Auswahl der wissenschaftlichen Literatur zum Thema „Piezoceramic materials“

Piezoelectric materials have an ability to efficiently transform mechanical energy to electric energy and vice versa, which makes them useful as structural dampers. The objective of this work is to investigate the damping capabilities of a piezoceramic shunted by different types of passive electrical circuits. The material properties of the shunted piezoceramic are modeled and the analytical results show that the shunted piezoceramic exhibits different damping potentials depending on the piezoelectric properties of the material and the shunt circuits. An experimental set-up of a cantilever beam with surface bonded piezoceramics is proposed to investigate the damping characteristics of the shunted piezoceramic. An analytical model is developed to describe the influence of the shunted piezoceramic on the dynamic response of the beam. The damping performances of the piezoceramic shunted by different circuits are compared respectively and the experimental results show approximate agreement with the numerical simulations of the model.

Piezoelectric transducers have applications from ultrasonic structural health monitoring to micro-electromechanical systems. Small physical size coupled with large actuation is desirable in many applications, requiring unique transducer designs to take advantage of the material properties. Screen-printed piezoceramics were developed as a means of mass producing mezzo-scale transducers that are geometrically small and light weight, but large enough to generate significant actuation. Screen-printed piezoceramic transducers display significantly different properties than chemically identical bulk ceramic elements, largely attributed to high void fraction of screen-printed piezoceramic materials and detrimental to the functionality of traditional transducer designs. This article presents analysis, simulation, and initial testing of new designs for screen-printed piezoceramic transducers with concentric through-thickness electrodes. Analytical models were developed enabling analysis across material properties and design parameters. Analytical results were verified against finite element models for some designs. Prototypes were created and underwent initial testing to assess the properties of the design.

In this paper, transition probability analysis for piezoceramic actuators is presented. Nonlinear constitutive equations and resulting system models quantifying the non-linear and hysteretic field-displacement relations inherent to piezoceramic elements are developed. In the model development, lattice-level energy relations are combined with stochastic homogenization techniques to construct non-linear constitutive relations which accommodate the piezoceramic hysteresis. Simulation results demonstrated the effectiveness of the theoretical model development using transition probability analysis.

The motivation of this study was design, fabrication and characterization of bolt-clamped Langevin type transducers (BLT) from lead-free K0.5Na0.5NbO3 (KNN) based piezoceramics for high-power ultrasonic cutting applications. Hard and lead-free KNN piezoceramics was obtained by adding K4CuNb8O23 (KCN) together with ZnO and SnO2. Densification and high-power characteristics of KNN-KCN piezoceramics were enhanced in the presence of ZnO and SnO2. BLTs made from hard PZT4 (commercial Pb(Zr,Ti)O3) or Zn,Sn co-doped KNN-KCN piezoceramic rings (KNN-KCN-ZnSn) were modelled through ATILA finite element analysis software package. Simulated and experimentally measured impedance spectra, resonance modes and harmonic analysis results of BLTs were compared with each other. Longitudinal vibration displacement at the tip of the horns of BLTs at approximately 30 kHz was measured via photonic sensor device to compare their performances. At the end, based on the simulation and experimental results, a prototype ultrasonic cutting device was fabricated from lead-free KNN-KCN-ZnSn piezoceramic rings. Its cutting action on both plastic and ceramic materials was demonstrated for the first time. In summary, it was found that a hard KNN-KCN based lead-free piezoceramics were good potential replacements for their lead-based counterparts for commercial high-power BLT applications.

This paper concerns the homogenization problems for porous piezocomposites with infinitely thin metalized pore surfaces. To determine the effective properties, we used the effective moduli method and the finite element approaches, realized in the ANSYS package. As a simple model of the representative volume, we applied a unit cell of porous piezoceramic material in the form of a cube with one spherical pore. We modeled metallization by introducing an additional layer of material with very large permittivity coefficients along the pore boundary. Then we simulated the nonuniform polarization field around the pore. For taking this effect into account, we previously solved the electrostatic problem for a porous dielectric material with the same geometric structure. From this problem, we obtained the polarization field in the porous piezomaterial; after that, we modified the material properties of the finite elements from dielectric to piezoelectric with element coordinate systems whose corresponding axes rotated along the polarization vectors. As a result, we obtained the porous unit cell of an inhomogeneously polarized piezoceramic matrix. From the solutions of these homogenization problems, we observed that the examined porous piezoceramics composite with metalized pore boundaries has more extensive effective transverse and shear piezomoduli, and effective dielectric constants compared to the conventional porous piezoceramics. The analysis also showed that the effect of the polarization field inhomogeneity is insignificant on the ordinary porous piezoceramics; however, it is more significant on the porous piezoceramics with metalized pore surfaces.

