Dengren Jin

Intra-grain composition nonuniform barium strontium calcium titanate ceramics by sol–gel pervasion techniques

The use of ferroelectric ceramics in microwave devices requires that they possess low-loss, frequency-stable and highly tunable properties. The problems of traditional barium strontium calcium titanate ceramics are higher loss and inappropriate work temperature dependence. In this work, a conventional mixed oxide route was used to prepare BaTiO3, SrTiO3 and CaTiO3 precursor powders. The BaTiO3, SrTiO3 and CaTiO3 powders were thoroughly ball mill mixed. They were then added to 5 wt% polyvinyl alcohol and pressed under a uni-axial pressure of 220 MPa into discs of 12 mm diameter. We introduced nano-grains of barium strontium titanate (BST) into the BSCT ceramic by nano-grain pervasion techniques to fabricate compositionally nonuniform BSCT ceramic samples. The nano-particles of BST are prepared with the sol–gel method. The sol–gel was subjected to ultrasonic irradiation and then vacuum methods in order to easily introduce nanoparticles into bulky BSCT. The ceramics do not show a sharp change in the dielectric constant and have a wide range of Curie temperature distribution. This is attributed to the presence of a compositionally nonuniform micro-area in the samples. Compared with uniform-composition BSCT, compositionally nonuniform BSCT has favourable dielectric properties. These results suggest that the compositionally nonuniform BSCT ceramics are promising candidates as tunable microwave elements.

Synthesis and Photocatalytic Property of Preferred-oriented Bi2Fe4O9 Crystals by Using Different Organic Additives

Bi2Fe4O9 crystallites were prepared by modified hydrothermal methods with different organic additives. It was found that addition of polyethylene glycol (PEG) 400 and citric acid (CA) have great influence on the crystalline morphologies and orientation. Bi2Fe4O9 crystallites with (001) preferred orientation could be synthesized by adding appropriate amount of PEG or CA. Excess of organic additives would result in the formation of second phases. The photocatalytic properties of Bi2Fe4O9 crystallites have been evaluated under the visible light irradiation. The results reveal that PEG-modified (001) oriented Bi2Fe4O9 crystallites have great degradation rate to methyl orange (MO).

Effects of la concentration on the structural and dielectric properties of 0.57BiFeO/sub 3/-0.43PbTiO/sub 3/ crystalline solutions

Crystalline solutions of 0.57(B1-xLax)FeO3-0.43PbTiO3 (BLF-PT) for x=0, 0.1, 0.2 and 0.3 have been fabricated by traditional solid state reaction method. X-ray diffraction (XRD) analysis reveals that the tetragonal to rhombohedral phase transformation of BLF-PT occurs with the increase of La content. The dielectric and ferroelectric properties of BLF-PT were investigated at room temperature for different La contents. BLF-PT reveals strong ferroelectric characteristics for the lower La composition, which transfers to the relaxor ferroelectrics for x>0.2. The dielectric constant and remanent polarization achieve of 1461 and 33.5 muC/cm respectively for BLF-PT of x=0.2. The dielectric constant and polarization of BLF-PT are enhanced simultaneously with increasing La content. Our results demonstrate that BLF-PT are competitive piezoelectric ceramics.

Structural and Multiferroic Properties of 1-x(Bi0.85La0.15)FeO3–xPbTiO3 Solid Solutions

A series of solid solutions of 1-x(Bi0.85La0.15)FeO3–xPbTiO3 for x = 0.35, 0.4, 0.415, 0.43, 0.45, 0.47)(BLFPT) are prepared by the mixed oxide method. The X-ray diffraction analysis shows that BLF-PT has a single perovskite phase with mixed tetragonal and rhombohedral phases in x = 0.415. The dielectric constant and Curie temperature of BLF-PT for x = 0.415 is 836 at 102 Hz and 419 °C, respectively. The remnant polarization and magnetization of x = 0.415 reach 39 μC/cm2 and 0.03 emu/g, showing a coexistence of ferroelectricity and ferromagnetism in the vicinity of the morphotropic phase boundary. The structure refinement is used to explain the correlation between structural and multiferroic properties of BLFPT solid solutions, which may be due to the existence of the monoclinic and orthorhombic phases lies on both sides of morphotropic phase boundary.

