* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Relaxor Behavior, Polarization Buildup, and Switching in
Energy harvesting wikipedia , lookup
Carbon nanotubes in interconnects wikipedia , lookup
Scanning SQUID microscope wikipedia , lookup
Shape-memory alloy wikipedia , lookup
Glass transition wikipedia , lookup
Ferromagnetism wikipedia , lookup
Condensed matter physics wikipedia , lookup
Paleostress inversion wikipedia , lookup
Tunable metamaterial wikipedia , lookup
Metamaterial wikipedia , lookup
Superconductivity wikipedia , lookup
Nanochemistry wikipedia , lookup
Negative-index metamaterial wikipedia , lookup
Nanogenerator wikipedia , lookup
Semiconductor wikipedia , lookup
Strengthening mechanisms of materials wikipedia , lookup
History of metamaterials wikipedia , lookup
Piezoelectricity wikipedia , lookup
Nanomaterials wikipedia , lookup
full papers M. Alguer et al. Nanostructured ceramics DOI: 10.1002/smll.200700284 Relaxor Behavior, Polarization Buildup, and Switching in Nanostructured 0.92 PbZn1/3Nb2/3O3–0.08 PbTiO3 Ceramics Miguel Alguer,* Teresa Hungra, Harvey Amorn, Jesffls Ricote, Jean Galy, and Alicia Castro The relaxor-type behavior, electrical polarization buildup, and switching in 0.92Pb(Zn1/3Nb2/3)O3–0.08PbTiO3 nanostructured ceramics with a grain size of 20 nm is reported for the first time. This composition presents the highest-known piezoelectric coefficients, yet phase stability is an issue. Ceramics can only be obtained by the combination of mechanosynthesis and spark-plasma sintering. The results raise the possibility of using nanoscale, perovskite-relaxor-based morphotropic-phase-boundary materials for sensing and actuation in nanoelectromechanical systems. Keywords: · ceramics · ferroelectrics · nanostructures · perovskites · spark-plasma sintering 1. Introduction Piezoelectric, ferroelectric ceramic materials are a mature and ubiquitous technology. These ceramics are the active elements in a range of piezoelectric devices and perform functions such as sensing and actuation.[1] Piezoelectric devices are no exception to the current miniaturization trends in ceramic technology for microelectronics. Ceramic elements are approaching a characteristic thickness of 1 mm, which requires submicrometer grain sizes close to the nanoscale for device reliability.[2] Similar and even smaller sizes are involved in ferroelectric thick and thin films on Si-based substrates for their integration into piezoelectric microelectromechanical systems.[3] Piezoelectric transduction is also being considered to implement sensing and actuation in nanoelectromechanical systems,[4, 5] which require a further [*] Dr. M. Alguer, Dr. T. Hungra, Dr. H. Amorn, Dr. J. Ricote, Dr. A. Castro Instituto de Ciencia de Materiales de Madrid (ICMM) Cantoblanco, 28049 Madrid (Spain) Fax: (+ 34) 913-720-623 E-mail: [email protected] Dr. T. Hungra, Dr. J. Galy Centre d’Elaboration de Mat5riaux et d’Etudes Structurales (CEMES) 29 rue Jeanne Marvig BP 94347, 31055 Toulouse (France) 1906 reduction of dimensions; therefore, ultrathin ferroelectric films have been the focus of recent studies.[6] Nanoscale epitaxial films and islands have been investigated for high-density, nonvolatile, ferroelectric random-access memory deACHTUNGREvices.[7, 8] Also, nanostructured ferroelectrics have been demonstrated for the tuning of the transport properties of nanofibers of a conductive polymer,[9] and for the electrical switching of the magnetization of epitaxial columnar nanostructures of a ferrimagnetic spinel.[10] The use of nanoscale ferroelectrics in these technologies rests on the downscaling behavior of the properties. FerroACHTUNGREelectricity is a cooperative phenomenon, and it was long thought that a minimum volume was necessary to sustain the spontaneous polarization; this raises the existence of a fundamental size limit below which ferroelectricity vanishes.