NIH/USC Transducer grant Report 2009-2010(PennState)

Development and Characterization of Piezoelectric and Matching Materials for Ultrasound Transducers

1. Recent progress in piezoelectric materials

Owing to the superior piezoelectric properties d33 and the high electromechanical coupling coefficient k33, PMN-PT single crystals already started to replace PZT in many ultrasonic imaging transducers. The ultrabroad bandwidth transducers made of PMN-PT enable doctors to perform second harmonic imaging at ease. However, because the phase transition temperature of PMN-PT system is relatively low, its temperature stability and field electric field endurance need to be improved.

In the past year, we continue to investigate novel piezoelectrics, materials characterization, advanced fabrication methods, and more accurate property characterization method. One noticeable progress is the development of ternary compound PMN-PIN-PT single crystals. This relaxor-based single rystal system not only has the same piezoelectric performance as that of binary PMN-PT single crystals, its phase transition temperature is being pushed up by more than 20 C (Trt>120oC) and the coercive field is more than double at room temperature (EC5kV/cm) so that the temperature stability is much enhanced and the crystal can also sustain higher field operation. Shown in Fig. 1 are the frequency dependence of the electromechanical coupling coefficient k33 for PMN-PIN-PT single crystal, PMN-PT single crystals and PMN-PT ceramics. One can see that the frequency stability is much better for the newly developed PMN-PIN-PT single crystals.

Fig. 1 Electromechanical coupling k33 as function of frequency range.

One can see from Fig. 1 that the new PMN-PIN-PT is much more suitable for high frequency applications compared to PMN-PT single crystals, which show severe degradation at frequencies higher than 30 MHz.

In order to use the new PMN-PIN-PT single crystals, we have characterized the full set of electromechanical, dielectric and elastic properties. As shown in Table I, the piezoelectric properties, dielectric properties and elastic properties of this ternary compound are very similar to that of PMN-PT single crystals. Due its much higher Trt transition temperature and more than 2 times of coercive field, we can anticipate that this PMN-PIN-PT single crystals will become the preferred piezoelectric materials for high frequency medical ultrasonic transducers.

Table I Measured and derived material constants of 0.27PIN-0.40PMN-0.33PT multidomain single crystal poled along [001]c (Density: )

Elastic stiffness constants: cij (1010 N/m2)
a / a / / a / a / a / / / / a / a / a
12.2 / 11.3 / 10.8 / 11.2 / 6.9 / 6.2 / 12.3 / 11.4 / 9.9 / 17.1 / 7.5 / 6.2
Elastic compliance constants: sij (10-12 N/m2)
* / / / a / / / / / / a / /
75.5 / -38.3 / -35.8 / 77.8 / 14.5 / 16.1 / 61.0 / -52.8 / -4.7 / 11.3 / 13.3 / 16.1
Piezoelectric coefficients: ei(C/m2) / di (10-12 C/N) / gi (10-3 Vm/N) / hi (108 V/m)
16.0 / -2.7 / 18.6 / 232 / -1337 / 2742 / 2.6 / -13.4 / 42.7 / 3.8 / -4.6 / 31.9
Dielectric constants: / / Electromechanical coupling factors
a / a / a / a / / / / / a / a / a / a
4736 / 659 / 10081 / 7244 / 2.1 / 15.2 / 1.0 / 1.4 / 0.20 / 0.65 / 0.95 / 0.59

a directly measured properties.

Led by environmental concerns, lead free piezoelectrics based on the perovskite families of KNN (K,Na-Niobates) and NBKT ( Na,Bi,potassiumniobates) have beendeveloped and subsequently characterized in relation to their PZT counterparts. (ref.1) As the environmental laws become more and more strict, research on lead-free piezoelectric materials is one of the hottest topic in materials field.

II. Progress on matching layer design and characterization

Matching layer is an important component of ultrasonic transducer, which helps increase the sensitivityof ultrasonic transducers. Because it becomes very thin for high frequency transducers, design and fabricate good matching layers become a real challenge. In addition, quarter wavelength matching layer has limited bandwidth, which becomes the limiting factor for ultrabroadband transducers, such as those made of PMN-PT single crystals. We have designed several gradient matching layers, which can work at very high frequencies. As shown in Fig. 2, computer simulation indicated that our designs can practically work for ultrasonic transducers of any frequency, and it is particularly good for very high frequencies (> 100 MHz) and ultrabroadband transducers. The low frequency cut-off can be pushed to lower frequencies with the increase of the matching layer thickness, but quarterwavelength is no more a constraint.

We have characterized the frequency dependent velocity and attenuation of light polymer matching materials, whose density is lighter than water (~ 0.82 g/cm3). Typical results are shown in Figs. 3&4. The ultrasonic velocity in this material showed very strong frequency dependence for this material. These data are not available in the literature.

Figure 3 Sound velocity of MX002.

Figure 4 Sound attenuation of MX002.

