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弛豫铁电单晶（Relaxor-PT）材料与水声换能器
压电材料能够实现电能与声能的相互转换，是水声换能器的核心组成部分，对换能器的整体性能起着决定性的作用。20世纪90年代以来，随着生长工艺的不断完善，以铌锌酸铅-钛酸铅[Pb(Zn1/3Nb2/3)O3–PbTiO3，(PZNPT)]，铌镁酸铅-钛酸铅[Pb(Mg1/3Nb2/3)O3–PbTiO3，(PMNPT)]，和铌铟镁酸铅-钛酸铅[Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3，(PIN–PMN–PT)]为代表的大尺寸弛豫铁电单晶生长制备逐渐成熟（图1），推动了换能器技术的飞速发展 [1] [2] [3]。
图1 (a) PZN-PT [4]；(b) PMN-PT [5]；(c) PIN-PMN-PT [6]
弛豫铁电单晶材料是一种由驰豫铁电体（Relaxor）和常规铁电体（例如钛酸铅PbTiO3, PT）构成的固溶体压电单晶，具备非对称钙钛矿晶体结构（图2），其性质与晶体组分、相位、切型和极化方向密切相关。随着PT含量的增加，弛豫铁电单晶材料将发生三方相（rhombohedral）→ 斜方相（orthorhombic）/单斜相（monoclinic）→ 四方相（tetragonal）的相变，如图3所示。弛豫铁电单晶材料的宏观对称性与极化方向密切相关，如图4所示，沿非极轴方向极化的晶体为多畴状态，被称为“工程畴结构”。按照极化后可能出现的电畴种类和数量，工程畴结构可表示为‘4R’、‘2R’、‘2T’等 [7]。
图2 弛豫铁电单晶钙钛矿结构 [8][9]
图3 弛豫铁电单晶相位图 [6]
图4 弛豫铁电单晶相结构、极化方向、畴结构与宏观对称性的关系 [5]
极化后的三方相弛豫铁电单晶具备优异的压电性质和应变能力，其压电常数（d33 > 2000 pC/N）与机电耦合系数（k33 > 0.9）远超传统锆钛酸铅[Pb(ZrxTi (1-x) )O3，PZT]多晶陶瓷材料（表1） [10] [11]。由弛豫铁电单晶材料驱动的水声换能器的频率带宽可高达PZT陶瓷的2～3倍，声源级可提高12dB。同时，弛豫铁电单晶材料具备更高的弹性顺度常数sijE），能够在相同频率下实现更加紧凑的换能器结构设计。上述特征使得弛豫铁电单晶适用于制备新一代小型化、大带宽、高转换效率、高发射电压响应、高声源级的高性能水声换能器。
表1. 磁电传感器性能总结
压电材料
d33(pC/N)
d31(pC/N)
k33
k31
ε33T(ε)
S33E(pm2/N)
PZT4
289
-123
0.70
0.30
1300
15.5
PZT8
225
-97
0.64
0.33
1000
13.5
PZT5A
374
-171
0.71
0.34
1700
18.8
PZT5H
593
-273
0.75
0.39
3400
20.7
PMN–33%PT
2820
-1335
0.96
0.59
8200
119.6
PZN–5.5%PT
2009
-979
0.92
0.49
5265
102.3
0.27PIN–0.40PMN–0.33PT
2742
-1331
0.95
0.65
7244
77.8
弛豫铁电单晶材料在水声技术领域的应用是从复合棒（纵向）换能器的研制开始的。美国宾夕法尼亚州立大学的Meyer等人研究了33-和32-模式的PMN-PT复合棒换能器，并与PZT8换能器进行了对比研究（图5）。其研究结果显示，在相同谐振频率下，由PMN-PT驱动的复合棒换能器的声源级与频率带宽分别较PZT8换能器提升4dB和2倍，并且其晶堆长度仅为后者的30% [12]。新加坡国立大学和Microfine Materials Technologies公司的Lim等人研制了32模式的PZN-PT复合棒换能器，能够以17W的输入功率实现大于180dB（re 1μPa/V.m）的声源级和两个倍频的频率带宽（图6） [13]。美国水下作战中心（Naval Undersea Warfare Center）的Robinson等人研制了单晶复合棒换能器阵列（图7），其频率带宽可达到PZT换能器阵列的3倍，声源级提高15dB [14]。
图5 33-模式的PMN-PT与PZT8复合棒换能器 [12]
图6 32-模式的PZN-PT复合棒换能器 [13]
图7 PMN-PT复合棒换能器阵列 [14]
参考文献
[1] L. C. Lim and K. K. Rajan, "High-homogeneity High-performance flux-grown Pb(Zn1/3Nb2/3)O3–(6–7)%PbTiO3 single crystals," Journal of Crystal Growth, vol. 271, no. 3-4, pp. 435-444, 2004.