Tube piezoceramic used for the laying of a variety of sensors with a relatively small diameter to the size of a few micrometer to a few milli meters. Materials used in Piezoceramic Tube specially formulated standards for cylinders, so many different kinds of sensors which has a cylindrical shape for use as a place Piezoceramic. Use of Piezoceramic Tube one to measure ultrasonic flow. In the ultrasonic flow rate measurement distinction is made between two different measurement principles, namely the Doppler effect and timing analysis wave. In both cases Piezoceramic transducer placed on the walls of the tube produces ultrasonic waves, which are then transmitted into the liquid diagonal to the direction of flow.

This study evaluates the application of smart damping materials for reducing structural noise and vibrations. The primary purposes of this study are to: 1. Explore the feasibility of smart damping materials, such as piezoelectric materials, for augmenting and improving the noise and vibration benefits of passive damping materials, and 2. Provide a preliminary evaluation of the noise and vibration benefits, and weight savings of smart damping material as compared to conventional damping treatments. To achieve the objectives of the study, a special test rig, designed to measure both vibrations and structure-borne noise of a test plate, was constructed and validated in the early stages of the study. Upon validating the test rig and the instrumentation that was set up for data collection and processing, a series of tests were performed. The tests were intended to establish a baseline for the test rig and compare the performance of smart damping materials with a number of passive interior automotive treatments. Further, in order to evaluate the effect of smart damping materials on the sound transmission loss, a series of tests were conducted according to the SAE J1400 test specifications. The tests evaluate the transmission loss for smart damping materials for an undamped and a damped plate. The passive damping technique used for this study involved attaching piezoelectric patches with resonant electrical shunts. The vibration modes of the plate were determined both analytically and experimentally, using laser measurement techniques, in order to determine effective placement of the piezoceramic materials. Three piezoceramic patches were applied to control four structural resonance frequencies of the plate. The tests show that smart damping materials have substantial performance benefits in terms of providing effective noise and vibration reduction at a frequency range that is often outside the effective range of passive damping materials. Further, judging by the acceleration and noise reduction per added weight, the test results indicate that smart damping materials can decrease the vibration peak of a steel plate at 151 Hz by up to 16.24 dB with an additional weight of only 0.11 lb. The addition of constrained-layer damping (CLD) can decrease that same peak by 18.65 dB, but it weighs 10 times more. This feature of smart damping materials is particularly useful for solving particular noise or vibration problems at specified frequencies, without adding any weight to the vehicle or changing the vehicle structure.
Master of Science

This master‘s thesis deals with study of basic physical, microstructural and mechanical properties of doped piezoceramic materials based on BaTiO3 prepared by electrophoretic deposition. The dopants used were rare earth oxides, i.e. Eu2O3, Er2O3, CeO2, Dy2O3 and Tb4O7 in amounts 1, 3 and 5 wt. %. The influence of dopants and their amount on density, phase composition, mean grain size, hardness, elastic modulus, fracture toughness, and flexural strength was examined. Suitable dopant choice enabled decrease in mean grain size and increase in relative density, hardness, elastic modulus, fracture toughness and flexural strength of sintered specimens. Relative densities up to 99 %, mean grain size below 1 m, hardness up to 13,1 GPa, elastic modulus up to 199 GPa, fracture toughness above 1 MPa·m1/2 and flexural strength above 115 MPa were achieved.

Thesis (M.S. in Engineering Acoustics)--Naval Postgraduate School, March 2004.
Thesis advisor(s): Thomas R. Howarth, Dehua Huang. Includes bibliographical references (p. 67-69). Also available online.

