Papers by Author: J. Wang

Abstract: Nanohybrid thin films consisting of nanocrystalline TiO2 particles in poly(methyl methacrylate)(PMMA) were successfully synthesized by in-situ sol-gel and polymerization assisted by spin coating. Using titanium isoproproxide (Ti-iP), methyl methacrylate (MMA) and 3-(trimethoxysily)propyl methacrylate (MSMA) as the starting materials, nanohybrids containing up to 60% Ti-iP in PMMA were realized. The resulting nanohybrid thin films coated on quartz substrates are optically transparent and demonstrate nonlinear optical behaviour, where their nonlinear absorption increases with the loading of Ti-iP in PMMA, as confirmed by Z-scan measurements. Using pump-probe technique, these thin films are shown to exhibit an ultrafast relaxation time of ~1.5 picosecond.

Abstract: Molluscan shells is a natural ceramic composite with excellent fracture strength and fracture toughness, which are attributed to their unique microstructures. Sanning electron microscope (SEM) observation on Bivalva shell showed that the shell consists of laminated aragonite and organic layers. These aragonite and organic layers are provided with the scale and characteristics of nanometer. The effect and function of these nanometer structures were analyzed based on Griffith criterion and energy-dissipation idea. The higher fracture strength and fracture roughness of bionanocomposite-molluscan shell were well explained with nanometer viewpoint.

Abstract: To study the effects of doping the layered perovskite SrBi2Ta2O9 with an appropriate amount of tungsten, both undoped and W-doped SrBi2Ta2O9 (SBT) of nanocrystallinity were synthesized by mechanical activation of constituent oxides of strontium oxide, bismuth oxide, tantalum oxide and tungsten oxide at room temperature. A nanocrystalline single perovskite phase was observed in SrBi2(Ta1-xWx)2O9 with up to x=0.1. SrBi2(Ta0.9W0.1)2O9 shows a higher Curie temperature than that of undoped SBT, although it exhibits a very similar layered perovskite structure. The ferroelectric and impedance behaviors of SrBi2 (Ta0.9W0.1)2O9 were studied over a range of test temperatures and frequencies, in order to understand the effects of W-doping in SBT, given that W exhibits a similar ionic size to Ta but with a variable valence.

Abstract: Nanocrystalline calcium bismuth titanate (CaBi4Ti4O15), which exhibits a layer structure, has been successfully synthesized by mechanical activation of constituent oxides of CaO, Bi2O3 and TiO2 in a nitrogen atmosphere at room temperature. The phase-forming calcination at elevated temperatures that is always required is skipped. CaBi4Ti4O15 derived from mechanical activation consists of nanocrystallites, which occur as aggregates of ~50 nm in sizes. It demonstrates an improved sinterability and was sintered to a density of 93.4% theoretical density at 1175oC for 2 hours. Ferroelectric properties of sintered CaBi4Ti4O15 derived from mechanical activation have been studied. A peak dielectric constant of 1049 at the Curie temperature of 774oC was measured at 1MHz for CaBi4Ti4O15 sintered at 1175oC.