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ABSTRACT: The crack growth resistance behavior of single crystal and polycrystalline 0.71Pb(Mg1/3Nb2/3)O3-0.29PbTiO3 (PMN-29%PT) was determined with compact-tension specimens. Two different single crystal orientations were produced by the solid-state crystal growth technique (SSCG) and characterized, allowing for the direct comparison to polycrystalline material. Single crystal R-curve behavior was observed to be anisotropic, which is explained by the effects of ferroelasticity and stress-induced phase transformations on toughening. Results of the polycrystalline samples display comparable toughness to that observed in single crystal measurements.
Journal of the American Ceramic Society 06/2011; 94(9):2728 - 2730. · 2.27 Impact Factor
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ABSTRACT: Piezoelectric actuators outperform other technological solutions in the area of high-speed, high-force and high-accuracy displacement, but are only able to generate strains of about 0.2%. The load capability is generally quantified in terms of a blocking force, which is the force sustained under electric field at zero displacement. Stress–strain curves in a temperature regime from room temperature up to 150 °C on electrically loaded soft lead zirconate titanate (PZT) are generated to determine the blocking stress. The ensuing nonlinear behaviour is discussed in terms of ferroelectric and ferroelastic switching and contrasted to idealized linear constitutive behaviour as often assumed by manufacturers. The blocking stress is shown to increase with temperature due to an additional stiffening effect as a function of electric field. The actual mechanical work done is found to be larger than in the idealized case where linear constitutive behaviour is assumed.
Journal of Physics D Applied Physics 08/2010; 43(36):365401. · 2.54 Impact Factor
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ABSTRACT: The ferroelastic properties of a hard acceptor-doped lead zirconate titanate (PZT) ceramic are investigated between room temperature and 300°C. Comparison with a soft PZT shows that acceptor doping has a stronger influence on mechanically induced domain switching than on switching caused by electric fields. A quantitative analysis of spontaneous and remanent strain and polarization indicates that poling in the soft material is dominated by 180° domain processes, while non-180° processes dominate the strain behavior. If the mechanical load exceeds a threshold level, the “hardening” effect of the acceptor doping vanishes, and hard and soft materials behave identically. The results are discussed based on the defect dipole model and the charge drift model for hardening and aging in acceptor-doped ferroelectric ceramics.
Journal of the American Ceramic Society 04/2010; 93(9):2850 - 2856. · 2.27 Impact Factor
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ABSTRACT: The mechanism of the giant unipolar strain recently observed in a lead-free piezoceramic, 0.92( Bi <sub>0.5</sub> Na <sub>0.5</sub>) TiO <sub>3</sub>-0.06 BaTiO <sub>3</sub>-0.02( K <sub>0.5</sub> Na <sub>0.5</sub>) NbO <sub>3</sub> [S.-T. Zhang, A. B. Kounga, E. Aulbach, H. Ehrenberg, and J. Rödel, Appl. Phys. Lett. 91, 112906 (2007) was investigated. The validity of the previously proposed mechanism that the high strain comes both from a significant volume change during the field-induced phase transition, from an antiferroelectric to a ferroelectric phase and the domain contribution from the induced ferroelectric phase was examined. Monitoring the volume changes from the simultaneously measured longitudinal and transverse strains on disk-shaped samples showed that the phase transition in this specific material does not involve any notable volume change, which indicates that there is little contribution from a volume change due to the phase transition to the total strain response. Temperature dependent hysteresis measurements on unpoled samples of a nearby ferroelectric composition, 0.93( Bi <sub>0.5</sub> Na <sub>0.5</sub>) TiO <sub>3</sub>-0.06 BaTiO <sub>3</sub>-0.01( K <sub>0.5</sub> Na <sub>0.5</sub>) NbO <sub>3</sub> demonstrated that the origin of the large strain is due to the presence of a nonpolar phase that brings the system back to its unpoled state once the applied electric field is removed, which leads to a large unipolar strain.