[11, 12] First-principles calculations and experimental studies on nanostructured films,[13–16] wires,[17, 18] particles,[19, 20] and ceramics[21] have shown that ferroelectricity persists at the nanoscale and thus, that the downscaling of ferroelectricbased piezoelectric technologies is feasible. However, most studies focused on prototype, simple perovskites, such as BaTiO3, PbTiO3, or tetragonal PbACHTUNGRE(Zr,Ti)O3, whereas results on high-piezoelectric-coefficient morphotropic-phase-boundary (MPB) materials are scarce.[22, 23] The highest piezoelectric coefficients have been reported for relaxor-ferroelectric PbZn1/3Nb2/3O3–PbTiO3 single : 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim small 2007, 3, No. 11, 1906 – 1911 Perovskite Nanostructured Ceramics crystals with values of 2500 pC N 1.[24] Unfortunately, powders of this phase cannot be synthesized by the solid-state reaction of precursors and a pyrochlore-type nonferroelectric phase always results.[25] The perovskite has only been obtained by high-pressure synthesis[26] and as a nanocrystalline powder by mechanosynthesis.[27] However, the phase decomposes into the pyrochlore phase, ZnO, and PbO under subsequent heating, which prevents ceramics from being processed. We have succeeded in processing perovskite-phase 0.92PbZn1/3Nb2/3O3–0.08PbTiO3 nanostructured ceramics by Spark-plasma sintering (SPS) of a nanocrystalline powder obtained by mechanosynthesis. This allowed us to study the electrical properties and thus the polar states present at the nanoscale for this relaxor-based MPB material, which are reported here for the first time. 2. Results and Discussion rates up to 600 K min 1. Hence, densification takes place in a short time, typically about 15 min, and a powder compact of small grain size is obtained.[31] The combination of mechanosynthesis and SPS has already been successfully used for the processing of ferroelectric oxides and the study of size effects.[32] When applied to the PbZn1/3Nb2/3O3–PbTiO3 system, ceramics can only be obtained by the synergy between the two techniques; the thermal decomposition of the nanocrystalline perovskite at temperatures between 673 and 873 K shows a slow kinetics as compared with the duration of the SPS process,[27] and pressure helps to stabilize the PbZn1/3Nb2/3O3 perovskite.[26] Densification of the nanocrystalline powder started above 773 K and density increased exponentially, so that values above 90 % were obtained at 898 K. However, perovskite decomposition also occurred in this temperature range and significant amounts of pyrochlore were already present after SPS at the latter temperature. Figure 2 shows the XRD patterns for ceramics process- Nanocrystalline 0.92PbZn1/3Nb2/3O3–0.08PbTiO3 powders were obtained by mechanochemical activation of binary oxides in a high-energy planetary mill. This is a powerful technique for the preparation of functional nanocrystalline materials[28] that allows most of the ferroelectric perovskites to be mechanosynthesized.[27, 29] A transmission electron microscopy (TEM) image of the powder and its particle size distribution are shown in Figure 1. The Feret=s diameter was Figure 2. XRD patterns of the nanostructured 0.92PbZn1/3Nb2/3O3– 0.08PbTiO3 materials processed by SPS at several temperatures. Pe: perovskite; Py: pyrochlore. Figure 1. TEM image and particle size distribution of the nanocrystalline 0.92PbZn1/3Nb2/3O3–0.08PbTiO3 powder used for the processing of nanostructured materials. measured for an ensemble of more than 100 particles, and an average size of 12 nm resulted. This value is in a good agreement with the crystal size obtained from X-ray diffraction (XRD) data using the full width at half-maximum (FWHF) of the perovskite (110) diffraction peak and the Scherer equation. Nanostructured ceramics have been processed by SPS.