Pyroelectric properties of rhombohedral and tetragonal Pb(In1/2Nb1/2)Pb(Mg1/3Nb2/3)-PbTiO3 crystals Junjie Gao, Zhuo Xu, Fei Li, Chonghui Zhang, Zhenrong Li et al. Citation: J. Appl. Phys. 110, 106101 (2011); doi: 10.1063/1.3662951 View online: http://dx.doi.org/10.1063/1.3662951 View Table of Contents: http://jap.aip.org/resource/1/JAPIAU/v110/i10 Published by the American Institute of Physics.
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JOURNAL OF APPLIED PHYSICS 110, 106101 (2011)
Pyroelectric properties of rhombohedral and tetragonal Pb(In1/2Nb1/2)-Pb(Mg1/3Nb2/3)-PbTiO3 crystals Junjie Gao,1,2,a) Zhuo Xu,1,2 Fei Li,1,2 Chonghui Zhang,1,2 Zhenrong Li,1,2 Xiaoqing Wu,1,2 Linghang Wang,1,2 Yi Liu,3 Gaomin Liu,3 and Hongliang He3
1 Electronic Materials Research Laboratory, Key Laboratory of the Ministry of Education, Xi’an Jiaotong University, Xi’an 710049, People’s Republic of China 2 International Center for Dielectric Research, Xi’an Jiaotong University, Xi’an 710049, People’s Republic of China 3 National Key Laboratory of Shock Wave and Detonation Physics, Institute of Fluid Physics, CAEP, Mianyang 621900, People’s Republic of China
(Received 1 September 2011; accepted 22 October 2011; published online 21 November 2011) Pyroelectric properties of rhombohedral and tetragonal single crystals Pb(In1/2Nb1/2)Pb(Mg1/3Nb2/3)-PbTiO3 (PIN-PMN-PT) were investigated, with temperature from 100 C to 100 C. At room temperature, the pyroelectric coefficient p and the figure of merit Fd of rhombohedral crystals are 7.81 104 C/m2 K and 10.9 105 Pa1/2, respectively, and 6.84 104 C/m2 K and 11.67 105 Pa1/2, respectively, for tetragonal crystals. Although the coefficient p and Fd at room temperature are similar for rhombohedral and tetragonal crystals, the Fd of tetragonal crystal is much more stable with respect to temperature, owing to its higher phase transition temperature and stable mono-domain state. From room temperature to 100 C, the Fd of rhombohedral crystal decreases from 10.74 105 Pa1/2 to 5.3 105 Pa1/2, while that of tetragonal crystals is nearly independent of temperature. Such investigation reveals that tetragonal PIN-PMN-PT crystal is more suitable for uncooled infrared detectors and imagers when compared C 2011 American Institute of Physics. [doi:10.1063/1.3662951] with its rhombohedral counterpart. V
INTRODUCTION
Pyroelectric infared detectors are widely used in consumer products and military/paramilitary applications, due to the low microphonic noise, low power loss, faster response, and high temperature stability.1,2 Triglycine sulfate (TGS), LiTaO3, barium strontium titanate (BST) and lead scandium tantalate (PST) are generally used as pyroelectric materials for infared device. However, the level of dielectric permittivity for TGS and LiTaO3, are quite low (50), making them unfavorable for uncooled infrared focal plane arrays (UFPA) devices.3 On the other hand, the BST and PST need temperature stabilization and bias electric field,1 which makes their utilization inconvenient. In the past few years, relaxor-PT based crystals Pb(Mg1/3Nb2/3)-PbTiO3 (PMN-PT)4,5 were reported possessing excellent pyroelectric performance, low dielectric loss and high dielectric permittivity, being good candidate for UFPA and imagers. Recently, rhombohedral PIN-PMN-PT crystals6,7 have attracted much attention, because of their broadened temperature usage range (TR-T > 120 C) and comparable pyroelectric properties when compared to those of PMN-PT crystals. Thus, some investigations were carried out on pyroelectric properties of rhombohedral PIN-PMN-PT crystals.8,9 In this paper, the pyroelectric performance of both rhombohedral and tetragonal crystals PIN-PMN-PT was comparatively studied with temperature from 100 C to 100 C. The PIN-PMN-PT single crystals were grown by the modified Bridgman technique.10 The composition and phase of the a)
Author to whom correspondence should be addressed. Electronic mail:
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investigated single crystals were inferred from temperaturedependent-dielectric behavior.7 The crystals were oriented using the three-dimensional rotation orientation method11 and then cut into 5 5 0.5 mm3 rectangles with the large face perpendicular to h111idirection for rhombohedral crystals and h001i direction for tetragonal crystals. All the samples were electrode by vacuum sputtered gold on the polished surface. In order to avoid the cracking, the crystal samples were poled by high temperature poling process. The rhombohedral samples were poled along the h111i direction by applying a dc electric field of 10 kV/cm at 90 C for 10 min, and field cooled down to room temperature (RT), while the tetragonal samples were poled along the h001i direction by applying a dc electric field of 3 kV/cm at 300 C for 10 min, and field cooled down to RT.
