| It is well known naomaterials exhibit various novel physical and chemical properties compared with their bulk counterparts. The differences between namomaterials and bulk materials are usually attributed to the confinement effect and surface effect owing to the decrease of the particle size and the enlargement of surface-area/particle-size ratio. In order to clearly reveal the nano-effects, many works have been carried out around this topic and made effective progresses. And the researches confirm the properties of nanomaterials such as optical and electrical properties, mechanical stability and phase-transition mechanics are sensitive dependency on size, shape and structure. Thus, tailoring the size, shape and structure of nanostructure becomes a hot topic.High pressure physics is a novel cross-disciplinary, which bases on Material physics, Geophysics and Astronomy. High pressure can effectively change the distances between molecules and atoms. The changes of structure will do strong effects on the properties of materials. Measurements of the high-pressure properties not only directly characterize the physical properties of material, but also indirectly reveal its corresponding intrinsic characteristics. Thus, high-pressure technology is an important and effective route for us to understand the structures, properties and even their relationship. In recent years, nanotechnology develops rapidly. Nanotechnology combines with high-pressure technology, and it will reveal many attractive and novel phenomena, structures and mechanics.Germanium dioxide (GeO2), is an important inorganic material and exhibits many interesting physiochemical properties for applications in optical, electronic, and optoelectronic devices. Moreover, it is a promising material for optical waveguides and nanoconnections in optoelectronic communication and vacuum technology. Very recently, pioneering studies have found that emulsions can be used to fabricate monodispersed nano-GeO2 particles and also to tune the shape and size of GeO2 effectively. In this thesis, we report a facile solution-phase route for the mass synthesis of GeO2 crystals with different morphologies, GeO2 nanoframes and nanocages, GeO2 nanospheres. And on the basis of experiment and characterization, we also did an in-depth study on shape, structure, growth, mechanism and catalytic and gas sensor properties. Some important results are obtained.Hollow GeO2 walnuts are synthesized for the first time via a facile one-step route in emulsion system, and the growth mechanism and optical properties of the products are also investigated. It is found that reactive temperature and addition of ethanol are crucial factors to control the morphology of GeO2. Above the ethanol boiling temperature, hollow walnuts are formed, while well-dispersed solid GeO2 polyhedrons and dimers are obtained interestingly below the critical point. The possible formation mechanism of the hollow interior is proposed as gas bubble template effect released by the boiling ethanol accompanying the Ostwald ripening prcocess. Photoluminescence measurement shows an enhanced and obvious blue shift of emission peak at 538 nm for hollow GeO2 walnuts compared with the solid structure. These attractive results provide us a new simple method to fabricate other specific hollow structure in emulsion and indicate hollow walnuts may have potential applications in light-emitting nanodevices.We report, for the first time, the synthesis of PVP-capped rutile GeO2 nanocrystals through a simple hydrothermal process. PVP, which is a water soluble polymer, was used as capping polymer molecules to stabilize the GeO2 nanoparticles. Through the surface modification by PVP, highly monodisperse GeO2 nanoparticles were prepared, which exhibited highly chemical stability and significantly enhanced luminescence. Our study provides a new hybrid material which has potential application in the field of nanoscale device.The in situ high pressure X-ray diffraction studies are devoted in a diamond anvil (DAC) cell at room temperature. A phase transformation of q-GeO2 to monoclinic GeO2, are detected while the monoclinic phase of walnut GeO2 are not well crystallized due to the defect effect. While the onset of the transition pressures for the beta GeO2-to-monoclinic phase transition are found to be approximately 8.99-10.11 GPa for the walnut GeO2 sample, and 7.28-9.18 GPa for the hollow waxberry GeO2 sample, respectively. This result strongly suggests defects in the nanosized material, may play a key role for the phase transformation of beta GeO2. The two transformation were both not quenchable after pressure release. By fitting the compression data to the Birch-Murnaghan equation of state, the bulk moduli of the walnut and waxberry nanosphere beta GeO2 phases were determined to be 33±5, and 38±4 GPa with B0'=3, respectively.
|
PDF Full Text Request