Effect of temperature on dielectric property and microwave heating behavior of low grade Panzhihua ilmenite ore

The permittivity of low grade Panzhuhua ilmenite ore at 2.45 GHz in the temperatures from 20 ℃ up to 100 ℃ was measured using the technology of open-ended coaxial sensor combined with theoretical computation. The results show that both the real （ε′） and imaginary （ε′） part of complex permittivity （ε′-jε′） of the ilmenite significantly increase with temperature. The loss tangent （tanδ） is a quadratic function of temperature, and the penetration depth of ilmenite decreases with temperature increase from 20 ℃to 100 ℃ The increase of the sample temperature under microwave radiation displays a nonlinear relationship between the temperature （T） and microwave heating time （t）. The positive feedback interaction between complex permittivity and sample temperature amplifies the interaction between ilmenite and the microwave radiation. The optimum dimensions for uniform heat deposition vary from 10 cm to 5 cm （about two power penetration depths） in a sample being irradiated from both sides in a 2.45 GHz microwave field when temperature increases from room temperature to 100 ℃

Study on Microwave Dielectric Property of Carbon Black and Short Carbon Fibers

Carbon black and carbon fibers of different lengths were introduced in different matrices at different ratios to explore their microwave dielectric properties under 8.2 GHz-12.4 GHz. It is found that the actual dielectric constants of the samples containing carbon black are in a two-order function of the contents of carbon black （ε＇, ε＂=Av2＋Bv＋C） and the complex dielectric constants show an obvious frequency response. Of the added fibers of different lengths, the 4 mm-long one could well disperse in the matrices having not only good frequency response, but also larger real parts, imaginary parts and loss values. The imaginary parts and the loss values （tanδ）of the samples with 4 mm-long carbon fibers added increase linearly with the contents of fiber increasing. So it is practicable to adjust the dielectric parameters of the material in a wide range by changing the added amount of carbon black, and the carbon fiber or altering the lengths of the carbon fiber added.

Microstructure and Dielectric Property of 3D BNf/Si3N4 Fabricated by CVI Process

As potential wave-transparent materials applied at high temperatures, 3D BNf/Si3N4 ceramic matrix composites were prepared by low pressure chemical vapor infiltration or deposition（LPCVI/CVD） process from SiCl4-NH3-H2-Ar gas precursor at 800 oC. The densification process, microstructure and dielectric properties of 3D BNf/Si3N4 composites were investigated. The results indicated that 3D BNf/Si3N4 was successfully fabricated by LPCVI/CVD, with final open porosity of 2.37% and density of 1.89 g/cm3. Densification kinetics of 3D BNf/Si3N4 is a typical exponential pattern. The Si3N4 matrix was uniformly infiltrated into porous BNf preform. The deposited Si3N4 matrix was amorphous by XRD analysis. Introduction of BN fiber into Si3N4 ceramic lowered the permittivity of Si3N4. The fabricated BNf/Si3N4 composites possess low permittivity of 3.68 and low dielectric loss of lower than 0.01, which are independent of temperature below400 oC. Transmission coefficient of BNf/Si3N4 composite is 0.57 and keeps stable below 400 oC. BNf/Si3N4 can be fabricated at low temperature and may be candidates for the microwave transparent materials.

Broad Microwave Dielectric Property of Single-walled Carbon Nanotube Composites

Microwave dielectric measurements over the broad bandwith of 10 MHz to 20 GHz were conducted on composites comprising bundles of single-walled carbon nanotubes （SWNT） embedded in an epoxy matrix, in comparison to the nano-graphite and MWNT. It is found that both relative real and imaginary permittivity of the nanocomposites are strong functions of the SWNT concentration, showing large, wide dielectric and electrical response. Distinct resonance around 1.5 GHz is observed at high SWNT concentrations, accompa- nied by the downshift of the resonance frequency with increasing concentration. Largely, the SWNT-epoxy composites share the behavior of the MWNT owing to structural similarity, much more effective than the nano-graphite. The remarkable, broadband dielectric and electrical properties of the nanotubes acquired in the work originate from their unique seamless graphene architectures, modeled by two major contributions, dielectric relaxation/resonance and electronic conduction, which is substantiated by the agreement between theoretical analysis and experimental results. The carbon nanotube composites are prospective for microwave applications and offer experimental evidence for fundamental studies in low-dimensional systems.