Journal of Applied Physics 06/2009; · 2.17 Impact Factor
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ABSTRACT: Temperature-dependent electrical properties of lead-free 0.94Bi0.5Na0.5TiO3–0.06BaTiO3 (BNT–BT) ceramics were investigated. Below 100°C, this rhombohedral–tetragonal morphotropic phase-boundary composition shows dominant ferroelectric order with typical ferroelectric polarization–electric field (P(E)) loop and butterfly bipolar strain–electric (S(E)) curve. Antiferroelectric order tends to prevail when temperature reaches about 100°C, characterized by a pinched P(E) loop and altered bipolar S(E) butterfly. Near the ferroelectric–antiferroelectric transition temperature, the composition shows a giant bipolar and unipolar strain of 0.40% and 0.42%, respectively. The highest value of maximum strain divided by the applied field (i.e., Smax/Emax) reaches 700 pm/V at 100°C. With a further increase of temperature to 200°C, a slight decrease of the strain is observed. Especially, it is found that the hysteresis of the unipolar S(E) curve decreases with increasing temperature. These results may be helpful for further understanding and thus designing new BNT-based lead-free piezoelectric systems.
Journal of the American Ceramic Society 10/2008; 91(12):3950 - 3954. · 2.27 Impact Factor
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ABSTRACT: The poling behavior of a lead-zirconate-titanate piezoelectric ceramic is investigated by measurements of the ferroelectric hysteresis, the longitudinal piezoelectric coefficient, and field-cooling poling experiments. At high temperatures, the decrease in the coercive field facilitates poling at lower electric fields, resulting in higher values of the longitudinal piezoelectric coefficient. However, there exists a threshold field of about 150 V/mm, below which fully poled samples cannot be obtained even when field cooling from temperatures above the transition. Further, a temperature regime below the Curie temperature is observed, where a polarization under field can be measured, but a remanent polarization is not stable. The results are discussed with respect to the phase transition behavior.
Journal of Applied Physics 08/2008; · 2.17 Impact Factor
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ABSTRACT: In many polycrystalline piezoelectric ceramics, domain switching during the poling process leads to the development of a macroscopic polarization and piezoelectric behavior. Traditionally, poling involves the application of electric fields across two parallel electrodes. In the present work, a radial mechanical compressive stress is applied transverse to the electric field, increasing the potential for domain alignment during poling by taking advantage of ferroelasticity. Experiments demonstrate that poling of lead zirconate titanate using a combination of an electric field and a transverse mechanical compressive stress increases the d33 coefficient from 435 to 489 pC/N. Using neutron diffraction and pole figure inversion methods, the degree of non-180° domain switching is described using pole density distributions of the tetragonal c-axis (002). The degree of 002 domain alignment parallel to the electric field after the electromechanical poling process increases from 1.30 multiples of a random distribution (mrd) to >1.40 mrd at stresses exceeding 40 MPa.
Journal of the American Ceramic Society 03/2008; 91(5):1586 - 1590. · 2.27 Impact Factor
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ABSTRACT: Lead-free piezoelectric ceramics, (1-x-y) Bi <sub>0.5</sub> Na <sub>0.5</sub> Ti O <sub>3</sub>–x Ba Ti O <sub>3</sub>–y K <sub>0.5</sub> Na <sub>0.5</sub> Nb O <sub>3</sub> ( 0.05≤x≤0.07 and 0.01≤y≤0.03 ), have been synthesized by a conventional solid state sintering method. The room temperature ferroelectric and piezoelectric properties of these ceramics were studied. Based on the measured properties, the ceramics were categorized into two groups: group I compositions having dominant ferroelectric order and group II compositions displaying mixed ferroelectric and antiferroelectric properties at room temperature. A composition from group II near the boundary between these two groups exhibited a strain as large as ∼0.45% at an electric field of 8 kV / mm . Polarization in this composition was not stable in that the piezoelectric coefficient d<sub>33</sub> at zero electric field was only about 30 pm / V . The converse piezoelectric response becomes weaker when the composition deviated from the boundary between the groups toward either the ferroelectric or antiferroelectric compositions. These results were rationalized based on a field induced antiferroelectric-ferroelectric phase transition.