[30] In this technique, sintering is activated by the use of uniaxial pressures and pulsed direct current, which results in heating small 2007, 3, No. 11, 1906 – 1911 ed at 823, 873, and 898 K. Densification levels of 70, 80, and 90 % of the theoretical value were achieved at these temperatures, respectively. Studies were focused on the ceramics with a very minor pyrochlore phase, that is, those spark-plasma sintered at 823 and 873 K. The amount of nonferroelectric phase for the latter material is of the order of 5 % according to XRD, and the phase has a relative permittivity of 100,[33] so its effect on the properties is not significant as compared to that of porosity. The crystal sizes obtained from XRD data with the Scherer equation were 16 and 18 nm for the materials proACHTUNGREcessed at 823 and 873 K, respectively. TEM images and the Feret=s diameter distribution of the two materials are shown in Figure 3. Single lognormal distributions were found in both cases, with an average of 14 and 21 nm for the ceramics spark-plasma sintered at 823 and 873 K, respectively. Note the consistency among the sizes obtained by the two techniques, which unambiguously confirms a grain size of 20 nm. Electrical characterization was carried out on ceramic disks on which Pt electrodes had been deposited by sputter- : 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim www.small-journal.com 1907 full papers M. Alguer et al. Figure 4. Dielectric permittivity and losses as a function of temperature at several frequencies for a nanostructured 0.92PbZn1/3Nb2/3O3– 0.08PbTiO3 material with a grain size of 20 nm. Figure 3. TEM images and grain size distributions of the nanostructured 0.92PbZn1/3Nb2/3O3–0.08PbTiO3 materials processed by SPS at a) 823 and b) 873 K. ing. As-sintered materials presented very high dielectric losses at room temperature that strongly decreased after annealing in air at 623 K for 2 h. This is a common observation for nanostructured ceramics processed by SPS, which has been associated with the reducing sintering conditions within the graphite die and the formation of large numbers of oxygen vacancies in the perovskite during the process.[21] The temperature dependence of the dielectric permittivity and losses of a ceramic spark-plasma sintered at 873 K is shown in Figure 4 at several frequencies. The permittivity initially increases on heating and reaches a broad maximum at a temperature that increases with frequency between 210 and 240 K. Below this maximum, permittivity decreases when the frequency is increased, while dielectric losses increase with this parameter. This is the typical behavior of a relaxor material, such as the prototype Pb(Mg1/3Nb2/3)O3.[34] At higher temperatures, a Debye-type relaxation is observed, which indicates the presence of dipolar defects. Also, dielectric losses linearly increase with the reciprocal frequency in this temper- 1908 www.small-journal.com ature range because of electrical conduction. We found analogous dielectric relaxation and conduction in coarse-grained PbZn1/3Nb2/3O3–PbFe1/2Nb1/2O3–PbTiO3 ceramics processed from powders by mechanosynthesis, which indicates that the defects responsible for the high-temperature relaxation and conduction are generated during the mechanosynthesis and not during the SPS; their nature is outside the scope of this paper. Therefore, the main intrinsic feature is the existence of a relaxor-type behavior with the dispersive maxima in permittivity below room temperature for this material with a grain size of 20 nm. This behavior must be compared with that of 0.92Pb(Zn1/3Nb2/3)O3–0.08PbTiO3 single crystals. The roomtemperature phase is ferroelectric rhombohedral with space group R3m (No. 160) that transforms into ferroelectric tetragonal P4mm (No. 99) at 340 K, and then to a relaxor state at 440 K.