共查询到20条相似文献,搜索用时 31 毫秒
1.
L. V. Zhoga M. I. Dmitruk A. V. Gabrielyan I. L. Zhoga K. A. Zakharov 《Bulletin of the Russian Academy of Sciences: Physics》2011,75(10):1394-1398
The motions of domain walls at low stresses are known to result in the relaxation of structural over-stresses and their balancing,
while at high stresses we observe overstress increases and microcrack formation, i.e., the changing of resonance frequencies
and emerging of spurious resonances of piezoelectric elements [1, 2]. In view of the above, the influence of electromechanical
impacts on ceramics of compositions PZT-19 and PZT-35 are investigated in order to estimate the resonance curve changes. 相似文献
2.
The combination of ultrasound with atomic force microscopy (AFM) opens the high lateral resolution of scanning probe techniques in the nanometer range to ultrasonics. One possible method is to observe the resonance frequencies of the AFM sensors under different tip-sample interaction conditions. AFM sensors can be regarded as small flexible beams. Their lowest flexural and torsional resonance frequencies are usually found to be in a range between several kHz and several MHz depending on their exact geometrical shape. When the sensor tip is in a repulsive elastic contact with a sample surface, the local indentation modulus can be determined by the contact resonance technique. Contact resonances in the ultrasonic frequency range can also be used to improve the image contrast in other dynamic techniques as, for example, in the so-called piezo-mode. Here, an alternating electric field is applied between a conducting cantilever and a piezoelectric sample. Via the inverse piezoelectric effect, the sample surface is set into vibration. This excitation is localised around the contact area formed by the sensor tip and the sample surface. We show applications of the contact resonance technique to piezoelectric ceramics. 相似文献
3.
The mechanical pre-stress applied in piezotransducers used to generate high power ultrasound is needed to avoid ceramics fracture on traction cycle. Pre-stress levels inferior to 50 MPa can yield resonance shifting due to effectiveness of acoustic coupling between transducer pieces. Symmetrical transducers with different thickness of passive parts were submitted to axial mechanical pre-stress up to 50 MPa and their resonances were measured. The experimental results show the increasing of the resonances frequencies with the level of applied pre-stress. Similar effect is verified in simulations by using a model based on Mason's equivalent electric circuit. Due to the similarity of these effects, a relation between applied pre-stress and pieces coupling was proposed for the transducer assembled. In addition, the dependence of the thickness of non-piezoelectric pieces on the coupling effectiveness between them is discussed. The results show that transducers with small thickness present more expressive shifting resonance ratio. 相似文献
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Lead magnesium niobate ceramics (PMN) are promising materials for application in the field of high power transducers. The advantage of PMN materials are the large strains generated under moderate electric field and the low hysteresis. The electrostrictive effect is non-linear, the corresponding physical constants depend on temperature and frequency and a DC electrical bias is required. These difficulties must be considered at the design stage. A finite element model has been developed and validated in the ATILA code for non-linear static and time-domain analyses. These numerical modelings are used to design and test two Langevin-type electrostrictive transducers. The first transducer is made of PMN-PT-La (90-10-1%) ceramics (TRS Ceramics), the second one of ESCI ceramics (Morgan Matroc). For given static mechanical prestresses, resonance frequencies and effective coupling coefficients are measured at different DC electric fields and temperatures. 相似文献
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A. I. Dedyk A. D. Kanareykin E. A. Nenasheva Ju. V. Pavlova S. F. Karmanenko 《Technical Physics》2006,51(9):1168-1173
The properties of ferroelectric ceramics based on barium strontium titanate and doped by admixtures with low permittivity and dielectric loss tangent are studied experimentally. These ceramics are viewed as a promising material for microwave devices applied in the acceleration technology. Ceramic samples the I-V characteristics of which contain long horizontal segments are found to have good insulating properties. Various conductivity mechanisms in these ceramics are discussed, and their effect on the amount and character of dielectric hysteresis in these samples is considered. 相似文献
8.
G. A. Komandin V. I. Torgashev A. A. Volkov O. E. Porodinkov A. A. Pronin L. D. Iskhakova A. A. Bush 《Physics of the Solid State》2012,54(6):1191-1198
The nature of the contribution (additional to the phonon one) to the permittivity of bismuth ferrite ceramics has been studied using submillimeter and Fourier transform infrared spectroscopy. It has been shown that its numerical value depends on morphological features of samples, and the nature is determined by the defectness and crystallite interfaces. The effect of structure-phase features of bismuth ferrite ceramics on antiferromagnetic resonance line frequencies is indicated. 相似文献
9.
