Advances in Applied Ceramics: Structural,Functional and Bioceramics

For Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ (PMN-PT) single crystals, the measured pyroelectric coefficient (at constant stress) is determined by the piezoelectric effect due to thermal strain (secondary pyroelectric effect). This provides new capabilities to characterise the PMN-PT crystal poling procedure using the thermal square wave method at constant frequency. In this work, the authors demonstrate for the first time the determination of the depth profile of the piezoelectric response of PMN-PT single crystals with a composition near the morphotropic phase boundary by means of thermal waves. A commercial PMNT-28 sample, poled along [001] direction, electroded with NiCr/Au and covered additionally with a black absorption layer was investigated.

Piezoelectric effect is a versatile method to generate force and movement in microsystems as well as electrical feedback in sensors and smart packages. On the other hand, low temperature cofired ceramic (LTCC) has been utilised as a base material for hybrid circuit boards, packages as well as some microfluidic devices; however, new means to introduce integrated functionalities for it are needed. In this paper, a 10×5 mm rectangle and 10 mm in diameter round PZT samples fully embedded and cofired with Heraeus HeraLock LTCC were manufactured and their hysteresis, dielectric, displacement and microstructure properties and coupling factors were characterised. Relative permittivity of the LTCC embedded varied from 1300 for the rectangle sample to 1500 for the round sample at 1 kHz, while_r of 2209-2406 was obtained for corresponding bare bulk samples respectively. Measured piezoelectric d₃₃ coefficient was in the range of 324-441 pm V⁻¹ for embedded structures, while 553-567 pm V⁻¹ was obtained for free bulk samples at 100 Hz. Results show that LTCC has significant impact for electromechanical performance mainly due to constraining of the LTCC layers. In spite of this, feasible figures of merits were obtained for LTCC embedded PZT materials, while further improvements can be obtained by optimising the process and structures for LTCC based microsystems, sensors and actuators.

The Curie point T_c of ferroelectrics sets the upper temperature limit for their application as piezoelectrics. Some Aurivillius phase and perovskite-like layer structured (PLS) materials are good candidates for high temperature piezoelectric applications because of their high T_c. The Aurivillius phase CaBi₂Nb₂O₉ and PLS Sr₂Nb₂O₇ were densified by ordinary sintering and/or spark plasma sintering (SPS). All of the materials were single phase, and their grains were plate-like. Their density was >95%. The spark plasma sintered ceramics had grain oriented, textured microstructures. The Curie point of CaBi₂Nb₂O₉ was measured as 943±5°C. Ferroelectric switching in CaBi₂Nb₂O₉ was observed at room temperature. The d₃₃ of the textured CaBi₂Nb₂O₉ materials was nearly three times that of ordinary sintered materials. The Curie point of Sr₂Nb₂O₇ was measured as 1327±5°C. Ferroelectric and piezoelectric (2·8 pC N⁻¹) properties were observed for spark plasma sintered textured Sr₂Nb₂O₇ ceramics.

Piezoelectric materials are used in many applications, at increasingly smaller scales. Methods of measuring their hydrostatic properties have been developed where the piezoelectric charge is produced as a result of a varying hydrostatic pressure generated within a sealed chamber. In this paper, the authors explore an anomalous generation of charge in thin laminar samples and show this is a result of the pyroelectric effect. The authors model the change in temperature in the sealed chamber caused by the adiabatic expansion of the gas and relate this to the observed generation of charge, using finite element modelling to investigate the temperature profile through the material. The implications of these results are relevant for the successful integration of piezoelectric thin and thick films into MEMS devices.

Thermal decompositions of the precursors for chemical solution deposition of 0·7 Pb(Mg_1/3Nb_2/3)O₃-0·3 PbTiO₃ (0·7PMN-0·3PT) thin films were studied. The precursors were prepared from lead acetate or acetylacetone modified lead acetate by diol based route and dried at 100°C. Thermal decompositions of the PT, PMN and PMN-PT precursors in air occur stepwise. Between room temperature and ∼200°C, the weight loss of a few per cent is due to the evaporation of residual solvents. Organic groups decompose in the ranges 200-400°C and 400-650°C. The thermal decompositions are affected by the choice of the Pb compound and chemical composition of the sample.

Parasitic harvesting of energy from environment is being investigated as a possible solution for powering electronic devices. One possible solution is to harvest energy generated from human walking, by placing a piezoelectric elements inside footwear. As the amount of available energy is extremely low, conversion effectiveness is of prime importance. This paper deals with a micropower source, designed to harvest energy from walking, built in a form of a shoe insole containing a piezoelectric material (43 μm thick polyethylene foil). Laboratory investigation of the piezoelectric properties is presented first, followed by a measurement result of an actual generator with 0·6 μW output power. Finally, a modification of the generator, by adding springy elements, is presented, resulting in ninefold increase in power output (to 5·6 μW).

