Showing papers on "Ferroelectric ceramics published in 1974"

Grain-size effects on properties of some ferroelectric ceramics

Abstract: 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.

Piezoelectricity in Ceramics of Ferroelectric Bismuth Compound with Layer Structure

Abstract: Piezoelectric properties have been studied on ferroelectric ceramics comprising bismuth compounds with layer structure, PbBi2Nb2O9, PbBi4Ti4O15, SrBi4Ti4O15 and Na0.5Bi4.5Ti4O15. These ceramics have the high mechanical quality factor Q(2000~7200), low aging rate of frequency constant Nt(30~60 ppm/time decade), low temperature coefficients both of Nt(-50 ppm/°C) and of coupling factor kt(70 ppm/°C), low Poisson's ratio σ(0.23~0.27), and large anisotropy in coupling factor. A small value of kt in these ceramics probably relates to two-dimensional restriction on permissible rotation of the spontaneous polarization. The poling characteristics in the ceramics can be improved by some additives. Grain boundaries in these ceramics are of nearly rectangular shape, and an etch pattern of fine stripes appears always in parallel to the length of the boundary.

Electric field dependence of the dielectric constant of PZT ferroelectric ceramics

Abstract: Bias (dc electric field) dependence of the dielectric constant of ferroelectric ceramics of the Pb(Zr,Ti)O3 type has been investigated. Measurements were carried out at various temperatures in the ferroelectric phase and at several frequencies between 1 kHz and 1 MHz. The bias characteristics of the dielectric constant show a temperature‐dependent asymmetry in the electric field direction. A model in which the coercive fields of the 180° and 90° domains are distributed around some average value is considered. The total dielectric constant of the material is calculated by considering the contributions of each type of domain, taking into account the difference between the differential and incremental dielectric constants. This model explains the dependence of dielectric constant on electric field. A comparison of the calculated and experimental results is presented.

The doping effects of transition elements on the PTC anomaly of semiconductive ferroelectric ceramics

Abstract: The influence of the addition of mainly 1st row of transition elements on the resistivity anomaly of BaTiO3 semiconducting ceramics has been examined. The results showed that Mn ion is the most effective in increasing the PTC anomaly by up to a factor of 109. The high temperature chemical behaviour of the ceramics was investigated. Discussions about the influence of Mn ion, its distribution and the nature of grain boundary phases on the formation of the ceramic structure adequate to the origin of the sharp PTC anomaly are given.

Analysis of phase mixtures in ferroelectric ceramics by dielectric measurements

Abstract: At morphotropic phase boundaries of ferroelectric solid solutions a maximum in the electromechanical activity is found. This is essential for technical application of Pb(ZrxTi1_x)O3. It is demonstrated that at those phase boundaries the mixture of phases can be analysed by dielectric measurements. Thus an exact phase diagram near the morphotropic phase boundary can be obtained. The measurements also indicate that fluctuations of the Zr-concentration are jointly responsible for the coexistence-region at these phase boundaries.

Further study of the pyroelectric properties of lanthanum-modified PZT ferroelectric ceramics

Abstract: A wide range of compositions of hot-pressed mixed oxide PLZT ferroelectric ceramics, covering both the rhombohedral and tetragonal phases, have been investigated with an emphasis on the room temperature pyroelectric properties. Systematic variations of the pyroelectric coefficient (p) and the relative dielectric constant (e) are observed as the Zr/Ti ratio and the La concentration are varied. However, the ratio p/√e is essentially independent of composition in each phase at room temperature.

