Advanced Cerametrics (United States)

Langanite (LGN, La/sub 3/Ga/sub 55/Nb/sub 0.5/O/sub 14/), Langatate (LGT, La/sub 3/Ga/sub 55/Ta/sub 0.5/O/sub 14/) single-crystal piano-convex resonators were driven in thickness modes by lateral field excitation using a custom fixture. Resonance behavior was characterized as a function of in-plane (azimuthal) rotation angle for the thickness vibration modes of doubly rotated orientation. Specifically, S/sub 11/ reflection coefficients were measured for the first and third overtones of the c-mode and the b-mode using a network analyzer and converted into relative piezoelectric coupling coefficients. Results are presented in terms of relative lateral piezoelectric coupling coefficients versus azimuthal angle. Comparison with theoretical predictions, made for: the case of simple thickness modes (i.e., plane waves) using an extension of the Christoffel-Bechmann method with published materials constants, shows good agreement. Furthermore, it is demonstrated that lateral field excitation of some doubly rotated cuts of LGN and LGT offers the potential for significantly enhancing c-mode piezoelectric coupling, and for tuning out the unwanted b-mode, as compared to thickness-field excitation.

Lead zirconate titanate (PZT) fibers 50 to 70 /spl mu/m in diameter, formed by the Viscous Suspension Spinning Process (VSSP) were sized and incorporated into piezoelectric ceramic/polymer composites. Water soluble polymer solutions containing polyvinyl alcohol, polyethylene glycol, and ethylene glycol were used as sizing agents. The sized fibers formed a multifilament collimated bundle called a tow. The number of individual fibers in a tow varied between 10 and 500. The sized tows were dried at room temperature and cut to desired lengths, heat treated to remove the organic and fired to form straight rods. The rods were bundled and embedded in spurrs epoxy to fabricate 1-3 composites. Green tows were also woven into plain fabric and carpet structures. After firing, the diameter of the individual PZT fibers was 10 to 30 /spl mu/m. The effect of sizing solution chemistry and concentration on tow tightness and flexibility is reported. The microstructure and electromechanical properties of composites with a variety of architectures are also discussed.

Piezoelectric ceramic/polymer composites with 1‐3 connectivity were made by weaving sized lead zirconate titanate (PZT) fiber bundles through a honeycomb support. Bundles comprised of fine‐scale, 20‐50 μm green fibers, made using the viscous suspension spinning process, were sized to increase their manageability. The sizing step comprised of soaking the green PZT fiber bundles in an aqueous solution of poly(vinyl alcohol), then pulling the wet fibers through a steel sizing die. Sizing resulted in dense and flexible fiber bundles, which facilitated composite construction and led to composites with increased volume fractons. Sintering, polymer embedding, and machining produced a composite exhibiting 1‐3 connectivity. Composites with 10 vol% PZT yilded d33 values of 230 pC/N and a dielectric constant of 130.