T. Sareein 《Physics letters. A》2009,373(17):1583-1587
The influences of compressive stress and aging on dielectric properties of undoped and Fe-doped sodium bismuth titanate (NBT) ceramics were investigated. The dielectric properties were decreased significantly with the compressive stress applied parallel to the electric field direction, while the changes were reversed with the stress applied perpendicularly. In addition, lower changes of the dielectric properties with stress were observed in Fe-NBT ceramics, likely caused by an enhanced relaxor characteristic with the acceptor doping, which also reduced the aging rate in the ceramics. Finally, the aging behavior of the NBT and Fe-NBT ceramics followed the slightly stretched exponential law, and the aging rate in both ceramics was found to decrease with frequency, a result of the pinning of the polarization components. These observations clearly confirmed the role of the acceptor dopant in enhancing the relaxor ferroelectric characteristics in the NBT-based ceramics. 相似文献
10.
A. A. Kaminskii V. V. Balashov E. A. Cheshev Yu. L. Kopylov A. L. Koromyslov O. N. Krokhin V. B. Kravchenko K. V. Lopukhin I. M. Tupitsyn V. V. Shemet 《Bulletin of the Lebedev Physics Institute》2016,43(12):371-374
The effect of sintering aids of SiO2, ZrO2, B2O3, and MgO oxides on the optimum sintering temperature, ceramics grain growth, total volume of residual pores, and optical quality of obtained ceramics is studied. The best combinations of sintering aids are found; as a result, YAG:Nd (1 at%) samples of ceramics of high optical quality are obtained. An original method for characterizing laser properties of ceramics is developed. Comparative measurements of main laser characteristics of the obtained ceramics and ceramics of the Konoshima Chemical Corp. Ltd wellknown in the world practice, are performed. 相似文献
11.
Thermally activated dislocation emission in high-temperature ferroelectric ceramics is investigated through an assumption of thermal stability and a novel analytical method. The stress intensity factor (SIF) arising from domain switching is evaluated by using a Green's function method, and the critical applied electric field intensity factor (CAEFIF) for brittle fracture at room temperature is obtained. Besides, the lowest temperature for single dislocation emission before brittle fracture is also obtained by constructing an energy balance. The multi-scale analysis of facture toughness of the ferroelectric ceramics at high temperature is carried out. Through the analysis, the CAEFIF for crack extension is recalculated. The results show that the competition and interaction effects between dislocation emission and brittle fracture are very obvious. Besides, the higher critical activation temperature, the more columns of obstacles will be overcome. Additionally, the shielding effect arising from thermally activated dislocations is remarkable, thus, the brittle-ductile transition can promote the fracture toughness of high-temperature ferroelectric ceramics. 相似文献
12.
A model is proposed to explain observations on electric breakdown of BaTiO3 ceramics: Ceramics made by usual sintering technique contains TiO2-rich intermediate layers between the grains of the polycrystalline structure. Field inhomogeneities are shown to result, with the field enhanced by factors of up to 100 or more in places. The very high field strength ensueing when the applied test voltage approaches its breakdown value causes inner field emission, with currents abruptly rising to very high values and thermally destroying the sample at once. 相似文献
13.
Thermally activated dislocation emission in high-temperature ferroelectric ceramics is investigated through an assumption of thermal stability and a novel analytical method. The stress intensity factor (SIF) arising from domain switching is evaluated by using a Green's function method, and the critical applied electric field intensity factor (CAEFIF) for brittle fracture at room temperature is obtained. Besides, the lowest temperature for single dislocation emission before brittle fracture is also obtained by constructing an energy balance. The multi-scale analysis of facture toughness of the ferroelectric ceramics at high temperature is carried out. Through the analysis, the CAEFIF for crack extension is recalculated. The results show that the competition and interaction effects between dislocation emission and brittle fracture are very obvious. Besides, the higher critical activation temperature, the more columns of obstacles will be overcome. Additionally, the shielding effect arising from thermally activated dislocations is remarkable, thus, the brittle-ductile transition can promote the fracture toughness of high-temperature ferroelectric ceramics. 相似文献
14.
