| The structural, vibrational and dielectric properties of Y2O3 are calculated from first principles using the plane-wave pseudopotential method. Firstly, the structures have been fully relaxed through first principles method. Then the zone-center phonon-mode frequencies are evaluated within the framework of density functional perturbation theory (DFPT). Group theory is adopted to identify these phonon modes at the center of Brillouin zone and the LO/TO (longitudinal optic and transverse optic) splittings of the infrared active optic mode are presented. Finally, properties related to electrical perturbation, including electronic dielectric tensors, Born effective charges for all of the atoms, static dielectric tensors and dielectric spectrum, are reported. And dielectric, refractive index, extinction coefficient and infrared reflectance spectra of Y2O3 are given. The calculation indicates that strong IR reflection occurs in the range 400-800 cm-1 by reason of several strong IR-active modes, resulting in a poor transmission property. Relatively good transmission properties are presented in the range above 800 cm-1 or below 400 cm-1 with low reflectivity and dissipation due to no IR-active mode or weak modes.Synthesis of nanocrystalline Y2O3 powder by chemical coprecipitation method and fabrication of transparent Y2O3 ceramics have been investigated. Precursor precipitate of Nitrate hydroxide hydrate is synthesized from Y(NO3)3 solution and NH3·H2O. (NH4)2SO4 is used as a dispersant. It is found that precursor precipitates have better dispersion after it is washed off by ethanol so that to reduce the reunion in the drying process. Nanocrystalline Y2O3 powder is obtained by calcining the precursor at 1100℃for 4 hours. The powder shows better sintering and high activity behavior. After isostatic pressure forming, this powder is sintered into a good transparent body by low vacuum sintering at 1650℃for 10 hours and annealing at 1400℃for 5 hours.
|
PDF Full Text Request