Preparation, Characterization and Dielectric Property of Sr_5LaTi_3Nb_7O_(30) Ceramic

Sr-5LaTi-3Nb-7O- 30 ceramic was prepared by the conventional high temperature solid-state reaction route. The sintered samples were characterized by X-ray diffraction, scanning electron microscopy (SEM), differential thermal calorimetry (DSC) and dielectric measurements.The results show Sr-5LaTi-3Nb-7O- 30 belongs to paraelectric phase of filled tetragonal TB structure at room temperature, and undergoes a diffuse phase transition in the temperature range of -54-34 ℃.And Sr-5LaTi-3Nb-7O- 30 ceramic shows a high dielectric constant of 479 with a low dielectric loss of 0.005 at 1MHz. In comparison with Ba-based ceramics with TB structure, the temperature coefficients of the dielectric constant (τ-ε) is significantly reduced.

Electrical conductivity and dielectric property of fly ash geopolymer pastes

The electrical conductivity and dielectric property of fly ash geopolymer pastes in a frequency range of 100 Hz-10 MHz were studied.The effects of the liquid alkali solution to ash ratios（L/A） were analyzed.The mineralogical compositions and microstructures of fly ash geopolymer materials were also investigated using X-ray diffraction（XRD） and scanning electron microscopy（SEM）.The 10 mol sodium hydroxide solution and sodium silicate solution at a sodium silicate-to-sodium hydroxide ratio of 1.0 were used in making geopolymer pastes.The pastes were cured at 40℃.It is found that the electrical conductivity and dielectric constant are dependent on the frequency range and L/A ratios.The conductivity increases but the dielectric constant decreases with increasing frequency.

Investigation on dependence of BiFeO_3 dielectric property on oxygen content

The influence of oxygen content on the dielectric property of BiFeO3 ceramics is studied by experiment and firstprinciples calculation. The experimental result demonstrates that the dielectric constant of BiFeO3 is strongly dependent on introduced oxygen and oxygen vacancies. By comparison with BiFeO3, the introduced oxygen and oxygen vacancies can lead to a reduction in dielectric constant of BiFeO5 at a lower frequency. The first-principles calculation also shows a similar result when photon energy is in a range of 2.0-4.1 eV. A likely explanation is that this oxygen content dependence may be ascribed to the distortion of Fe-O octahedron structure due to oxygen vacancies or excess oxygen ions in the crystal structure of BiFeO3.

Synthesis, Structure and Dielectric Property of Ba_(1- x)Sr_xZr_yTi_(1- y)O_3

A sieres of Ba 1- x Sr x Zr y Ti 1- y O 3(0≤ x ≤0.4, 0< y <0.3) solid solutions was synthesized by soft chemical method below 100 ℃. The XRD and cell parameters component figures of the series of the solid solutions powder demonstrate that the compounds are mutually miscible in the solid solutions. Furthermore, the observation through a TEM showed that the product has a shape of uniform, substantially spherical particles with an average particle size of 60 nm in diameter. The result of prepared ceramics shows that after being adulterated with Sr 2+ and Zr 4+ in pure BaTiO 3 phase, the dielectric constant was increased eight times at room temperature, while the dielectric loss was decreased three times.

