Super high electromechanical coupling and zero temperature coefficient surface acoustic wave substrates in KNbO(3) single crystal

The propagation characteristics of surface acoustic waves (SAW) and piezoelectric leaky surface waves in KNbO(3) single crystal have been investigated theoretically and experimentally. The results show that the electromechanical coupling coefficient k(2) of the surface wave propagating along the X-axis of the rotated Y-cut plate is very large with k(2)=0.53. This is about 10 times as large as that of LiNbO(3) in the surface wave branch. Experimental results for wideband SAW filters show low loss and temperature stable characteristics. The bandwidth is about 20%, and insertion losses are less than 2 to 6 dB. Simulation results for a ladder type filter using Y-cut KNbO(3) indicate that a bandwidth of 40% should be possible. The KNbO(3) substrates exhibit zero temperature coefficient of frequency (TCF) around 20 degrees C in rotated Y-cut substrates.     

Orientation dependence of electromechanical properties of relaxor based ferroelectric single crystals

The orientation dependence of electromechanical properties of relaxor based ferroelectric single crystals Pb(Zn_1/3Nb_2/3)O₃–(6–7)%PbTiO₃ and Pb(Mg_1/3Nb_2/3)O₃–33%PbTiO₃ has been calculated by coordinate transformation. Different from previous studies, the optimum cutting orientations have been predicted in terms of their piezoelectric responses in the corresponding crystal planes. The calculation results indicated that the anisotropic piezoelectric effects of [001] _c and [011] _c poled multi-domain crystals mainly come from the intrinsic contribution. However, the strong dielectric anisotropy of [001] _c poled multi-domain crystals mainly comes from extrinsic domain and domain wall contributions. For [011] _c poled multi-domain crystals, the intrinsic orientation effect enhances the dielectric anisotropy.     

Effects of nonlinear elastic constants on electromechanical coupling factors

We studied the electromechanical coupling factor of an electroelastic plate from the nonlinear theory for large deformations and strong fields, in particular the effects of nonlinear elastic constants on the factor. The case of nonlinear thickness-shear deformation of an AT-cut quartz plate is calculated as an example.     

Electrode effects on frequency spectra and electromechanical coupling factors of HBAR

In this paper, effects of electrodes on the spectra of high-overtone bulk acoustic resonator are analyzed phenomenologically by numerical simulations. Acoustic impedance ratio of the substrate to piezo-film, Zsb/Z0, and acoustic impedance ratio of the electrode to piezo-film, Ze/Z0, are taken as the category parameters for different combinations of three kinds of substrates, three kinds of piezo-films, and seven kinds of electrodes. The numerical simulations for all of the combinations are carried out. The results indicate that the acoustic impedance ratio of the substrate to piezo-film is a key factor for the variations of the space of parallel resonance frequency and the effective coupling factor versus the mode order. The mechanical effects of the electrodes have significant contribution as well. Several approximate formulae are given to evaluate the effective coupling factor for different combinations.     

Compact reflection-grating-based phase conjugator in KNbO(3):Fe crystals

We present the design and the results of experimental investigations of a self-pumped phase conjugator through a reflection grating in a special-cut photorefractive KNbO(3):Fe crystal. High reflectivity, good phase-conjugate fidelity, and fast response time are obtained.     

Orientation dependence in near-field scattering from TiO(2) particles

This scattering of light by small particles embedded in a continuous transparent medium is influenced not only by the bulk optical properties of the particles and the medium but also by the size, shape, and spatial arrangement of the particles-that is, by the microstructure. If the particles are close together, as in agglomerated coatings or stereolithographic suspensions, interactions between the radiation fields of adjacent particles can lead to variations in the magnitude and spatial arrangement of the scattered light in the near and the far field, which can affect the color and hiding power of a coating, the cure depth and homogeneity in stereolithography, and the threshold intensity for stimulated emission in random lasers. Our calculations of the near- and the far-field scattering distribution for 200-nm TiO(2) spheres in pairs of various orientations and in an ordered array of five particles show that, depending on the orientation of the particles with respect to the incident light, these interactions can either increase or decrease the scattering efficiency, the isotropy of the scattering, and the magnitude of the electric field strength within the matrix and the particles. In the mid-visible range, two particles in line increase the backscattering fraction by 28% and the scattering strength by 38% over that of a single particle, whereas if the particles are in the diagonal configuration the backscattering fraction and scattering strength are actually reduced by addition of the second particle. At shorter or longer wavelengths the backscattering fraction is reduced regardless of the location of the second particle, by as much as 60% when five particles are arranged in the zigzag configuration. These results are surprising in that it is generally assumed that multiple scattering enhances backscattering. Simple models of multiple scattering or scattering of two particles as a single, larger particle are inadequate to explain these results.     