Method of preparing ferroelectric ceramics

Abstract: METHOD OF PREPARING FERROELECTRIC CERAMICS ABSTRACT OF THE DISCLOSURE A process for preparing strengthened ferroelectric ceramics, which comprises sintering ceramic materials and then heat treating the sintered ceramics at a temperature from about 100°C to about 400°C lower than the final sintering temperature of ceramics, for about 1 to about 60 hrs, and then cooling at a rate from about 300°C to about 10°C per hour Strengthened ferroelectric ceramics are obtained among the following ferro-electric ceramic compositions: I) Pb([B1]ATa1-A)O3-pbTiO3-pbZrO3, where [B1] is Mg, Zn, Cd, Sn, Mn, Fe, Co, and Ni when A=1/3 and [B1] is Li and Cu when A=1/4, II) Pb([B2]BTa1-B)O3-Pb([B3]CTa1-C)O3-PbTiO3-PbZrO3, where [B2] and [B3], [B2]?[B3], are Mg, Zn, Cd, Sn, Mn, Fe, Co and Ni when B and C=1/3, and [B2] and [B3], [B2]?[B3], are Li and Cu when B and C=1/4, III) Pb([B1]ATa1-A)O3PbTiO3-PbZrO3 with MnO2, where [B1] is Mg, Zn, Cd, Sn, Fe, Co and Ni when A=1/3, and [B1] is Li and Cu when A=1/4, and IV) Pb([B2]BTa1-B)O3-Pb([B3]CTa1-C)O3-PbTiO3-PbZrO3 with MnO2, where [B2] and [B3], [B2]?[B3], are Mg, Zn, Cd, Sn, Fe, Co and Ni when B and C=1/3, and [B2] and [B3], [B2]?[B3], are Li and Cu when B and C = 1/4

Calculation of the dielectric constants of ferroelectric ceramics

Abstract: It is shown with reference to BaTiO3 and PbTixZr1−xO3 ceramics that the dielectric properties of ferroelectric ceramics can be calculated in agreement with experimental values from Devonshire's theory of ferroelectrics with the aid of a suitable averaging procedure. For this purpose, the expansion coefficients of Devonshire's representation of the free energy of ceramics are determined. With the aid of these coefficients the phase relations of PbTixZr1−xO3 near the morphotropic phase boundary can be calculated in agreement with experiment. An BaTiO3- und PbTixZr1−xO3-Keramik wird gezeigt, das man die dielektrischen Eigenschaften ferroelektrischer Keramik aus der Devonshireschen Theorie der Ferroelektrika mit Hilfe von geeigneten Mittelungsverfahren in Ubereinstimmung mit experimentellen Werten berechnen kann. Hierfur werden die Entwicklungskoeffizienten der Devonshireschen Darstellung der freien Energie and Keramik bestimmt. Mit diesen Koeffizienten last sich speziell fur PbTixZr1−xO3 das Phasensystem nahe der morphotropen Phasengrenze in Ubereinstimmung mit Messungen berechnen.

A model of ferroelectric ceramics: Dielectric constant dependence on electric field

Abstract: A model, describing the electric field dependence of the dielectric constant of ferroelectric ceramics of tetragonal or rhombohedral symmetry, is presented. Perovskite type ferroelectric ceramics of tetragonal symmetry have two types of domains: 90° and 180° domains, while those with rhombohedral symmetry have three types: 71°, 109° and 180°. Since the dielectric behaviour of 71° and 109° domains in rhombohedral phase is actually similar to 90° domains in tetragonal phase, it is sufficient to take into account, for both symmetries, two types of domains: 90° and 180°. The ceramic is composed of a large number of domains of the two kinds. In the model, the coercive fields of these domains are described by two distribu- tion functions. The number of 180° and 90° switchings, caused by applying external d.c. field, is determined by the values of the distribution functions at various field values. This enables one to calculate the electric field dependence of the incremental dielectric constant. As a r...

PLZT ceramic numeric display devices

Abstract: The longitudinal fringe-field electrooptic effect in slim-loop lead lanthanum zirconate titanate (PLZT) ceramics offers the best known possibility of using ferroelectric ceramics for low-voltage, high-contrast numeric and alphanumeric display devices. Such devices appear feasible using either transmitted or reflected ambient light. When using ceramics 75 µrn to 250 µm thick, ON-OFF contrast ratios exceeding 10 dB are obtained with electric fields of 8 kV/cm, and contrast ratios exceeding 20 dB are obtained at 16 kV/cm. These results imply that equally high contrast ratios may be achieved in very thin samples at comparable electric fields but at correspondingly lower applied voltages; e.g., 20–30 volts for a 10 dB contrast ratio with a 25 µm thick ceramic, and 40–60 volts for a 20 dB contrast ratio.