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This Special Issue of IEEE Transactions on Dielectrics and Electrical Insulations collects a total of 23 invited and contributed articles from eminent scientists and engineers in the field of electrets and related phenomena. These articles have been substantially extended from their contributions presented at the 17th International Symposium on Electrets (ISE) held at the Bernal Institute of the University of Limerick, Ireland between 2–6 September 2019. The conference was sponsored by IEEE Dielectrics and Electrical Insulation Society and supported by European Materials Characterisation Council (EMCC). Analog Devices International provided financial sponsorship.

Hydroxyapatite (HA) is a major component of bone in humans and animals. Until about 10 years ago, it was considered to have a centrosymmetric crystal structure and could not contribute to the well-known piezoelectric effect in bone. This review describes the theoretical and experimental studies that showed that HA does have a non-centrosymmetric structure. Recent experiments have shown that HA exhibits piezoelectricity, pyroelectricity, and ferroelectricity. It has been made in the form of thick films and as space-charge electrets. It has an important biomedical application as an implant for bone cell attachment and growth.

The introduction of porosity into ferroelectric ceramics has been of great interest in recent years. In particular, studies of porous lead-zirconate-titanate ceramic (PZT) have been made. In the research reported, samples of Ferroperm Pz27 with porosities of 20, 25 and 30% were studied. Very complete measurements were made of all of the physical properties relevant for ferroelectric applications including thermal conductivity and diffusivity, heat capacity, dielectric, pyroelectric, piezoelectric and elastic properties. Scanning electron micrographs indicated a change from 3-0 to 3-3 connectivity with increasing porosity. Although most of the physical properties are degraded by the presence of porosity, both piezoelectric and pyroelectric flgures-of-merit are improved because of the markedly reduced relative permittivity. Porous ferroelectric ceramics are very promising materials for a number of applications.

Nano-sized BaSrTiO3 particles and a dispersant were incorporated in samples of low density polyethylene (LDPE). The nanoparticle loading was 2% or 10% by weight, and the dispersant loading was 4 parts per hundred relative to BaSrTiO3. dc conductivity measurements were made in the temperature range 30-70°C in vacuum, and in air at 30 °C. The vacuum dc conductivity in LDPE with 0.4% dispersant was approximately five times larger than in LDPE, but in LDPE containing 0.4% dispersant and 10% nanoparticles it was approximately a factor of 6-7 smaller than in LDPE. Since the conductivity of the latter composite was smaller than that of its least conductive component, it may be that the interface regions between the nanoparticles and the LDPE control the dc conductivity. The dispersant and the nanoparticles both increased e', the real part of the relative permittivity. The e' values for the nanoparticles, implied by the Lichtenecker-Rother equation for a three-part composite, were of order several hundred, much smaller than the value of at least 10,000 quoted by the nanoparticle suppliers. Space charge measurements were made in air using the Laser Intensity Modulation Method (LIMM), and the profiles calculated using the LIMM Monte Carlo method. The maximum space charge density adjacent to the negative poling electrode was 600 C/m3, for the pure LDPE and the LDPE with dispersant, and 200 C/m3 near the positive electrode. The corresponding maxima in samples with dispersant and nanoparticles were approximately an order of magnitude smaller. The Monte Carlo method is more accurate than other methods of analyzing LIMM data, and this may account for the very large densities close to the electrodes.

The Laser Intensity Modulation Method (LIMM) is widely used for the determination of the spatial distribution of polarization in polar ceramics and polymers, and space charge in non-polar polymers. The analysis of experimental data requires a solution of a Fredholm integral equation of the 1st kind. This is an ill-posed problem that has multiple and very different solutions. A number of methods have been used to solve this problem. In this paper, a comparison is made among three different techniques: the Scale Transformation Method, the Polynomial Regularization L-Curve Method and the Monte Carlo Method. The accuracy and ease of use of the three techniques are compared using both simulated and experimental data.

A new, non-destructive technique for the analysis of electret materials is presented. Thermal-pulse tomography produces three-dimensional images of space-charge and polarization distributions with a lateral resolution of better than 50 μm and a depth resolution of less than 0.5 μm. A focused-pulsed laser heats a circular spot on the opaque upper electrode. While diffusing through the sample, the thermal pulse causes local changes in the sample geometry or dielectric properties, resulting in a short-circuit current in the presence of space charge or electric dipoles. From the transient current, the distribution of the internal electric field can be reconstructed by means of scale transformation or regularization methods.