Aircraft and satellite structures are exposed to a wide range of temperatures during normal operation cycles. These fluctuations in temperature may result in significant changes of the structural dynamics. Aircraft, automotive, and satellite structures are also subject to various vibration sources. Passive and active vibration suppression techniques have been developed to minimize acoustic noise and fatigue stress damage. Featuring low weight solutions and high performance, active control techniques are becoming increasingly common. Structures with varying dynamics require more sophisticated active control techniques, such as adaptive control.

This research uses a special vibration test rig for evaluating the performance of different vibration suppression systems on a representative aircraft panel. The test panel is clamped rigidly in a frame and can be excited in various frequencies with an electromagnetic shaker. To simulate temperature fluctuations the temperature on the panel can be increased up to 65°C (150°F). Smart material based sensors and actuators are used to interface the mechanical system with the electronic controller. The active controller utilizes three positive position feedback (PPF) filters implemented through a digital signal processor board. This research develops two different adaptation methods to perform vibration suppression in the presence of thermally induced frequency changes of the representative panel. To adjust the PPF filter parameters an open-loop adaptation method and an auto-tuning method are investigated. The open-loop adaptation method uses a measurement of the plate temperature and a look-up table with pre-determined parameters to update the filters accordingly. The auto-tuning methods identifies the frequencies of the poles and zeros in the structure's collocated transfer function. From the knowledge of the pole and zero locations the optimal PPF parameters are calculated online.

The results show that both adaptation methods are capable of reducing the vibration levels of the test specimen over the temperature range of interest. Three PPF filters with parameter adaptation through temperature measurement achieve magnitude reductions of the resonance peaks as high as 13.6 decibel. Using the auto-tuning method resonance peak reductions up to 17.4 decibel are possible. The pole/zero identification routine proves to detect the frequencies correctly. The average identification error remained at around one percent even in the presence of external disturbances.
Master of Science

