Ferroelectric ceramics were born in the early 1940s with the discovery of the phenomenon of ferroelectricity as the source of the unusually high dielectric constant in ceramic barium titanate capacitors. Since that time, they have been the heart and soul of several multibillion dollar industries, ranging from high-dielectric-constant capacitors to later developments in piezoelectric transducers, positive temperature coefficient devices, and electrooptic light valves. Materials based on two compositional systems, barium titanate and lead zirconate titanate, have dominated the field throughout their history. The more recent developments in the field of ferroelectric ceramics, such as medical ultrasonic composites, high-displacement piezoelectric actuators (Moonies, RAINBOWS), photostrictors, and thin and thick films for piezoelectric and integrated-circuit applications have served to keep the industry young amidst its growing maturity. Various ceramic formulations, their form (bulk, films), fabrication, function (properties), and future are described in relation to their ferroelectric nature and specific areas of application.

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Ferroelectric ceramics : History and technology

Multilayer ceramic capacitor (MLCC) production and sales figures are the highest among fine-ceramic products developed in the past 30 years. The total worldwide production and sales reached 550 billion pieces and 6 billion dollars, respectively in 2000. In the course of progress, the development of base-metal electrode (BME) technology played an important role in expanding the application area. In this review, the recent progress in MLCCs with BME nickel (Ni) electrodes is reviewed from the viewpoint of nonreducible dielectric materials. Using intermediate-ionic-size rare-earth ion (Dy2O3, Ho2O3, Er2O3, Y2O3) doped BaTiO3 (ABO3)-based dielectrics, highly reliable Ni-MLCCs with a very thin layer below 2 µm in thickness have been developed. The effect of site occupancy of rare-earth ions in BaTiO3 on the electrical properties and microstructure of nonreducible dielectrics is studied systematically. It appears that intermediate-ionic-size rare-earth ions occupy both A- and B-sites in the BaTiO3 lattice and effectively control the donor/acceptor dopant ratio and microstructural evolution. The relationship between the electrical properties and the microstructure of Ni-MLCCs is also presented.

https://iopscience.iop.org/article/10.1143/JJAP.42.1/pdf

Base-Metal Electrode-Multilayer Ceramic Capacitors: Past, Present and Future Perspectives

▪ Abstract This paper reviews the literature on size effects in ferroelectric materials, with an emphasis on thin film perovskite ferroelectrics. The roles of boundary conditions, defect chemistry, electrode interfaces, surface layers, and microstructure in controlling the measured properties of ferroelectric films, as well as the observed deviation from bulk properties are discussed. Examples of the manifestation of size effects in terms of the low and high field dielectric properties, the piezoelectric effect, and the leakage behavior of films are given.

The Properties of Ferroelectric Films at Small Dimensions

Hot-pressed ceramics of the lead titanate zirconate system with different grain sizes were prepared and some of their electrical properties measured. The values of the dielectric and piezoelectric properties were analysed together with information on barium titanate ceramics already published in the literature. Many similarities were found between both systems. There are two main contributions to the properties; the single-crystal single-domain intrinsic effect and the contribution of the wall motion. The intrinsic effect is analysed considering the grains as monodomains. A model is developed which proposes that each grain has a different transition temperature Tc. The Tc values are taken as following a Gaussian distribution and the behaviour of the dielectric constant against temperature is computed and checked with experimental results. All the results can be explained qualitatively with the model; a connection between findings and the idea of diffuse phase transitions is outlined.

https://iopscience.iop.org/article/10.1088/0022-3719/7/17/024/pdf

Grain-size effects on properties of some ferroelectric ceramics

Piezoelectric materials play a crucial role in a large number of devices and applications modern society would not like to miss. Mobile phones and ultrasonic imaging are just the most prominent ones. Since two decades, miniaturization of mechanical devices in silicon technology is a major research direction in engineering known under name of MEMS, which stands for micro-electro-mechanical systems. Piezoelectricity fits very well into this concept and was expected right from the beginning to play its role in MEMS. The breakthrough was made with RF filters in mobile phones working on the principle of standing thickness waves in AlN films. What counts here is acoustic quality and stability. The force champion among piezoelectric thin film materials, Pb(Zr,Ti)O3 gave more problems in processing, and requires more patience to meet requirements and needs for a mass applications. It seems, however, that the breakthrough is imminent. This article attempts to give an overview of the field, highlighting recent achievements, introduce operation principles, and describe some applications.