Sol–gel techniques were used to prepare thin films of Pb(Zr x ,Ti1−x )O3 (PZT) with three different Zr/Ti ratios and a graded PZT film with three different compositional layers. A Michelson interferometer was used to measure the thickness strains due to an applied ac electric field. Effective d 33 piezoelectric strain coefficients were computed from the experimental data. Interfacial pinning caused these coefficients to differ from the true ones. They were corrected for the pinning using both an analytical model and finite-element analysis. The corrected coefficients of the PZT (52/48) sample were in excellent agreement with values of bulk materials. The coefficients of the multilayer sample were very low, probably due to insufficient poling or domain switching.

The 39 papers in Part I of this special issue focus on the applications of ferroelectrics. The issue seeks to address the current state of the field by providing an overview of the fundamental materials science required to advance the discipline, as well as detailed papers on the applications of ferroelectric materials.

DC conductivity and ac impedance measurements were made in air and in vacuum on samples of low density polyethylene to which nano-sized and micro-sized ZnO particles and a dispersant had been added. The samples were 150-200 mum thick. The temperature range was 30-70degC. The temperature dependence of the vacuum dc conductivity in samples containing the dispersant and 10% w/w nanosized ZnO followed an Arrhenius relationship closely, the conductivity being 1-2 orders of magnitude lower than that of a sample containing dispersant only. The addition of 10% w/w microsized ZnO had very little effect on the dc conductivity. The ac measurements were made in the frequency range 10 mHz-1 MHz. Addition of nanoparticles increased the ac conductivity at higher frequencies but decreased it at lower frequencies, the cross-over frequency increasing with increasing temperature. The real part of the relative permittivity of samples with nanoparticles was increased relative to that of samples containing dispersant only, at all temperatures, but the corresponding values in samples with microparticles were unchanged, within experimental error. Space charge profiles were obtained using the laser-intensity-modulation-method (LIMM). Space charge densities of order 300 Cm-3 were measured in the bulk near the electrodes, several hours after poling at field strengths around 30 kV/mm.

A bibliography is given containing 1683 references published during 2005 on piezoelectric and pyroelectric properties of materials and their applications. It contains listings of journal articles, patents and dissertations with complete bibliographic citations. References in which the first author's name begins with letters between N and Z are given in the current guide. Journal articles and patents by authors with names beginning with the letters A through M were published in Guide 27. This bibliography is the continuation of a series published semi-annually.

The Laser Intensity Modulation Method (LIMM) is a technique for the determination of polarization and/or space charge profiles in the thickness direction of ceramic and polymeric samples. The experimental data are analyzed by means of a Fredholm integral equation of the first kind. This equation admits to multiple and very different solutions. A number of techniques have been developed in order to obtain the most physically reasonable profile. Several techniques based on the regularization method have been proposed. A recent version, polynomial regularization, was developed by Lang. A completely different approach is the Monte Carlo method of Tuncer and Lang. Several sets of both simulated and experimental data are analyzed by the two methods in this paper. Conclusions concerning speed and accuracy are presented.

Electric field/space charge profiles obtained using the laser-intensity-modulation-method (LIMM) are presented for XLPE samples machined from power cable insulation cross-linked using dicumyl peroxide. The samples, 110 mum thick with vacuum-evaporated aluminium electrodes, were subjected to DC fields of 48 kV/mm and both polarities at room temperature for at least 24 hr. The LIMM measurements were made at room temperature, and at various times after the end of poling. Electric field and space charge profiles obtained using the scale-transformation and polynomial regularization methods were in fair quantitative agreement over much of the sample thickness, except when the electric field showed a maximum or minimum. Simulation data for assumed electric field profiles strongly suggested that the polynomial regularization method is more accurate. Most of the space charge was concentrated near the electrodes, with densities of order 5-10 Cm-3 in those regions. Charge of the same sign tended to accumulate adjacent to a given physical electrode, for both poling polarities

The piezoelectric effect was first observed in polyvinylidene fluoride polymer (PVDF) in 1969, and the pyroelectric effect was found several years later. A number of additional ferroelectric polymers have been discovered since that time including the copolymer PVDF with trifluoroethylene (P(VDF-TrFE)), and the odd-numbered nylons. A large number of applications of piezoelectricity and pyroelectricity have been developed. The magnitudes of the effects in polymers are much lower than those of ferroelectric ceramics (an exception is the piezoelectric effect in porous polymers). However, other factors make these very desirable materials for applications. The polymers have low permittivities, low acoustic impedances and low thermal conductivities. They are available in large area sheets, flexible, and relatively low in cost. Major applications include microphones and loudspeakers, ultrasonic devices, SAW transducers, actuators, single-element infrared detectors and many others. This review will describe some of the lesser-known applications of these materials in the areas of tactile devices, energy conversion, porous polymers, property measurement, pyroelectric infrared sensors, shock sensors and space science.