Piezoelectric materials find use as actuators and sensors in automotive, aerospace and other related industries. Automotive applications such as fuel injection nozzles and engine health monitoring systems require operating temperatures as high as 300-500 oC. The commercially used piezoelectric material PbZr1-xTixO3 (PZT) is limited to operating temperatures as low as 200 oC due to the temperature induced depolarization effects. PZT, in the undoped state exhibits a piezoelectric coefficient (d33) of 223 pC/N and ferroelectric-paraelectric transition temperature (Tc) of 386 oC. The enhanced properties of PZT occur at a region between the tetragonal and rhombohedral phases, called the Morphotropic Phase Boundary (MPB). Therefore, search for new materials with higher thermal stability and better sensing capabilities were focused on systems that exhibit a PZT-like MPB. This led to the discovery of (x)BiScO3-(1-x)PbTiO3 (BSPT), which exhibits an MPB with enhanced Tc (450 oC) and exceptionally high piezoelectric response (d33 = 460 pC/N). Theoretical studies have shown that the mechanism of enhanced piezoresponse in ferroelectric systems is related to the anisotropic flattening of the free energy profiles. An alternative view point attributes the anomalous piezoelectric response to the presence of high density of low energy domain walls near an inter-ferroelectric transition. Diffraction is a versatile tool to study the structural and microstructural changes of ferroelectric systems upon application of electric field. However, characterization of electric field induced structural and microstructural changes is not a trivial task, since in situ electric field dependent diffraction studies almost invariably give diffraction patterns laden with strong preferred orientation effects, due to the tendency of the ferroelectric/ferroelastic domains to align along the field direction. Additionally, diffraction profiles of MPB compositions exhibit severe overlap of Bragg peaks of the coexisting phases, and hence, it is difficult to ascertain with certainty, if the alteration in the intensity profiles upon application of electric field is due to change in phase fraction of the coexisting phases or due to preferred orientation induced in the different phases by the electric field. The characterization of electric field induced phase transformation in MPB systems, has therefore eluded researchers and has been considered of secondary importance, presumably due to the difficulties in unambiguously establishing the structural changes upon application of electric field. In fact, majority of the in situ electric field dependent diffraction studies have been carried out on compositions just outside the MPB range, i.e. on single phase compositions. In such studies, the focus has been mainly on explaining the piezoelectric response in terms of motions of the non-180° domain walls and field induced lattice strains. In this dissertation, the BSPT system has been systematically investigated with the view to understand the role of different contributing factors to the anomalous piezoelectric response of compositions close to the MPB. Using a comparative in situ electric field dependent diffraction study on a core MPB composition exhibiting highest piezoelectric response and a single phase monoclinic (pseudo-rhombohedral) composition just outside the MPB, it is demonstrated that, inspite of the significantly large domain switching and lattice strain (obtained from peak shifts) in the single phase composition, as compared to the MPB composition, the single phase composition shows considerably low piezoelectric response. This result clearly revealed that the anomalous piezoelectric response of the MPB composition is primarily associated with field induced inter-ferroelectric transformation and the corresponding field induced interphase boundary motion. A simple strategy has been employed to establish the field induced structural transformation for the MPB compositions, by overcoming the experimental limitation of in situ electric field dependent diffraction studies. The idea stemmed from the fact that, if the specimens for diffraction study can be used in powder form instead of pellet, the problems associated with preferred orientation effects can be eliminated, and the nature of field induced structural changes can be accurately determined. A comparative study of the diffraction profiles from poled (after subjecting the specimen to electric field) and unpoled (before subjecting the specimen to electric field) powders could precisely establish the nature of electric field induced phase transformation for the MPB compositions of BSPT and provided a direct correlation between the electric field induced structural changes and the enhanced piezoelectric response. A new ‘powder poling’ technique was devised, which involves application of electric field to powder form of the specimen. Using this technique, it was possible to study separately, the effect of stress and electric field on the nature of structural transformation. A unique outcome of this study was, it could demonstrate for the first time, analogous nature of the stress and electric field induced structural transformation. A comparative study of the dielectric response of poled and unpoled samples was used to show a counterintuitive phenomenon of field induced decrease in polarization coherence for the MPB compositions. This approach was used to suggest that the criticality associated with the MPB extends beyond the composition boundary conventionally reported in literature based on bulk diffraction techniques (x-ray and neutron powder diffraction). The layout of the dissertation is as follows: Chapter 1 gives a brief