Effects of HfO_2 buffer layers on the dielectric property and leakage current of Ba_(0.6)Sr_(0.4)TiO_3 thin films by pulsed laser deposition

Ba0.6Sr0.4TiO3 （BST） thin films with and without HfO 2 buffer layer were fabricated on Pt/Ti/SiO2/Si substrates by pulsed laser deposition. Dependences of HfO 2 thickness on the dielectric property and leakage current of BST thin films were focused. The dielectric constant of BST thin films increased and then decreased with the increase of HfO 2 thickness, while the dielectric relaxation was gradually improved. The loss tangent and leakage current under positive bias decreased with the HfO 2 thickness increasing. The leakage current analysis based on the Schottky emission indicated an improvement of the BST/Pt interface with HfO 2 buffer layer. The loss tangent, tunability and figure of merit of optimized HfO 2 buffered BST thin film achieved 0.009 8, 21.91% （E max = 200 kV/cm）, 22.40 at 10 6 Hz, respectively.

Effects of rare earth addition on sintering process and dielectric property of cordierite based glass-ceramics

The effects of rare earth oxide on the sintering and dielectric property of cordierite-based glass-ceramics with non-stoichiometric composition prepared by quenching of molten droplets were investigated. The results show that the addition of rare earth oxide can lower the sintering temperature of cordierite glass-ceramics, improve the densification process and obviously reduce sintering activation energy. It is found that the densification of cordierite-based glass-ceramics is a liquid phase sintering process. The dielectric constant of the sintered compacts enhances with the increase of the density. When the sintering temperature is identical, the rare earth addition is found to have a noticeable effect on the dielectric loss of glass-ceramics. The properties of the glass-ceramics containing rare earth oxide appear to be correct for low firing temperature substrates.

Boosting the piezoelectric property of relaxor ferroelectric single crystal via active manipulation of defect dipole polarization

To further enhance the property of piezoelectric materials is of great significance to improve the overall performance of electro-mechanical devices.Here in this work,we propose a thermal annealing and high temperature poling approach to achieve significantly enhanced piezoelectricity in Pb(In_(1/2)Nb_(1/2))O_(3)single bondPb(Mg_(1/3)Nb_(2/3))O_(3)single bondPbTiO_(3)(PIN-PMN-PT)crystals with a morphotropic phase boundary(MPB)composition.The main idea of our approach is to realize a more sufficiently polarized crystal via active manipulation of defects and orientation of defect polarization.Manipulation of defect dipoles by the high temperature poling is proved by the piezo-response force microscopy.Finally,a d_(33)of 3300 pC/N and a SE of 0.25%are obtained,nearly 60%higher than that of conventionally poled crystals.Moreover,such a boosting of piezoelectric property is obtained under a maintained Curie temperature.Our research not only reveals the active control of defect dipole via modified poling method in the PIN-PMN-PT crystal,but also provides a feasible strategy to further improve the property of piezoelectric materials.

Phase transition and piezoelectric property of (Ag,K)NbO_(3) ceramics

AgNbO_(3) is an antiferroelectric (AFE) material with double hysteresis loop. Both the antiferroelectricityand ferroelectricity can be enhanced by doping. Herein, the ferroelectricity of AgNbO_(3) ceramics wasenhanced via K-doping and the phase diagram of the (Ag_(1-x)K_(x))NbO_(3) ceramics was upgraded. In details,(Ag_(1-x)K_(x))NbO_(3) ceramics are ferrielectric (FIE) M1 phase as x=5.00-5.50 mol% and ferroelectric (FE) Ophase as x=5.75-6.00 mol% before poling, and FE O phase as x=5.00-6.00 mol% after poling at roomtemperature. With increasing temperature, (Ag_(1-x)K_(x))NbO_(3) ceramics show the phase evolutions from FIEM1, AFE M2 to paraelectric (PE) T phase at x=5.00-5.50 mol% and from FE O, FE T to PE T phase at x=5.75-6.00 mol% before poling, and from FE O, FE T to PE T phase at x=5.00-6.00 mol% after poling.High d33 values of 180 pC/N and 285 pC/N are obtained at the FE O-FE T and FE T-PE T phase boundaries.This work sheds light on a novel and promising lead-free piezoelectric system.