Piezoelectric properties of low loss and high Curie temperature (Bi, La)FeO3-Pb(Ti, Mn)O3 ceramics with Mn doping

Piezoelectric ceramics of 0.6(Bi0.9La0.1)FeO3-0.4Pb(Ti1−xMnx)O3 (BLF-PTM) for x=0, 0.01, 0.02, and 0.03 were prepared by sol-gel process combined with a solid-state reaction method. The tan δ for BLF-PTM of x=0.01 is just 0.006 at 1 kHz, drastically decreasing by using Mn dopants. The TC increases to 490 °C for BLF-PTM of x=0.02. Furthermore, Mn modification effectively enhances the poling state and the piezoelectric properties of BLF-PTM. The kp, Qm, d33, and g33 of 0.34, 403, and 124 pC·N−1 and 37×10−3 Vm·N−1 are achieved for BLF-PTM of x=0.01. The results indicate that Mn modified BLF-PTM is a competitive high power and high temperature piezoelectric material with excellent piezoelectric properties.

Effects of the sol-concentration on the structural and dielectric properties of Pb 0.3 Sr 0.7 TiO 3 thin films derived by the sol-gel method

Pb0.3Sr0.7TiO3(PST) thin films were deposited on Pt coated Si(100) substrates by sol-gel techniques using different sol-concentrations. The structural and dielectric characteristics of PST thin films as a function of the sol-concentration were investigated. PST thin films reveal a columnar texture through the thickness when the sol-concentration is lower than 0.3 M. PST thin films derived from 0.35 M sol show better dielectric characteristics with the dielectric constant, dielectric loss, tunability and FOM of 206, 0.01009, 47.5% and 47.07, respectively. The temperature dependence of the dielectric constant, dielectric loss and tunability of PST thin films were investigated in the temperature range of -140~120 exhibiting a dielectric peak of around -45 .

Effects of La Concentration on the Structural and Dielectric Properties of 0.57BiFeO 3 -0.43PbTiO 3 Crystalline Solutions

Crystalline solutions of 0.57(B1-xLax)FeO3-0.43PbTiO3 (BLF-PT) for x=0, 0.1, 0.2 and 0.3 have been fabricated by traditional solid state reaction method. X-ray diffraction (XRD) analysis reveals that the tetragonal to rhombohedral phase transformation of BLF-PT occurs with the increase of La content. The dielectric and ferroelectric properties of BLF-PT were investigated at room temperature for different La contents. BLF-PT reveals strong ferroelectric characteristics for the lower La composition, which transfers to the relaxor ferroelectrics for x>0.2. The dielectric constant and remanent polarization achieve of 1461 and 33.5 muC/cm respectively for BLF-PT of x=0.2. The dielectric constant and polarization of BLF-PT are enhanced simultaneously with increasing La content. Our results demonstrate that BLF-PT are competitive piezoelectric ceramics.

PVA(Polyvincyl Acohol)-assisted Hydrothermal Preparation of Bi 25 FeO 40 and Its Photocatalytic Activity

A PVA-assisted hydrothermal synthesis route was utilized to fabricate single-phase Bi 25 FeO 40 crystallites.X-ray diffraction results indicated that sillenite Bi 25 FeO 40 have been synthesized at the temperature of 200 ℃ using the KOH concentration of 7 M. Scanning electron microscopy showed the morphology of the as-prepared products were cubic shape with side length of 26μm. The band gap of Bi 25 FeO 40 was determined to be 1.8 eV (688 nm) by using UV-vis diffuse reflectance spectroscopy. It was found that Bi 25 FeO 40 exhibited a high photocatalytic activity for the degradation of methyl orange under UV-Vis irradiation, being a potential material for photocatalytic decomposition of organic contaminants.

Effects of the Sol-concentration on the Structural and Dielectric Properties of Pb 0.3 Sr 0.7 TiO 3 Thin Films derived by Sol-gel Method

Pb0.3Sr0.7TiO3(PST) thin films were deposited on Pt coated Si(100) substrates by sol-gel techniques using different sol-concentrations. The structural and dielectric characteristics of PST thin films as a function of the sol-concentration were investigated. PST thin films reveal a columnar texture through the thickness when the sol-concentration is lower than 0.3 M. PST thin films derived from 0.35 M sol show better dielectric characteristics with the dielectric constant, dielectric loss, tunability and FOM of 206, 0.01009, 47.5% and 47.07, respectively. The temperature dependence of the dielectric constant, dielectric loss and tunability of PST thin films were investigated in the temperature range of -140~120 exhibiting a dielectric peak of around -45 .

The influence of piezoceramic actuator on the stator vibrations in traveling wave ultrasonic motor

Based on the 3D finite element modeling of the stator in disc-type traveling wave ultrasonic motor, the influence of several kinds of piezoelectric ceramics bonded underneath the surface of the stator on exciting ultrasonic vibrations was investigated. Taken electromechanical coupling effect into account, numerical simulations were carried out by using the ANSYS finite element software package due to the boundary conditions we proposed. Vibration modes, resonance frequencies and voltage-induced displacements were obtained. The calculated results were in good agreement with the experimental data we measured.