Hui Jun Ren

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).

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.

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 Yttrium Hydroxide Nanotubes

Yttrium hydroxide nanotubes were synthesized by hydrothermal method using Y(NO)3•6H2O as raw materials. X-ray powder diffraction (XRD) and scanning electron microscopy (SEM) were used to analyze the crystal phase and morphology of the as-prepared yttrium hydroxide nanotubes. In this paper, the hydrothermal temperature and the concentration of the mineralization agent were studied to have the effects on the formation of yttrium hydroxide nanotubes and their forming mechanism. The results indicate that the yttrium hydroxide nanotubes are prepared by hydrothermal method with the following optimal conditions: water as a solvent, NaOH concentration is 0.6 mol/L, the reaction temperature is 200°C, and the reaction time is 8h. In the growth process of yttrium hydroxide nanotubes, the hexagonal crystal nucleus of yttrium hydroxide is obtained first because the hexagonal crystal nucleus has the crystallization habit of growing along c axis orientationally. The yttrium hydroxide nanorods are obtained. The surface activating energy of the nanorods is stronger than that in its center. The yttrium hydroxide nanotubes are got finally.

Properties of BiFeO3 Thin Films Prepared with Self-Assembled Monolayers by Liquid Phase Deposition

Using iron nitrate, bismuth nitrate, citric acid and glacial acetic acid as the raw materials, the BiFeO3 thin films in crystalline state were prepared on FTO substrate with the self-assembled monolayers by liquid phase deposition after graded induction and annealing at 550°C for 30min. The physical phase composition, the surface morphology and dielectric properties of the thin films were characterized respectively by XRD, SEM, and Precision LCR Meter. This paper studied that the deposition temperature and the number of film layers had the effects on the thin films. The results show that the as-prepared thin films show the random orientation and good crystalline. When the deposition temperature is 70°C, the surface of the as-prepared thin film is smooth and uniform. The size of grain is 100nm. The thin film has a dense structure without the apparent pore phase. When the test frequency is between 1kHz and 1MHz, the loss of the thin films is decreased as the increase of the number of the film layers. When the number of the layers is 15, the dielectric constant of the thin films is 44 and the loss is 0.02 when the test frequency is 10kHz.

Synthesis of Bismuth Titanate Thin Films by Liquid-Phase Self-Assembled Monolayers

Using (NH4)2TiF6, Bi(NO3)3•5H2O and H3BO3 as raw materials, Bi4Ti3O12 thin films were synthesized with liquid phase self-assembled monolayers on the glass substrate. The different precursor solution concentrations and acid contents had the effects on the physical phase and morphology of Bi4Ti3O12 thin films. The Bi4Ti3O12 thin films were characterized by X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). The results indicate that the precursor solution with 10.0 mmol/L concentration was prepared by 3:4:9 molar ratio of (NH4)2TiF6: Bi(NO3)3•5H2O: H3BO3 and 6.0 ml acid content, depositing at 50°C for 20h, and heat treating at 590°C for 2h. The as-prepared thin films are well-crystal. The surface is even and dense. The formation mechanism of the Bi4Ti3O12 thin films is as follows: [TiF6-n(OH)n]2- complex ions are formed in the (NH4)2TiF6 aqueous solution. Then H3BO3 continually consumed F- ions of the solution, which made the amounts of [TiF6-n(OH)n]2- ions increase gradually. Under the induction of the electrostatic force, Bi3+ ions and [TiF6-n(OH)n]2- ions would grow naturally on the substrate surface in the form of Bi2[TiF6-n(OH)n]3 or Bi2[TiF6-nOm/2(OH)n-m]3. The samples lost the bound water after the heat treatment and finally the Bi4Ti3O12 thin films with pure phase were obtained.

