Showing papers on "Ferroelectric ceramics published in 1991"

The extrinsic nature of nonlinear behavior observed in lead zirconate titanate ferroelectric ceramic

Abstract: The nonlinear electric and electromechanical responses of lead zirconate titanate Pb(ZrxTi1−x)O3 ceramics to an external ac electric field have been measured under different driving levels. The onset of measurable nonlinearity is observed to be accompanied by the appearance of hysteresis loops. This lossy nature suggests that the nonlinearities in a ferroelectric ceramic are generated by the domain‐wall motion. In addition, aging experiments and the bias field dependence of the threshold field (onset of nonlinearity) all indicate the extrinsic nature of the nonlinear behavior of ferroelectric ceramics. A phenomenological theory of Arlt, Dederichs, and Herbiet [Ferroelectrics 74, 34 (1987)] has been extended to include the nonlinear contributions. With only 90° wall vibration being considered, the theory leads to some basic understanding of the experimental results.

Force constant and effective mass of 90° domain walls in ferroelectric ceramics

Abstract: Domain wall contributions to the dielectric, piezoelectric, and elastic properties of tetragonal ferroelectric ceramics, as discussed extensively in the past, are calculated. A simple model shows that the motion of 90° domain walls causes a shear deformation and an approximately homogeneous electric field in the grain. The elastic and electric field energies involved allow the calculation of the force constant for the domain wall displacement by external fields. The displacements agree with experimental results. In a moderate electric field the displacement is a small fraction of the lattice cell only. By averaging over the orientational distributions of all grains the contributions of the 90° domain walls to the material properties are calculated for unpolarized and for polarized ceramics and agree with experimental results. The effective mass, which has to be attributed to the domain walls is the mass of the whole grain reduced by the factor S0 (spontaneous deformation), is independent of the domain wid...

Pyroelectric ceramics and devices for thermal infra-red detection and imaging

Abstract: Pyroelectric detectors offer major advantages in terms of cost and ease-of-operation over cooled photon detectors of long wavelength infra-red radiation. This paper reviews the requirements of a pyroelectric material to maximise its effectiveness in different types of detector and compares the properties of ferroelectric ceramics with those of different single crystal materials. The control of the electrical properties of modified lead zirconate by doping is discussed. The concept of using a ferroelectric close to Tc under an applied electric bias as a dielectric bolometer is introduced and the properties of three different ferroelectric ceramics, barium strontium titanate, lanthanum-doped lead magnesium niobate and lead scandium tantalate are compared. It is shown that figures-of-merit can be achieved in lead scandium tantalate under DC bias which are up to three times greater than more conventional pyroelectric materials. Finally, the use of pyroelectric ceramics is illustrated by reference to ...

Laser intensity modulation method (LIMM): Experimental techniques, theory and solution of the integral equation

Abstract: The Laser Intensity Modulation Method (LIMM) was developed for the determination of the spatial distribution of polarization or space charge through the thickness of a dielectric sample. It has been used in measurements on a number of ferroelectric ceramics and polymers, single crystals and pyroelectric glass-ceramics. Its applications have included poling studies, determination of crystallite orientation in glass-ceramics and influence of surface treatments on polarization of ceramics. The experimental technique and the theory are reviewed, and modifications for increase of accuracy are discussed. A major difficulty in the analysis of LIMM measurements is the necessity of solving a Fredholm integral equation of the 1st kind using experimental data. This is an ill-posed problem which can inherently yield a number of solutions, each of which satisfies the measured data to within experimental accuracy. A technique was developed for solving this class of equations by a modification of the constraine...

The role of 90° domain wall displacements in forming physical properties of perovskite ferroelectric ceramics

Abstract: A proposed model which takes into account an elastic interaction between a polydomain grain and a surrounding ceramic matrix under weak external mechanical stresses has been used for evaluating a contribution from 90° domain wall displacements to piezoelectric and elastic constants of the perovskite ferroelectric ceramics. A difference between experimental and averaged constants of BaTiO3 ceramics can be explained by the estimated contribution.

Effect of Barium Titanate on Microstructural Evolution and Properties of Lead Zinc Magnesium Niobate Ceramics

Abstract: BaTiO3 (BT) addition vastly alters the dielectric behavior of lead zinc magnesium niobate (PZMN) relaxor ferroelectrics. Heat treatment, including the sintering process, influences the dielectric properties through changes in the distribution of heterogeneous compositions and in the extent of diffused phase transition. With more than 15 mol% BaTiO3 addition, two cubic phases composed of Ba-rich and Ti-rich PZMN substances exist. The destruction of the BaTiO3 phase and reconstruction of Ba-rich and Ti-rich regions are initiated during heat treatment, and the extent of destruction and reconstruction determines the dielectric properties of the PZMN ceramics. The BT-rich PZMN phase, which occurs with higher BaTiO3 addition, plays a less important role in the present investigation.