Recent Progress in Materials Issues for Piezoelectric MEMS

A group of transparent ferroelectric hot-pressed (Pb0.92La0.08)-(Zr0.65Ti0.35)0.98O3 specimens with controlled grain size and constant porosity and a group of similar specimens with controlled porosity and constant grain size were prepared. The electrical and optical constants and polarization-reversal properties of these ceramics were determined as functions of grain size and porosity. When poled PLZT ceramics were aged, the polarization-reversal characteristic was quite asymmetric, apparently because a space-charge field, E8p, was generated during aging. From a detailed study of the behavior of the E8p, including its (1) generation with increasing aging time, (2) relaxation with repeated polarization reversals, (3) relaxation by heat depolarization, and (4) grain-size and porosity dependence, it is concluded that the space-charge layer is present inside every domain. This layer also explains the grain-size dependencies of the remanent polarization, piezoelectric constants, and Curie point.

Effects of Grain Size and Porosity on Electrical and Optical Properties of PLZT Ceramics

Fracture strength and stress-strain behavior under tensile stress in piezoelectric ceramics have been investigated with special emphasis on the effects of poling conditions. The materials used in this work are the commercial piezoelectric ceramics, PbZrO3-PbTiO3 (PZT) and BaTiO3. First, an attempt was made to evaluate the tensile strength properties of samples having a specially designed specimen geometry. In the actual tensile test, fracture did not occur at the gripping portion at all, indicating usefulness of the present tensile test method. Not only fracture strength, but also elastic properties, tensile modulus and Poisson's ratio, were evaluated. Second, an investigation was performed on the stress-strain behavior under tension in this material. As a result, stress-strain response under tension was confirmed to be nonlinear. The nonlinearity in the stress-strain relationship under compression loading has already been reported by some investigators. However, very little work has been done on the tensile stress-strain relationship studied in this paper. Third, acoustic emission monitoring was performed simultaneously during tensile tests, and thus the tensile failure process in piezoelectric ceramics was discussed.

https://iopscience.iop.org/article/10.1143/JJAP.32.4233/pdf

Tensile Stress-Strain Behavior of Piezoelectric Ceramics

The yields for the ionization and excitation from each molecular orbital of a water molecule irradiated by 10 keV electrons were calculated using the classical binary-encounter approximation. On further assuming fragmentation processes of the excited or ionized states consistent with the photochemical and mass spectrometrical results in the literature, we obtained, as the radiolysis yields of water vapor: G(electron)=2.96; G(OH−)=0.04; G(H3O+)=3.00; G(H)=4.83–5.21, including G(‘hot’ H-atoms)≤0.87; G(H2)=0.28–1.15; G(O)=0.83–1.21; G(OH)=6.70–7.08, and G(–H2O)=G(ionized water)+G(excited water)=2.91+4.96=7.87.

The Calculation of the Primary Radiolysis Yield of Water Vapor Irradiated by 10-keV Electrons

The binary-encounter collision theory has been applied to the calculation of the G-values for the ionization and excitations of diatomic molecules irradiated by 100 keV electrons. The obtained G-values of electrons are as follows, in the order of H2, N2, CO, NO, and O2: 2.83, 2.55, 2.68, 3.61, and 2.98. These values are in fair agreement with the experimental ones. The present non-empirical method is compared with the semi-empirical ones proposed by other investigators. The G-values of some other products were also calculated: the excited hydrogen atoms in the radiolysis of H2 (0.9) and the ozone formation in the radiolysis of O2 (12.6). These G-values are also in fair agreement with the experimental ones.

Kiyoshi Okazaki

Papers

Effects of Grain Size and Porosity on Electrical and Optical Properties of PLZT Ceramics

Tensile Stress-Strain Behavior of Piezoelectric Ceramics

The Calculation of the Primary Radiolysis Yield of Water Vapor Irradiated by 10-keV Electrons

Non-empirical Calculation of the G-Values for the Ionization and Excitations in Diatomic Molecules Irradiated by 100 keV Electrons

Preparation of High Tc Superconductor Oxide Ceramics by Partial Oxalate Method and Their Evaluations