The sintering kinetics and microstructural evolution of alumina tubes (ϳ17 mm length, ϳ9 mm inner diameter, and ϳ11 mm outer diameter) were studied by conventional and microwave heating at 2.45 GHz. Temperature during microwave heating was measured with an infrared pyrometer and was calibrated to ؎10°C. With no hold at sintering temperature, microwave-sintered samples reached 95% density at 1350°C versus 1600°C for conventionally heated samples. The activation energy for microwave sintering was 85 ؎ 10 kJ/mol, whereas the activation energy for conventionally sintered samples was 520 ؎ 14 kJ/mol. Despite the difference in temperature, grains grew from ϳ1.0 m at 86% density to ϳ2.6 m at 98% density for both conventionally sintered and microwave-sintered samples. The grain size/density trajectory was independent of the heating source. It is concluded that the enhanced densification with microwave heating is not a consequence of fast-firing and therefore is not a result in the change in the relative rates of surface and grain boundary diffusion in the presence of microwave energy. Fig. 7. Grain growth trajectories of microwave-sintered and conventionally sintered samples.

Textured (1-x)(Mg 1/3 Nb 2/3 )O 3 -xPbTiO 3 (PMN-PT) ceramics obtained by the templated grain growth process possess a significant fraction of the piezoelectric properties of Bridgman-grown single crystals at a fraction of the cost. However, for integration of these materials into transducer and actuator designs, a more comprehensive characterization of texture quality than possible with Lotgering analysis is needed. In this study, X-ray diffraction (XRD) and electron backscatter diffraction techniques were used to characterize the fiber texture in /001Soriented PMN-28PT. The March-Dollase equation was fitted to the intensity data to describe the texture in terms of the texture fraction, f, and the degree of texture of the oriented fraction using the March parameter, r. Although each of the techniques used was quantitatively in agreement, XRD rocking curve collection and analysis was the most time-efficient technique for making a comprehensive measurement of texture (f 5 0.69, r 5 0.29, FWHM 5 13.91) for fiber-oriented PMN-28PT. 1965J ournal

Highly textured PMN-28PT (0.72Pb(Mg 1/3 Nb 2/3 )O 3 -0.28PbTiO 3 ) ceramics were produced by templated grain growth on o0014 oriented platelet-shaped SrTiO 3 template particles with an aspect ratio of 10-15. The templates were aligned in PMN-28PT matrix powder via tape casting and fired in an O 2 -PbO atmosphere at 11501C for up to 15 h. This resulted in textured ceramics with a 40 micrometer grain size and without residual templates. The volume fraction of textured material ( f ) and the orientation parameter (r) were quantified by fitting X-ray diffraction rocking curve data to the MarchDollase equation. Processing conditions were optimized to achieve the best possible values of f and r for the chosen templates and matrix powder. A texture fraction of at least 81 vol% and an orientation parameter of 0.2 were achieved when all random matrix grains were consumed (a perfect textured ceramic would show a texture fraction of 100 vol% and an orientation parameter of 0).

Abstract

Tonpilz transducers are fabricated from 001 fiber-textured 0.72Pb(Mg(1/3)Nb(2/3))O(3)-0.28PbTiO(3) (PMN-28PT) ceramics, obtained by the templated grain growth process, and PMN-28PT ceramic and Bridgman grown single crystals of the same composition. In-water characterization of single element transducers shows higher source levels, higher in-water coupling, and more usable bandwidth for the 81 vol % textured PMN-28PT device than for the ceramic PMN-28PT element. The 81 vol % textured PMN-28PT tonpilz element measured under large signals shows linearity in sound pressure levels up to 0.23 MV/m drive field but undergoes a phase transition due to a lowered transition temperature from the SrTiO(3) template particles. Although the textured ceramic performs well in this application, it could be further improved with compositional tailoring to raise the transition temperature and better processing to improve the texture quality. With these improvements textured piezoelectric ceramics will be viable options for medical ultrasound, actuators, and sonar applications because of their ease of processing, compositional homogeneity, and potentially lower cost than single crystal.