introduction of the fundamental concepts related to ferroelectric materials. The theories that explain the enhanced piezoresponse of MPB based ferroelectric systems have been outlined. Detailed information of the existing literature is presented in the relevant chapters. Chapter 2 presents the details of the solid state synthesis of BSPT compositions and structural analysis using diffraction studies. The dielectric measurements were used to establish the Tc for the different compositions. The enhanced ferroelectric and piezoelectric properties were observed for the MPB compositions, which were shown to exhibit coexistence of tetragonal and monoclinic phases from structural studies. The critical MPB composition exhibiting highest piezoelectric and ferroelectric properties was established to be x = 0.3725. The thermal stability of the critical MPB composition was established to be 400 oC using ex situ thermal depolarization studies. The common approach of structural analysis in the unpoled state failed to provide a unique relationship between the anomalous piezoelectric response and the structural factors at the MPB, emphasizing the need to characterize these system using electric field dependent structural studies. Chapter 3 presents the results of in situ electric field dependent diffraction measurements carried out at Argonne National Laboratory, USA. The quasi-static field measurements could successfully quantify the non-180o domain switching fractions and the field induced lattice strains. The changes in the integrated intensities were used to obtain the non-180o domain switching fraction and the shift in peak positions were used to quantify the field induced lattice strains. The in situ studies could successfully explain the macroscopic strain response for the single phase pseudo-rhombohedral (monoclinic) composition on the basis of domain switching mechanisms and field induced lattice strains. The MPB compositions were shown to have additional contributions from interphase boundary motion, resulting from change in phase fraction of the coexisting phases. The results emphasized the need to investigate the electric field induced transformation for MPB compositions, in order to give a comprehensive picture of the various contributions to the macroscopic piezoreponse. While Rietveld analysis could be used to investigate the phase transformation behaviour upon application of electric field, textured diffraction profiles obtained using in situ studies, in addition to the severely overlapping Bragg reflections of the coexisting phases for the MPB compositions hindered reliable estimation of the structural parameters. An alternate approach to investigate the field induced phase transformation is presented in Chapter 4. The stroboscopic measurements on the MPB composition showed evidence of non-180o domain wall motion even at sub-coercive field amplitudes as low as 0.1 kV/mm. Chapter 4 presents the results of the ex situ electric field dependent structural study, wherein the diffraction profiles collected from poled powders is compared to that of unpoled powders. The diffraction profiles from the poled powders did not exhibit any field induced crystallographic texture and could successfully be analyzed using Rietveld analysis. High resolution synchrotron diffraction studies (ESRF, France) carried out on closely spaced compositions revealed that, the composition exhibiting the highest piezoelectric response is the one, which exhibits significantly enhanced lattice polarizability of both the coexisting (monoclinic and tetragonal) phases. The enhanced lattice polarizability manifests as significant fraction of the monoclinic phase transforming irreversibly to the tetragonal phase after electric poling. The monoclinic to tetragonal transformation suggested the existence of a low energy polarization rotation pathway towards the [001]pc direction in the (1 1 0)pc pseudocubic plane of the monoclinic phase. The results are discussed on the basis of the existing theories that explain piezoresponse in MPB systems and are in support of the Polarization rotation model, in favor of a genuine monoclinic phase. Chapter 5 discusses the ferroelectric-ferroelectric stability of the MPB compositions in response to externally applied stress and electric field independently. Using the newly developed ‘powder poling’ technique, which is based on the concept of exploiting the irreversible structural changes that occur after application of electric field and stress independently, it was possible to ascertain that, both moderate stress and electric field induce identical structural transformation - a fraction of the monoclinic phase transforms irreversibly to the tetragonal phase. The powder poling technique was also used to demonstrate field induced inter-ferroelectric transformation at sub-coercive field amplitudes. In addition, the analysis of the dielectric response before and after poling revealed a counterintuitive phenomenon of poling induced decrease in the spatial coherence of polarization for compositions around the MPB and not so for compositions far away from the MPB range. Exploiting the greater sensitivity of this technique, it was demonstrated that, the criticality associated with the inter-ferroelectric transition spans a wider composition range than what is conventionally reported in the literature based on bulk x-ray/neutron powder diffraction techniques. Chapter 6 presents the closure and important conclusions from the present work and summarizes the key results, highlighting the proposed mechanism of enhanced piezoresponse in BSPT. The last part of the chapter deals with suggestions for future work from the ideas evolved in the present study. vi