A worldwide effort is underway to remove lead from many commercial products. Most ferroelectric ceramics contain lead, principally those based on lead-zirconate-titanate solid solutions. Recently a new non-lead containing composition series has been developed by Saito et al. These are alkaline niobate based materials with the composition (K0.5Na0.5)1 − x (Nb1 − y Ta y )O3. The d33 piezoelectric coefficient of these materials is comparable to that of PZT4. Measurements of many of the properties of these new materials are reported here for the first time. These include piezoelectric coefficients, permittivity and loss tangent, and coercive field and remanent polarization. Special emphasis is placed on the pyroelectric studies.

A bibliography is given containing 1887 references published during 2004 on piezoelectric and pyroelectric properties of materials and their applications. It contains listings of journal articles and patents with complete bibliographic citations. Journal and patent references from 2004 in which the first author's name began with letters between A and K were given in Guide 25 (published previously). Journal articles and patents by authors with names beginning with the letters L through Z are published in the present Guide. This bibliography is the continuation of a series published semi-annually.

The Laser Intensity Modulation Method (LIMM) is widely used for the determination of the spatial distribution of polarization in polar ceramics and polymers, and space charge in non-polar polymers. The analysis of experimental data requires a solution of a Fredholm integral equation of the 1st kind. This is an ill-posed problem that has multiple and very different solutions. One of the more frequently used methods of solution is based upon Tikhonov regularization. A new method, the Polynomial Regularization Method (PRM), was developed for solving the LIMM equation with an 8th degree polynomial using smoothing to achieve a stable and optimal solution. An algorithm based upon the L-curve method (LCM) was used for the prediction of the best regularization parameter. LIMM data were simulated for an arbitrary polarization distribution and were analyzed using PRM and LCM. The calculated distribution function was in good agreement with the simulated polarization distribution. Experimental polarization distributions in a poorly poled sample of polyvinylidene fluoride (PVDF) and in a LiNbO3 bimorph, and space charge in polyethylene were analyzed. The new techniques were applied to the analysis of 3-dimensional polarization distributions.

A bibliography is given containing 2067 references published during 2002 and 2003 on piezoelectric and pyroelectric properties of materials and their applications. It contains listings of journal articles with complete bibliographic citations. This bibliography is the continuation of a series published semi-annually.

A package of programs written using the symbolic mathematics program, Mathematica®, has been developed. Its principal usage is in teaching the LIMM method to students and demonstrating data analysis by means of the Polynomial Regularization Method (PRM). A large number of variables can be changed in the program and their effects can be shown graphically. Students at the University of Potsdam and Monash University have used the program successfully. **On sabbatical leave from Department of Chemical Engineering, Ben-Gurion University of the Negev, Beer Sheva, Israel. E-mail: lang@bgumail.bgu.ac.il

A new form of biomineralization in the pineal gland of the human brain has been studied. It consists of small crystals that are less than 20 /spl mu/m in length and that are completely distinct from the often-observed mulberry-type hydroxyapatite concretions. Cubic, hexagonal and cylindrical morphologies have been identified using scanning electron microscopy. Energy dispersive spectroscopy, selected-area electron diffraction and near infrared Raman spectroscopy established that the crystals were calcite. Experiments at the European Synchrotron Radiation Facility (ESRF) to study the biomineralization showed the presence of sulfur originating from both heteropolysaccharides and amino acids. Other studies at the ESRF furnished information on the complex texture crystallization of the calcite. With the exception of the otoconia structure of the inner ear, this is the only known non-pathological occurrence of calcite in the human body. The calcite microcrystals are believed to be responsible for the previously observed second harmonic generation in pineal tissue sections. There is a strong possibility that the complex twinned structure of the crystals may lower their symmetry and permit the existence of a piezoelectric effect.

