOH nanoflakes and their compression behaviors under high pressures

Boehmite, gamma-AlOOH, has attracted increasing research enthusiasm due to its scientific and technological importance. The compression behaviors of gamma-AlOOH are of vital relevance to the insight into geophysical and geochemical processes in Earth's mantle. In this work, free-standing gamma-AlOOH nanoflakes with high purity and crystallinity have been synthesized via a template-free, one-step solvothermal alcoholysis strategy. The nanoflakes have high aspect ratio, with the lateral size ranging from 100 to 300 nm, and the thickness ranging from 20 to 45 nm. The band gap of the obtained g-AlOOH nanoflakes is estimated to be 3.35 eV through UV-vis absorption spectra recorded at room temperature. A broad PL emission band can be observed in the 400 to 700 nm spectrum range, with the maximum at 480 nm. The compression behaviors of gamma-AlOOH nanoflakes have been investigated by in situ high pressure synchrotron radiation angle dispersive X-ray diffraction up to 54.9 GPa and Raman scattering spectroscopy up to 22.4 GPa at room temperature. The compression is nearly linear and anisotropic, with b axis more compressible than a and c axes. The zero-pressure bulk modulus of gamma-AlOOH nanoflakes is estimated to be 135.2 GPa, higher than the theoretical value of its bulk counterpart. The frequencies of the observed Al-O related Raman modes increase monotonously in a linear manner with increasing pressure. The mode Gruneisen coefficients are estimated, which may provide important information about the anharmonicity in the bonding nature of gamma-AlOOH.