Temperature- and electric-field-dependent domain structures and phase transformations in (001)-cut tetragonal Pb ( Mg 1 ∕ 3 Nb 2 ∕ 3 ) 1 − x Ti x O 3 ( x = 0.40 ) single crystal R. R. Chien, V. Hugo Schmidt, L.-W. Hung, and Chi-Shun Tu Citation: Journal of Applied Physics 97, 114112 (2005); doi: 10.1063/1.1927288 View online: http://dx.doi.org/10.1063/1.1927288 View Table of Contents: http://scitation.aip.org/content/aip/journal/jap/97/11?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Roles of microcracking and phase transition on electric fatigue for [001]-oriented Pb ( Mg 1 / 3 Nb 2 / 3 ) O 3 – PbTiO 3 single crystals J. Appl. Phys. 106, 094107 (2009); 10.1063/1.3253741 Correlation between non- 180 ° domain structures in ( 1 − x ) PbA 1 ∕ 3 Nb 2 ∕ 3 O 3 − x PbTiO 3 single crystals ( A = Mg or Zn) under an applied [001] electric field J. Appl. Phys. 102, 024103 (2007); 10.1063/1.2753585 Intersection of a domains in the c -domain matrix driven by electric field in tetragonal ferroelectric crystal J. Appl. Phys. 96, 2805 (2004); 10.1063/1.1775307 E‐Field and Temperature Dependent Transformation in 〈102〉‐Cut PMN‐PT Crystal AIP Conf. Proc. 677, 152 (2003); 10.1063/1.1609949 Temperature dependence of electrostriction in rhombohedral Pb(Zn 1/3 Nb 2/3 ) O 3 – PbTiO 3 single crystals J. Appl. Phys. 92, 461 (2002); 10.1063/1.1486028 Reuse of AIP Publishing content is subject to the terms at: https://publishing.aip.org/authors/rights-and-permissions. Download to IP: 153.90.170.56 On: Fri, 29 Apr 2016 16:04:48 Temperature- and electric-field-dependent domain structures and phase transformations in „001…-cut tetragonal Pb„Mg1/3Nb2/3…1−xTixO3 „x=0.40… single crystal R. R. Chiena! and V. Hugo Schmidt Department of Physics, Montana State University, Bozeman, Montana 59717 L.-W. Hung and Chi-Shun Tu Department of Physics, Fu Jen University, Taipei, Taiwan 242, Republic of China sReceived 8 June 2004; accepted 14 April 2005; published online 6 June 2005d Temperature- and electric sEd-field-dependent domain structures and phase transformations in a s001d-cut PbsMg1/3Nb2/3d0.6Ti0.4O3 sPMNT40%d single crystal have been investigated by polarizing microscopy and dielectric permittivity. The unpoled crystal has tetragonal phase domains s15–60 mm wided with polarizations along f100g and f010g, which are separated by 90° domain walls. They coexist with a small fraction of the monoclinic phase domains near 200 K. The tetragonal domains increase rapidly at the expense of the monoclinic domains as the temperature increases toward room temperature. This may account for the steplike dielectric anomaly in «8 from around 280 K. The whole crystal reaches the cubic phase near 464 K. The E-field-dependent domain structures at room temperature show a significant change near 11 kV/cm when the polarizations rotate to the tetragonal f001g sT001d direction through the monoclinic phase. Microcrackings begin to develop near 12.5 kV/cm. The entire crystal becomes T001 monodomain near 33 kV/cm. After the E field is removed, the crystal does not reestablish the T100 and T010 macrodomains, but instead breaks up into tetragonal microdomains. © 2005 American Institute of Physics. fDOI: 10.1063/1.1927288g I. INTRODUCTION High-strain ferroelectric sFEd single crystals PbsMg1/3Nb2/3d1−xTixO3 sPMNTxd and PbsZn1/3Nb2/3d1−x TixO3 sPZNTxd exhibit extremely large electromechanical coupling factor k33 s.94% d, ultrahigh piezoelectric coeffi- cient d33 s.2500 pC/Nd, a large strain level sup to ,1.7%d, and low hysteresis.1 Such high piezoelectric performance, which converts mechanical and electric energies, gives ex- tremely promising applications in medical imaging, actua- tors, sonar, and accelerometers. The exceptional piezoelectric properties have been related to the existence of MA-, MB-, and MC-type monoclinic sMd and orthorhombic sOd phases in the morphotropic phase boundary sMPBd region between rhombohedral sRd and tetragonal sTd phases.2,3 The