Journal of Applied Physics 03/2008; · 2.17 Impact Factor
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ABSTRACT: The temperature dependence of the dielectric and ferroelectric properties of lead-free piezoceramics of the composition (1-x-y) Bi <sub>0.5</sub> Na <sub>0.5</sub> Ti O <sub>3</sub>–x Ba Ti O <sub>3</sub>–y K <sub>0.5</sub> Na <sub>0.5</sub> Nb O <sub>3</sub> ( 0.05≤x≤0.07 , 0.01≤y≤0.03 ) was investigated. Measurements of the polarization and strain hystereses indicate a transition to predominantly antiferroelectric order when heating from room temperature to 150 ° C , while for 150≪T≪200 ° C both remnant polarization and coercive field increase. Frequency-dependent susceptibility measurements show that the transition is relaxorlike. For some samples, the transition temperature T<sub>d</sub> is high enough to allow mostly ferroelectric ordering at room temperature. These samples show a drastic increase of the usable strain under an external electric field just after the transition into the antiferroelectric state at high temperatures. For the other samples, T<sub>d</sub> is so low that they display significant antiferroelectric ordering already at room temperature. In these samples, the usable strain is relatively stable over a wide temperature range. In contrast to T<sub>d</sub> , the temperature T<sub>m</sub> of the transition into the paraelectric high-temperature phase depends far less on the sample composition. These results confirm that the high strain in this lead-free system is due to a field-induced antiferroelectric-ferroelectric phase transition and that this effect can be utilized in a wide temperature range.
Journal of Applied Physics 03/2008; · 2.17 Impact Factor
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ABSTRACT: Lead-free piezoelectric ceramics (1-x-y)Bi{sub 0.5}Na{sub 0.5}TiO{sub 3}-xBaTiO{sub 3}-yK{sub 0.5}Na{sub 0.5}NbO{sub 3} (0.05{<=}x{<=}0.07 and 0.01{<=}y{<=}0.03), have been synthesized by a conventional solid state sintering method. The room temperature ferroelectric and piezoelectric properties of these ceramics were studied. Based on the measured properties, the ceramics were categorized into two groups: group I compositions having dominant ferroelectric order and group II compositions displaying mixed ferroelectric and antiferroelectric properties at room temperature. A composition from group II near the boundary between these two groups exhibited a strain as large as {approx}0.45% at an electric field of 8 kV/mm. Polarization in this composition was not stable in that the piezoelectric coefficient d{sub 33} at zero electric field was only about 30 pm/V. The converse piezoelectric response becomes weaker when the composition deviated from the boundary between the groups toward either the ferroelectric or antiferroelectric compositions. These results were rationalized based on a field induced antiferroelectric-ferroelectric phase transition.
Journal of Applied Physics. 01/2008; 103(3).
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ABSTRACT: Piezoelectric actuators convert electrical into mechanical energy and are implemented for many large-scale applications such as piezoinjectors and ink jet printers. The performance of these devices is governed by the electric-field-induced strain. Here, the authors describe the development of a class of lead-free (0.94-x) Bi <sub>0.5</sub> Na <sub>0.5</sub> Ti O <sub>3</sub>–0.06 Ba Ti O <sub>3</sub>–x K <sub>0.5</sub> Na <sub>0.5</sub> Nb O <sub>3</sub> ceramics. These can deliver a giant strain (0.45%) under both unipolar and bipolar field loadings, which is even higher than the strain obtained with established ferroelectric Pb ( Zr , Ti ) O <sub>3</sub> ceramics and is comparable to strains obtained in Pb-based antiferroelectrics.
Applied Physics Letters 10/2007; · 3.84 Impact Factor
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Journal of Applied Physics. 105(9):094102-5.