A bibliography is given containing 2399 references published during 2001 and 2002 on piezoelectric and pyroelectric properties of materials and their applications. It includes journal articles, patents and doctoral dissertations with complete bibliographic citations. This bibliography is the continuation of a series published semi-annually.

Physical properties of a bimorph and two trimorph multilayer BaTiO3 ceramic compositions with a gradient in Sn content were studied. The measurements made included polarization and strain hysteresis, dielectric permittivity, thermal diffusivity and polarization distributions by means of the Laser Intensity Modulation Method (LIMM).

A technique for the measurement of the thermal diffusivity of thin samples of solid materials is presented. It is based on the measurement of the phase retardation of a thermal wave passing through the test material. The test material, which can be either ferroelectric or non-ferroelectric, is attached by means of a high thermal conductivity cement to a LiTaO 3 pyroelectric detector. A sinusoidally-modulated laser beam impinges on the upper surface of the sample and is absorbed as heat. The heat diffuses in the form of thermal waves through the test sample to the LiTaO 3 detector, generating a pyroelectric current. The phase lag between the pyroelectric current and the laser beam intensity is a unique function of the sample thickness and its thermal diffusivity. It is not necessary to know either the pyroelectric coefficient of the detector or the intensity of the laser beam. Thermal diffusivity measurements on LiTaO 3 , glass and a porous PZT 3-3 composite are presented.

A bibliography is given containing 2039 references published during 1999 and 2000 on piezoelectric and pyroelectric properties of materials and their applications. It includes journal articles, patents and doctoral dissertations with complete bibliographic citations. This bibliography is the continuation of a series published semi-annually.

A new form of biomineralization has been studied in the pineal gland of the human brain. It consists of small crystals that are less than 20 microm in length and that are completely distinct from the often observed mulberry-type hydroxyapatite concretions. A special procedure was developed for isolation of the crystals from the organic matter in the pineal gland. Cubic, hexagonal, and cylindrical morphologies have been identified using scanning electron microscopy. The crystal edges were sharp whereas their surfaces were very rough. Energy dispersive spectroscopy showed that the crystals contained only the elements calcium, carbon, and oxygen. Selected area electron diffraction and near infrared Raman spectroscopy established that the crystals were calcite. With the exception of the otoconia structure of the inner ear, this is the only known nonpathological occurrence of calcite in the human body. The calcite microcrystals are probably responsible for the previously observed second harmonic generation in pineal tissue sections. The complex texture structure of the microcrystals may lead to crystallographic symmetry breaking and possible piezoelectricity, as is the case with otoconia. It is believed that the presence of two different crystalline compounds in the pineal gland is biologically significant, suggesting two entirely different mechanisms of formation and biological functions. Studies directed toward the elucidation of the formation and functions, and possible nonthermal interaction with external electromagnetic fields are currently in progress.

A new form of biomineralization has been found in the pineal gland of the human brain. The crystals are 10 to 20 w m in length and have well-defined morphologies. Several structure types have been identified using scanning electron microscopy (SEM). Energy dispersive spectroscopy (EDS) showed that the crystals contain only the elements calcium, carbon and oxygen. Selected-area electron diffraction (SAED) and near infrared Raman spectroscopy established that the crystals are calcite. With the exception of the otoconia structure of the inner ear, this is the first report of the presence of non-pathological calcite in the human body. These microcrystals are believed to be responsible for the previously observed second harmonic generation (SHG) in pineal tissue samples and they may also exhibit piezoelectricity, suggesting a unique electromechanical biological transducer mechanism in the human brain.

Direct current electrical poling of textured hydroxyapatite (HAp) ceramics is reported here to exhibit weak ferroelectricity and pyroelectricity, but a remarkably higher (six orders of magnitude) piezoelectricity. The piezoelectric strain coefficient is an order higher than that of bone and of the same order as that of quartz crystal and uncalcified collagen in tendon. The piezoelectric charge coefficient is an order higher than bone, and three orders higher than that of tendon. Piezoelectric constants of poled HAp ceramics are high enough to have physiological relevance such as in the use of bone grafts for stimulated calcification or in energy harvesting from physiological motions. Piezoelectricity in these ceramics can be tuned by controlling texture, and poling parameters. The density of power that can be harvested from HAp ceramics is currently just one order lower than biocompatible ferroelectric ceramic such as barium titanate.

