The Synthesis Of Group ?A Metal Oxyhydroxides And Their High-Pressure Studies

In recent years,the synthesis,properties and applications of metal oxyhydroxides have attracted more and more research interest,which have become one of the focus of nowadays materials science.Metal oxyhydroxides were potentially applicable in various fields,such as catalysis,adsorption,and so on.Thus the systematical investigations on metal oxyhydroxides are fundamental from the viewpoints of both theoretical study and applications.When subjected to high pressures,materials may exhibit new effects and new phenomena.Thus an exploratory examination of the compression behavior of metal oxyhydroxides is crucial for the understanding of the geophysical and geochemical processes of the mantle.In this dissertation,the synthesis and characterization of aluminum oxyhydroxide and gallium oxyhydroxide were carried out by employing hydrothermal and solvothermal methods.By regulating the compositions,the temperature,and the solvents,the possible ways to control the morphology of the final products are studied.By using in situ high pressure synchrotron radiation X-ray diffraction and Raman scattering spectroscopy techniques,the compression behaviors of Al OOH is studied.The main findings are listed as the following: 1.In this work,free-standing ?-Al OOH nanoflakes with high purity and crystallinity have been synthesized via a template-free,one-step solvothermal alcoholysis strategy.The samples were characterized by powder X-ray diffraction(XRD),scanning electron microscopy(SEM),transmission electron microscopy(TEM),UV-Visible absorption and photoluminescence(PL)spectra.It is found that the nanoflakes are quasi-hexagonal,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 ?-Al OOH nanoflakes is estimated to be 3.35 e V 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.2.Gallium oxyhydroxide powders are successfully prepared by solvothermal and hydrothermal methods,respectively.It is found that the addition of water in the reaction process may help to generate samples with uniform morphology and better crystallinity.The sample produced in the hydrothermal process also possess a smaller size of about 1 ?m in length and 200 nm in diameter.3.The compression behaviors of ?-Al OOH 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 ?-Al OOH 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 Grüneisen coefficients are estimated,which may provide important information about the anharmonicity in the bonding nature of ?-Al OOH.This work may bear great relevance to the study on the compression behaviors of hydrogen bonding systems including group ?A metal oxyhydroxides under high pressures.