NIH/USC Transducer grant Report 2009-2010 (Penn State)
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>120 oC) and the
coercive field is more than double at room temperature (EC> 5kV/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:   8198kg / m3 )
Elastic stiffness constants: cij (1010 N/m2)
c11E a
c12E a
c13E
12.2
11.3
10.8
E
c33
a
E a
c44
E
c66
6.9
6.2
11.2
c11D
c12D
c13D
D
c33
12.3
11.4
9.9
17.1
a
a
D a
c44
D
c66
7.5
6.2
a
Elastic compliance constants: sij (10-12 N/m2)
s11E *
s12E
s13E
E a
s33
E
s44
E
s66
s11D
s12D
s13D
D a
s33
D
s44
D
s66
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)
e15
e31
e33
d15
16.0
2.7
18.6
232
d 31
gi (10-3 Vm/N)
d 33
-1337 2742
hi (108 V/m)
g15
g 31
g 33
h15
h31
h33
2.6
-13.4
42.7
3.8
-4.6
31.9
Dielectric constants:  ( 0 )
 (10 4 /  0 )
Electromechanical coupling factors
11S a
 33S a
11T a
T a
 33
11S
 33S
11T
 33T
k15
a
k31 a
k33 a
kt
4736
659
10081
7244
2.1
15.2
1.0
1.4
0.20
0.65
0.95
0.59
a
directly measured properties.
a
Led by environmental concerns, lead free piezoelectrics based on the perovskite
families of KNN (K,Na-Niobates) and NBKT ( Na,Bi, potassium niobates) have been
developed 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 sensitivity of 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 PMNPT 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 quarter wavelength is no more a constraint.
Fig. 2 The thickness of matching layer was changed to provide a good matching design for
lower frequencies. The initial transmission coefficient curve at low frequencies becomes
steeper and the first total transmission peak appears at 18MHz for an 80 micron thick matching
layer.
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
damages could 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)O3–0.06PbTiO3 single crystals”,
Appl. Phys. Lett., 96, 092902 (March 1, 2010).
Award and Honor:
“Electroceramic Bridge Building Award”
14th US-Japan Seminar on Dielectric and Piezoelectric Materials, Welches, Oregon,
October 13, 2009.
Invited talks at international conferences
1.
2.
W. Cao, “Ferroelectrics in Extremes”, Workshop on Research Frontiers and Capability
Gaps for Controlling and Designing Functional Materials, Jan 20-22, 2009, Los Alamos,
NM.
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.