Most of those techniques used for the measurement of elastic coefficients for bulk piezoelectric ceramics are not applicable to films deposited on thick substrates because the measured properties, such as the resonant frequency, are usually dominated by the presence of the thick substrate. This work presents a preliminary study for the application of the automatic iterative method of Alemany et al. for the determination, from complex impedance measurements, of the film properties using a conventional self-supported cantilever design used in microelectromechanical system applications and fabricated from a PZT thick film on a Si based substrate.

0-3 and 1-3 composites were fabricated using piezoelectric single crystals (PSCs). These two connectivities were specifically chosen for large area fabrication. In particular, a lamination technique was used for 1-3 piezocomposites instead of the standard ‘dice and fill’ method. For 0-3 connectivity, the thickness coupling factor of the fabricated materials using PSC phase was twice that obtained using standard PZT powder for the same volume fraction (60%). However, the efficiency of the poling remained low. For the 1-3 piezocomposites, the properties (such as the thickness coupling factor which reached 74%) of the samples fabricated by the lamination technique were comparable to those obtained with standard methods. Finally, three ultrasonic transducers with centre frequencies between 600 and 850 kHz were fabricated to evaluate the performance of these new piezoelectric composites.

We present a computer simulation and theoretical study of composite multiferroics acting as magnetic field detectors. Our set-up consists of a layer of piezoelectric sandwiched between two magnetostrictive layers. When magnetic field is applied the magnetostrictive strains and this is passed onto the piezoelectric producing a detectable voltage. We model the device using our own finite element code and calculate open circuit voltage and input impedance. Good agreement is shown with analytical formulas. We then optimise the coupling by altering the ratio of piezoelectric to magnetostrictive volume and the shape of the inner piezoelectric layer: the former effect is more important. We show that nearly equal amounts of piezoelectric and magnetostrictive give best coupling but the exact optimal ratio depends on the relative stiffnesses of the two materials. Most calculations carried out in previous literature have assumed that the magnetic field found in the device is simply the applied field. Here we show to what extent such an applied field can enter the device by simulating also the air region around the detector. The field in the device is calculated to be ∼17% less than the applied field.

A piezoelectric actuated two-bar two-flexure motion amplification mechanism for flapping wing micro-aerial vehicle application has been investigated. f_r*A as an optimisation criterion has been introduced where f_r is its fundamental resonant frequency of the system and A the vibration amplitude at the wing tip, or the free tip deflection at quasi-static operation. This criterion can be used to obtain the best piezoelectric actuation mechanism with the best energy transmission coefficient for flapping wing micro-aerial vehicle applications, and is a measurable quantity therefore can be compared with experimental results. A simplified beam model has been developed to calculate the fundamental resonant frequency for the full system consisted of piezoelectric actuator, motion amplification mechanism and the attached wing and the calculated values were compared with the measured results. A clear trend of the criteria f_r*A varying with the two-flexure dimension, stiffness and setting angle have been obtained from the measured data and also the predicted results as a guideline for optimal design of the system.

The active elasticity control of a piezoelectric actuators connected to the negative capacitance (NC) circuits represents an efficient tool for the suppression of vibrations in mechanical structures. In this paper, the authors study theoretically and experimentally the vibration transmission through a piezoelectric bimorph connected to the NC circuit. The clamped end of the bimorph is attached to the electrodynamic shaker. The vibration amplitude of its free end, which is loaded by a discrete mass, is measured by a photonic sensor. The authors present the theoretical calculation of the transmissibility of vibrations through the piezoelectric bimorph, which is controlled by its effective flexural rigidity. The authors demonstrate experimentally a simple way of suppressing the vibrations transmitted through the piezoelectric bimorph, which is achieved by the proper active control of its flexural rigidity using the connected NC circuit.

In this study, a characterisation method for graded porosity piezoceramic discs is presented. A sample with graded porosity from about 5 to about 40% along the thickness has been produced. Two homogeneous samples with respectively low and high porosity are used as references. Density measurements have been performed in order to estimate the average porosity of samples. Using an equivalent circuit model including the mechanical and dielectric losses and a fitting technique, the electroacoustic properties of the constant porosity samples have been extracted. Then, based on a model of multilayer piezoceramics, the graded porosity sample properties are simulated assuming it is made of 10 layers stacked along the sample thickness.