Non-centrosymmetric materials that can be polarized under applied mechanical stress or electric field are piezoelectric in nature and the phenomenon is called piezoelectric effect. They are broadly classified as direct and converse piezoelectric effects. Piezo-ceramics have a wide range of applications such as piezoelectric actuators, sensors, and transducers. Among piezoceramics, ferroelectric based materials are imperative owing to the existence of spontaneous polarization in these systems. Several materials are investigated starting from naturally occurring crystals to synthetic ceramics but are limited in their application range. The piezoelectric and ferroelectrics properties of the solid-solutions based on lead zirconate and lead titanate called lead zirconate titanate (PZT), lead magnesium niobate-lead titanate (PMN-PT), lead zinc niobate-lead titanate (PZN-PT) (near morphotrophic phase boundary (MPB)) demonstrate their potential for myriad device applications besides inciting a great deal of academic interest. They have been widely used for commercial applications such as ultra sound transducers, ultrasonic motors, fuel injector actuators, nano positioners in scanning electron microscope etc. However, these materials contain more than 60% lead by weight and volatization of Pb at higher temperature, and disposal of lead results in environmental pollution and are fatal to human health. This gave an insight to search for lead-free solid solutions covering a wide spectrum of applications akin to that of PZT. The search for alternatives to lead based piezoelectric materials is now being focused on modified barium titanates and alkali niobates in which the incidence of MPB was reported similar to that of PZT. In this thesis the results pertaining to the various investigations carried out on modified barium titanates, Ba(Zr0.2Ti0.8)O3- x(Ba0.7Ca0.3)TiO3(BCZT), and alkali niobates, potassium sodium niobate (KNN), are presented. Especially, lead-free piezoelectric material Ba(Zr0.2Ti0.8)O3-x(Ba0.7Ca0.3)TiO3(BCZT) with x= 0.5 has attracted great attention due to its excellent piezoelectric properties. Contrary to the other Pb-free systems, the BZT–BCT phase diagram shows a Morphotropic Phase Boundary (MPB) characterized by the existence of a tri-critical point (TCP), which is also the case for PZT and PMN–PT. One drawback of the BZT–xBCT (x=0.5) is its high sintering temperature (where it exhibits the largest d33 of 550 – 620pC/N). Several methods have been adopted and various additives are being added to bring down the sintering temperature, since high d33 requires an optimized sintering temperature of around 1540oC which also shows excellent ferroelectric properties. However, the methods that were reported in the literature to synthesize the above materials do not guarantee compositional homogeneity and also there is a limitation in obtaining ceramics of enhanced grain size as the ceramics comprising larger grains are demonstrated to exhibit high piezoelectric coefficients. Therefore to address these issues, the simple soft chemical route was adopted to synthesize chemically homogenous powder and the influence of microstructure (grain size) and ferroelectric domains on piezoelectric properties of the BCZT at nano and micron sized crystallites was studied. The results obtained are classified into chapter 3 and chapter 4 accordingly apart from introduction, materials, and methods. Another challenging area of research in lead free piezoceramics for nanoscale device application is to synthesize materials and to visualize the piezoelectric properties at nanoscale with controlled shapes and sizes. For that, Mg2+ ion was chosen as the dopant especially on Ba2+ sites to synthesize Ba0.95Mg0.05Zr0.1Ti0.9O3 (BMZT) nanocrystals, as MgO is known to be an effective grain growth inhibitor in many functional and structural ceramics. Therefore in the present thesis Mg2+ ion was chosen to exercise a strict control over the grain size. The results obtained from this title compound are discussed in chapter 5. Another class of material is K0.5Na0.5NbO3 (KNN), which has been considered a good candidate for lead-free piezoelectric materials. KNN exhibits an MPB around 50% K and 50% Na separating two orthorhombic phases from the complete solid solution of NaNbO3 (Anti-ferroelectric) and KNbO3 (ferroelectric). The major problem associated with KNN ceramic is its complex densification process; difficulty in processing and volatilization of sodium at higher sintering temperature leading to stoichiometric discrepancy. To overcome these difficulties, in the present investigations, an attempt has been made to fabricate KNN ceramics by employing the liquid phase sintering method. In this chapter, B2O3 and borate based glass (0.5 Li2O - 0.5K2O- 2B2O3) were chosen to improve the densification, grain size and their effects on the physical properties of the KNN ceramics are discussed in chapter 6. In chapter 7, KNN crystallites (with size varying from nano to micrometers) were dispersed in the Polyvinylidene fluoride (PVDF) matrix to obtain a polymer/nano or micro crystal composites and the effect of nano and micron sized KNN fillers on the structural, dielectric and piezoelectric properties were investigated. The results obtained pertaining to these aforementioned investigations are organized as follows. In Chapter 1, a brief introduction to the field of ferroelectricity, piezoelectricity, and piezoelectric