[35] Permittivity presents a sharp increase at the ferroelectric-to-relaxor transition, and typical relaxor behavior above this temperature.[36] The absence of any dielectric feature associated with the transition between the relaxor and ferroelectric states for the nanostructured material down to 77 K strongly suggests that this transition has disappeared as a size effect. This finding is in good agreement with recent results for 0.65Pb(Mg1/3Nb2/3)O3–0.35PbTiO3, also a perovskite relaxor-based MPB material; structural analysis and dielectric measurements showed that the ferroelectric phase vanished below a size of 200 nm, and that a relaxor state existed down to 30 nm.[23] Below this size, a maximum of dielectric permittivity was not observed, and the authors proposed that a conventional paraelectric phase was present. However, our results indicate that a relaxor state exists for 0.92Pb(Zn1/3Nb2/3)O3–0.08PbTiO3 with a size of 20 nm. The presence of such a relaxor state is further supported by the room-temperature nonlinear electric response, which is shown in Figure 5 for the ceramic spark plasma sintered at 873 K. Current density at increasing electric fields up to 1 kV mm 1 and 0.1 Hz is presented, which clearly shows polarization-switching maxima. This result demonstrates that an electrical polarization builds up and then is switched under the field at room temperature for this nanostructured : 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim small 2007, 3, No. 11, 1906 – 1911 Perovskite Nanostructured Ceramics Figure 5. Nonlinear electrical response at 0.1 Hz for a nanostructured 0.92PbZn1/3Nb2/3O3–0.08PbTiO3 material with a grain size of 20 nm. material. Polarization switching is already observed at a field of 0.2 kV mm 1, and the polarization continuously increases with the field with no signs of saturation at 1 kV mm 1. This is indicated by the height and width of the maxima, although quantification is not possible because of nonlinear conduction. This is why we chose to show the current loops rather than the charge ones, which are strongly deformed by the conduction, yet ferroelectriclike inflection points can still be observed, as is also illustrated in Figure 5 for the highest field applied. Note that polarization switching is observed at room temperature, which is slightly above the temperature of the permittivity maximum. This is a typical behavior of relaxors. Polarization switching disappeared when the frequency was raised to 1 Hz; the buildup of polarization thus has a characteristic time above 1 s. The study of macroscopic polarization shows the behavior of the aggregate of crystals, and the measurement is very sensitive to extrinsic factors, such as porosity, second phases, and the quality of the electrode/ceramic electrical contact, which is an issue for the nanostructured materials under investigation. Also, ceramic samples suffered dielectric breakdown under high-voltage dc (or very low frequency) electrical loading, which prevented bulk conventional electromechanical characterization. Local measurements with scanning force microscopy (SFM) provide information closer to the behavior of individual nanocrystals and are not affected by these factors. The basis of piezoresponse force microscopy (PFM) is the application of an electric field between a conductive tip and the sample, which induces a piezoelectric response that is recorded. With this technique, we obtained in-field piezoelectric hysteresis loops, such as the one shown in Figure 6 a. The loop is typical of relaxors; high effective piezoelectric coefficients are attained under field, associated with the buildup of polarization, which change sign with switching, but low remanence is found.