Grain orientation and electrical properties of Sr2Nb2O7 ceramics

Abstract: Sr2Nb2O7 ceramics sintered at 1753 K and the hot-pressed compacts annealed at 1073 K possess low density because of the formation of voids by large expansion. The expansion is attributed to cleavage and due to the preferential grain growth along the direction. An increase in dielectric constant at temperatures over 973 K and a parabolic decrease of resistivity with increasing temperature are observed. The constant variation corresponds well to the decrease in thermal strain and the grain orientation factor along the direction.

Electron emission from ferroelectric ceramics

Abstract: The results of experiments on the emission of electrons from ferroelectrics are reported. A sample of PZT is pulsed to reverse the direction of the spontaneous polarization within the material. This releases the surface charge accumulated on the ferroelectric, which is needed to reduce the external electric field to a low value. Surface charge densities may amount to about 0.5 C/m/sup 2/. In these experiments, the emitted electron current density reaches a peak value of up to 70 A/cm/sup 2/ for a diode gap of 4 mm and an extraction voltage of 500 V. Beam current densities exceed the Child-Langmuir law for space-charge-limited emission by factors of up to 400. Measurements showing the dependence of the emission on the diode voltage and spacing are presented. The authors' understanding of the emission process and its limitations are summarized. >

Pyroelectric properties of bismuth layer-structured ferroelectric ceramics

Abstract: Pyroelectric properties of a bismuth layer-structured ferroelectric (BLSF) family are studied on ordinarily fired (OF) (nonoriented) and grain-oriented ceramics for pyrosensor materials. The pyroelectric figure of merit, Fv and FD , are evaluated from the measured values of the pyroelectric coefficient, p, the dielectric constant, e = e33 T/e0, and the loss tangent, tan δ. Infrared frequency response measurements give the voltage responsivity, R v, and the detectivity, D* , for infrared sensing figure of merits, which are related with the Fv and FD , respectively. The grain orientation effects using the hot-forging (HF) method enhance the pyroelectric properties by two or more times those of nonoriented (OF) ones. The Mn-doped and grain-oriented (HF) (Na1/2 Bi1/2)1-xCaxBi4Ti4O15[NCBT] ceramics with a lower free permittivity, e33 T/e0(= ∼130), a higher electromechanical coupling factor, k 33(= 33 ∼ 40%) and a higher anisotropy, k 33/k 31(= 13 ∼ 17) have a comparable value of Fv and D* to that of P...

Sintering and characterization of Bi4Ti3O12 ceramics

Abstract: Polycrystalline ferroelectric Bi4Ti3O12 ceramics have been prepared by the method of reactive liquid phase sintering. The sintering behaviour of the Bi2O3-TiO2 composite was examined by plotting the isothermal densification curves. The results indicate that the starting oxides are involved in the reaction even at temperatures lower than or equal to 800°C, but the reaction advances at a very slow rate. Above solidus, the liquid phase promotes an extended reaction. Saturation observed in two densification curves, at 875 and 1100°C demonstrate that the reaction proceeds by two steps. A completion of the Bi4Ti3O12 formation occurs after 60 min of sintering at 1100°C. Optical micrographs of sintered bismuth titanate ceramics show randomly oriented ferroelectric grains separated by a paraelectric intergranular layer. The Bi4Ti3O12 crystallites exhibit a platelike morphology, similar in the appearance to mica, as evidenced by scanning electron micrographs. Isothermal annealing (750 to 950°C) does not affect the microstructure and electric properties of sintered bismuth titanate. The considerable value of dielectric permittivity and the appearance of hysteresis have been correlated to the presence of oxygen vacancies within the pseudotetragonal structure of Bi4Ti3O12. The oxygen vacancies are preferentially sited in the vicinity of bismuth ions as evidenced by X-ray photoemission data. XPS and AES measurements confirm that the surface concentration of cations comprising the Bi4Ti3O12 ceramics does not deviate from the nominal bulk composition.