Study on the Pressureless Sintering and Properties of (K0.5Na0.5)1-xLixNb1-yTayO3 Lead-Free Piezoelectric Ceramics

Potassium sodium niobate ((K0.5Na0.5)1-xLixNb1-yTayO3) powers were prepared by solid phase synthesis and (K0.5Na0.5)1-xNb1-yTayO3 lead-free piezoelectric ceramics were fabricated by the pressuerless sintering. The relationship among the powder phase composition and electric properties was studied. The results show that when x=0.5, the sintering temperature is 1050°C,and the polarization voltage is 3 kV/mm, the (K0.5Na0.5)1-xLixNb1-yTayO3 piezoelectric ceramics with the better piezoelectric properties are prepared. (The relative density is 94%, the piezoelectric constant d33=105pC/N, the planar electro-mechanical coupling coefficient kp=0.39, the medium loss tanδ=0.29, the mechanical quality factor Qm=45, and the dielectric constant εr=720). As the increase of the polarization votage, the ceramic piezoelectric properties are increased. When the polarization voltage E=3kV/mm, the polarization tends to be saturation on the whole.

On Preparation of SrTiO3 Thin Films with Self-Assembled Monolayers by Liquid Phase Deposition and its Dielectric Properties

In this paper, titanium ammonium fluoride ((NH4)TiF6), strontium nitrate (Sr(NO3)2) and boric acid (H3BO3) were used as raw materials, the precursor solution was prepared with molar ratio of AHFT/SN/BA=1/1/3. SrTiO3 dielectric thin films were deposited with the self-assembled monolayers (SAMs) by the liquid-phase deposition on FTO substrate. X-ray diffraction (XRD), scanning election microscopy (SEM) and Agilent E4980A precision LCR Meter were used to characterize the SrTiO3 films. The precursor solution concentration and the pH values of precursor solution had the effects on the dielectric properties of the as-prepared thin films. When the precursor concentration was 0.0125mol/L, the crystallization of as-prepared SrTiO3 thin films was high and the grain sizes on the film surface were even and dense. When the frequency was 15~100KHz, the optimal dielectric constant was up to 1060, the minimal dielectric loss was 4.053. As pH=3.30, the frequency of the as-prepared SrTiO3 thin films was 15~100KHz. The optimal dielectric constant was up to 1060, too. The minimal dielectric loss was 1.914. The optimal dielectric constants were 346.3 and 424.1 when the pH was 3.1 and below 3.5 respectively. The minimal dielectric losses were respectively 18.10 and 54.82.

Effects of Annealing Temperature on Morphology and Dielectric Property of BiFeO3 Films

Fe(NO3)3•9H2O and Bi(NO3)3•5H2O were used as raw materials. BiFeO3 thin films were prepared by sol-gel method. The effects of annealing temperatures on the morphology and dielectric property of the thin films were studied. XRD results show that the multi-crystal thin films with pure phase are obtained when annealed at 500°C and 550°C. But annealing at 580°C will lead to the appearance of Bi2.46Fe5O12 phase.AFM images show that as the increase of annealing temperatures the surface toughness of the thin film is decreased, but the surface undulation of the thin films is decreased gradually. Within the frequency range of 1KHz~1MHz, the dielectric constant of BiFeO3 thin films is kept over 125 and it does not change very much from 500°C to 580°C. Annealed at 550°C, the BiFeO3 thin films with the lower loss are obtained. At 1MHz, the dielectric loss is 0.12.

Preparation of Nd and Co Co-Doped BiFeO3 Thin Films Co-Doping Nd and Co by Sol-Gel Method

BiFeO3 thin films co-doping Nd and Co were prepared on FTO/glass substrate by sol-gel method with Bi(NO3)3•5H2O, Fe•(NO3)3•9H2O, Nd(NO3)3•6H2O and Co(NO3)2•6H2O as raw materials, 2-methoxyethanol together with acetic anhydride as a solvent. XRD, FE-SEM, Agilent E4980A Precision LCR Meter and TF 2000 Ferroelectric Analyzer were used to characterize the structure, morphology, dielectric property and ferroelectric property of the BiFeO3 thin films. The results show that after Nd and Co co-doping, the BiFeO3 thin films still keep the perovskite structure. The crystal structure turns square or orthogonal from rhombus. The thickness of the BiFeO3 thin films is about 500nm and the grain size is 80nm to 30nm. BiFeO3 thin films co-doping Nd and Co have the larger dielectric constant and the lower dielectric loss compared with Nd doping. BiFeO3 thin films co-doping Nd10% and Co1% have the dielectric constant of over 170 and the dielectric loss of below 0.03. Both have the better frequency stability. Co-doping Nd and Co could decrease the coercive electric field of BiFeO3 thin films.