interme- diate phases sM and Od have been found in both PMNTx and PZNTx, and strongly depend on titanium content, tempera- ture, history, strength of external E field, and crystallographic orientation. In addition, tetragonal PMNTx single crystals have shown excellent properties for promising optical applications.4 Physical properties such as their thermal phase stability and E-field poling effect in the PMNT crystals and the mechanism underlying them should be addressed and understood so that such materials can be reliably used in devices. The discovery of the intermediate phases has opened a window for searching for the origin of high piezoelectric responses. However, whether the intermediate phases are in- trinsic, or merely appear as stress-induced responses to forces exerted by neighboring R, T, and/or cubic sCd do- mains or regions is not yet clear. In addition, how do the intermediate phases play a role in phase transformations among R, T, and C as temperature or applied E field changes? In this paper, we have investigated thermal phase stability and how poling affects polarizations in a s001d-cut PMNT40% crystal. By using relations of crystallographic symmetry and optical extinction, polarizing microscopy is capable of revealing orientations of the polarizations and their corresponding crystal phases. For interpreting polariz- ing microscopy domain observation among various phases, a review of principles of optical extinction for the s001d-cut crystal can be found in Ref. 5. II. EXPERIMENTAL PROCEDURE The PMNT40% single crystal was grown using a modi- fied Bridgman method and was cut perpendicular to the k001l direction. The Ti concentration x was determined by using the dielectric maximum temperature Tm, i.e., x= sTm +10d /5, where T is in °C.6 A variable-frequency Wayne– Kerr precision analyzer PMA3260A with four-lead connec- tions was used to obtain dielectric permittivity with gold electrodes deposited by radio frequency sputtering. A Janis CCS-450 closed-cycle refrigerator was used with a Lake- shore model 340 temperature controller. The heating/cooling ramping rate was 1.5 K/min. The domain structures were studied by means of a Nikon E600POL polarizing microscope with a crossed polarizer- analyzer sP/Ad pair. A Linkam THMS600 heating/cooling adAuthor to whom correspondence should be addressed; electronic mail: chien@physics.montana.edu JOURNAL OF APPLIED PHYSICS 97, 114112 s2005d 0021-8979/2005/97~11!/114112/4/$22.50 © 2005 American Institute of Physics97, 114112-1 Reuse of AIP Publishing content is subject to the terms at: https://publishing.aip.org/authors/rights-and-permissions. Download to IP: 153.90.170.56 On: Fri, 29 Apr 2016 16:04:48 stage was mounted on the polarizing microscope for study- ing temperature-dependent domain structures. To minimize the superimposition of domains, the sample was polished to a thickness of about 45 mm. Transparent conductive films of indium tin oxide sITOd were deposited on the sample sur- faces for E-field-dependent domain observation. The experi- mental configuration for E-field-dependent domain observa- tion can be found in the reference of Ref. 5. The crystal was annealed before all domain observations. III. RESULTS AND DISCUSSION A. Temperature-dependent domain observation Before the zero-field-heating sZFHd domain observation, the unpoled sample was cooled to 200 K after annealing. Figure 1 shows domain pictures of the unpoled s001d-cut PMNT40% crystal at various temperatures. Every angle ex- pressed in the picture is the angle between one of the P/A pair axes and f010g. For instance, P/A: 45° in the upper right corner in the left column means that the domain picture was taken when the angle between one of the P/A pair axes and f010g was 45°. The angles 0°, 20°, 72°, and 76° appearing near the “cross” indicate that those domains exhibit extinc- tion when the angles between one of the P/A pair axes and f010g are 0°, 20°, 72°, and 76°, respectively. As