Papers by Author: Gao Rong Han

Abstract: Rhombohedral bismuth ferrite (BiFeO₃) powders were hydrothermally synthesized by using C₆H₈BiNO₇ and Fe (NO₃)·5H₂O as precursors, KOH as a mineralizer and poly sodium-p-styrenesulfonate (PSS) as an additive. The phase formation and morphology of the as-prepared powders were characterized by X-ray diffraction,raman spectroscopy, and field-emission scanning electron microscopy. In order to investigate the effects of PSS, a series of experiments were performed by changing the introduced amount of PSS and the hydrothermal reaction time. The results showed that the introduction of the PSS leads to the synthesized bismuth ferrite changes from the mixture of Bi₂Fe₄O₉ and BiFeO₃ to pure rhombohedral BiFeO₃. Corresponding to the phase composition evolution, the particle morphology alters from nanosheets to microparticles. The magnetic properties of single-crystalline BiFeO₃ powders were also characterized. Based on the experimental results, the phase formation mechanism of the rhombohedral BiFeO₃ hydrothermally synthesized assisted with PSS was discussed.

Abstract: Pre-perovskite PbTiO₃ nanofibres were synthesized by hydrothermal method with four butyl titanate ((C₄H₉O)₄Ti) and lead nitrate (Pb (NO₃)) as the main precursors and Tetramethylammonium Hydroxide (TMAH) as mineralizer. X-ray diffraction (XRD), Raman, Scanning Electronic Microscopy (SEM), Transmission electron microscopy (TEM), high-resolution TEM (HRTEM), and the corresponding selected area electron diffraction (SEAD) were used to characterize the crystal structure and morphology of the obtained products. The results showed that the nanofibers are of a few to tens micrometer at length size, and 50~300 nm at diameter size. Based on the experimental results, the effect of Tetramethylammonium Hydroxide (TMAH) was simply discussed.

Abstract: Perovskite lead titanate crystals with various morphologies were successfully synthesized via a hydrothermal reaction route with different lead sources. X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) were employed to characterize the phase composition and the morphology of the synthesized products. In order to investigate the effect of the lead source on the phase formation and morphology evolution of the synthesized pervoskite PbTiO₃ crystals, PbO, PbF₂, PbSO₄ and Pb (CH₃COO)₃ ·3H₂O, were used as starting precursor lead source introduced into the hydrothermal reaction system, respectively. Accordingly, perovskite PbTiO₃ brken cubes, irregular particles, cubic particles, and microplates were obtained, respectively. Based on the experimental results, the effect of lead source was simply discussed.

Abstract: CdS nanocrystallites with different morphologies have solvothermally prepared with ethylenediamine (en) and glycol as solvents. Solvent-dependent experiments were carried out by adjusting the ratios of en/glycol to investigate the effects of the solvents on the product phase formation and morphology. It was found that the morphology of CdS nanocrystallite develops from a rough spherical nanoparticle to a rod-, twinrod-, and tetrapod-shaped nanoparticle by increasing the ratio of en/glycol, meanwhile the phase composition changes from coexistence of tetragonal zinc blende CdS and hexagonal wurtzite CdS to pure hexagonal wurtzite CdS. Based on the experimental results, a possible shape evolution mechanism of CdS nanocrystallites is simply discussed.

Abstract: Intragranular porous aluminum titanate ceramics were prepared by using graphite powder as pore-forming agent and magnesium-doped aluminum titanate powder as starting material. FESEM was employed to observe the microstructure. In order to investigate the expansion behavior and mechanical property, the dilatometric curve and three-point flexural strength of the prepared aluminum titanate ceramics were measured respectively. The results demonstrate that because of the formation of the intragranular pores, the aluminum titanate ceramics are of low thermal expansion and high strength simultaneously.

Abstract: Single-crystal PbTiO3 nanoflakes have been synthesized successfully by a hydrothermal method. The as-prepared powders were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), and selected area electron diffraction (SAED). It was found that KOH concentration played a key role in the growth of single-crystal tetragonal perovskite PbTiO3 nanoflakes, and the morphology of PbTiO3 crystallites can be controlled by adjusting the KOH concentration.

Abstract: PbTiO3 microrods were successfully synthesized via a surfactants-free hydrothermal method. The powders were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and photoluminescent spectra techniques (PL). It was found that the precursor played a key role in the formation of PbTiO3 microrods.

Abstract: Titanium nitride coatings were prepared on common glass slides using TiCl4 and NH3 by atmospheric pressure chemical vapor deposition. The deposition temperature range from 450-650 °C was applied. X-ray diffraction, scanning electron microscope, energy dispersive X-ray Spectrometer, four-point probe sheet resistance instrument and UV-Vis spectrometer were employed to characterize the obtained coatings. The crystallization and electrical conductivity of the coatings was improved with increasing deposition temperature. The reflectance and transmittance spectra showed all the coatings exhibited solar control performance. The coating prepared at 650 °C presented the optimum solar control performance in the present study.

Abstract: AZO/TiO2 double-layered semiconductor coupled films were prepared through sequentially depositing AZO and TiO2 films on glass substrates by radio frequency (RF) magnetron sputtering. PVP-pretreatment and post-annealing were performed on these double-layers to achieve an exposure of the AZO buried-layer in different baring conditions. The photocatalytic efficiencies of these buried-layer bared structures were measured through dye decomposition under ultraviolet irradiation. Silver mirror reactions were operated to explore a possible photocatalytic mechanism associated with these buried-layer bared conditions. The buried-layer bared AZO/TiO2 coupled films present 2 ~3 times of photocatalytic activity comparing to the normal AZO/TiO2 double-layered or single layered ones. It suggested that the self-built electrical field formed from coupling semiconductors reduces the recombination of electron-hole pairs, increases the yield of surface photogenerated charges, and enhances the photocatalysis.

Abstract: In order to investigate the effects of doping boron on the self-cleaning properties of TiO2 thin films, sol-gel method was employed to prepare TiO2 films with various amount of boron on the glass substrates. Atomic Force Microscope (AFM) and X-ray diffraction (XRD) were carried out to investigate the effects of boron on the microstructure and crystallization behavior of the thin films. The photocatalytic activity and the hydrophilicity of the films were also measured. The results showed that the photocatalytic activity of TiO2 films was improved by doping boron, and its hydrophilicity wasn’t destroyed. This can be ascribed to the enhancement of the surface energy, which was caused by the reduction of the crystal grain size of TiO2.