Showing papers on "Ferroelectric ceramics published in 1996"

Fundamentals of ceramics

Abstract: INTRODUCTION Introduction Definition of Ceramics Elementary Crystallography Ceramic Microstructures Traditional Versus Advanced Ceramics General Characteristics of Ceramics Applications The Future BONDING IN CERAMICS Introduction Structure of Atoms Ionic versus Covalent Bonding Ionic Bonding Ionically Bonded Solids Covalent Bond Formation Covalently Bonded Solids Band Theory of Solids Summary Appendix 2A: Kinetic Energy of Free Electrons STRUCTURE OF CERAMICS Introduction Ceramic Structures Binary Ionic Compounds Composite Crystal Structures Structure of Covalent Ceramics Structure of Silicates Lattice Parameters and Density Summary Appendix 3A: Ionic Radii EFFECT OF CHEMICAL FORCES ON PHYSICAL PROPERTIES Introduction Melting Points Thermal Expansion Young's Modulus and the Strength of Perfect Solids Surface Energy Summary THERMODYNAMIC AND KINETIC CONSIDERATIONS Introduction Free Energy Chemical Equilibrium and the Mass Action Expression Chemical Stability Domains Electrochemical Potentials Charged Interfaces, Double Layers, and Debye Lengths Gibbs-Duhem Relation for Binary Oxides Kinetic Considerations Summary Appendix 5A: Derivation of Eq. (5.27) DEFECTS IN CERAMICS Introduction Point Defects Linear Defects Planar Defects Summary DIFFUSION AND ELECTRICAL CONDUCTIVITY Introduction Diffusion Electrical Conductivity Ambipolar Diffusion Relationships between Self-, Tracer, Chemical, Ambipolar, and Defect Diffusion Coefficients Summary Appendix 7A: Relationship between Fick's First Law and Eq. (7.30) Appendix 7B: Effective Mass and Density of States Appendix 7C: Derivation of Eq. (7.79) Appendix 7D: Derivation of Eq. (7.92) PHASE EQUILIBRIA Introduction Phase Rule One-Component Systems Binary Systems Ternary Systems Free-Energy Composition and Temperature Diagrams Summary FORMATION, STRUCTURE, AND PROPERTIES OF GLASSES Introduction Glass Formation Glass Structure Glass Properties Glass-Ceramics Summary Appendix 9A: Derivation of Eq. (9.7) SINTERING AND GRAIN GROWTH Introduction Solid-State Sintering Liquid-Phase Sintering Hot Pressing and Hot Isostatic Pressing Summary Appendix 10A: Derivation of the Gibbs-Thompson Equation Appendix 10B: Radii of Curvature Appendix 10C: Derivation of Eq. (10.20) Appendix 10D: Derivation of Eq. (10.22) MECHANICAL PROPERTIES: FAST FRACTURE Introduction Fracture Toughness Strength of Ceramics Toughening Mechanisms Designing with Ceramics Summary CREEP, SUBCRITICAL CRACK GROWTH, AND FATIGUE Introduction Creep Subcritical Crack Growth Fatigue of Ceramics Lifetime Predictions Summary Appendix 12A: Derivation of Eq. (12.24) THERMAL PROPERTIES Introduction Thermal Stresses Thermal Shock Spontaneous Microcracking of Ceramics Thermal Tempering of Glass Thermal Conductivity Summary DIELECTRIC PROPERTIES Introduction Basic Theory Equivalent Circuit Description of Linear Dielectrics Polarization Mechanisms Dielectric Loss Dielectric Breakdown Capacitors and Insulators Summary Appendix 14A: Local Electric Field MAGNETIC AND NONLINEAR DIELECTRIC PROPERTIES Introduction Basic Theory Microscopic Theory Para-, Ferro-, Antiferro-, and Ferrimagnetism Magnetic Domains and the Hysteresis Curve Magnetic Ceramics and their Applications Piezo- and Ferroelectric Ceramics Summary Appendix 15A: Orbital Magnetic Quantum Number OPTICAL PROPERTIES Introduction Basic Principles Absorption and Transmission Scattering and Opacity Fiber Optics and Optical Communication Summary Appendix 16A: Coherence Appendix 16B: Assumptions Made in Deriving Eq. (16.24) INDEX *Each chapter contains Problems and Additional Reading.