shown in Fig. 1sed, at 200 K most of the domain matrix exhibits ex- tinction at 0°, i.e., one of the P/A axes is along the f010g direction. A small fraction of the domain matrix exhibits ex- tinction at nonzero angles, such as 20°, 72°, and 76°. When observing the s001d-cut sample along the f001g direction be- tween a crossed P/A pair, the extinction angle is 0° +m90° for all T domains, where m is any integer. We will measure all extinction angles in this work from the vertical direction, and will henceforth omit m90° terms and only consider angles in the 0° łf,90° range. Note that O domains also have extinction at 0°. However, if O domains exist in the sample, extinction would likely be seen also at 45°, which was not found in this study, as seen in Fig. 1sad, for 200 K. The extinction at 20°, 72°, and 76° corresponds to M or triclinic strid phases, which are indistinguishable in the polar- izing microscopy. However, a tri phase has not yet been re- ported in PMNT crystals. Thus, the extinctions at 20°, 72°, and 76° most likely correspond to an M phase. As evidenced in Figs. 1sad–1scd, the 15–60-mm-wide domains separated by 90° domain walls are dominated by T phase domains with polarizations P along the f100g and f010g axes sT100 and T010d. Therefore, it was evidenced that the dominant T do- mains coexist with a small fraction of M domains at 200 K. As the temperature increases, the T domains gradually in- crease from 200 to 270 K and rapidly increase above 270 K at the expense of the M domains, as seen in Figs. 1sfd and 1sgd. This may account for the broad steplike anomaly in «8 near 280 K and the weak bump in «9 near 260 K, as shown in Fig. 2. A similar broad steplike anomaly was also obtained near 200–210 K in our s001d-cut PMNT35% and PMNT38% crystals in the FR-ZFH process spoled at room temperature and then zero-field heatedd.7 A long-range trans- formation of TsMd→T was evidenced from the polarizing microscopy and x-ray diffraction results.7 TsMd represents that dominant T domains coexist with a smaller fraction of M domains. In addition, «8 and «9 exhibit unexpected shoulders near 450 and 460 K sFig. 2d, which were not usually seen in other FIG. 1. sColor onlined Temperature-dependent domain structures for the unpoled s001d-cut PMNT40% crystal. FIG. 2. Temperature- and frequency-dependent dielectric permittivities. 114112-2 Chien et al. J. Appl. Phys. 97, 114112 ~2005! Reuse of AIP Publishing content is subject to the terms at: https://publishing.aip.org/authors/rights-and-permissions. Download to IP: 153.90.170.56 On: Fri, 29 Apr 2016 16:04:48 close Ti concentration compounds, such as PMNT38% and 39%.7,8 As evidenced in Fig. 1sdd, some C phase regions appear near 460 K and expand throughout the whole crystal as the temperature increases gradually to 464 K, which is consistent with the dielectric maximum temperature Tm in Fig. 2. Therefore, the unexpected shoulders near 450 and 460 K most likely correlate to phase segregation that has often been seen in the PMNT system due to spatial hetero- geneity of Ti content. Similar phase segregation was also observed in a s001d-cut PMNT29% crystal.7 B. E-field-dependent domain observation The E-field-dependent domain structures, as shown in Fig. 3, were taken at P/A: 45° while a dc E field was applied along f001g at room temperature. At E=0 kV/cm fFig. 3sadg, the domain matrix mostly exhibits an extinction at 0° and some at nonzero degrees such as 18° and 82° with respect to the f010g direction. This indicates the coexistence of a small fraction of M phase and a dominant T phase with polariza- tions P along the f100g and f010g axes. As the E field in- creases, the domain matrix does not essentially change until 11 kV/cm, as seen in Fig. 3sbd. At E=11 kV/cm, the do- main structure displays the T001 domain with polarization P along the f001g axis, which is associated with extinction at every orientation of the crossed polarizer/analyzer pair