FIG. 1. (Color online) The temperature dependence of the dielectric permittivity and loss for rhombohedral and tetragonal PIN-PMN-PT single crystals.
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FIG. 2. (Color online) The dielectric permittivity and loss dependence on frequency for PIN-PMN-PT crystals.
The temperature dependence of the dielectric permittivity and loss for PIN-PMN-PT crystals were determined using a LCR meter (HP4284) connected to a computer-controlled temperature chamber. The dielectric permittivity and loss with respect to frequency for PIN-PMN-PT crystals were measured from an impedance analyzer (HP4294). Pyroelectric coefficients of PIN-PMN-PT crystals were determined using Byer-Roundy meathod.12 In this experiment, the pyroelectric current could be measured by KEITHLEY6485 picoammeter connected to computer-controlled LINKAM heating-cooling stage. Each sample was measrued at least two cycles of heating-cooling so as to confirm that the pyroelectric performance for the samples was reversible and repeatable in the temperature range from 100 C to 100 C. At RT, the remnant polarization of samples is determined from the P-E hysteresis loop using a Sawyer-Tower circuit at 1 Hz. The specific heat per unit mass Cp of PIN-PMN-PT crystals was measured by differential scanning calorimetry (NETZSCH DSC 200 PC) in the temperature region from 100 C to 100 C. Figure 1 shows the temperature dependence of dielectric permittivity and loss for rhombohedral and tetragonal PINPMN-PT crystals. At RT, the dielectric permittivity and loss are 550 and 0.17% for the rhombohedral crystals, and 465 and 0.13% for the tetragonal crystals. Such low dielectric permittivity and loss are attributed to the mono-domain state of the crystal and free of polarization rotation process. For the rhombohedral crystals, the rhombohedral-tetragonal and tetragonal-cubic phase transitions occur at 123 C and 166 C, respectively, while only one phase transition, tetragonal-cubic phase transition, occurs at about 240 C for the tetragonal crystals. Thus, the tetragonal crystals allow a wider operation temperature range in practical applications when compared with their rhombohedral counterpart. From 100 C to 100 C, both dielectric permittivity and loss
J. Appl. Phys. 110, 106101 (2011)
FIG. 3. (Color online) The remnant polarization and pyroelectric coefficients as a function of temperature for PIN-PMN-PTe crystals.
increase, from 320 and 0.09% to 2060 and 0.58% for rhombohedral crystals, and from 390 and 0.07% to 600 and 0.16% for the tetragonal crystals, as shown in the inset of Fig. 1. The temperature stability of permittivity, defined as @er =@T, is 8.7/ C for rhombohedral crystals, and 1.0/ C for tetragonal crystals. On the other hand, the temperature stability of dielectric loss, defined as @tand=@T, is 0.025%/ C for the rhombohedral crystal, and 0.0045%/ C for tetragonal crystals. It is obvious that the dielectric permittivity and loss of tetragonal crystals are much more stable when compared to their rhomboheral counterpart. Such temperature stability can be attributed to the following two factors. Firstly, the mono-domain state in tetragonal PIN-PMN-PT crystals was more stable than that in rhombohedral crystals,13–15 consequently, the contribution from domain wall motion to dielectric permittivity and loss are relatively small for tetragonal PIN-PMT-PT crystals at elevated temperature. Secondly, it can be inferred from the thermodynamic approach16 that the increase of intrinsic dielectric permittivity for the tetragonal crystals is less than that for the rhombohedral crystals with the temperature close to 100 C, because the phase transition temperature of tetragonal PIN-PMN-PT crystals is much higher than that of rhombohedral PIN-PMN-PT crystals (240 C versus 123 C). Most of the pyroelectric detectors are used in the low frequency range, so the frequency dependence of dielectric response for PIN-PMN-PT crystals was investigated in the low frequency range from 40 Hz to 10 kHz. As shown in Fig. 2, the dielectric permittivity and loss are nearly independent of frequency, demonstrating that the PIN-PMN-PT crystals possess good frequency stability for pyroelectric applications. Figure 3 presents the remnant polarization and pyroelectric coefficients as a function of temperature. At RT, the values of remnant polarization are 44.4 lC/cm2 and 43.2 lC/cm2 for the rhombohedral and tetragonal crystals, respectively. As the temperature increases from 100 C to 100 C, the remnant
FIG. 4. (Color online) The temperature dependence of (a) current responsivity Fi, (b) voltage responsivity Fv, (c) detectivity Fd for PIN-PMN-PT crystals.