materials. The emphasis has been on the ferroelectric based piezoelectric materials belonging to the perovskite family of oxides. A brief exposure to the conventional lead based piezoceramics, lead zirconate titanate (PZT) is discussed. Furthermore, drawbacks associated with lead based ceramics are highlighted and alternatives to PZT based ceramics such as modified barium titanate and alkali niobate solid solutions are focused, leading to the motivation and objectives of our work. Chapter 2 describes the various experimental techniques that are employed to synthesize and characterize the materials under investigation. Chapter 3 deals with details concerning the characterization of Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT) nanocrystals prepared via complex oxalate precursor route at a relatively low temperature (800°C/5h). The phase formation temperature of BCZT at nanoscale was confirmed by thermogravimetric (TG), differential thermal analysis (DTA) followed by X-ray powder diffraction (XRD) studies. Fourier Transform Infrared (FTIR) spectroscopy was carried out to confirm the complete decomposition of oxalate precursor into BCZT phase. The XRD and profile fitting revealed the coexistence of cubic and tetragonal phases and was also corroborated by Raman study. Transmission electron microscopy (TEM) studies carried out at 800°C and 1000°C/5h heat treated BCZT powder revealed the crystallite size to be in the range of 20 – 50 nm and 40 – 200 nm respectively. The optical band gap for BCZT nanocrystalline powder was obtained using Kubelka Munk function and was found to be around 3.12 ± 0.02 eV and 3.03± 0.02 eV respectively for 800°C (20 – 50 nm) and 1000°C/5h (40 – 200 nm) heat treated samples. The piezoelectric properties were studied for two different crystallite sizes (30 and 70 nm) using piezoresponse force microscope (PFM). The d33 coefficients obtained for 30 nm and 70 nm sized crystallites were 4 pm/V and 47 pm/V respectively. These were superior to those of BaTiO3 nanocrystal (≈ 50 nm) and promising from the technological/industrial applications perspective. Chapter 4 deals with the studies concerning the effect of microstructure (Grain size) and ferroelectric domains on physical properties of Ba0.85Ca0.15Zr0.1Ti0.9O3 ceramics. Fine powders comprising nanocrystallites of Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT) were synthesized via oxalate precursor method which facilitated to obtain homogenous and large grain sized ceramics at a lower sintering temperature. The compacted powders were sintered at various temperatures in the range of 1200°C - 1500°C for an optimized duration of 10h. Interestingly the one that was sintered at 1450°C/10h exhibited well resolved Morphotrophic Phase Boundary (MPB). The average grain size associated with this sample was 30 µm accompanied by higher domain density mostly with 90° twinning. These were believed to make a significant contribution towards obtaining large strain of about 0.2 % and piezoelectric coefficient as high as 563 pC/N. The maximum force that was generated by BCZT ceramic (having 30 µm grain size) was found to be 161 MPa which is much higher than that of known actuator materials such as PZT (40 MPa) and NKN-5-LT (7 MPa). Chapter 5 reports the details involving the synthesis, structural, optical, and piezoelectric response of lead free Ba0.95Mg0.05Zr0.1Ti0.9O3 nanocrystalline powder. Nanocrystalline powders of Ba1-xMgxZr0.1Ti0.9O3 (x=0.025 - 0.1) were synthesized via citrate assisted sol-gel method. Interestingly, the one with x=0.05 in the system Ba1-xMgxZr0.1Ti0.9O3 exhibited fairly good piezoelectric response apart from the other physical properties. The phase and structural confirmation of synthesized powder was established by X-ray powder diffraction (XRD) and Raman Spectroscopic techniques. Two distinct Raman bands i.e., 303 cm-1 and 723 cm-1 characteristic of the tetragonal phase were observed. Thermogravimetric analysis (TGA) was performed to evaluate the phase decomposition of the as-synthesized Ba0.95Mg0.05Zr0.1Ti0.9O3 sample as a function of temperature. The average crystallite size associated with Ba0.95Mg0.05Zr0.1Ti0.9O3 was calculated using Scherrer formula based on the XRD data and was found to be 25 nm. However, Scanning and Transmission Electron Microscopy studies revealed the average crystallite size to be in the range of 30-40 nm. Kubelka-Munk function was employed to determine the optical band gap of these nanocrystallites. The piezoelectric response of 26 pm/V was observed for Ba0.95Mg0.05Zr0.1Ti0.9O3 nanocrystal by Piezoresponse Force Microscopy (PFM) technique. Photoluminescence (PL) study carried out on these nanocrystals exhibited a blue emission (470 nm) at room temperature. Chapter 6 describes the effect of the addition of B2O3 on the density, microstructure, dielectric, piezoelectric and ferroelectric properties of K0.5Na0.5NbO3 ceramics. Boron oxide (B2O3) addition to pre-reacted K0.5Na0.5NbO3 (KNN) powders facilitated swift densification at relatively low sintering temperatures which was believed to be a key to minimize potassium and sodium loss. The base KNN powder was synthesized via solid-state reaction route. The different amounts (0.1 to 1 wt %) of B2O3 were added, and ceramics were sintered at different temperatures and durations to optimize the amount of B2O3 needed to obtain KNN pellets with the highest possible density and grain size. The 0.1 wt% B2O3 added KNN