si.e., total optical extinctiond, and some M domains with various nonzero-degree extinction angles, such as 12°, 68°, 80°, and 82° at the expense of the T domains. In other words, as the E field increases to 11 kV/cm, some of the T domains have transformed to T001 and M domains. With increasing E field fFig. 3scdg, more of the M domains have been poled to the T001 domains, revealed by the total optical extinction, and the other M domains have changed their polarization orienta- tions with various nonzero-degree extinction angles, such as 12° and 16°. Microcracking caused by the dc E-field poling process starts to develop at ,12.5 kV/cm along f010g, as shown in Fig. 3scd, where Cs indicate the cracks. As the E field increases to ,25 kV/cm fFig. 3sddg, cracking along f100g appears and the entire domain matrix exhibits total optical extinction si.e., the T001 domaind except a stripe ori- ented along f010g. The entire crystal becomes T001 mon- odomain near E=33 kV/cm, as seen in Fig. 3sed. However, a s001d-cut rhombohedral PMNT24% single crystal cannot reach a tetragonal monodomain and no microcracking was found under a higher E field s44 kV/cmd applied along f001g at room temperature.5 As the poling E field decreases from 33 kV/cm, the T001 monodomain does not exhibit apparent change until E =12.5 kV/cm. Then T domains with polarizations P along the f100g and f010g axes begin to appear at the expense of the T001 monodomain. After the E field was removed fFig. 3sfdg, the domain structure did not return to the broad T100 and T010 domains separated by the 90° domain walls fFig. 3sadg. However, the extinction pattern is in agreement with tetragonal microdomains with polarizations P along the f100g or f010g axes. IV. CONCLUSIONS In this study, it was evidenced that a few M phase do- mains coexist with the dominant T100 and T010 domains near 200 K in the unpoled s001d-cut PMNT40% crystal. These T100 and T010 domains are 15–60 mm wide and separated by 90° domain walls. As the temperature increases from 200 K to room temperature, the T100 and T010 phase domains in- crease rapidly at the expense of the M phase domains. The crystal reaches the C phase near 464 K. Instead of a T→C transition proposed for PMNT40% by the phase diagram,2 a transition sequence of TsMd→T→C was found. The E-field-dependent domain observation at room temperature found that T001 phase domains were induced near 11 kV/cm by the process sT100 or T010d→M→T001, and this T001 phase expanded through the whole crystal by this process as the E field increased further. Microcracking phenomenon starts near 12.5 kV/cm. The crystal becomes entirely T001 mon- odomain near 33 kV/cm. After the E field was removed, the T100 and T010 macrodomains, and 90° domain walls cannot be obtained again. Instead, the crystal exhibits non-T001 te- tragonal microdomains. ACKNOWLEDGMENTS The authors express sincere thanks to Dr. H. Luo and H. Cao for the crystal. This work was supported by DoD EPS- CoR Grant No. N00014-02-1-0657 and NSC Grant Nos. 92- 2112-M-030-007 and 93–2112–M-030–001. 1S.-E. Park and T. R. Shrout, J. Appl. Phys. 82, 1804 s1997d. 2T. R. Shrout, Z. P. Chang, N. Kim, and S. Markgraf, Ferroelectr., Lett. Sect. 12, 63 s1990d. 3B. Noheda, Curr. Opin. Solid State Mater. Sci. 6, 27 s2002d. FIG. 3. sColor onlined E-field-dependent domain structures at room tem- perature with a dc E field applied along f001g. The P/A angle was 45°. 114112-3 Chien et al. J. Appl. Phys. 97, 114112 ~2005! Reuse of AIP Publishing content is subject to the terms at: https://publishing.aip.org/authors/rights-and-permissions. Download to IP: 153.90.170.56 On: Fri, 29 Apr 2016 16:04:48 4C.-S. Tu, F.-T. Wang, R. R. Chien, V. H. Schmidt, and G. F. Tuthill, J. Appl. Phys. 97, 064112 s2005d. 5R. R. Chien, V. H. Schmidt, C.-S. Tu, L.-W. Hung, and H. Luo, Phys. Rev. B 69, 172101 s2004d. 6Z. Y. Feng, H. S. Luo, Y. P. Guo, T. H. He, and H. Q. 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