[37] Also, the loop is shifted towards negative voltages, which indicates that an internal electric field has built up under the applied inhomogeneous electric field beneath the tip, most probably associated with the separation of free charge carriers. The results on macroscopic properties reported here have only been obtained thanks to the densification levels small 2007, 3, No. 11, 1906 – 1911 Figure 6. PFM of the nanostructured 0.92PbZn1/3Nb2/3O3–0.08PbTiO3 material with a grain size of 20 nm: a) piezoelectric coefficient hysteresis loop; b) piezoelectric response. achieved by SPS. The fact that we observed relaxor behavior for a grain size of 20 nm, while paraelectric behavior was described for MPB Pb(Mg1/3Nb2/3)O3–PbTiO3 below 30 nm,[23] is most probably not due to any intrinsic difference between these relaxor-based systems but to the densification levels of the materials prepared. In this work, a densification of 80 % was obtained in comparison with the 60 % reported in ref. [23] for the materials with the smallest size. Electric measurements in such powder compacts are difficult and the real dielectric behavior of the material can be masked. The effect of densification on the dielectric properties of the Pb(Zn1/3Nb2/3)O3–PbTiO3 nanostructured materials is illustrated in Figure 7, where the temperature dependence of the relative permittivity and dielectric losses at 1 MHz is given for the ceramics spark-plasma sintered at 873 and 823 K, with densification levels of 80 and 70 %, respectively. Note the increase of permittivity and decrease of losses associated with electrical conduction with the increase in densification. Nevertheless, the relaxor maximum is still observed for the material processed at 823 K. The results clearly demonstrate that a relaxor state exists in 0.92Pb(Zn1/3Nb2/3)O3–0.08PbTiO3 nanostructured ceramics with a grain size of 20 nm, and that a macroscopic electrical polarization can be built up and switched with an electric field at room temperature. This was not the case : 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim www.small-journal.com 1909 full papers M. Alguer et al. linear piezoelectric response under bias is found by PFM. This is the first time that these phenomena have been observed in a nanostructured, ferroelectric, relaxor-based MPB material. 4. Experimental Section Figure 7. Dielectric permittivity and losses as a function of temperature at 1 MHz for nanostructured 0.92PbZn1/3Nb2/3O3–0.08PbTiO3 materials with different levels of densification. for very dense ( 97 %) BaTiO3 nanostructured ceramics with similar grain size, for which ferroelectric switching could not be induced in spite of them being in the ferroelectric phase.[21, 38] Lack of switching was proposed to be due to the clamping of transgranular ferroelectric domains at the grain boundaries. Porosity might disrupt domain continuity across the grains and result in smaller domains with lessclamped walls, as is suggested by the report of ferroelectric switching in BaTiO3 materials with a grain size of 40 nm and a densification of 90 %.[39] Nevertheless, the mechanism of polarization in relaxors is not that of conventional ferroelectrics: the nucleation and growth of ferroelectric domains. Polarization for relaxors is built up by the growth and merging of polar nanoregions within a paraelectric matrix. This phenomenon seems to scale well in the nanoscale, as a nanostructured relaxor material with a size of a few tens of nanometers still presents polarization reversal. It must be pointed out that polarization in relaxors is not stable after the removal of the electric field above the freezing temperature. However, relaxors present high piezoelectric coefficients under bias field, and a highly linear, nonhysteretic electromechanical response that is currently used in actuation. This effect is illustrated in Figure 6 b for the nanostructured Pb(Zn1/3Nb2/3)O3–PbTiO3 material, where the local piezoelectric response under the built-in field measured by PFM is shown. 