Guo Qiang Tan

Co-Precipitation Synthesis of BiFeO3 Powders

Bismuth ferrite powders were synthesized by a simple citric acid complexing co-precipitation method at much lower temperature of 600°C. The work studies the calcination temperature and molar ratio of Fe and Bi on the structure and morphology. The as-prepared BiFeO3 powder was characterized by X-ray diffraction, field emission scanning electron microscopy, transmission electron microscope and Fourier transform infrared spectrophotometer. The result shows that the phase pure BiFeO3 powders with cubic morphology were prepared as the calcination temperature was 600°C and molar ratio of Fe and Bi was 1:1. The nanoparticles was uniform with the size of about 200nm.

Low Temperature Synthesis of BiFO3 Film by Hydrothermal Method

Polycrystalline BiFeO3 multiferroic films were fabricated on Ti substrates by hydrothermal method from an aqueous Bi (NO3)3•5H2O, FeCl3•6H2O and NaOH solution. The films grow in alkaline solution at low temperatures of 120°C-240°C for 18 hours. XRD analysis showed that well-developed crystallines with single perovskite crystal phase were obtained. It was also found that the increase of reaction temperature and concentration of NaOH were favorable for crystal growth and crystallographic regularization. The microstructure, thickness and cross-section of the films were characterized by FE SEM and EDS. Results indicated that dense and homogeneous BiFeO3 thin films could be obtained in an appropriate hydrothermal condition.

Influence of Ta5+ Doping on the Piezoelectric Properties of KNN Ceramics

In this study, the KNbO3, NaNbO3 and NaTaO3 powders were synthesized by hydrothermal method and the KNN ceramics were prepared by conventional sintering technique. The physical phase constitution and morphology were analyzed by X-ray diffraction and SEM. The KNN ceramics sintering temperature and the influence of Ta5+ doping on ceramic properties were explored. The results indicate that the optimal sintering temperature of KNN ceramics is 950°C, and the main phase is orthorhombic structure. After the substitution of Ta5+, the optimal sintering temperature is increased to 975°C. As the increase of doping amount, the piezoelectric properties have been significantly enhanced. The specimen doping 0.08 mol% Ta5+ exhibits the enhanced electrical properties (d33=125pC/N, Qm=131, and kp=0.24).

Hydrothermal Preparation of Bismuth Titanate Nanopowders

Bismuth titanate nanopowders were prepared by the hydrothermal method from Bi(NO3)3·5H2O, TiCl4 and KOH aqueous solution. The influences of reaction temperature and KOH concentration on the crystalline phase, morphology, and grain size of the prepared Bi4Ti3O12 powders were investigated. The results showed that well-crystallized, dispersive Bi4Ti3O12 nanopowders could be prepared by the hydrothermal treatment at 220–260°C for 6 h, in the case of [Ti]= 0.1 M, Bi:Ti = 4:3 and [KOH]=1.0–2.0 M. The prepared Bi4Ti3O12 powders of the orthorhombic structure were observed to be rectangle slice-shaped, and the grain sizes were about 30 nm in width and above100 nm in length. It was also confirmed that the desired concentration of KOH decreased with increasing of the treatment temperature.

Synthesis and Photocatalytic Activities of Bamboo-Like FeVO 4 Nanocrystalline

The bamboo-like FeVO4 nanocrystallines were synthesized by a two-step method of the microwave hydrothermal-calcination, using Fe (NO3)3·9H2O and NH4VO3 as raw materials. The physical and photophysical properties of the as-prepared photocatalysts were fully characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), UV-vis diffuse reflectance spectra and photoluminescence (PL) analysis. The photocatalytic activities were evaluated by the decolorization of RhB solution under UV and visible light irradiation. The results reveal that the precursor solution concentration is 0.15 mol/L, the molar ratio n (Fe)/n (V) is 1, pH=3.0. The microwave hydrothermal reaction is at 180 °C for 120 min and then calcinated under 550 °C for 3 h so as to obtain the triclinic FeVO4 nanocrystalline. Along [120] and [110], the fore and aft phases of the crystal orientation are bonded self-assembly to grow into the bamboo-like nanocrystalline with the energy gap of 2.42 eV. Under the UV-light irradiation for 240 min, the degradation rate of RhB is up to 91.2%. Adding 0.1 mL H2O2 to the solution, the out-phase photo-fenton reaction occurs and the degradation rate to RhB can reach to 98.8% after 8 h visible-light irradiation.