[2] H. Luo, G. Xu, P. Wang and Z. Yin, "Growth and characterization of relaxor ferroelectric PMNT single crystals," Ferroelectrics, vol. 231, no. 1, pp. 97-102, 1999.
[3] J. Tian, P. Han, X. Huang, H. Pan, J. F. Carroll and D. A. Payne, "Improved stability for piezoelectric crystals grown in the lead indium niobate–lead magnesium niobate–lead titanate system," Applied Physics Letters, vol. 91, no. 22, p. 222903, 2007.
[4] “www.microfine-piezo.com,” [联机].
[5] S. Zhang, F. Li, X. Jiang, J. Kim and J. Luo, "Advantages and challenges of relaxor-PbTiO3 ferroelectric crystals for electroacoustic transducers – A review," Progress in Materials Science, vol. 68, pp. 1-66, 2015.
[6] E. Sun and W. Cao, "Relaxor-based ferroelectric single crystals: Growth, domain engineering, characterization and applications," Progress in Materials Science, vol. 65, pp. 124-210, 2014.
[7] 李飞, 张树君, 李振荣 和 徐卓, “弛豫铁电单晶的研究进展—压电效应的起源研究,” 物理学进展, 卷 32, 编号 4, pp. 178-198, 2012.
[8] J. Zhu, W. Li, G. Xu, K. Jiang, Z. Hu and J. Chu, "A phenomenological model of electronic band structure in ferroelectric Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 single crystals around the morphotropic phase boundary determined by temperature-dependent transmittance spectra," Acta Materialia, vol. 59, no. 17, pp. 6684-6690, 2011.
[9] S. P. Alpay, J. Mantese, S. Trolier-McKinstry, Q. Zhang and R. W. Whatmore, "Next-generation electrocaloric and pyroelectric materials for solid-state electrothermal energy interconversion," MRS Bulletin, vol. 39, no. 12, pp. 1099-1111, 2014.
[10] S.-E. Park and T. R. Shrout, "Characteristics of Relaxor-Based Piezoelectric Single Crystals for Ultrasonic Transducers," IEEE TRANSACTIONS ON ULTRASONICS, FERROELECTRICS, AND FREQUENCY CONTROL, vol. 44, no. 5, pp. 1140-1147, 1997.
[11] S.-E. Park and T. R. Shrout, "Ultrahigh strain and piezoelectric behavior in relaxor based ferroelectric single crystals," Journal of Applied Physics, vol. 82, no. 4, pp. 1804-11, 1998.
[12] R. J. Meyer, T. C. Montgomery and W. J. Hughes, "Tonpilz transducers designed using single crystal piezoelectrics," in Oceans Conference Record (IEEE), Mississippi, 2002.
[13] L. C. Lim, S. Zhang, Y. X. Xia, D. H. Lin and N. H. L. Goh, "Pb(Zn1/3Nb2/3)O3–PbTiO3 single crystal and device development," Journal of Advanced Dielectrics, vol. 4, no. 1, p. 1350026, 2014.
[14] H. Robinson, "PiezoCrystal Transducers for Sonar Applications," in International Symposium on PiezoCrystals and Their Applications 2019, Lausanne, 2019.