Transparent glass nanocomposites in the pseudo binary system (100 - x) SrB4O7 (SBO)-x Bi2VO5.5 (BiV) (0 less than or equal to n less than or equal to 70) were prepared by the splat quenching technique. The nano-crystallization of bismuth vanadate (BiV) in 50 SBO-50 BiV (in mol%) glass composite has been demonstrated. These were characterized for their structural, thermal and dielectric properties. As-quenched composites under study have been confirmed to be amorphous by X-ray powder diffraction (XRD) studies. The glass transition temperature (T-g) and crystallization temperatures (T-er) were determined using differential thermal analyses (DTA), High resolution transmission electron microscopic (HRTEM) studies carried out on heat-treated samples reveal the presence of spherical nanosize crystallites of Bi2VO5.5 (BiV) dispersed in the glassy matrix of SrB4O7 (SSO). The dielectric constant (epsilon (r)) and the dielectric loss (D) measurements were carried out on the as-quenched and heat-treated glass nanocomposite samples in the frequency range 100 Hz-10 MHz. The as-quenched and the heat-treated at two different temperatures (720 and 820 K) samples exhibited broad dielectric anomalies in the vicinity of the ferroelectric-to-paraelectric transition temperature of the parent BiV ceramics. The Curie-Weiss law was found to be valid at a temperature above the transition temperature, establishing the diffused nature of the transition. (C) 2001 Elsevier Science Ltd. All rights reserved.

A bibliography of 1433 references on piezoelectric and pyroelectric properties of materials and their applications published during 1998 is given. It includes journal articles, published conference proceedings, books, chapters in books, patents, doctoral theses and reports. Complete bibliographic citations and additional information such as language and conference presentation data are given. Previously published bibliographies in this series are available on the Gordon and Breach Publishing Group Internet Website as the “Piezoelectricity and Pyroelectricity Database.” The URL for the site is: http://www.gbhap-us.com/c3/lit_guide/.

The Laser Intensity Modulation Method (LIMM) has recently been extended to the study of thin-film ferroelectrics on a substrate. The analysis of the experimental data requires the numerical solution of a Fredholm integral equation of the 1st kind, an ill-posed problem having multiple solutions. The techniques that have been applied previously for thick film analyses are not useable in this case because of the interference of the top electrode. The “principle of parsimony” which limits the amount of detail obtainable and the assumption of 1-dimensional diffusion of heat are discussed. Two new solution techniques, based on neural networks and power series, are presented.

A thermal analysis is a critical part of the design of thin-film pyroelectric infrared detectors. Because of the high thermal conductivity of the silicon substrate, it is necessary to isolate the pyroelectric layer thermally. The isolation is accomplished by either use of a low thermal conductivity insulating layer or a bridge structure. If the heat conduction in the detector is only in the direction normal to the detector surface, the thermal problem can be solved analytically using matrix formalism. A number of studies of this type have been presented in the literature. However, a one-dimensional analysis overestimates the responsivity of the detector because a part of the energy of the impinging radiation diffuses in the lateral direction. An analytical solution of the two-dimensional heat transfer problem is not possible, but solutions can be obtained by finite element methods. Analyses are presented in this paper for both ceramic and polymeric detectors and for both insulating layer and brid...

A bibliography of 1212 references on piezoelectric and pyroelectric properties of materials and their applications published during 1997 is given. It includes journal articles, published conference proceedings, books, chapters in books, patents, doctoral theses and reports. Complete bibliographic citations and additional information such as language and conference presentation data are given. Previously published bibliographies in this series are available on the Gordon and Breach Publishing Group Internet Website as the “Piezoelectricity and Pyroelectricity Database”. The URL for the site is: http://www.gbhap-us.com/c3/lit_guide/.

Determination of the polarization distribution in ferroelectrics using LIMM requires the solution of a Fredholm integral equation of the 1st kind. The constrained regularization method which has been used successfully to solve this problem for single-layer ferroelectrics fails when applied to thin films on a multi-layer substrate. A new approach based on neural networks has been developed to alleviate these problems. In this method, a functional form containing a small number of undetermined parameters is selected to represent the unknown polarization. The LIMM equation is used to synthesize a very large number of data sets (current vs frequency), each one corresponding to a polarization distribution with a different set of parameters. These data are used to “train” the neural network. Then the neural network is used to predict parameters for data sets on which it was not “trained.”

