PROCESSING, PROPERTIES, AND APPLICATION OF TEXTURED 0.72Pb(Mg1/3Nb2/3)O3-0.28PbTiO3 CERAMICS
Open Access
- Author:
- Brosnan, Kristen H
- Graduate Program:
- Materials Science and Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- January 04, 2007
- Committee Members:
- Gary Lynn Messing, Committee Chair/Co-Chair
Richard Joseph Meyer Jr., Committee Chair/Co-Chair
Susan E Trolier Mckinstry, Committee Member
Thomas R Shrout, Committee Member - Keywords:
- PMN-PT
templated grain growth
ferroelectrics
piezoelectrics
ceramic
microstructure control - Abstract:
- Textured (1-x)(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-xPT) ceramics obtained by the templated grain growth (TGG) process possess a significant percentage of the piezoelectric properties of the Bridgman grown single crystals with the potential of lower cost. In this work, TGG materials with high texture volume (81 %) were developed. Highly anisotropic (aspect ratio > 10) SrTiO3 template crystals were aligned by tape casting in a fine, calcined, perovskite PMN-28PT matrix. The processing conditions used in this study produced higher quality textured PMN-28PT with a corrected x-ray diffraction (XRD) rocking curve full width half maximum (FWHM) of 7.6¡Æ. The textured PMN-28PT ceramic had high texture volume (f = 0.81), narrow orientation distribution (r = 0.21), and high density (7.8 g/cc, 98% TD). Until recently, characterization of texture in this material had been limited to Lotgering analysis (a comparison of the relative intensity of XRD peak heights). In this study, XRD and electron backscatter diffraction (EBSD) techniques were used to characterize the fiber texture in oriented PMN-28PT and the intensity data were fit with a texture model (the March-Dollase equation) that describes the texture in terms of texture fraction (f), and the width of the orientation distribution (r). EBSD analysis confirmed the <001> orientation of the microstructure, with no distinguishable randomly oriented, fine grain matrix. Although XRD rocking curve and EBSD data analysis gave similar f and r values, XRD rocking curve analysis was the most efficient and gave a complete description of texture fraction and texture orientation (f = 0.81 and r = 0.21, respectively). XRD rocking curve analysis was the preferred approach for characterization of the texture volume and the orientation distribution of texture in fiber-oriented PMN-PT. The dielectric, piezoelectric and electromechanical properties for random ceramic, 69 vol% textured, 81 vol% textured, and single crystal PMN-28PT were fully characterized and compared. The room temperature dielectric constant at 1 kHz for highly textured PMN-28PT was ¥å r ¡Ã 3600 with low dielectric loss (tan ¥ä = 0.004). The temperature dependence of the dielectric constant for 81 vol% textured ceramic followed a similar trend as the single crystal PMN-28PT up to the rhombohedral to tetragonaltransition temperature (TRT) at 104¨¬C. 81 vol% textured PMN-28PT consistently displayed 60 to 65% of the single crystal PMN-28PT piezoelectric coefficient (d33) and 1.5 to 3.0 times greater than the random ceramic d33 (measured by Berlincourt meter, unipolar strain-field curves, IEEE standard resonance method, and laser vibrometry). The 81 vol% textured PMN-28PT displayed similarly low piezoelectric hysteresis as single crystal PMN-28PT measured by strain-field curves at 5 kV/cm. 81 vol% textured PMN-28PT and single crystal PMN-28PT displayed similar mechanical quality factors of QM = 74 and 76, respectively. The electromechanical coupling (k33) of 81 vol% textured PMN-28PT (k33 = 0.79) was a significant fraction of single crystal (k33 = 0.91) and was higher than a commercial PMN-PT ceramic (k33 ~ 0.74). The nonlinearity of the dielectric and piezoelectric response were investigated in textured ceramics and single crystal PMN-28PT using the Rayleigh approach. The reversible piezoelectric coefficient was found to increase significantly and the hysteretic contribution to the piezoelectric coefficient decreased significantly with an increase in texture volume. This indicates that increasing the texture volume decreases the non-180¨¬ domain wall contribution to the piezoelectric response in PMN-28PT. Finally, 81 vol% textured ceramics were also integrated into a Navy SONAR transducer design. In-water characterization of the transducers showed higher source levels, higher in-water coupling, higher acoustic intensity, and more bandwidth for the 81 vol% textured PMN-28PT tonpilz single elements compared to the ceramic PMN-28PT tonpilz element. In addition, an 81 vol% textured PMN-28PT tonpilz element showed large scale linearity in sound pressure levels as a function of drive level under high drive conditions (up to 2.33 kV/cm). The maximum electromechanical coupling obtained by the 81 vol% textured PMN-28PT transducer under high drive conditions was keff = 0.69. However, the resonance frequency shifted significantly during high drive tests (¥Äfs = -19% at 3.7 kV/cm), evidence of a ¡°soft¡± characteristic of the 81 vol% textured PMN-28PT, possibly caused by Sr2+ from the template particles. The results suggest there are limitations on the preload compressive stress (and thus drive level) for these textured ceramics, but this could be addressed with compositional modifications. The dielectric, piezoelectric and electromechanicalproperties have been significantly improved in textured PMN-PT ceramics of this study. Furthermore, scale-up in processing for incorporation into devices of highly textured ceramics with reproducible texture (and hence narrow properties distribution) was achieved in these materials. SONAR applications could benefit from textured ceramic parts because of their ease of processing, compositional homogeneity and potentially lower cost.