ceramics sintered at 1100°C for 7h exhibited higher density (98%) with grain size of ~5 µm. Scanning electron microscopy (SEM) studies confirmed an increase in average grain size with increasing B2O3 content at the appropriate temperature of sintering and duration. The B2O3 added KNN ceramics exhibited improved dielectric and piezoelectric properties at room temperature. For instance, 0.1 wt% B2O3 added KNN ceramic exhibited d33 value of 116 pC/N which is much higher than that of pure KNN ceramics. Interestingly, all the B2O3 added (0.1 to 1wt %) KNN ceramics exhibited polarization – electric field (P vs E) hysteresis loops at room temperature. The remnant polarization (Pr) and coercive field (Ec) values are dependent on the B2O3 content and crystallite size. The details pertaining to the effect of the addition of borate based glass (0.5 Li2O - 0.5K2O- 2B2O3) on the physical properties of K0.5Na0.5NbO3 ceramics are also reported in this chapter. The addition of powdered 0.5 Li2O - 0.5K2O- 2B2O3 (LKBO) glass (0.5 to 2 wt%) to potassium sodium niobate, K0.5Na0.5NbO3 (KNN) powder facilitated higher densification which resulted in improved physical properties that include dielectric, piezoelectric and ferroelectric. The required polycrystalline powders of KNN were synthesized through solid-state reaction route, while LKBO glass was obtained via the conventional melt-quenching technique. Pulverized glass was added to KNN powders in different wt% and compacted at room temperature and these were sintered around 1100°C. Indeed the addition of optimum amount (1 wt %) of LKBO glass to KNN ceramics facilitated lowering of sintering temperature accompanied by larger grains (8 µm) with improved density. The dielectric constant (εr) measured at room temperature was 475 (at 10 kHz), whereas it was only 199 for the LKBO glass free KNN. The piezoelectric coefficient (d33) was found to be 130 pC/N for 1wt% LKBO added glass, which was much higher than that of pure KNN ceramics (85 pC/N). Indeed, the LKBO glass added samples did exhibit well saturated P versus E hysteresis loops at room temperature. Though there was no particular trend observed in the variation of Pr with the increase in glass content, the Pr values were higher than those obtained for KNN ceramics. The improved physical properties of KNN ceramics encountered in these studies were primarily attributed to enhancement in density and grain size. Chapter 7 presents a comparative study on the structural, dielectric and piezoelectric properties of nano and micron sized K0.5Na0.5NbO3 fillers in PVDF composites. Polymer nanocrystal composites were fabricated by embedding polyvinylidene fluoride (PVDF) with different vol% of K0.5Na0.5NbO3 (KNN) nanocrystallites using hot-pressing technique. For comparison, PVDF-KNN microcrystal composites of the same compositions were also fabricated which facilitated the crystallite size (wide range) effect studies on the dielectric and piezoelectric properties. The structural, morphological, dielectric, and piezoelectric properties of these nano and micro crystal composites were investigated. The incorporation of KNN fillers in PVDF at both nano and micrometer scale above 10vol% resulted in the formation of polar β-form of PVDF. The room temperature dielectric constant as high as 3273 at 100Hz was obtained for PVDF comprising 40 vol% KNN nanocrystallites due to dipole –dipole interactions (as the presence of β-PVDF is prominent), whereas it was only 236 for PVDF containing the same amount (40 vol%) of micron sized crystallites of KNN at the same frequency. Various theoretical models were employed to predict the dielectric constants of the PVDF-KNN nano and microcrystal composites. PVDF comprising 70 vol% micronmeter sized crystallites of KNN exhibited d33 value of 35pC/N, while the nanocrystal composites of PVDF-KNN did not exhibit any piezoelectric response perhaps due to unrelieved internal stress within each grain besides having less number of domain walls. The Thesis ends with summary and conclusions, though each chapter is provided with conclusions and a complete list of references.

Modeling nonlinear behaviour of polycrystalline piezoceramics accurately can result in an improvement in the wide range of their application, either as actuator or sensor. Two of the main nonlinear behaviours in piezoceramics are hysteresis and creep. These nonlinear and complex macroscopic behaviours of piezoceramics under an electro-mechanical loading are results of domain wall motion in the microscopic level. We developed a micromechanical model to simulate creep and hysteresis behaviour in a piezoceramic. We considered a polycrystal piezoceramic with a random structural configuration of crystals in an isothermal process. An appropriate finite element method (FEM) was used to solve mechanical and electrical governing equations. Each element in FEM represents a crystal in actual polycrystal piezoceramics. volume fractions are needed to evaluate spontaneous polarization and strain caused directly by switching of tetragonal crystal. We improved the constitutive law introduced by Huber et al. [1] in order to consider the effect of exhausted domains in switching process. We used our model to simulate the electromechanical response of a piezoelectric stack under different loading conditions. Our results show a good qualitative agreement with the published experimental results. This model can predict creep as well as hysteresis.