弛豫铁电单晶（Relaxor-PT）材料与水声换能器
压电材料能够实现电能与声能的相互转换，是水声换能器的核心组成部分，对换能器的整体性能起着决定性的作用。20世纪90年代以来，随着生长工艺的不断完善，以铌锌酸铅-钛酸铅[Pb(Zn1/3Nb2/3)O3–PbTiO3，(PZNPT)]，铌镁酸铅-钛酸铅[Pb(Mg1/3Nb2/3)O3–PbTiO3，(PMNPT)]，和铌铟镁酸铅-钛酸铅[Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3，(PIN–PMN–PT)]为代表的大尺寸弛豫铁电单晶生长制备逐渐成熟（图1），推动了换能器技术的飞速发展 [1] [2] [3]。
图1 (a) PZN-PT [4]；(b) PMN-PT [5]；(c) PIN-PMN-PT [6]
弛豫铁电单晶材料是一种由驰豫铁电体（Relaxor）和常规铁电体（例如钛酸铅PbTiO3, PT）构成的固溶体压电单晶，具备非对称钙钛矿晶体结构（图2），其性质与晶体组分、相位、切型和极化方向密切相关。随着PT含量的增加，弛豫铁电单晶材料将发生三方相（rhombohedral）→ 斜方相（orthorhombic）/单斜相（monoclinic）→ 四方相（tetragonal）的相变，如图3所示。弛豫铁电单晶材料的宏观对称性与极化方向密切相关，如图4所示，沿非极轴方向极化的晶体为多畴状态，被称为“工程畴结构”。按照极化后可能出现的电畴种类和数量，工程畴结构可表示为‘4R’、‘2R’、‘2T’等 [7]。
图2 弛豫铁电单晶钙钛矿结构 [8][9]
图3 弛豫铁电单晶相位图 [6]
图4 弛豫铁电单晶相结构、极化方向、畴结构与宏观对称性的关系 [5]
极化后的三方相弛豫铁电单晶具备优异的压电性质和应变能力，其压电常数（d33 > 2000 pC/N）与机电耦合系数（k33 > 0.9）远超传统锆钛酸铅[Pb(ZrxTi (1-x) )O3，PZT]多晶陶瓷材料（表1） [10] [11]。由弛豫铁电单晶材料驱动的水声换能器的频率带宽可高达PZT陶瓷的2～3倍，声源级可提高12dB。同时，弛豫铁电单晶材料具备更高的弹性顺度常数sijE），能够在相同频率下实现更加紧凑的换能器结构设计。上述特征使得弛豫铁电单晶适用于制备新一代小型化、大带宽、高转换效率、高发射电压响应、高声源级的高性能水声换能器。
表1. 磁电传感器性能总结
| 压电材料 | d33(pC/N) | d31(pC/N) | k33 | k31 | ε33T(ε) | S33E(pm2/N) |
|---|---|---|---|---|---|---|
| PZT4 | 289 | -123 | 0.70 | 0.30 | 1300 | 15.5 |
| PZT8 | 225 | -97 | 0.64 | 0.33 | 1000 | 13.5 |
| PZT5A | 374 | -171 | 0.71 | 0.34 | 1700 | 18.8 |
| PZT5H | 593 | -273 | 0.75 | 0.39 | 3400 | 20.7 |
| PMN–33%PT | 2820 | -1335 | 0.96 | 0.59 | 8200 | 119.6 |
| PZN–5.5%PT | 2009 | -979 | 0.92 | 0.49 | 5265 | 102.3 |
| 0.27PIN–0.40PMN–0.33PT | 2742 | -1331 | 0.95 | 0.65 | 7244 | 77.8 |
弛豫铁电单晶材料在水声技术领域的应用是从复合棒（纵向）换能器的研制开始的。美国宾夕法尼亚州立大学的Meyer等人研究了33-和32-模式的PMN-PT复合棒换能器，并与PZT8换能器进行了对比研究（图5）。其研究结果显示，在相同谐振频率下，由PMN-PT驱动的复合棒换能器的声源级与频率带宽分别较PZT8换能器提升4dB和2倍，并且其晶堆长度仅为后者的30% [12]。新加坡国立大学和Microfine Materials Technologies公司的Lim等人研制了32模式的PZN-PT复合棒换能器，能够以17W的输入功率实现大于180dB（re 1μPa/V.m）的声源级和两个倍频的频率带宽（图6） [13]。美国水下作战中心（Naval Undersea Warfare Center）的Robinson等人研制了单晶复合棒换能器阵列（图7），其频率带宽可达到PZT换能器阵列的3倍，声源级提高15dB [14]。
图5 33-模式的PMN-PT与PZT8复合棒换能器 [12]
图6 32-模式的PZN-PT复合棒换能器 [13]
图7 PMN-PT复合棒换能器阵列 [14]
参考文献
[1] L. C. Lim and K. K. Rajan, "High-homogeneity High-performance flux-grown Pb(Zn1/3Nb2/3)O3–(6–7)%PbTiO3 single crystals," Journal of Crystal Growth, vol. 271, no. 3-4, pp. 435-444, 2004.