Acceleration and Deceleration of Bone-Like Crystal Growth on Ceramic Hydroxyapatite by Electric Poling

Abstract: Bone-like crystals were acceleratingly grown in a simulated body fluid on the negatively charged surface of electrically poled hydroxyapatite ceramics, while the crystal growth was completely inhibited on the opposite surface. The poling effect was generalized by the enhanced crystal growth on the poled ferroelectric ceramics of BaTiO3 and CaTiO3.

The Rayleigh law in piezoelectric ceramics

Abstract: The direct longitudinal piezoelectric effect in lead zirconate titanate, barium titanate, bismuth titanate and strontium bismuth titanate ceramics was investigated with respect to the dependence on the amplitude of an alternating pressure. At low alternating pressure amplitudes, the behaviour of the piezoelectric charge and the piezoelectric coefficient may be explained in terms of the Rayleigh law originally discovered for magnetization and magnetic permeability in ferromagnetic materials. The charge versus pressure hysteresis loops measured for piezeoelectric ceramics may similarly be described as the Rayleigh loops. The results presented show that the Rayleigh law can be applied to irreversible displacement of several types of non- ferroelectric domain walls and imply universal validity of the Rayleigh law for displacement of ferromagnetic, ferroelastic and ferroelectric domain walls.

Ferroelectric Thin Films in Micro-electromechanical Systems Applications

Abstract: Ferroelectric ceramic thin films fit naturally into the burgeoning field of microelectromechanical systems (MEMS). Microelectromechanical systems combine traditional Si integrated-circuit (IC) electronics with micromechanical sensing and actuating components. The term MEMS has become synonymous with many types of microfabricated devices such as accelerometers, infrared detectors, flow meters, pumps, motors, and mechanical components. These devices have lateral dimensions in the range of 10 μm–10 mm. The ultimate goal of MEMS is a self-contained system of interrelated sensing and actuating devices together with signal processing and control electronics on a common substrate, most often Si. Since fabrication involves methods common to the IC industry, MEMS can be mass-produced. Commercial applications for MEMS already span biomedical (e.g., blood-pressure sensors), manufacturing (e.g., microflow controllers), information processing (e.g., displays), and automotive (e.g., accelerometers) industries. More applications are projected in consumer electronics, manufacturing control, communications, and aerospace. Materials for MEMS include traditional microelectronic materials (e.g., Si, SiO2, Si3N4, polyimide, Pt, Al) as well as nontraditional ones (e.g., ferroelectric ceramics, shapememory alloys, chemical-sensing materials). The superior piezoelectric and pyroelectric properties of ferroelectric ceramics make them ideal materials for microactuators and microsensors.

Defect-dipole alignment and tetragonal strain in ferroelectrics

Abstract: We show the alignment of defect dipoles along the direction of the spontaneous polarization in polycrystalline Pb(Zr,Ti)O3 and BaTiO3 ferroelectric ceramics using electron paramagnetic resonance (EPR). The alignment is demonstrated via orientation dependent paramagnetic centers in the polycrystalline materials and computer modeling of the EPR line shapes. It is shown that defect dipoles can become aligned by oxygen vacancy motion in the octahedron about a negatively charged center for the oxygen vacancy‐related dipole complexes or by defect displacement and domain realignment in the lattice for isolated defect centers. We find that the alignment is not observed in nonferroelectric materials such as SrTiO3, and is destroyed in ferroelectric materials by heating above the Curie temperature. These observations suggest an interplay between distortion in the unit cell and the ability to align defect dipoles, as is the case more generally for ferroelectric dipole alignment. We also directly observe aligned intr...

Dependence of the direct piezoelectric effect in coarse and fine grain barium titanate ceramics on dynamic and static pressure

Abstract: The direct piezoelectric effect in fine and coarse grain barium titanate ceramics is examined as a function of the external alternating and static pressure. It is found that domain wall vibrations contribute to the piezoelectric effect in both types of ceramics, but this contribution is smaller in the fine grain material. The external static pressure reduces domain wall contributions in the coarse grain samples and has little effect on the properties of the fine grain material. The results are consistent with the presence of a strong internal pressure in the fine grain ceramics.

