Ceramic composites piezoelectricity

Composite piezoelectric transducers made from poled Pb-Ti-Zr (PZT) ceramics and epoxy polymers form an interesting family of materials which highlight the advantages of composite structures in improving coupled properties in soilds for transduction applications A number of different connection patterns have been fabricated with the piezoelectric ceramic in the form of spheres, fibers, layered, or three-dimensional skeletons Adding a polymer phase lowers the density, the dielectric constant, and the mechanical stiffness of the composite, thereby altering electric field and concentrating mechanical stresses on the piezoelectric ceramic phase. 

Nunes-Pereira, J., Sencadas, V, Correia, V, Rocha, J.G., Lanceros-M ndez, S., 2013. Energy harvesting performance of piezoelectric electrospun polymer fibers and polymer/ceramic composites. Sensors Actuat. A Phys. 196,55-62. 

The ceramic compositions of (l-x)(Ko,48Nao4iLio,04)Nb03-xBaTi03 [(l-x)KNLN-xBT] and 0.99(Ko,48Nao,48Lio,04)(Nbi.ySby)03-0.01BaTi03 (KNLN. ySy-BT), were used as model systems to illustrate the variation of piezoelectric constant. The ceramics were synthesized by conventional solid-... 

Dogan A, Uchino K, Newnham RE (1997) Composite piezoelectric transducer with truncated conical endcaps Cymbal . IEEE Trans UFFC 44 597-605 Elissalde C, Cross LE (1995) Dynamic characteristics of Rainbow ceramics. J Am Ceram Soc 78 2233-2236... 

The research works on toughening mechanisms and fracture toughness of ceramic composites with piezoelectric phases have been limited, while those for monolithic piezoelectric/ferroelectric materials have been available, as mentioned above. Therefore, details of toughening behavior and mechanisms in composite materials with piezoelectric phases have been still not clear. 

Runt, J. and Galgoci, E. C., Polymer/piezoelectric ceramic composites Polystyrene and poly(methyl methacrylate) with PZT, J. AppL Polym. ScL, 29, 611-617 (1984). 

Newnham, R. E. and Runt, J. P., Polymer-piezoelectric ceramic composites, Polym. News, 10,132-138 (1984). 

As mentioned above, a composite in general is a heterostructural materuJ whose properties are determined by the contents, the number of different phases of which the material is composed, their properties, and the ways in which different phases are interconnected (73.67]. The latter is the most important feature of composites, since the mixiiig rules of a given property are controlled by the self-connectiveneas of individual phases. Piezoelectric polymer-ceramic composites, for example, have a number of appUcatioas. since their properties can be tailored to the requirements of various devices by combining the superior properties of a polymer and those of ceramics [67]. 

Composite piezoelectric materials may be represented by the so-called simple series, simple parallel and the modified cubes diphasic models (Fig. 6.4). The modified cubes model was developed as a generalization of the series, parallel and cubes models. It is adapted for the representation of 0-3 composite sheet materials. Estimated values of the average longitudinal piezoelectric strain coefficient 33 and the average piezoelectric voltage coefficient 33 for the composite may be evaluated in terms of these models. References to the piezoelectric ceramic and the polymer phase will be indicated by superscripts 1 and 2 respectively. 

Piezocomposite transducers are an advancement of piezoelectric ceramics. Instead of the classic piezoceramic material, a compound of polymer and piezoceramic is used for the composite element to improve specific properties. The 1-3 structure, which is nowadays mostly used as transducer material, refers to parallel ceramic rods incorporated in an epoxy-resin matrix (see Fig. 1). 

Based upon a piezoelectric 1-3-composite material, air-bome ultrasonic probes for frequencies up to 2 MHz were developped. These probes are characterized by a bandwidth larger than 50 % as well as a signal-to-noise ratio higher than 100 dB. Applications are the thickness measurement of thin powder layers, the inspection of sandwich structures, the detection of surface near cracks in metals or ceramics by generation/reception of Rayleigh waves and the inspection of plates by Lamb waves. 

Ferroelectric Ceramic—Polymer Composites. The motivation for the development of composite ferroelectric materials arose from the need for a combination of desirable properties that often caimot be obtained in single-phase materials. For example, in an electromechanical transducer, the piezoelectric sensitivity might be maximized and the density minimized to obtain a good acoustic matching with water, and the transducer made mechanically flexible to conform to a curved surface (see COMPOSITE MATERIALS, CERAMiC-MATRix). 

The development of active ceramic-polymer composites was undertaken for underwater hydrophones having hydrostatic piezoelectric coefficients larger than those of the commonly used lead zirconate titanate (PZT) ceramics (60—70). It has been demonstrated that certain composite hydrophone materials are two to three orders of magnitude more sensitive than PZT ceramics while satisfying such other requirements as pressure dependency of sensitivity. The idea of composite ferroelectrics has been extended to other appHcations such as ultrasonic transducers for acoustic imaging, thermistors having both negative and positive temperature coefficients of resistance, and active sound absorbers. 

Ferroelectric—polymer composite devices have been developed for large-area transducers, active noise control, and medical imaging appHcations. North American Philips, Hewlett-Packard, and Toshiba make composite medical imaging probes for in-house use. Krautkramer Branson Co. produces the same purpose composite transducer for the open market. NTK Technical Ceramics and Mitsubishi Petrochemical market ferroelectric—polymer composite materials (108) for various device appHcations, such as a towed array hydrophone and robotic use. Whereas the composite market is growing with the invention of new devices, total unit volume and doUar amounts are small compared to the ferroelectric capacitor and ferroelectric—piezoelectric ceramic markets (see Medical imaging technology). 

R. Y. Ting, "Evaluation of New Piezoelectric Composite Materials for Hydrophone AppUcations," presented at the Bernard Jaffe Memorial Colloquium, American Ceramics Society, 86 Meeting, Pittsburgh, 1984. 

CH2—CI2—) —(—CF2— CFH—) (39). Ceramic crystals have a higher piezoelectric efficiency. Their high acoustic impedance compared to body tissues necessitates impedance matching layers between the piezoelectric and the tissue. These layers are similar in function to the antireflective coatings on a lens. Polymer piezoelectric materials possess a more favorable impedance relative to body tissues but have poorer performance characteristics. Newer transducer materials are piezoelectric composites containing ceramic crystals embedded in a polymer matrix (see Composite materials, polymer-MATRIX Piezoelectrics). 

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. 

---