Controlled Synthesis And Characterization Of Ultrafine Zirconate And Stannates Complex Oxides

Complex oxide materials display novel physical and chemical properties different from their single counterparts. During the past decade, a wide range studies has been performed on the shape- and size-controlled synthesis of nanostructured/monodisperse materials due to their strong size- and shape- dependent properties. Therefore, it is very important to fine tune the size, dimensionalities, crystal structure and compositions of complex oxides in nanoscale, which may serve as a powerful tool for the tailoring of physical/chemical properties of complex oxides in a controllable fashion. In this dissertation, some solution-based routes have been exploited to rationally synthesize nanostructured/monodisperse barium zirconates, transitional metal, alkaline earth metal and rare earth metal stannates complex oxides in high yield. At the same time, optical and sensing properties characterization of the as-synthesized complex oxide materials has been carried out. The main point can be summarized as follows:A facile modified hydrothermal approach has been exploited to rationally synthesize perovskite-structured BaZrO3 microcrystals with the shapes of truncated rhombic dodecahedron and sphere. The polarity variation by ethanol introduction to the solutions plays a significant role in determining the geometric morphology of the final products. The BaZrO3 microcrystals can serve as host materials for rare earth photoluminescence, and shape-dependent luminescence properties of an Eu3+-doped material has been observed.Nearly monodispersed ZnSn(OH)6 nanocubes with controllable size as precursors are hydrothermally prepared in the presence of PVP surfactant. Thermal decomposition of the nanocube precursors at a temperature of 800 C under inert gas protection leads to the formation of ultrafine aggregates of Zn2SnO4-SnO2 nanocomposites. The aggregates are roughly spherical and structurally porous. The electrical conductivity measurements demonstrate that thin film type sensor based on this material shows high selectivity, sensitivity and durability to ethanol. The same procedure was taken to successfully produce some other transition metal stannates nanocomposites.A PVP-assisted hydrothermal process has been established for the large-scale synthesis of CaSnO3 micro/nano -cubes with perovskite structure. A series of shape evolutions of CaSnO3 particles from the transient species such as multi-pod and star-shaped particles to cubic crystals have been arrested based on TEM and SEM observation. Preliminary gas-sensing investigations showed that the CaSnO3 cubes exhibited both high sensitivity and reversibility to ethanol afterrare earth doping and noble metal loading. Single crystal SrSn(OH)6 nanorods were prepared in high yield by a hydrothermal process in the presence of surfactant CTAB. Thermal decomposition of the rod-like precursors at a temperature of 500 C under inert gas protection leads to the formation of porous structured SrSnO3 polycrystalline nanorods. UV-absorption spectrum was employed to evaluate the band gap of the as-synthesized SrSnO3 polycrystalline nanorods in comparison to their bulk counterpart. Porous perovskite-structured BaSnO3 polycrystalline nano/mico- rods were also successfully produced by the CTAB-assisted hydrothermal procedure. Ultrafine BaSn(OH)6 nanocrystals can be produced in a PEG/PVP mixture solution, which transforms into porous spherical BaSnO3 nanocrystals with perovskite structure after heatment.A facile CTAB-assisted sol-gel approach has been successfully exploited to synthesize a series of rare earth stannates (Lm2Sn2O7) nanocrystals with pyrochlore structure. The route involves first the formation of CTAB-inorganics mesostructures as precursors and then their thermal decomposition to yield the final product. The as-synthesized Y2Sn2O7 nanocrystals display a band-gap blue-shift when comparing to their bulk counterpart. Preliminary photoluminescence investigations show that the as-prepared Y2Sn2O7 nanomaterials have promising potentials in use as host matrix for Eu3+ fluorescence.