3. Conclusions We have succeeded in processing 0.92Pb(Zn1/3Nb2/3)O3– 0.08PbTiO3 nanostructured ceramics with a grain size of 20 nm by the SPS of a nanocrystalline powder obtained by mechanosynthesis, and in characterizing their electrical properties. The results indicate that the relaxor-to-ferroelectric phase transition does not occur in the nanoscale material, and that a relaxor state exists instead of the ferroelectric R3m phase. An electrical polarization can be built up and switched with an electric field in the 0.92Pb(Zn1/3Nb2/3)O3– 0.08PbTiO3 nanostructured material, and a local, highly 1910 www.small-journal.com Mechanosynthesis and powder characterization: A stoichiometric mixture of analytical grade PbO, ZnO, Nb2O5, and TiO2 (3 g) was initially homogenized by hand in an agate mortar, then placed in a stainless-steel pot with five stainless-steel balls (2 cm in diameter, weight 35 g) for mechanochemical activation. This was carried out in air with a Pulverisette 6 model Fritsch planetary mill (300 rpm), and mechanosynthesis was completed after 70 h. Phases and morphology were characterized by XRD with a Seifert 3000 TT apparatus and Cu Ka radiation, and by TEM with a Philips CM12ST microscope (120 kV). Spark-plasma sintering: A cylindrical graphite die (8-mm inner diameter) was filled with the powder for use with a SPS 2080 Sumitomo apparatus. A pulsed direct current was then passed through the die while an increasing uniaxial pressure was applied (up to 100 MPa) and the sample was heated to the final temperature (100 K min 1). The final conditions of sintering temperature and 100 MPa were maintained for 3 min. Ceramic characterization: Phases were characterized by XRD with a Siemens D500 powder diffractometer with Cu Ka radiation (2q = 0.058 steps and 5 s dwell time). Samples for TEM were prepared and characterized with the Philips CM12ST microscope for determining the grain size. The dependences of the dielectric permittivity and losses on temperature were measured with an HP 4192A impedance analyzer (100 Hz, 1 kHz, 10 kHz, 100 kHz, and 1 MHz frequencies). Measurements were dynamically accomplished during heating from 77 to 573 K (1.5 K min 1). For characterizing the nonlinear electric response at room temperature, voltage sine waves were applied (frequencies of 0.1 and 1 Hz and amplitude up to 1000 V) by the combination of a synthesizer/function generator (HP 3325B) and a bipolar operational power supply/amplifier (Kepco BOP 1000M). Charge was measured with a homebuilt charge-to-voltage converter and software for loop acquisition and analysis. Current was obtained by numerical differentiation of the charge data. Samples for SFM were prepared by polishing with Al2O3 suspensions with decreasing sizes (down to 0.05 mm) and etching in acetic acid (20 min) to reveal the grain boundaries. Measurements were carried out with a Nanotec Electr?nica microscope and WSxM software. PFM was carried out with Pt/Ir-coated tips from Nansensors (ac voltage 1 V, frequency 50 kHz). Acknowledgements This research was funded by MEC (Spain) through the MAT2005-01304 and MAT2004-00868 projects. Drs. T. Hungr,a and H. Amor,n are grateful for financial support by the : 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim small 2007, 3, No. 11, 1906 – 1911 Perovskite Nanostructured Ceramics EC FPVI NoE MIND (NMP3-CT2005-515757) and MEC (JdC Program), respectively. Collaboration between ICMM and CEMES is framed within the ESF COST Action 539 ELENA. Technical support by I. Mart,nez (ICMM) and Ph. Salles (CEMES) is also acknowledged. [1] Piezoelectric Materials in Devices (Ed.: N. Setter), EPFL, Lausanne, 2002, ISBN 2-9700346-0-3. [2] C. Pithan, D. Hennings, R. Waser, Int. J. Appl. Ceram. Technol. 