Dielectric ferroelectric ceramics

In the broad range of ceramic materials that are used for electrical and electronic apphcations, each category of material exhibits unique property characteristics which directiy reflect composition, processing, and microstmcture. Detailed treatment is given primarily to those property characteristics relating to insulation behavior and electrical conduction processes. Further details concerning the more specialized electrical behavior in ceramic materials, eg, polarization, dielectric, ferroelectric, piezoelectric, electrooptic, and magnetic phenomena, are covered in References 1—9. 

An ideal single crystal shows a P E) behavior as depicted in Figure 1.6. The non-ferroelectric dielectric ionic and electronic polarization contributions are clearly linear, and are suposed by the spontaneous polarization Ps (dashed curve in Figure 1.6). To reverse the polarization an electrical field with an amplitude E > Ec is required. In opposite to single crystals in polydomain ferroelectric ceramics, the remanent polarization Pr is smaller than the spontaneous one Ps due to backswitching even for opposite fields as shown in Figure 1.6. In that case Ps can be estimated by extrapolation of (non-switching) P-values to E — 0. 

Two types of contributions to dielectric and piezoelectric properties of ferroelectric ceramics are usually distinguished [6], [9-12], One type is called an intrinsic contribution, and it is due to the distortion of the crystal lattice under an applied electric field or a mechanical stress. The second type is called an extrinsic contribution, and it results from the motion of domain walls or domain switching [8], To provide an understanding of material properties of pzt, several methods to separate the intrinsic and extrinsic contributions were proposed. These methods are indirect, and are based on measurements of the dielectric and piezoelectric properties of ferroelectric ceramics [8], [10-12], In the experiments reported in this paper a different approach is adopted, which is based on measurements of high-resolution synchrotron X-ray powder diffraction. The shift in the positions of the diffraction peaks under applied electric field gives the intrinsic lattice deformation, whereas the domain switching can be calculated from the change in peak intensities [13,14],... 

Ferroelectric ceramics (such as barium titanate, lead zircanate titanate) Sensors and actuators, electronic memory, optical applications Tape casting, sputtering, pressing, templated grain growth Improved dielectric and piezoelectric properties... 

Tagantsev AK (1993) Phonon mechanisms of intrinsic dielectric loss in crystals. In Setter N, CollaEL (eds) Ferroelectric ceramics. Birkhauser, Basel, p 127... 

Use Ferroelectric ceramics (single crystals either pure or doped with iron) are used in storage devices, dielectric amplifiers, and digital calculators. 

In addition to dealing with magnetic ceramics, this chapter also deals with dielectric ceramics, such as ferroelectrics, for which the dielectric response is nonlinear. Ferroelectricity was first discovered in 1921 during the investigation of anomalous behavior of Rochelle salt. A second ferroelectric material was not found until 1935. The third major ferroelectric material, BaTi03, was reported in 1944. Ferroelectric ceramics possess... 

Table 15.6 Summary of dielectric data for a number of ferroelectric ceramics...

H. Beltran, B. Gomez, N. Maso, E. Cordoncillo, P. Escribano and A. R. West, Electrical properties of ferroelectric BaTi205 and dielectric Ba6Tii7O40 ceramics, J. Appl. Phys., 97 084104-1-6 (2005). 

Inorganic nanoflllers such as clays or ceramics may improve mechanical properties and dielectric properties. An abundant literature has been devoted to layered silicates for applications in the biomedical domain, hydroxyapatite (HAp e.g., nanoparticles of 300 nm in Figure 13.1a) might be of interest. Ferroelectric ceramics are attractive for their high dielectric permittivity and electroactive properties. As an example, BaTiOa particles with d 700 nm are shown in Figure 13.1b. Conductive nanoparticles should induce electrical conductivity in polymeric matrices, but to preserve the mechanical properties, small amount should be used. Consequently, there is great interest in conductive nanotubes [i.e., carbon nanotubes (CNTs)], which exhibit the highest... 

Kamzina LS, Ruan W, Li GR, Zeng JT (2012) Transparent ferroelectric ceramics PbMgia Nb2/303-xPbZro.53Tio.4703 dielectric and electro-optical properties. Phys Solid State 54 2024-2029... 

Kamzina LS, Wei R, Zeng JT, Li GR (2011) Effect of the La concentration on the dielectric and optical properties of the transparent ferroelectric ceramics 75PbMgi/3Nb2a03-25PbTi03. Phys Solid State 53 1608-1613... 

Finally, it is worth mentioning that a phenomenon analogous to the difference between the normal and giant flexoelectricity of calamitic and bent-core nematics, respectively, exists in crystals, ceramics and polymers too. The flexoelectric response (defined in Eq. (3.1)) of perovskite-type ferroelectrics, " of relaxor ferroelectric ceramics and polyvinylidene fluoride (PVDF) films are four orders of magnitude larger than the flexoelectricity of dielectric crystals. In those sohd ferroelectric materials the polarization induced by flexing is evidently of piezoelectric origin. 

The first area of ferroelectric ceramic application was that of capacitor engineering, where the dielectric effect is exploited. Most ceramic capacitors are, in reality, high-dielectric-constant ferroelectric compositions in which the ferroelectric properties (hysteresis loop) are suppressed with suitable chemical dopants while retaining a high dielectric constant over a broad temperature range. Historically, the first composition used for such capacitors was BaTi03 and its modifications, but today lead-containing relaxors and other compositions are also included. 

Class II dielectrics comprise the ferroelectrics. These materials offer much higher dielectric constants than Class I dielectrics, but with less stable properties with temperature, voltage, frequency, and time. The diverse range of properties of the ferroelectric ceramics requires a subclassification into two categories, defined by temperature characteristics. 

Ferroelectric materials, especially polyciystalhne ceramics, are utihzed in various devices such as high-permittivity dielectrics, ferroelectric memories, pyroelectric sensors, piezoelectric transducers, electrooptic devices, and PTC (positive temperature coefficient of resistivity) components. 

The most important improvement in the effective material properties appears in the value of gh due to the lower dielectric constant of the composite with respect to the ferroelectric ceramic grains (for example lOOOeo for PZT, lOeo... 

Relatively few applications have utilized the ferroelectric effect in ceramics. Ferroelectric ceramics have been widely employed because of the other properties that they display, however. Their dielectric, piezoelectric, and pyroelectric properties have led to their use in capacitor, actuator and other piezoelectric applications, and infrared detection devices. Again, the most widely used materials are the lead-based ABO perovskite compounds. 

Figure 8.2 Temperature dependence of spontaneous polarization Ps and dielectric permittivity e, of a ferroelectric ceramics in the vicinity of the Curie temperature, Tq.

Experimental evidence exists that the grain size of a polycrystalline ferroelectric ceramic strongly influences the crucial dielectric properties such as permittivity. 

In conclusion, complex perovskite relaxor ceramics are characterized by a very diffuse range of the ferroelectric-paraelectric OD phase transition, owing to nano-scopic compositional fluctuations. The minimum domain size that stiU sustains cooperative phenomena leading to ferroelectric behavior is the so-called Kiinzig region (Kanzig, 1951), and is on the order of 10 to lOOnm in PMN. In contrast to normal ferroelectric ceramics, relaxor ceramics show a frequency dependence of the dielectric permittivity as well as the dielectric loss tangent, which presumably is caused by the locally disordered structure that creates shallow, multipotential wells. 

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