The pore size distribution of porous media can be determined in a completely non-invasive manner using a new nuclear magnetic resonance (NMR) technique which monitors the magnetization decay due to diffusion in internal fields (DDIF). However, using of the DDIF technique is restricted to the low-phase encoding limit when only the relaxation mode and the first-order diffusion mode are excited. In the present work the fulfillment of such a limit is verified for a progressive increase of the magnetic impurity content of the porous media. If the higher order diffusion modes are excited they lead both to a stronger attenuation of the echo signal and to the appearance of ripples in the DDIF spectra which cannot be related to a pore size distribution. The samples used in this study are porous ceramics prepared using the replication technique and the magnetic impurity is iron (III) oxide which is introduced in an increasing concentration inside the porous matrix. All NMR experiments were done on water filling such porous ceramics using a low-field instrument operating at a proton resonance frequency of 20 MHz. The average pore dimension obtained with the DDIF technique in the weak encoding limit indicates a satisfactory agreement with that observed in optical microscopy images. 相似文献
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In some circumstances, large vibrational displacements at ultrasonic frequency must be generated using a low voltage drive. This result cannot be obtained with monolithic PZT ceramics which require voltages larger than 1000 V to produce displacements of the micrometer order at resonance. The use of multilayered hard lead zirconate titanate ceramics as transduction material in resonant devices is experimentally investigated for Langevin-type transducers. Large amplitudes are obtained under low drive (5 microm under 10 V). Material constant (compliance, losses) variations under large dynamic stress are, at least, one order of magnitude larger than for monolithic ceramics. Depolarization is found to be a critical issue when the transducer is driven continuously. It is demonstrated that this problem can be solved by polishing the interfaces between different parts of the device and applying an electrical DC bias to the transducer. 相似文献
17.
Diego A. Ochoa Rafel Pérez Jose E. García 《Applied Physics A: Materials Science & Processing》2013,112(4):1081-1088
The alteration of the high-field electrical permittivity (nonlinear response) of PZT-based ceramics when an electrical bias field is applied is reported in this work. Large differences are observed between soft and hard PZT behaviours. While in soft PZT a bias field does not modify the nonlinear behaviour, a notable dependence is verified in hard PZT. The Preisach model is satisfactorily used to describe experimental results. A distribution function containing the first terms of the Maclaurin development series of a function composed by two Gaussian-like functions of different amplitudes is proposed. The model gives a satisfactory explanation for the fact that the permittivity depends not only on the amplitude of the applied electric field, but also on the bias field, both for soft and hard ceramics and for poled or unpoled samples. 相似文献
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Thermomechanical ceramics have interesting properties: mainly high hardness, high wear resistance, good chemical resistance, good mechanical strength at high temperatures and generally low thermal conductivity. But, the engineering use of ceramics as structural parts is at the moment limited by their inherent brittleness. The toughness values of ceramics are between about to 5 MPa √m whereas the toughness values of metals are much higher (from 20 to 200 MPa √m). To avoid this brittleness, composite ceramics have to be used. Two types of composite materials can be developed: particle-reinforced composites and fiber-reinforced composites. In this paper, some examples of reinforcement of ceramics are presented. Two cases will be developed: second-phase reinforcement with zirconia particles or other particles, and the composites reinforced by fibers or whiskers. 相似文献
20.
Manjima Bhattacharya Riya Chakraborty Arjun Dey Ashok Kumar Mandal Anoop Kumar Mukhopadhyay 《Applied Physics A: Materials Science & Processing》2012,107(4):783-788
In all contact-related applications such as the wear-resistant inserts, biomedical implants, high strain rate impact-resistant plates, etc., nanohardness, i.e. the intrinsic contact resistance at the nano scale, plays a major role. In spite of the wealth of literature, the studies on nanohardness of dense, coarse-grain alumina ceramics which represent many commercial varieties; have reasonably good hardness at the macro scale and characteristically exhibit R-curve behaviour, are far from significant. Here, to the best of our knowledge, we report for the first time the experimental observations of the increase in intrinsic contact resistance at the nano scale with the loading rate applied to a high-density (~95?% of theoretical) coarse-grain (~20?μm) alumina ceramics. These observations were explained in terms of the initiation of nanoscale plasticity and maximum shear stress generated just underneath the nanoindenter. 相似文献