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TABLE I. Summary of property parameters of LiTaO3, TGS, PMN-xPT, Mn-doped PMN-xPT, and PIN-PMN-PT single crystals for pyroelectric devices at room temperature. Composition LiTaO3 TGS PMN-0.26PT PMN-0.29PT Mn-PMN-0.26PT PIMNT(42=30=28) Rhom. PIN-PMN-PT Tetr. PIN-PMN-PT
Tc ( C)
TR-T ( C)
p (104 C=m2K)
er (1 kHz)
tand (1 kHz)
Fi (1010 m=V)
Fv (m2=C)
Fd (105 Pa1=2)
References
620
–-
121 135 120 187 166 240
92 103 90 152 123 –
2.3 5.5 15.3 12.8 17.2 9.0 7.8 6.8
47 55 640 520 660 700 550 470
0.0005 0.025 0.0028 0.0063 0.0005 0.002 0.0017 0.0013
0.72 2.12 6.10 5.25 6.88 3.60 3.19 2.77
0.17 0.43 0.11 0.11 0.12 0.06 0.06 0.07
15.8 6.1 15.3 9.8 40.2 10.2 10.9 11.7
Ref. 3 Ref. 3 Ref. 5 Ref. 4 Ref. 9 Ref. 9 this work this work
polarization continuously reduces, from 49.8 lC/cm2 to 37.9 lC/cm2 for rhombohedral crystals, and from 47.5 lC/cm2 to 39 lC/cm2 for the tetragonal crystals. At RT, the pyroelectric coefficients are 7.81 104 C/m2 K and 6.74 104 C/m2 K for rhombohedral and tetragonal crystals, respectively. With increasing temperature from 100 C to 100 C, the pyroelectric coefficient increases from 4.43 104 C/m2 K to 13.5 104 C/m2 K for rhombohedral PIN-PMN-PT crystals, and from 5.56 104 C/m2 K to 8.83 104 C/m2 K for the tetragonal crystals. The temperature stability factor of p (@p=@T) are 0.045 104 and 0.016 104 (C/m2 K)/ C for rhombohedral and tetragonal crystals, respectively. It can be seen that the pyroelectric response of tetragonal PIN-PMN-PT crystals is more stable when compared to rhombohedral PIN-PMN-PT crystals. The pyroelectric performance of PIN-PMN-PT crystals was further analyzed by three major figures of merit (FOMs): current responsivity Fi ¼ p=Cv , voltage responsivity Fv ¼ p=Cv e0 er , and detectivity Fd ¼ p=ðCv ðe0 er tandÞ1=2 Þ, where p, Cv, e0 , er , and tand are the pyroelectric coefficient, volume specific heat, permittivity of free space, relative dielectric permittivity, and dielectric loss, respectively.3 The density of crystals is about 8.1 103 kg/m3 at room temperature. The volume specific heat (Cv) is on the order of 2.45 106 J/m3 K for both rhombohedral and tetragonal PIN-PMN-PT crystals. Compared with other parameters, the density variation with respect to temperature is very limited, thus its influence on the three FOMs is negligible. At RT, Fi, Fv and Fd are 3.19 1010 m/V, 0.06 m2/C, and 10.92 105 Pa1/2 for the rhombohedral crystals, and 2.77 1010 m/V, 0.07 m2/C and 11.72 105 Pa1/2 for the tetragonal crystals. The temperature dependence of Fi, Fv and Fd is shown in Fig. 4. The p plays a dominant role in the equation Fi ¼ p=Cv , so the variation of Fi with temperature is similar to that of p. With temperature increasing from 100 C to 100 C, Fi increases from 1.77 1010 m/V to 5.4 1010 m/V for the rhombohedral crystals, and from 2.3 1010 m/V to 3.59 1010 m/V for the tetragonal crystals. The temperature stability of Fi (@Fi =@T) are 0.018 1010 m/V/ C and 0.006 1010 m/V/ C for rhombohedral and tetragonal crystals, respectively. The remarkable advantage of the tetragonal PINPMN-PT crystals is the temperature stability of Fv and Fd. With temperature from 100 C up to 100 C, the variation of Fv and Fd for the tetragonal crystals are only 6 4.3% and 5.2%, while for the rhombohedral crystal, the variation of Fv (from 0.064 m2/C to 0.03 m2/C) and Fd (from 11 105 Pa1/2 to
5.3 105 Pa1/2) were significantly large, being on the order of 50%. Such large variation is directly attributed to the increase of dielectric permittivity and loss with respect to temperature. In summary, the pyroelectric performances of monodomain rhombohedral and tetragonal PMN-PIN-PT crystals were investigated. Both rhombohedral and tetragonal crystals possess relatively high delectric permittivity, pyroelectric coefficient and FOMs at room temperature, making them promising candidate for the next generation of high performance uncooled infrared detectors and imagers. Table I summarizes the pyroelectric parameters of PIN-PMN-PT, LiTaO3, TGS, and PMN-PT crystals for comparison. Of particular interest is that tetragonal PIN-PMN-PT crystals exhibit much better thermal stability of dielectric permittivity, pyroelectric coefficient and FOMs when compared to its rhombohedral counterpart. These merits demonstrate that tetragonal PMN-PIN-PT crystals should be proper candidates for pyroelectric device where the temperature stability is desired. ACKNOWLEDGMENTS
This work was financially supported by the National Basic Research Program of China (973 Program) (Grant No. 2009CB623306), and the National Natural Science Foundation of China—NSAF (Grant No. 10976022), and the National Natural Science foundation of China (Grant No. 51102193), and International Science & Technology Cooperation Program of China (Grant No. 2010DFR50480). 1
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