Lead-free KNbO(3) ferroelectric nanorod based flexible nanogenerators and capacitors

In spite of high piezoelectricity, only a few one-dimensional ferroelectric nano-materials with perovskite structure have been used for piezoelectric nanogenerator applications. In this paper, we report high output electrical signals, i.e.?an open-circuit voltage of 3.2?V and a closed-circuit current of 67.5?nA (current density 9.3?nA?cm(-2)) at 0.38% strain and 15.2%?s(-1) strain rate, using randomly aligned lead-free KNbO(3) ferroelectric nanorods (～1?μm length) with piezoelectric coefficient (d(33)?～?55?pm?V (-1)). A flexible piezoelectric nanogenerator is mainly composed of KNbO(3)-poly(dimethylsiloxane) (PDMS) composite sandwiched by Au/Cr-coated polymer substrates. We deposit a thin poly(methyl methacrylate) (PMMA) layer between the KNbO(3)-PDMS composite and the Au/Cr electrode to completely prevent dielectric breakdown during electrical poling and to significantly reduce leakage current during excessive straining. The flexible KNbO(3)-PDMS composite device shows a nearly frequency-independent dielectric constant (～3.2) and low dielectric loss (<0.006) for the frequency range of 10(2)-10(5)?Hz. These results imply that short and randomly aligned ferroelectric nanorods can be used for a flexible high output nanogenerator as well as high-k capacitor applications by performing electrical poling and further optimizing the device structure.     

Determination of electromechanical coupling factors of low Q piezoelectric resonators operating in stiffened modes

The electromechanical coupling coefficient is usually determined from the relative spacing of the frequencies of resonance and antiresonance. The conventional formula is derived from equations describing the electrical behavior of an ideal piezoelectric resonator in the absence of losses. In this paper, the influence of the intrinsic material losses on the shift of the resonance/antiresonance frequencies, and therefore on the accuracy of the standard formula to determine k, is analyzed. The exact one-dimensional model of the piezoelectric resonator vibrating in a pure stiffened mode, with a rigorous account of the internal mechanical losses, has been taken as a reference, instead of the frequently used lumped approximate equivalent circuit (Butterworth-Van Dyke). It is shown that the coupling coefficient determined from the frequencies f(s) and f(p) is less than the intrinsic coupling coefficient, and that the error increases for highly attenuating materials with weak electromechanical coupling. The error due to the effect of attenuation, which increases with the decrease of the product Q(m)k of the resonator intrinsic parameters, has been systematically evaluated and plotted for 0.5相似文献   

Invariants of electromechanical coupling coefficients in piezoceramics

The relationships between coefficients of electromechanical coupling (CEMC) of various types of piezoceramic resonator (PR) vibrations are considered. Being constant for a given piezoceramic state, the range of variation of piezoceramics dielectric permittivity from a mechanically "free" condition at relatively low frequencies up to an "overall clamped" condition at high frequencies is determined by a consecutive "clamping", caused by a complex of CEMCs of various particular vibrational modes peculiar to the resonator. As the difference between "free" and "overall clamped" permittivities is always determined by the maximal piezomaterial /spl kappa//sub i3/ coupling coefficient, the difference does not depend on the path that was gone through the low-high frequency range, which includes all the vibrational modes possible for a particular PR. The influence of the piezoelectric and elastic anisotropy of lead-zirconate-titanate (PZT) piezoceramic materials on relative CEMC variations was experimentally investigated.     

Modal coupling in one-dimensional electromechanical structured continua

Summary A passive continuously distributed control of mechanical vibrations is proposed. The piezoelectric actuators are interconnected by a linear electric transmission line. We introduce coupling and internal resonance criteria to determine the optimal choices for electric parameters. These criteria can be found decomposing the differential operator appearing in the linear evolutions according to a partition of the state vector into mechanical and electrical parts. The results we find allow for the design of an experimental set up.     

Synthesis of potassium niobate (KNbO3) nano-powder by a modified solid-state reaction

Crystalline lead-free piezoelectric potassium niobate (KNbO₃) powders have been synthesized through a modified solid-state reaction method. The thermal behavior of the K₂C₂O₄·H₂O and Nb₂O₅ raw material mixture was investigated by thermogravimetric analysis (TGA) and differential thermal analysis (DTA). The X-ray diffraction technique (XRD) was used to investigate the phase formation and purity. The morphology of the powder obtained was characterized using a scanning electron microscope (SEM). The XRD pattern showed that the monophasic perovskite phase of KNbO₃ could be synthesized successfully at a temperature as low as 550 °C for 240 min, with an average crystallite size of 36 ± 8 nm. The SEM images suggested that the average particle size of the powder obtained was 278 ± 75 nm.     

Phase-matching properties of KNbO3 in the mid-infrared

KNbO(3) has been found to be phase matchable for type 1 second-harmonic generation up to 2.4 mum at 22 degrees C. The improved Sellmeier equations that correctly reproduce the nonlinear experiments thus far reported in the literature and our new experimental results for harmonic generation of CO(2) laser harmonics between 3.5303 and 5.2955 mum are presented.     

Frequency Agile Infrared Lidar Based on a NonTracking KNbO(3) Optical Parametric Oscillator

We present what is to our knowledge the first mid-IR lidar system based on a KNbO(3) optical parametric oscillator pumped by a Ti:sapphire laser. The optical parametric oscillator works in a nontracking configuration and provides high-frequency agility from 1 to 4 mum. This system constitutes an extension to the IR of UV lidars described previously [Europhys. J. D 4, 231 (1998); Appl. Opt. 37, 2231 (1998); Atmos. Environ. 32, 2957 (1998)] for the determination of aerosol concentrations in urban atmospheres. As first field tests, measurements at 3.5 mum were performed in fog conditions. Water droplet size and concentration were determined from Mie calculations. Quantitative temporal mappings and angular profiles are presented.     

