Papers by Author: J.M. Xue

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: 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.