Electroactive ceramics properties

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]. 

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. 

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... 

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. 

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. 

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