Polarization dependence of the coupling ratio in LiTaO3 directional couplers

The effect of design and fabrication parameters on the polarization dependence of the splitting ratio in directional couplers produced in LiTaO3 by Zn diffusion has been investigated experimentally at a wavelength of 1558 nm. The directional couplers featured various combinations of waveguide width, separation gaps between waveguides, bending angle, and diffusion conditions. In each case the coupling region was 3.5 mm long. Of particular interest was the identification of parameter sets for which the sum of power splitting ratios from TE and TM inputs equals unity at the output, as needed for electro-optic tunable filters with relaxed beam-splitter requirements.     

Orientation dependence of the diffraction efficiency of holograms in cubic photorefractive (111)-cut piezocrystals

The diffraction efficiency of the transmission holograms in the photorefractive (111)-cut crystals of the classes [`4]3m\bar 43m and 23 depends on the orientation of the lattice vector. This effect is determined by combined manifestation of the piezoelectric and photoelastic properties of the crystal. The shape of this dependence is determined both theoretically and experimentally for the fixed linear polarizations of the readout light waves in a 2.1-mm-thick (111)-cut Bi₁₂SiO₂₀ crystal (class 23).     

Calculation of quasi-static electromechanical coupling coefficientsfor electrostrictive ceramic materials

The quasi-static coupling coefficients, k₁₃ and k₃₃, for electrostrictive ceramics are computed analytically. The calculation is based on a three-dimensional constitutive relation that models both electrostriction and nonlinear dielectric behaviors. The results show that the coupling factors depend on the amplitudes of the applied ac field and the dc bias, as well as the mechanical prestress. For an actuator without bias voltage or prestress, the coupling coefficients approach an asymptotic value with increasing electric field. The primary coefficients, k₁₃ and k₃₃ , for a lead magnesium niobate, Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃BaTiO ₃(PMN-PT-BT), based relaxor ferroelectric are computed as an example. The results show that the coupling coefficients for PMN-PT-BT materials are roughly comparable with those of existing piezoelectrics. These coefficients are important parameters for material section and power source design for transducer devices     

Strongly enhanced electromechanical coupling in atomically thin transition metal dichalcogenides

Flexoelectricity in thin films has emerged as an effective electromechanical response owing to appealing scaling law and universal existence. However, current studies show limited out-of-plane converse flexoelectric effect (CFE) of ultra-thin transition metal dichalcogenides (TMDs) when compared to their conventional in-plane piezoresponse. Here, we report converse flexoresponse of atomically thin TMDs such as molybdenum disulfide (MoS₂) and tungsten diselenide (WSe₂) which exceeds their intrinsic in-plane piezoresponses. Our piezoresponse force microscopy (PFM) measurements revealed strongly enhanced CFE of the atomically thin MoS₂ and WSe₂ than their bulk counterpart (∼700% enhancement in MoS₂, ∼400% enhancement in WSe₂). We observed an anomalous reduction in converse flexoresponse in the monolayer structure attributed to a puckering deformation. By inducing a built-in in-plane tension to reduce puckering, we estimated the CFE of monolayer WSe₂ to be 8.14 pm/V, the highest among the atomically thin TMDs.     

Modelling and simulation of KNbO3 ceramics dispersion

The dispersion of potassium niobate (KNbO₃) ceramics is analysed using the multiple-arc approach. This has revealed a high frequency arc that is unattainable by the Cole-Cole single arc analysis. The temperature dependence of the new arc is derived through the spread parameter of the relaxation distribution and interpreted in terms of the ferroelectric property of the KNbO₃ ceramics. It is shown that the overall dispersion behaviour of the ceramics is mainly due to the existence of two distinctly different polarisation mechanisms. The arc approach has also provided an effective tool for network simulation of dispersion whereby the ceramics are modelled by nine parallel R-C branches over the frequency range 10²-10⁵ Hz used     

Rapid synthesis of pervoskites (KNbO3, SrTiO3) and spinel (LiMn2O4) in presence of α-glycine with finished end product

Addition of Amino acid α-glycine to pervoskites like potassium niobate (KNbO₃) and strontium titanate (SrTiO₃) is seen to reduce the temperature of synthesis by several 100 degrees leading to formation of fine end product. Reduction of the grain size as much as 27% has been recorded in KNbO₃. The XRD Intensities were found to depend on the molar proportion of glycine. The average particle size of the KNbO₃ product with glycine is found to be in order of 140–290 nm having maximum tetragonal distortion of 1.206. SrTiO₃ synthesised in presence of glycine shows needle shaped structures with reduction in white aggregates. Glycine helps in liberation of carbon dioxide with fishy odour thereby leading to the early phase formation. Studies on LiMn₂O₄ spinel used in rechargeable lithium batteries in this direction have been included.