ZrO2 Thin Films Prepared by Self-Assembled Method

Octadecyltrichlorosilane (OTS) was prepared on glass substrate to form self-assembled monolayer (OTS-SAM). The OTS-SAM was then UV-irradiated to endow the film with good chemisorption ability. Zirconia films were formed on silanol SAM by the LPD method. The phase structure and surface configuration of the zirconia films were studied by XRD and SEM respectively. The XRD results indicate that the as-deposited ZrO2 thin films are pure tetragonal phase after being annealed at 500°C for 1 h. SEM images show the zirconia film is uniform, but not very compacted.

Preparation of Zn1-xCoxO Diluted Magnetic Semiconductor by Hydrothermal Method

Zn1-xCoxO diluted magnetic semiconductor was prepared by hydrothermal method at 200 °C and 240 °C for 24h with the Co2+ doping content of 5~15 mol%. NaOH was used as the mineralizer. X-ray diffraction analysis indicated that the as-prepared Co-doped ZnO had the pure ZnO wurtzite structure. UV–Visible spectroscopy had shown that the Co ions are substituted to Zn ions in ZnO matrix. Room temperature VSM revealed a paramagnetic behavior of the Co-doped ZnO samples. FE-SEM analyses showed that nanocrystalline powders of pure Zn095Co0.05O and Zn09Co0.1O could be prepared by the hydrothermal method.

Synthesizing Silicon Nitride Whiskers by Solvothermal and Carbothermal Methods

Xerogel was prepared by the sol-gel method using ethyl ester orthosilicate, alcohol, carbamide and glucose with various contents as raw materials. The precursor powders were obtained after xerogel was solvothermally treated at 220oC for 2.5 h. IR analyses showed that the Si-O-Si and Si-O-NH2 bond are obtained in the precursors. XRD analyses indicated that the powders prepared by the solvothermal method are amorphous. Si3N4 powders are produced by heat-treating the precursors at 1400 oC in N2. It was proved that the synthesized powders are α–Si3N4 whiskers. With the increase of the glucose contents and the heat-treating temperature, the crystallization of Si3N4 is obviously improved.

Hydrothermal Synthesis of Sodium-Potassium Niobate Nanopowders

Sodium-potassium Niobate (K0.4Na0.6NbO3, KNN) nanopowders were prepared by hydrothermal synthesis at the temperature range of 140-180°C for 12-48h using Nb2O5, NaOH and KOH as source materials. By means of XRD and SEM techniques, the effects of composition and hydrothermal treatment process, such as the rate of [R]/[Nb], the concentration of the alkali, the hydrothermal treatment temperature and the hydrothermal treatment time, on the microstructures and the crystallinity of alkali metals niobate were investigated in details. Results show that K0.4Na0.6NbO3 powders could be achieved by hydrothermal synthesis at the temperature range of 140-180°C with the alkalinity concentration of 2-8M. With the increase of hydrothermal reaction temperature and time, the crystallinity of KNN particles was improved. The obtained K0.4Na0.6NbO3 polycrystalline particles have rhombic structure.

Preparation and Magnetic Property of Bi2Fe4O9 Nanoparticles by Hydrothermal Method

Bi2Fe4O9 nanoparticles were prepared at low temperature via a facile, one-step hydrothermal synthesis process using iron(III) nitrate nonahydrate (Fe(NO3)3•9H2O) and bismuth nitrate pentahydrate (Bi(NO3)3•5H2O) as starting materials and sodium hydroxide (NaOH) as precipitant and mineralizer. XRD results indicated that the as-prepared nanoparticles are pure orthorhombic Bi2Fe4O9. SEM images revealed that the as-prepared Bi2Fe4O9 nanoparticles have a sheet-like morphology. They are paramagnetic at room temperature demonstrated by the magnetic measurements.