Electroactive ceramics

Recently, PVDF has been intensively studied by many authors as a polymer matrix for ceramic nanopowders such as BaTiOs [212,214-216], PbTiOs [217], CaCOs [218], and Pb(Zro.5TiOo.5)03 [215] because they combine the excellent ferroelectric properties of ceramics with the flexible mechanical properties of the polymer. The PVDF polymer composites with electroactive ceramic nanoparticles were prepared by sol-gel processes [214,217], a natural adsorption action between the nanosized BaTiOs and PVDF particles, and then a hot press process [216]. 

Shul, G., M. Saczek-Maj, and M. Opallo, 2004. Electroactive ceramic carbon electrode modified with hydrophobic polar solvent. Electroanalysis 16 1254—61. 

In the context of the voltammetry of microparticles methodology, the H-point standard addition method has been adapted for determining organic dyes [241] as well as lead and tin in ceramics [242]. Let us consider a mixture of material containing unknown amounts of two electroactive compounds, A and B, and a reference compound, R. It is assumed that weighted amounts of both materials are accurately powdered and thoroughly mixed so that the mass ratio between the A,B-containing material and the reference compound, m/mR, is known. 

Unless materials are chemically stable in service environments, their otherwise useful properties (strength, ductility, magnetic and electronic behavior, etc.) may be lost. This section describes research opportunities and needs associated with metastable metallic alloys, metal-matrix composites, electroactive polymers, and high-performance ceramics. 

In a quasi-binary system, interdiffusion of ions also results in a so-called interdiffusion diffusion that is also rate-limited by the diffusivity of the slower of the two ions. This process occurs, e.g., when solid-state reactions between ceramics or ion-exchange experiments are carried out. Solid electrolytes can be used as sensors to measure thermodynamic data, such as activities and activity coefficients. The voltage generated across these solids is directly related to the activities of the electroactive species at each electrode. 

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... 

Looking beyond ceramic materials to elec-trets, polymer and elastomeric piezoelectric materials, and so-caUed electroactive materials, a wide-open field of research in high-strain piezoelectric materials is appearing. Using the same technology to manipulate the chemical and physical stractures of complex ionic or nanotube-imbibed polymers, strains of well over 50 % have been obtained in this new class of material, many examples of which are biocompatible. Improvements in reliability, tolerance of extreme ambient conditions, and modeling are important areas that remain to be considered. 

Looking beyond ceramic materials to electrets, polymer and elastomeric piezoelectric materials, and so-called electroactive materials, a wide-open field of research in high-strain piezoelectric materials is appearing. Using the same technology to manipulate the chemical and physi-... 

Another approach to separate Li anode from direct contact with water has been realized by isolating the Li anode using a water impermeable Li+-conducting glass ceramic electrolyte (GCE). If the anode of such a battery is isolated from the aqueous environment by a hermetic pouch, such anodes can be used as a power source in sea water [156]. The electroactive species are water molecules that are reduced to molecular hydrogen at the battery cathode ... 

Electroactive polymers have piezoelectric and pyroelectric properties that are lower than those of ceramics materials. However, they have low permittivity as well as other advantages that enable their use in applications (Lang, 2008) such as acmators, vibrational control, ultrasonic transducers, and others such as shock sensors, health monitoring, tactile sensors, and energy conversion devices. 

This chapter discusses materials known as electroactive composites. These are mixtures of an electroactive (or in the present context, ferroelectric) ceramic phase and a polymer phase. Early sections will look at the individual phases, making use of piezoelectric parameters defined in Chapter 5. A summary of theoretical models will then be given, before preparation and characterization are discussed. Finally, the problems associated with producing an active device and examples of working systems will be considered. 

The ceramic is the electroactive part of the two-phase composite, and its properties, both inherent and poled, depend on the method of preparation. 

Although the ceramic phase of the composite makes the material electroactive, many of the important properties of the material are derived primarily from the properties of the polymer. Also, the choice of polymer can determine whether the best ceramic sensitivity can be realized. The electrical properties to be considered are the resistivity p, the relative permittivity (dielectric constant) the dielectric loss, the dissipation factor D, the power factor F and the dielectric strength. The variation of these properties with changes in the likely environment should also be considered, since many of them vary with temperature, frequency and humidity. 

---