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The orientation dependence of the longitudinal piezoelectric coefficient, d(33)(*), is investigated as a function of temperature in BaTiO3 and PbTiO3 crystals using the Landau-Ginsburg-Devonshire theory. We show that a presence of the ferroelectric-ferroelectric phase transitions in BaTiO3 leads to enhanced d(33)(*) along nonpolar directions. The reason for this is that in the vicinity of a phase transition temperature at which a polarization vector changes its direction (tetragonal-orthorhombic/monoclinic, orthorhombic/monoclinic-rhombohedral), the shear piezoelectric coefficients become high. It is shown for all ferroelectric phases of BaTiO3 that the shear stress deforms the crystal cell and changes the polarization direction in a similar way as the corresponding temperature-induced phase transition. The influence of the piezoelectric shear effect on the anisotropy of d(33)(*) is particularly pronounced in the orthorhombic/monoclinic phase where the piezoelectric shear coefficients are determined by the presence of both the high-temperature tetragonal and the low-temperature rhombohedral phases. In PbTiO3, which does not exhibit ferroelectric-ferroelectric phase transitions, the shear piezoelectric effect is weak and d(33)(*) has its maximum along the polar axis at all temperatures. These results can be generalized to include phase transitions induced by electric-field and composition variations and are valid for all perovskite materials, including complex relaxor-ferroelectric perovskites that have recently attracted attention for their exceptionally large piezoelectric properties. (C) 2003 American Institute of Physics.

Using recently published experimental data we calculated the piezoelectric response of rhombohedral 0.67Pb(Mg1/3Nb2/3)O-3-0.33PbTiO(3) monodomain single crystals along arbitrary directions. The calculations indicate that the value of the longitudinal piezoelectric coefficient along the [001] axis of the pseudocubic system ([111] axis of the rhombohedral system) of a monodomain crystal is close to the value determined experimentally along the same direction of a multidomain crystal with a so-called "engineered domain state." The results thus show that the large piezoelectric response in this material is dominated by intrinsic crystal lattice effects and that the multidomain state has a relatively minor effect (1900 pC/N for certain directions of the monodomain crystal. (C) 2003 American Institute of Physics.

This paper discusses the mechanisms that can contribute to the enhanced longitudinal piezoelectric effect along nonpolar directions in perovskite crystals, such as BaTiO3, PbTiO3, KNbO3, Pb(Mg1/3Nb2/3)O-3-PbTiO3 and Pb(Zn1/2Nb2/3)O-3-PbTiO3. Piezoelectric anisotropy is discussed in relation to temperature induced phase transitions, compositional variation in solid solutions with morphotropic phase boundaries, applied electric fields, the domain wall structure and domain wall displacement. (c) 2006 Springer Science + Business Media, Inc.

The influence of the uniaxial bias stress on the piezoelectric properties of tetragonal BaTiO3 and PbTiO3 monodomain crystals is modeled in the framework of the phenomenological Landau-Ginzburg-Devonshire theory. It is shown that tensile and compressive stresses, both applied along the spontaneous polarization direction, reduce and enhance the piezoelectric response, respectively. The enhancement effect is due to the flattening of the free-energy profile and the corresponding dielectric softening of crystals, caused by the compressive stress. In BaTiO3 crystals, at temperatures close to the tetragonal-orthorhombic phase transition temperature, the free-energy profile flattening and dielectric softening are the largest along axes perpendicular to the polarization direction, facilitating thus the polarization rotation away from the [001](c) polar axis. The resulting enhancement of the shear piezoelectric coefficient is directly responsible for the increase of the longitudinal piezoelectric coefficient along the [111](c) axis. At temperatures deep within the tetragonal phase in BaTiO3, and over the whole ferroelectric region of PbTiO3, the flattening of the free-energy profile and the dielectric softening by compressive stress are the strongest along the polar axis. The resulting enhancement of the longitudinal piezoelectric coefficient is thus the largest along the polar [001](c) direction. These results, which can be applied to other perovskite crystals, have broad implications.