2005, 2, 1 – 14. [3] S. Trolier-McKinstry, P. Muralt, J. Electroceram. 2004, 12, 7 – 17. [4] H. G. Craighead, Science 2000, 290, 1532 – 1535. [5] K. L. Ekinci, Small 2005, 1, 786 – 797. [6] J. Ricote, S. Holgado, P. Ramos, M. L. Calzada, IEEE Trans. Ultrason. Ferroelectr. Freq. Control 2006, 53, 2299 – 2304. [7] T. Tybell, P. Paruch, T. Giamarchi, J. M. Triscone, Phys. Rev. Lett. 2002, 89, 097 601. [8] I. Szafraniak, C. Harneaga, R. Scholz, S. Bhattacharyya, D. Hesse, M. Alexe, Appl. Phys. Lett. 2003, 83, 2211 – 2213. [9] M. Nikiforov, H. Liu, H. G. Craighead, D. Bonell, Nano Lett. 2006, 6, 896 – 900. [10] F. Zavaliche, H. Zheng, L. Mohaddes-Ardabili, S. Y. Yang, Q. Zhan, P. Shafer, E. Reilly, R. Chopdekar, Y. Jia, P. Wright, D. G. Schlom, Y. Suzuki, R. Ramesh, Nano Lett. 2005, 5, 1793 – 1796. [11] N. A. Spaldin, Science 2004, 304, 1606 – 1607. [12] C. H. Ahn, K. M. Rabe, J. M. Triscone, Science 2004, 303, 488 – 491. [13] P. Ghosez, K. M. Rabe, Appl. Phys. Lett. 2000, 76, 2767 – 2769. [14] J. Junquera, P. Ghosez, Nature 2003, 422, 506 – 509. [15] D. D. Fong, G. B. Stephenson, S. K. Streiffer, J. A. Eastman, O. Auciello, P. H. Fuoss, C. Thompson, Science 2004, 304, 1650 – 1653. [16] V. Nagarajan, S. Prasertchoung, T. Zhao, H. Zheng, J. Ouyang, R. Ramesh, W. Tian, X. Q. Pan, D. M. Kim, C. B. Eom, H. Kohlstedt, R. Waser, Appl. Phys. Lett. 2004, 84, 5225 – 5227. [17] W. S. Yun, J. J. Urban, Q. Gu, H. Park, Nano Lett. 2002, 2, 447 – 450. [18] J. E. Spanier, A. M. Kolpak, J. J. Urban, I. Grinberg, L. Ouyang, W. S. Yun, A. M. Rappe, H. Park, Nano Lett. 2006, 6, 735 – 739. [19] H. Fu, L. Bellaiche, Phys. Rev. Lett. 2003, 91, 257 601. small 2007, 3, No. 11, 1906 – 1911 [20] S. Ray, Y. V. Kolen’ko, D. Fu, R. Gallage, N. Sakamoto, T. Watanabe, M. Yoshimura, M. Itoh, Small 2006, 2, 1427 – 1431. [21] M. T. Buscaglia, M. Viviani, V. Buscaglia, L. Mitoseriu, A. Testino, P. Nanni, Z. Zhao, M. Nygren, C. Harneaga, D. Piazza, C. Galassi, Phys. Rev. B 2006, 73, 064 114. [22] C. Liu, B. Zou, A. J. Rondinone, Z. J. Zhang, J. Am. Chem. Soc. 2001, 123, 4344 – 4345. [23] J. Carreaud, P. Gemeiner, J. M. Kiat, B. Dkhil, C. Bogicevic, T. Rojac, B. Malic, Phys. Rev. B 2005, 72, 174 115. [24] S. E. Park, T. R. Shrout, J. Appl. Phys. 1997, 82, 1804 – 1811. [25] A. Halliyal, U. Kumar, R. E. Newham, L. E. Cross, Am. Ceram. Soc. Bull. 1987, 66, 671 – 676. [26] T. Fujiu, A. Tanaka, T. Takenaka, Jpn. J. Appl. Phys. 1991, 30, L298 – L301. [27] M. Alguer?, J. Ricote, A. Castro, J. Am. Ceram. Soc. 2004, 87, 772 – 778. [28] A. Giri, Adv. Mater. 1997, 9, 163 – 166. [29] J. Wang, W. Dongmei, X. Junmin, N. W. Beng, Adv. Mater. 1999, 11, 210 – 213. [30] Z. J. Shen, Z. Zhao, H. Peng, M. Nygren, Nature 2002, 417, 266 – 269. [31] Z. A. Munir, U. Anselmi-Tamburini, M. Ohyanagi, J. Mater. Sci. 2006, 41, 763 – 777. [32] T. HungrKa, M. Alguer?, A. B. HungrKa, A. Castro, Chem. Mater. 2005, 17, 6205 – 6212. [33] H. C. Ling, M. F. Yan, W. W. Rhodes, J. Mater. Sci. 1989, 24, 541 – 548. [34] L. E. Cross, Ferroelectrics 1994, 151, 305 – 320. [35] G. Y. Xuo, P. M. Gehring, G. Shirane, Phys. Rev. B 2006, 74, 104 110. [36] M. L. Mulvihill, S. E. Park, G. Risch, Z. Li, K. Uchino, T. R. Shrout, Jpn. J. Appl. Phys. 1996, 35, 3984 – 3990. [37] V. V. Shvartsman, A. L. Kholkin, M. Tyunina, J. Levoska, Appl. Phys. Lett. 2005, 86, 222 907. [38] X. Y. Deng, X. H. Wang, H. Wen, L. L. Chen, L. Chen, L. T. Li, Appl. Phys. Lett. 2006, 88, 252 905. [39] M. H. Frey, Z. Xu, P. Han, D. A. Payne, Ferroelectrics 1998, 206, 337 – 353. Received: April 23, 2007 Revised: August 21, 2007 Published online on October 12, 2007 : 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim www.small-journal.com 1911