III. Damage analysis

In order to increase the effective coupling coefficient k33, 1-3 or 2-2 types of piezocomposites are often used. It is found that the electromechanical coupling properties degrade in the composite, particularly when the center frequency goes up. Figure 5 presents the degradation in 1-3 piezoelectric polymer composites. We found that such degradation is mainly a consequence of structural damage due to mechanical dicing. Such damagescould be a few microns in depth from the surface. The good news is, in contrast to fine grain polycrystalline PMN-PT ceramics, the ternary crystals PMN-PIN-PT single crystals offer optimum performance in monolithic and composite transducers. It will be essential to further investigate the level of surface damage as related to the fabrication method in the coming year.

X. Jiang, K. Snook, W. Hackenberger, and X. Geng, Proc. SPIE 6531, 65310F (2007).

X. Jiang, K. Snook, T. Walker, A. Portune, R. Haber, X. Geng, J. Welter, and W. Hackenberger, Proc. SPIE 6934, 69340D (2008).

Fig. 5 Effective coupling factor as function of center frequency.

Refereed Journal Publications:

  1. S. J. Zhang, J. B. Lim, H. J. Lee and T. R. Shrout, “Characterization of “hard” piezoelectric lead free ceramics,” IEEE Trans. Ultrason. Ferroelectric. Freq. Control., 56 (2009) 1523.
  2. S. J. Zhang, J. Luo, W. Hackenberger, N. P. Sherlock, R. J. Meyer Jr. and T. R. Shrout, “Electromechanical characterization of PIN-PMN-PT crystals as a function of crystallographic orientation and temperature,” J. Appl. Phys. 105 (2009) 104506.
  3. S. J. Zhang, N. P. Sherlock, R. J. Meyer Jr. and T. R. Shrout, “Crystallographic dependence of loss in domain engineered Relaxor-PT single crystals,” Appl. Phys. Lett. 94 (2009) 162906.
  4. Chuanwen Chen, Rui Zhang and Wenwu Cao, “Theoretical study on guided wave propagation in (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 (x=0.29 and 0.33) single crystal plates”J. Phys. D, vol 42, 095411 (2009)
  5. X. Z. Liu, S. J. Zhang, J. Luo, T. R. Shrout and Wenwu Cao, “Complete set of material constants of (Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 single crystal with morphotropic phase boundary composition” J. Appl. Phys. 106 (2009) 074112.
  6. Yang Xian, Rui Zhang and Wenwu Cao, “Piezoelectric properties of domain engineered barium titanate single crystals with different volume fractions of domain walls”, J. Appl. Phys., vol. 106, 064102 (Sept, 2009).
  7. Xiuming Li, Rui Zhang and Wenwu Cao, “Surface Acoustic Wave Propagation Properties of 0.67PbMgNbO3-0.33PbTiO3 Single Crystal Poled along [111]c” Appl. Phys. Lett. Vol. 95, 242906 (2009)
  8. X. Z. Liu, S. J. Zhang, J. Luo, T. R. Shrout, Wenwu Cao, “A complete set of material properties of single domain 0.26PIN-0.46PMN-0.28PT single crystals,” Appl. Phys. Lett. 96 (2010) 012907.
  9. X. Z. Liu, S. J. Zhang, J. Luo, T. R. Shrout, Wenwu Cao, “Electric field dependence of nonlinearity parameters and third order elastic constants of 0.70PMN-0.30PT single crystal,” Appl. Phys. Lett., 96 (2010) 052905.
  10. F. Li, S. J. Zhang, Z. Xu, X. Y. Wei, J. Luo and T. R. Shrout, “Electromechanical properties of tetragonal PIN-PMN-PT ferroelectric crystals,” J. Appl. Phys. 107 (2010) 054107.
  11. S. J. Zhang, J. Luo, F. Li, R. J. Meyer Jr., W. Hackenberger and T. R. Shrout, “Polarization fatigue in PIN-PMN-PT single crystals,” Acta Materialia, 58, (2010) 3773-3780.
  12. Zhu Wang, Rui Zhang, Enwei Sun and Wenwu Cao “Contributions of domain wall motion to complex electromechanical coefficients of 0.62Pb(Mg1/3Nb2/3)O3–0.38PbTiO3 crystals”J. Appl. Phys.,107，014110 (Jan.13, 2010).
  13. Yang Xiang, Rui Zhang and Wenwu Cao, “ Optimization of piezoelectric properties for[001]c poled 0.94Pb(Zn1/3Nb2/3)O3–0.06PbTiO3single crystals”, Appl. Phys. Lett., 96, 092902 (March 1, 2010).

Award and Honor:

“ElectroceramicBridgeBuilding Award”

14th US-Japan Seminar on Dielectric and Piezoelectric Materials, Welches, Oregon, October 13, 2009.

Invited talks at international conferences

  1. W. Cao, “Ferroelectrics in Extremes”, Workshop on Research Frontiers andCapability Gaps for Controlling and Designing Functional Materials, Jan20-22, 2009, Los Alamos, NM.
  2. W. Cao, “Guided wave propagation in (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 single crystal plates”,The IMF-ISAF-2009, a joint meeting of 12th International Meeting on Ferroelectricity and 18th IEEE International Symposium on Applications of Ferroelectrics, August 23-27, 2009, Xi’an, China.