Many thousands of papers have been published on the piezoelectric, pyroelectric and ferroelectric properties of single crystals, ceramics, polymers and liquid crystals. Yet fewer than 100 papers have appeared on these properties in biological materials. Piezoelectric and pyroelectric effects have been measured on a number of plant and animal tissues and the possible existence of ferroelectricity has been suggested also. This paper reviews some measurements and speculates on their significance. Specific examples include piezoelectricity in a crystalline material in the pineal gland of the brain, pyroelectricity in the heat sensing organs of certain varieties of snakes and beetles, and ferroelectricity in the conduction of action potentials in nerve and muscle cells.

Pyroelectricity was probably first observed by the Greeks more than 23 centuries ago. The philosopher Theophrastus wrote that lyngourion, probably the mineral tourmaline, had the property of attracting straws and bits of wood. For 2000 years, the peculiar properties of tourmaline were more a part of mythology than of science. In the 18th Century, pyroelectric studies made a major contribution to the development of our understanding of electrostatics. In the 19th Century, research on pyroelectricity added to our knowledge of mineralogy, thermodynamics and crystal physics. Pyroelectricity gave birth to piezoelectricity in 1880 and to ferroelectricity in 1920. The field of pyroelectricity flourished in the 20th Century with many applications, particularly in infrared detection and thermal imaging. Pyroelectric sensors have been carried on many space missions and have contributed significantly to our knowledge of astronomy.

A bibliography of 1807 references on piezoelectric and pyroelectric properties of materials and their applications published during 1996 and 1997 is given. It includes journal articles, published conference proceedings, books, chapters in books, patents, doctoral theses and reports. Complete bibliographic citations and additional information such as language and conference presentation data are given. Previously published bibliographies in this series are available on the Gordon and Breach Publishing Group Internet Website as the “Piezoelectricity and Pyroelectricity Database.” The URL for the site is: http://www.gbhap-us.com/c3/lit_guide/.

The SLIMM (surface laser intensity modulation method) is used for the determination of polarization distributions near the surfaces of ferroelectric samples. The experimental data measured are pyroelectric currents as functions of frequency. The data analysis requires the solution of a Fredholm integral equation of the 1st kind. This is an ill-posed problem which has multiple and very different solutions. The constrained regularization method can be used to solve this problem. However, the choice of the proper regularization parameter is normally somewhat arbitrary and this can affect the solution drastically. In the technique used here, an optimal regularization parameter is found using a set of simulated data. These data are based on a polarization distribution constructed from a simple frequency-to-space transformation. It is shown that the conventional minimization of the deviations between experimental data and the predicted values according to the principles of least-squares gives meaningless results in an ill-posed problem of this type. Experimental data on lanthanum-doped lead-zirconate-titanate ceramics and LiNbO/sub 3/ are analyzed.

Triglycine sulfate-gelatin (TGS-gelatin) films were grown by evaporation of the water from a solution containing gelatin and TGS. The pyroelectric and dielectric properties of the films were highly dependent on their water content. Moist films had higher pyroelectric coefficients and lower coercive fields than dry films. The dielectric permittivity increased strongly with an increase of water content and had a fractional power frequency dependence. The results are explained using a model of the TGS-gelatin film structure in which the gelatin phase is a superionic conductor or solid electrolyte. Absorption of water causes the formation of electric double layers at the electrode film and TGS crystallite-gelatin phase interfaces.

A bibliography of 899 references on piezoelectric and pyroelectric properties of materials and their applications published during the period 1992-1994 is given. It includes journal articles, published conference proceedings, books, chapters in books, patents, doctoral theses and reports. Complete bibliographic citations and keywords are presented in a References section. The papers are classified according to materials studied and research objectives in an Index section.

Hydroxyapatite nanocrystals in natural form are a major component of bone- a known piezoelectric material. Synthetic hydroxyapatite is widely used in bone grafts and prosthetic pyroelectric coatings as it binds strongly with natural bone. Nanocrystalline synthetic hydroxyapatite films have recently been found to exhibit strong piezoelectricity and pyroelectricity. While a spontaneous polarization in hydroxyapatite has been predicted since 2005, the reversibility of this polarization (i.e. ferroelectricity) requires experimental evidence. Here we use piezoresponse force microscopy to demonstrate that nanocrystalline hydroxyapatite indeed exhibits ferroelectricity: a reversal of polarization under an electrical field. This finding will strengthen investigations on the role of electrical polarization in biomineralization and bone- density related diseases. As hydroxyapatite is one of the most common biocompatible materials, our findings will also stimulate systematic exploration of lead and rare-metal free ferroelectric devices for potential applications in areas as diverse as in vivo and ex vivo energy harvesting, biosensing and electronics.