Instabilities in the piezoelectric properties of ferroelectric ceramics

Abstract: The large piezoelectric effect of ferroelectric ceramics is utilized in many devices for sensing and actuating purposes. In this paper, the longitudinal direct piezoelectric effect in ceramics based on lead zirconate titanate, lead titanate, barium titanate and bismuth titanate is investigated as a function of the amplitude and frequency of the external pressure, the crystal structure and microstructure of the ceramics. The domain-wall contribution to the piezoelectric response appears to be a dominant extrinsic origin of instabilities in the observed piezoelectric effect but, for a given composition, it can be affected by dopants and microstructure. Other sources of instabilities in the piezoelectric response, such as chemical inhomogeneities and defects, are also discussed. It is shown that, with proper modifications, it is possible to freeze out completely the extrinsic part of the piezoelectric response in some of the examined compositions and to obtain a stable behaviour, independent of the frequency and magnitude of the external driving field.

Effects of Microstructure and Composition on the Curie Temperature of Lead Barium Niobate Solid Solutions

Abstract: The Curie temperature of normally sintered and hot-pressed Pb{sub 1{minus}x}Ba{sub x}Nb{sub 2}O{sub 6} (x = 0.30, 0.37, 0.41, and 0.50) was dependent on the sample preparation conditions. Samples with large amounts of pores and cracks had higher Curie temperatures than dense samples. Dense samples with fine grains had higher Curie temperatures than those with coarse grains. Comparison between microstructure and the Curie temperature revealed that the variation in Curie temperature was caused by internal stresses developed in the paraelectric-to-ferroelectric phase transition. Large internal stresses increased the free energy of the ferroelectric phase, and thus decreased the Curie temperature. The magnitude of internal stresses depended on the microstructure. Pores and cracks relaxed internal stresses, resulting in high Curie temperatures. Grain boundaries also relaxed internal stresses; samples with small grains had high Curie temperatures. Furthermore, the magnitude of internal stresses was dependent on the crystal structure of ferroelectric phases; samples with the tetragonal ferroelectric structure had internal stresses larger than those with the orthorhombic ferroelectric structure. The effect of crystal structure was discussed in terms of the relaxation of internal stresses by the formation of 90{degree} domains.

Microcracking and electric fatigue of polycrystalline ferroelectric ceramics

Abstract: The major obstacle preventing ferroelectric actuators from enjoying wide application is the so-called electric fatigue which results in reduction of actuation displacement/force after actuators have been subjected to many cycles of applied electric field. Experimental observations reveal that fatigued specimens often contain scattered microcracks, and hence suggest that microcracking may be the cause of electric fatigue. This paper presents a theoretical model developed within the framework of continuum electrodynamics for deformable dielectrics, to study the microcracking effect upon macroscopic properties of polycrystalline ferroelectric ceramics. The numerical results indicate that microcracking can indeed cause the observed fatigue behavior.

Switching and dielectric nonlinearity of ferroelectric ceramics

Abstract: The switching of the polarization in tetragonal ferroelectric ceramics can be achieved by the generation of one new 90° domain wall at the boundary of every grain and a transit of it through the grain driven by the electric field. This transient domain wall is perpendicular to the regular 90° domain walls. In any domain of the grain then the polarization is rotated by 90° and the average polarization of the grain is rotated by 180° due to the specific domain configurations. The observed relationship E0 ∼ P3 0 between the spontaneous polarization P 0 and the coercive field E 0 is confirmed by the model. The dielectric nonlinearity of ferroelectric ceramics can also be explained by the new 90° domain walls which have a very high mobility. Possibly the high permittivity of fine grained Barium Titanate can be attributed to these domain walls too.

Anelastic relaxation associated with the motion of domain walls in barium titanate ceramics

Abstract: The mechanical loss (Q −1) and shear modulus (G) were measured as a function of temperature in the range 130 K < T < 430 K for BaTiO3 ceramics by an inverted pendulum at low frequencies ranging between 1-0.01 Hz. The Q −1 (T) and G(T) curves exhibit the three phase transitions observed in BaTiO3. Each phase transition induces a loss peak and an anomaly in the elastic modulus. Moreover, three other loss peaks (R) are located below the phase transition temperature. These peaks can be described by an Arrhenius relationship, and the activation energies are determined as 0.92, 0.68, and 0.45 eV for the peak located in the tetragonal-, orthorhombic-, and rhombohedral-phase, respectively. These peaks are due to the interaction between the domain walls and the diffusion of oxygen vacancies in the domains.