Microstructural Characterization of Ferroelectric Thin Films in Transverse Section

Abstract: A technique has been developed for the TEM examination of ferroelectric thin films in transverse section. Some preliminary results are reported for three different thin-film/substrate systems. The microstructures of thin films of lead scandium tantalate deposited onto sapphire and MgO, and lead titanate deposited onto AIN, have been examined, with particular attention being paid to the quality of the thin-film/substrate interfaces and to the changes in the nature of the microstructures of the thin films as a function of distance from their substrates. It is demonstrated that the technique successfully produces adequate electron transparent regions for the characterization of the thin-film/substrate interface of all the samples examined and that it is possible to prepare transverse sections of ferroelectric thin films routinely.

The semiconductor properties on the system “metal-semiconductive ferroelectric ceramics-metal”

Abstract: On barium titanate basis ferroelectric ceramics with semiconductor properties was obtained and it was established that at the different deposited electrodes the dependence of the current intensity through it depending on the applied voltage has a nonlinear character and also presents characteristically marked PTC effect in the vicinity of the ferroelectric phase transition. The electrical properties of the samples of the system as metal-semiconductive ferroelectric ceramics-metal (M-S-M) are dependent on the type of electrode metal (M) and on the method of its deposition on the ferroelectric semiconductor ceramics (S). It was established that all the used electrodes may be divided into two groups: first, those causing the formation of a Schottky type contact layer and second, those forming transition layers on the boundaries of the system M-S. By suitable choice of the electrode material and the deposition method, it is necessary to control the electrical properties of the system M-S-M and in particular t...

The thermo-mechanical breakdown of ferroelectric ceramics

Abstract: It is demonstrated that brittle fracture plays an important role in the breakdown process of ferroelectric ceramics. Mechanical fracture and dielectric failure are recognized to be microstructure sensitive, and both of these have been shown to depend upon intrinsic-extrinsic microstructure parameters and the heat diffusion condition. The toughening-strengthening effect of dispersed ZrO/sub 2/ particles caused by t to m martensitic transformation, which leads to crack branching and crack closing in the breakdown process, is a reasonable compromise for improving fractural strength and modified electronic properties. A thermomechanical breakdown is proposed which can replace the typical thermal breakdown mechanism of brittle electrical ceramics with lower thermal conductivity. >

Structural investigation of (Pb,Ln)(Ti,Mn)O3 ceramics (Ln=rare earth)

Abstract: On etudie par diffraction RX la microstructure de ceramiques ferroelectriques de titanate de plomb substituees par des lanthanides

Optical and Electrical Properties of La-Modified (Pb-Ba)Nb2O6 Ferroelectric Ceramics

Abstract: Optical and electrical properties, together with phase transitions, were investigated for thc lanthanum-modificd lead-barium metaniobate (Pb1-yBay)1-xLaxNb2-x/5O6. Hot-pressed ceramics with compositions near the orthorhombic-tetragonal morphotropic phase boundary were found to have excellent optical characteristics and high piezoelectricity.

The effect of microstructure on residual stress-producing and -releasing mechanisms in ceramics processing

Abstract: A new non-destructive method has been developed for determining the internal stress of ferroelectric and ferromagnetic ceramic materials by comparing the relative changes in the permeability of the materials. The first experimental data of the relationship between the residual stress and the microstructure of the ceramic material has been obtained by this method. Residual stress-producing and -releasing behaviours in Ni-Cu-Zn ceramics processing depends on the microstructure of these materials. The experimental results show that more residual stress is produced in quenching and released in annealing for a sample with a lower density, smaller grain sizes and a higher pore fraction. Whether or not the residual stress in a quenched Ni-Cu-Zn ceramic sample is released back to its initial as-sintered state through an annealing process depends upon the microstructure. The stress produced by air-quenching was almost completely released by the annealing process when the relative densities of the samples were lower than 83%. However, the stress-releasing effect decayed rapidly with increasing density when the relative densities of the samples were higher than 94%. On the other hand, the residual stress in the Ni-Cu-Zn ceramics rose very rapidly when the air-quenching temperature was higher than 830 ‡C. The stress was estimated by considering the effect of magnetostriction on the initial magnetization process in the materials. A simple theoretical model has been developed to interpret the results.

Structure stabilization and dielectric properties of pzn ferroelectric ceramics

Abstract: Structure stabilization and dielectric properties of Pb (Zn1/3 Nb2/3)O3 -PbTiO3 -BaTio3 (PZN-PT-BT) ferroelectric ceramics have been carefully studied. Around morphotropic phase boundary (MPB) of PZN-PT system, heterovalant substitution of K+ for Pb2+ stabilizes the pesrovskite Structure, while substitution of La3+ for Pb2+ goes toward the other end. Nonstoichiometry addition of excess ZnO or BaO can also suppress the formation of pyrochlore phase.