Melatonin secretion by the pineal gland has been reported to be affected by exposure to electromagnetic fields (EMFs). In an initial investigation to determine if calcifications commonly found in the pineal gland could respond to EMFs by a transducer mechanism, studies were conducted to ascertain if pineal tissues were piezoelectric. Second harmonic generation (SHG) measurements showed that pineal tissues contained noncentrosymmetric crystals, thus proving the presence of piezoelectricity. Both mulberry-like and faceted crystalline calcifications were observed by scanning electron microscopy (SEM). Some of the calcifications had compositions similar to that of hydroxyapatite; others contained a high concentration of aluminum.

A bibliography of 1142 references on piezoelectric and pyroelectric properties of materials and their applications published during the period 1992–1995 is given. It includes journal articles, published conference proceedings, books, chapters in books, patents, doctoral theses and reports. Complete bibliographic citations and keywords are presented in a References section. The papers are classified according to materials studied and research objectives in an index section.

A bibliography of 1069 references on piezoelectric and pyroelectric properties of materials and their applications published during the period 1991–1994 is given. It includes journal articles, published conference proceedings, books, chapters in books, patents, doctoral theses and reports. Complete bibliographic citations and keywords are presented in a References section. The papers are classified according to materials studied and research objectives in an Index section.

The surface laser intensity modulation method (SLIMM) is used for the determination of the spatial distribution of the polarization normal to and near the surface of a ferroelectric sample. The experimental data measured are pyroelectric currents as functions of frequency. The data analysis requires the solution of a Fredholm integral equation of the first kind. This is an ill-posed problem which has multiple and very different solutions. The experimental method and a technique for data analysis are described. Experimental data on a weakly-poled polyvinylidene fluoride (PVDF) film are presented and the polarization distribution is calculated.

Optical waveguides are often fabricated from ferroelectrics such as LiNbO3, LiTaO3 and KTP because their domains can be inverted in polarity by various chemical and thermal treatments. Optical microscopy can be used to determine the thickness of the inverted layer, but this is a destructive technique. The nondestructive Surface Laser Intensity Modulation Method (SLIMM) can be used to determine the spatial polarization distribution and thus map the domain structure. In these experiments, a high-temperature thermal treatment was used to invert the domains in about half the thickness of a LiNbO3 crystal. This produced a “head to head” domain structure which was clearly shown, both by the symmetry of the SLIMM raw data and by optical microscopy. The quantitative polarization distribution was found by a nonlinear fit of the SLIMM data to a theoretical expression based on the “head to head” domain structure.

Electrical polarization has an important influence on various physiological functions of bone. It was investigated using a dynamic pyroelectric method in both moist and dry samples of turkey femur. A special calculation technique was developed to separate the pyroelectric and the thermally modulated conduction currents, based on their different frequency dependencies. An extremely large pyroelectric effect, comparable in magnitude to that of the best ferroelectric materials, could be induced by a small DC bias electric field on moist bone. The polarization and pyroelectric coefficients had very long relaxation times (order of 0.01 s). In the absence of a bias field, the pyroelectric coefficient was induced by an internal field and was spatially nonuniform. The phenomena observed are apparently related to the high orientational mobility and the viscous relaxation characteristics of dipolar water molecules in moist bone. In dry bone, the pyroelectric coefficient was very small, spatially uniform, and indepe...

A quartz crystal microbalance (QCM) measures mass per unit area by determining the change in frequency of a quartz crystal resonator caused by the addition of a small mass. The nominal resonance frequency of the shear mode of the quartz sensor is 5 MHz. A frequency change of 0.1 Hz corresponds to an addition of about 2 ng/cm2 of mass to the quartz surface. Sauerbrey was the first to recognize the potential usefulness of the QCM technology and demonstrate its extreme sensitivity to mass changes [1]. He developed the fundamental equation describing the QCM: equation Here Δƒ = change in frequency (Hz), ƒ 0 = fundamental frequency of resonator (MHz), ρ q = quartz density (2.648 g cm−3), μ q = shear modulus of AT-cut quartz (2.947 × 1011 g cm−1 s−2), and Δm = mass change/unit area (µg/cm2). The AT-cut is used because its resonant frequency is almost temperature-independent.