The orientation dependence of the longitudinal piezoelectric coefficient is investigated as a function of temperature in BaTiO/sub 3/ and PbTiO/sub 3/ crystals using Landau-Ginsburg-Devonshire theory. We show that a presence of the ferroelectric - ferroelectric phase transitions in BaTiO/sub 3/ leads to an enhanced piezoelectric longitudinal response along nonpolar directions. The reason for this is the abrupt increase of the shear piezoelectric coefficients in the vicinity of a FE - FE phase transition temperature. In PbTiO/sub 3/, which does not exhibit such phase transitions, the shear piezoelectric effect is weak and the longitudinal piezoelectric coefficient has its maximum along the polar axis at all temperatures. These results can be generalized to include phase transitions induced by electric-field and composition variation and are valid for all perovskite materials. Further, using Landau-Ginzburg-Devonshire theory and tetragonal BaTiO/sub 3/ as an example, we demonstrate that a strong electric bias fields applied anti-parallel to the spontaneous polarization may lead to a large enhancement of piezoelectric properties in monodomain perovskite crystals. The enhancement is due to the field-induced dielectric softening of the crystal.

Piezoelectric properties of ferroelectric crystals can be greatly enhanced in the proximity of electric and mechanical coercive fields. While the thermodynamic origin of the enhancement in both cases can be traced to the flattening of a free energy profile, we show using the Landau–Ginzburg–Devonshire theory that there is a qualitative difference in how the proximity of 90° and 180° polarization switching affects the piezoelectric response and its anisotropy. Taking as an example PbTiO3 monodomain single crystals biased by near-coercive electric and stress fields applied along the polar axis, it is shown that the antiparallel electric field softens the material along the polar direction while the compressive stress softens the crystal along nonpolar directions. In the former cases the piezoelectric enhancement is dominated by the polarization contraction along the polar axis while in the latter case it is dominated by the polarization rotation away from the polar axis. An analogy is made between the effec...

Note: Damjanovic, D Swiss Fed Inst Technol, EPFL, Dept Mat, Ceram Lab, CH-1015 Lausanne, Switzerland Swiss Fed Inst Technol, EPFL, Dept Mat, Ceram Lab, CH-1015 Lausanne, Switzerland721TJTimes Cited:6Cited References Count:3 Reference LC-ARTICLE-2003-009View record in Web of Science Record created on 2006-08-21, modified on 2017-05-10

Today, high crystal quality in sufficient size with high crystal growth yield appears to be a key point for a wide dissemination and use in ferroelectrics applications. So, this paper is related to the growth of PZN-PT solid solution compound like (1-x)(PbZn/sub 1/3/Nb/sub 2/3/O/sub 3/)-xPbTiO/sub 3/ and PMN-PT compound like (1-y)(PbMg/sub 1/3/Nb/sub 2/3/O/sub 3/)-yPbTiO/sub 3/. For these two relaxor ferroelectric single crystals promising properties are obtained near the Morphotropic Phase Boundary (MPB) transition which occurred at values closed to x=0.09 for PZN-PT and y=0.34 for PMN-PT. The complex unit cell phase transition combined with an adequate applied electric field, oriented in the pseudo /sub c/ direction; confer to these single crystals some interesting piezoelectric properties. We present some crystal growth results obtained by the Vertical Gradient Freeze-Solution Growth method (VGF-SG) for PZN-PT and by a pseudo Kyropoulos method developed for PMN-PT. The obtained single crystals, up to 120 g for PZN-PT and 160 g for PMN-PT are then analysed in term of composition and structure. Both PMN-PT and PZN-PT perovskite crystals are rhombohedral (@RT), they show a good global homogeneity. Samples demonstrate ferroelectric behaviour, and after polarisation process, dielectric constants up to 48000 near the Curie temperature (Tc /spl sim/174/spl deg/C @ 1kHz) are obtained for PZN-PT and respectively 74000 for PMN-PT (Tc /spl sim/ 142/spl deg/C @ 100 Hz). The piezoelectric coefficient d/sub 33/ gives values up to /spl sim/2200 pC/N (@RT 9 kV/cm) for PZN-PT and 1700 pC/N(@RT) for PMN-PT. A value up to 94% is measured for the electromechanical coupling coefficient k/sub 33/.

While in the paralectric phase of ferroelectrics, and in centrosymmetric materials in general, the dielectric tunability is symmetrical for positive and negative electric bias fields, in noncentrosymmetric materials this is not the case. By using the thermodynamic theory, and tetragonal phase of monodomain single-crystal perovskites BaTiO3 and Pb(Zr,Ti)O-3, as examples, we show that the theoretical tunability region of ferroelectrics may, in principle, be considerably broadened and tunability greatly enhanced by applying electric-bias field antiparallel to polarization. Available experimental data are in qualitative agreement with the theoretical predictions. (c) 2006 American Institute of Physics.