La Doping Effect on the Dielectric Property of Barium Strontium Titanate Glass-Ceramics

Ferroelectric barium strontium titanate （BST） glass-ceramics doped with different content of La2O3 were prepared via the melt-quenching technique followed by controlled crystallization. The microstructures of crystallized samples were examined by X-ray diffraction and scanning electron microscopy. Dielectric properties were also investigated. The aliovalent substitution of Ba by La induced dispersion of semiconducting BaxSr1-xTi03 crystallites sealed in a glassy silicate matrix, which increased the εr and loss tangent values of the BST glass- ceramic. The experimental results indicate that aliovalent substitution is an effective method to process glass-ceramics with better dielectric properties.

A Method to Adjust Dielectric Property of SiC Powder in the GHz Range

The SiC powders by AI or N doping have been synthesized by combustion synthesis, using AI powder and NH4Cl powder as the dopants and polytetrafluoroethylene as the chemical activator. Characterization by X-ray diffraction, Raman spectrometer, scanning electron microscopy and energy dispersive spectrometer demonstrates the formation of Al doped SiC, N doped SiC and the AI and N co-doped SiC solid solution powders, respectively. The electric permittivities of prepared powders have been determined in the frequency range of 8.2-12.4 GHz. It indicates that the electric permittivities of the prepared SiC powders have been improved by the pure AI or N doping and decrease by the AI and N co-doping. The paper presents a method to adjust dielectric property of SiC powders in the GHz range.

Dielectric Property Studies of Biologically Compatible Brushite Single Crystals Used as Bone Graft Substitute

The electrical characterization of bone is essential for the better understanding of the role of electrical stimulation in bone remodeling. Calcium Hydrogen Phosphate Dihydrate or brushite (CaHPO4 2H2O) has been used in bone substitution owing to their fast resorption under physiological condition. Brushite is a suitable matrix for osteoconductive bone grafts. In this work, Calcium Hydrogen Phosphate single crystals have been grown by single diffusion gel growth technique. The powder XRD studies revealed the monoclinic structure of the grown crystals. The vibrational analysis of the crystals is done with FTIR spectroscopy and the major functional groups and their assigned vibrations are discussed. The frequency dependence of dielectric constant and ac conductivity at different temperatures have been studied in detail. This study shows decrease in the dielectric constant with the increase in frequency and temperature. The variation of ac conductivity is found to be increasing with frequency and decreasing with temperature.

RESEARCH ON THE DYNAMIC PROPERTY OF PIEZOELECTRIC MICRO DISPLACEMENT ACTUATOR FOR BORING ERROR COMPENSATION

The dynamic property of piezoelectric micro displacement actuator (PMDA) isanalyzed, especially the mechanical characteristic, lag phase property and hysteresis phenomenon.The influence factors of static and dynamic mechanical characteristics and the lag phase propertyare analyzed systematically. Three main influence factors of lag phase property are discovered, Withcomparison to mechanical Coulomb friction, a generalized model of nonlinear hysteresis of PMDA isadvanced, based on the essential analysis of nonlinear phenomenon. Finally the application of PMDAin error compensation control system of boring is introduced, A good compensation result isachieved.

Effective property of piezoelectric composites containing coated nano-elliptical fibers with interfacial debonding

Based on both the spring layer interface model and the Gurtin-Murdoch surface/interface model,the anti-plane shear problem is studied for piezoelectric composites containing coated nano-elliptical fibers with imperfect interfaces.By using the complex function method and the technique of conformal mapping,the exact solutions of the electroelastic fields in fiber,coating,and matrix of piezoelectric nanocomposites are derived under far-field anti-plane mechanical and in-plane electrical loads.Furthermore,the generalized self-consistent method is used to accurately predict the effective electroelastic moduli of the piezoelectric nanocomposites containing coated nano-elliptical fibers with imperfect interfaces.Numerical examples are illustrated to show the effects of the material constants of the imperfect interface layers,the aspect ratio of the fiber section,and the fiber volume fraction on the effective electroelastic moduli of the piezoelectric nanocomposites.The results indicate that the effective electroelastic moduli of the piezoelectric nanocomposites can be significantly reduced by the interfacial debonding,but it can be improved by the surface/interface stresses at the small scale,which provides important theoretical reference for the design and optimization of piezoelectric nanodevices and nanostructures.