[2] H. Luo, G. Xu, P. Wang and Z. Yin, "Growth and characterization of relaxor ferroelectric PMNT single crystals," Ferroelectrics, vol. 231, no. 1, pp. 97-102, 1999.
[3] J. Tian, P. Han, X. Huang, H. Pan, J. F. Carroll and D. A. Payne, "Improved stability for piezoelectric crystals grown in the lead indium niobate–lead magnesium niobate–lead titanate system," Applied Physics Letters, vol. 91, no. 22, p. 222903, 2007.
[4] “www.microfine-piezo.com,” [联机].
[5] S. Zhang, F. Li, X. Jiang, J. Kim and J. Luo, "Advantages and challenges of relaxor-PbTiO3 ferroelectric crystals for electroacoustic transducers – A review," Progress in Materials Science, vol. 68, pp. 1-66, 2015.
[6] E. Sun and W. Cao, "Relaxor-based ferroelectric single crystals: Growth, domain engineering, characterization and applications," Progress in Materials Science, vol. 65, pp. 124-210, 2014.
[7] 李飞, 张树君, 李振荣 和 徐卓, “弛豫铁电单晶的研究进展—压电效应的起源研究,” 物理学进展, 卷 32, 编号 4, pp. 178-198, 2012.
[8] J. Zhu, W. Li, G. Xu, K. Jiang, Z. Hu and J. Chu, "A phenomenological model of electronic band structure in ferroelectric Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 single crystals around the morphotropic phase boundary determined by temperature-dependent transmittance spectra," Acta Materialia, vol. 59, no. 17, pp. 6684-6690, 2011.
[9] S. P. Alpay, J. Mantese, S. Trolier-McKinstry, Q. Zhang and R. W. Whatmore, "Next-generation electrocaloric and pyroelectric materials for solid-state electrothermal energy interconversion," MRS Bulletin, vol. 39, no. 12, pp. 1099-1111, 2014.
[10] S.-E. Park and T. R. Shrout, "Characteristics of Relaxor-Based Piezoelectric Single Crystals for Ultrasonic Transducers," IEEE TRANSACTIONS ON ULTRASONICS, FERROELECTRICS, AND FREQUENCY CONTROL, vol. 44, no. 5, pp. 1140-1147, 1997.
[11] S.-E. Park and T. R. Shrout, "Ultrahigh strain and piezoelectric behavior in relaxor based ferroelectric single crystals," Journal of Applied Physics, vol. 82, no. 4, pp. 1804-11, 1998.
[12] R. J. Meyer, T. C. Montgomery and W. J. Hughes, "Tonpilz transducers designed using single crystal piezoelectrics," in Oceans Conference Record (IEEE), Mississippi, 2002.
[13] L. C. Lim, S. Zhang, Y. X. Xia, D. H. Lin and N. H. L. Goh, "Pb(Zn1/3Nb2/3)O3–PbTiO3 single crystal and device development," Journal of Advanced Dielectrics, vol. 4, no. 1, p. 1350026, 2014.
[14] H. Robinson, "PiezoCrystal Transducers for Sonar Applications," in International Symposium on PiezoCrystals and Their Applications 2019, Lausanne, 2019.