A physical model for hysteresis curves of ferroelectric ceramics

Abstract: A general model for the simulation and for the interpretation of hysteresis curves is presented. The model opens the possibility to calculate hysteresis curves if the electrostatic interaction of grains in a critical volume can be treated quantitatively. The hysteresis curve is described by a progress parameter δ. The effective polarization P eff(δ) in the process of inversion is approximated by a switching procedure. The average polarization of most grains is inverted by 180°. The hysteresis function of the electric switching field E(δ) which is dependent on the same progress parameter δ is derived from an electrostatic equation which allows to calculate the electric field in a polar inclusion in a homogeneous ferroelectric matrix. In the model the ferroelectric matrix is replaced by the quasi-homogeneous ceramic and the inclusions are replaced by spherical regions with interacting grains. The average polarization in the regions lags more or less behind the effective polarization or is ahead of ...

Mechanical loss and Young's modulus associated with phase transitions in barium titanate based ceramics

Abstract: The mechanical loss (Q −1) and Young's modulus (E) were measured as a function of temperature in the range 100 K

Superoxidation and Electrochemical Reactions during Switching in Pb(Zr2Ti)O3 Ceramics

Abstract: Under ferroelectric switching in Pb(Zr,Ti)O{sub 3} (PZT) ceramics, the authors demonstrate that oxygen gas is emitted and degrades electrode microstructure. The oxygen is a direct result of the defect chemistry associated with superoxidation which is established during the processing of the ceramics. Under high alternating electric fields, electron injection into the ceramic surface induces a reduction process, and surface layers are believed to change from a p-type electronic compensation to an ionic compensation of oxygen vacancies and A-site lead vacancies. During this process, the authors noticed progressive changes in capacitance, loss, remnant polarization, and coercive field. The wider implications of this observation for PZT thin film nonvolatile memories are discussed in brief.

Dielectric Properties of KTN ferroelectric ceramics sintered with LiF

Abstract: Ceramics of the two compositions of KTa1−xNbxO3 (KTN) with x = 0.3 and 0.4 have been densified thanks to the addition of LiF. Densities been determined as a function of sintering temperature, time and amount of LiF. Dielectric investigations have shown that the composition corresponding to x = 0.4 is more densified than x = 0.3. The two compositions x = 0.3 and x = 0.4 exhibit a paraelectric-ferroelectric phase transition at about 310 and 360 K respectively. The phase transition is more diffure for x = 0.3. Oxygen is partially substituted for fluorine in the crystalline network.

Grain Size Dependence of Switching Properties of FerroelectricBaTiO3Ceramics

Abstract: Polarization reversal properties of BaTiO3 (BT) ferroelectric ceramics at room temperature were studied. Two types of samples, having g1=1.5 µ m and g2=70 µ m grain size, were used. The grain size effect on the transient switching current was analysed and compared with the results of two theoretical models accounting for size effects: a dipole lattice model and a finite grain size model (FGM) that uses a Kolmogorov-Avrami (K-A) type statistical approach of polarization reversal.

Crack Growth in Ferroelectric Ceramics and Actuators Under Mechanical and Electrical Loading

Abstract: Fracture mechanical behaviour of ferroelectric components under combined mechanical and electrical loading is investigated in order to improve reliability and understand fatigue mechanisms of multilayer actuator stacks.

Obtention and characterizationof modified Bi2 Sr Nb2 O9 aurivillius-typeceramics

Abstract: Aurivillius ferroelectric ceramics, based on the Bi2Sr Nb2O9 compound, have been developed by making isomorphic substitutions in the (Bi2O2)2+ layer. High density ceramics were obtained by the uniaxial hot-pressing sintering technique. The macroscopic characterization was carried out by measuring both the dielectric constant, in the frequency range from 100Hz to 15MHz at temperatures between 20°C and 850°C, and piezoelectric parameters. We found that increasing the amount of cation Bi3+ substitution results in higher transition temperature values. Samples showed a high electrical resistivity that made poling difficult. Anyway, we found an important piezoelectric activity in the samples with tellurium present in their composition, with d33 greater than 11pC/N.