Precise prediction of dielectric property for CaZrO_(3) ceramic

As for CaZrO_(3)(CZ)ceramic,the reported dielectric property values,especially dielectric constants,were much different from 23 to 32,which is reliable and credible?Without precise property data,CZ can’t be further developed and utilized accurately.Herein,CZ ceramic was fabricated by a traditional two-step sintering process,then simulated and calculated the dielectric properties precisely at a microscopic polarization angle using the lattice vibrational spectra and the Clausius-Mossotti(C-M)as well as damping equations.The Raman and Fourier transform far-infrared modes were analyzed and used to predict the intrinsic properties,which were consistent well with the values calculated from C-M and damping equations.The intrinsic permittivity,after precise prediction,is about 20,which is reliable and credible.As for the dielectric loss,the value of about 6
×10^(-4)was obtained after precise calculation,which is similar to other results.

Preliminary Research on Relationship Between Dielectric Property and Microstructure of Rabbit Liver

The dielectric properties in vitro present characteristic changes along with the alteration of metabolic activities, which can be detected from tissue micro- structure. The dielectric properties of tissues are closely related to its viability, but the relationship remains unclear to us. This study aims to specify the relationship between dielectric parameters and microstructure of living tissues and to try to explain the influence of tissue viability on dielectric properties. Nine rabbits were studied in this experiment. The impedance spectroscopy （10 Hz-1 MHz） and microstructure were determined at different time intervals （from 5 rain to 7 h） after samples were prepared. Some characteristic parameters were extracted to analyze the relationship between them. The inactivation process characterized by the mierostrueturs could be detected by means of dielectric parameters： the microstructures had no obvious change within 30 rain a.nd cell swelling caused by osmosis led to the decrease of extracellular ion concentration, resulting in the rise of lowfrequency impedance after 30 rain. The reduction of impedance was accompanied by the expanding intercellular area and irregular cell shape caused by the gradual destruction of cell membrane.The functions between alteration rate of intercellular area and Cole-Cole model parameters were also established. There is a strong correlative relationship between dielectric properties and microstructure. The dielectric spectrum can be a rapid and innocuous method to monitor the status of tissues. In the future, it may be of great help for clinical application, especially in transplantation.

Dielectric and piezoelectric properties of(110) oriented Pb(Zr_(1-x)Ti_x)O_3 thin films

A phenomenological Landau–Devonshire theory is developed to investigate the ferroelectric, dielectric, and piezoelectric properties of（110） oriented Pb（Zr_（1-x）Ti_x）O_3（x = 0.4, 0.5, 0.6, and 0.7） thin films. At room temperature, the tetragonal a_1 phase, the orthorhombic a_2c phase, the triclinic γ_1 phase, and the triclinic γ_2 phase are stable. The appearance of the negative polarization component P_2 in the a_2c phase and the γ_1 phase is attributed to the nonlinear coupling terms in the thermodynamic potential. The γ phase of the Pb（Zr_（1-x）Ti_x）O_3 thin films has better dielectric and piezoelectric properties than the a_2c phase and the a_1 phase. The largest dielectric and piezoelectric coefficients are obtained in the Pb（Zr_（0.5）Ti_（0.5））O_3 thin film. The piezoelectric coefficient of 110–150 pm/V is obtained in the（110） oriented Pb（Zr_（0.5）Ti_（0.5））O_3 thin film, and the Pb（Zr_（0.3）Ti_（0.7））O_3 thin film has the remnant polarization and relative dielectric constant of 50 μC/cm^2 and 100, respectively,which are in agreement with the experimental measurements reported in the literature.