Rejuvenation of Ferroelectric Fatigue in Modified Lead Zirconate Titanate Ceramics Near Tetragonal-Rhombohedral Morphotropic Phase Boundary,

Abstract: : Rejuvenation of ferroelectric fatigue is investigated in modified lead zirconate titanate ferroelectric ceramics near the tetragonal-rhombohedral morphotropic phase boundary. Ferroelectric fatigue rejuvenates with changes in the applied electric field direction. Spontaneous rejuvenation occurs in the absence of an electric field. A coupling among the applied electric field, oxygen vacancy related defect dipoles, and spontaneous polarizations is proposed to explain ferroelectric fatigue and rejuvenation.

Influence of heat treatment and poling on the microstructure of Pb(Zr,Ti)O3-type oxidic ceramics

Abstract: On etudie par diffraction RX la structure cristalline et la microstructure de la ceramique ferroelectrique correspondant a la composition Pb 0,98 Bi 0,02 Zr 0,5 Ti 0,31 Fe 0,1 Nb 0,08 U 0,01 O 3 . On examine l'influence d'un traitement thermique et d'une polarisation sur les parametres microstructuraux

The twin structures and the piezoelectric effect in ferroelectric ceramics

Abstract: Experimental evidence show that the piezoelectric effect in ferroelectric ceramics cannot be accounted for by the average of the intrinsic piezoelectric effect of the oriented ferroelectric domains. The measured values of piezoelectric moduli dij are usually 60-70% larger than the calculated average values at room temperature.1,2,3 The difference as well as the absolute values of dij become smaller when the system is cooled,4 which suggests that reversible ferroelectric/ferroelastic domain wall movement may be the cause for the discrepancy, because the walls are more mobile at higher temperatures.

An interactive computer simulation of global microstructures in polycrystalline ceramics

Abstract: Microstructure is the single most important structural characteristic of a ferroelectric ceramic in determining its useful properties, such as dielectric constant, piezoelectric constant, remnant polarization, electrical resistance, thermal expansion, thermal conductivity, electric resistance, light scattering, magnetic permeability, toughness, fracture strength, thermal expansion, etc. Key features of the three dimensional (3D) microstructure are the grain size distribution and the distribution of grain boundaries and grain shapes. By using stereological methods to interpret two dimensional (2D) cross sections, the experimentalist can obtain at best mean values of these properties, but little or no information on the width of the distributions or their extreme values. One of the most important parameters, the mean 3D grain size, can only be obtained from 2D cross sections by making restrictive assumptions about the grain shapes (spherical) leading to errors greater than 20%. A key point which is little a...

Niobium Oxide and Niobates

Abstract: Publisher Summary This chapter examines the properties and applications of niobium oxide (Nb2O5) and niobates Nb2O5is extensively used for the preparation of niobates and for the modification of the properties of ferroelectric ceramics It can be extracted from niobium-rich ores, which usually contain some tantalum, iron, titanium and tin, by either ion exchange or solvent extraction From the purified solutions, niobium is precipitated with the aid of ammonia After firing the precipitate in air above 1100°C, high-purity Nb2O5 is obtained in the form of an egg-shell-white powder This turns yellowish on heating because of the formation of oxygen vacancies in the lattice The structure of LiNbO3 is related to that of the perovskites, although the symmetry is lower As in perovskites, the basic building elements are oxygen octahedra with cations at their centers The characteristic feature of this structure is its high polarizability, which gives rise to piezoelectric, pyroelectric, and ferroelectric phenomena It is found that owing to its high spontaneous polarization and high Curie point, lithium niobate is widely used for piezoelectric and electro-optic devices

Modeling of Hysteresis Properties of Lead Zirconate Titanate Thin Films

Abstract: It is proposed that the polarization reversal mechanism in ferroelectric ceramics such as titanates is controlled by nucleation, growth, merging and shrinkage of ferroelectric domains. These domain phenomena are in turn determined by the nature of Barkhausen jumps, internal electric field, and dielectric relaxation times of the dipoles. Based on the proposed polarization reversal mechanism, a quantitative model was developed for simulating the hysteresis properties of lead zirconate titanate (PZT) thin films. The simulated hysteresis loops are in good agreement with the experimental results. It was observed that dielectric viscosity, which is very useful in understanding fatigue and aging behavior of PZT thin films, is one of the key parameters that controls the hysteresis properties.