Influence of the eutectic composition 1CaF2-4LiF on the sintering and the dielectric properties of BaTiO3

Abstract: High densified ceramics were prepared at low temperature (sint. ⩽ 1000°C) using the eutectic composition 1CaF2-4LiF (3-5 mol.%). The samples were studied by X-ray diffraction and scanning electron microscopy. Dielectric measurements were performed as a function of temperature (150 K ⩽ T ⩽ 450 K) and frequency (50 Hz ⩽ f ⩽ 4.107 Hz). The best dielectric performances were obtained from the starting mixture 1BaTiO3 + 0.03CaF2 + 0.03CaF2 + 0.12LiF sintered at 1000°C for 4 hours. The relative density reached 96% and the Curie temperature was about 310 K for the corresponding ceramic. High values of the dielectric constant (e > 6000) were observed at room temperature in the frequency range 102-3.105 Hz. A dielectric relaxation occurred in the temperature range investigated at frequencies much lower than in pure BaTiO3: 7.106 Hz instead of 5.108 Hz at 300 K.

Modeling of domain pinning effect in polycrystalline ferroelectric ceramics

Abstract: Experimental observations indicate that electric fatigue of polycrystalline ferroelectric ceramics is partially recoverable through thermal treatments at temperatures that are too low to heal microcracking which is considered to be the primary cause of electric fatigue. It has been conjectured that this thermally-recoverable fatigue is due to domain pinning. This paper presents a theoretical model for the domain pinning effect on macroscopic properties of polycrystalline ferroelectric ceramics. The numerical results suggest that domain pinning can indeed lead to the type of fatigue behavior as observed.

On the Influence of Material Objectivity on Electroelastic Dissipation in Polarized Ferroelectric Ceramics

Abstract: An earlier system of rotationally invariant electroelastic equations for deformable insulators, which was derived from a well-defined macroscopic model, is extended to include the simplest mechanical and electrical viscous-type dissipation. The resulting nonlinear description satisfies the principle of material objectivity. When the resulting description is linearized, the viscous-type linear electrical dissipative variable contains the spin tensor because a biasing polarization is present in the ferroelectric ceramic.

A processing and electrical property investigation of the solid solution : (x) Pb(In1/2Nb1/2)O3 − (1 − x) Pb(Sc1/2Ta1/2)O3

Abstract: Ceramics in the solution system (x) Pb(In½Nb½)O3 - (1 - x) Pb(Sc½Ta½)O3 [PIN:PST(x)] with compositions ranging from x = 0.0 to x = 1.0 have been fabricated. This paper presents the processing methods for producing 100% perovskite PIN and PST ceramics, as well as those for the PIN/PST solid solution. Various electrical properties including the dielectric constant and hysteresis, the pyroelectric and piezoelectric response, are measured on these compositions

Piezoelectric electron acoustic study of domain structures in ferroelectric ceramics BaTiO3

Abstract: The domain structures of ferroelectric ceramics BaTiO3 have been observed by piezoelectric electron acoustic probe without any special processing to the sample. It is found that multi-distribution of domain structures could exist in a single grain and a domain structure could cross several grains. Experimental results show that the orientations of arrangements of domain structures on the boundary of two neighboring grains are the same as far as possible and the width of domain depends on the magnitude of grain. The origins of electron acoustic image contrasts of BaTiO3 were mainly determined by the electronic properties of ferroelectric domains.

Poisson's ratio for piezoceramics

Abstract: Poisson's ratios, with respect to rotated coordinate axes, for hexagonal materials, and particularly, poled ferroelectric ceramics, have been obtained. Formulae are given for ceramics of arbitrary orientation and electrical immittance boundary conditions. A number of simple cases are obtained for open-circuit boundary conditions.

Grain oriented technology of ferroelectric ceramics

Abstract: Grain oriented technology of anisotropic grains of ferroelectric materials was originated from the two stages hot-pressing for strongest piezoelectric single crystal of SbSI in 1963. Anisotropic ferroelectrics are SbSI and SbSOI with needle shape grain, Bi/sub 2/TiO/sub 3/ like compounds with plate like grains and tungsten bronze like compounds with bar type grains. Doctor blade technology is also important for the developments of this technology.