O3-PbTiO3 Single Crystals Research Articles

Strong, high-frequency, ac electric-field-induced rhombohedra-tetragonal phase transition in Pb(Mg1∕3Nb2∕3)O3–PbTiO3 single crystal

Dielectric properties of Pb(Mg1∕3Nb2∕3)O3–PbTiO3 single crystals grown by a modified Bridgman method are investigated under strong, high-frequency (>100kHz) ac field. It is found that there is a phase transition due to the applied ac field, which may be due to the following reasons: (1) strong ac field periodically moves domains at fast speed that heats up the crystal due to the friction of domain change; and (2) phase transition happens because of the increase of the temperature. Compared with conventional heating techniques, ac field-induced phase transition is a quicker and more effective way. In addition, it is also found that continuous ac excitation can make the phase transition easier that may be due to the deaging effect caused by continuous ac excitation. Experimental results confirm the increase of d33 and the change of transmittance under strong ac field, which further verifies that phase transition indeed happens.

Optimum Compositions for Pb(Zn1/3Nb2/3)O3–PbTiO3 Single Crystal for High-Performance Applications

Pb(Zn1/3Nb2/3)O3–PbTiO3 single crystals of (6–7) mol% PbTiO3 (PT) grown by the high-temperature flux technique under near-equilibrium conditions exhibit improved composition homogeneity, superior and consistent dielectric and piezoelectric properties which are also the least sensitive to PT content variation in the material, and a depolarization temperature of approximately 100°C. This composition holds promise for the production of large-size high-homogeneity high-performance relaxor single crystals for commercial use.

Indentation induced mechanical and electrical response in ferroelectric crystal investigated by acoustic mode AFM

AbstractThe mechanical and electrical response of Pb (Mg1/3Nb2/3)‐ O3–PbTiO3 single crystals to micro‐indentation are investigated using the newly developed low frequency scanning probe acoustic microscopy which is based on the atomic force microscope. There are three ways to release the stress produced by indentation. Plastic deformation emerged directly underneath the indentor and along the indentation diagonals. In addition, indentation‐induced micro‐cracks and new non‐180° domain structures which are perpendicular to each other are also observed in the indented surface. Based on the experimental results, the relationship between the cracks and the domain patterns was discussed. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Temperature stability of the piezoelectric and elastic response of dc biased [001] and [110] oriented Pb(Zn1∕3Nb2∕3)O3-PbTiO3 single crystals

Temperature and field dependent investigations of the longitudinal electromechanical properties of [001]- and [110]-oriented 0.955Pb(Zn1∕3Nb2∕3)O3-0.045PbTiO3 single crystals have been performed. Electromechanical equivalence was found between [001] and [110] orientations in the ferroelectric rhombohedral FEr phase region, but not in the ferroelectric tetragonal FEt one. A dc bias of 0.4 MV∕m did not affect this equivalence. Softening of the dielectric constant (K), piezoelectric coefficient (d33), and Young’s modulus (Y) were observed along both the [001] and [110] orientations in the FEr phase region on heating towards the FEt one. Above the FEr-FEt phase transition, a significant anisotropy was observed in the electromechanical and elastic coefficients. These results demonstrate that the enhanced length extensional (33-mode) electromechanical coupling k33 of rhombohedral crystals far from the morphotropic phase boundary is not constrained to the ⟨001⟩ orientation, but rather to the (110) plane.

Polarization relaxation anisotropy in Pb(Zn1/3Nb2/3)O3-PbTiO3 single-crystal ferroelectrics as a function of fatigue history

Polarization relaxation was studied in Pb(Zn1/3Nb2/3)O3-PbTiO3 (PZN-PT) single crystals that show fatigue anisotropy. To excite prepoled crystals, a modest dc voltage (<1/2 of the coercive field) was applied along the poling direction. Upon removal of the voltage, the polarization decay in the time domain was measured. Experimental data were modeled with a stretched exponential function. Stretching exponent (β〈hkl〉) and characteristic time (τ〈hkl〉) constants for polarization relaxation were determined from data over four decades in the time domain at different stages of bipolar cycling. β〈hkl〉 values after 101 cycles were 0.146±0.002 and 0.247±0.0004 in the 〈001〉 and 〈111〉 orientations, respectively. The β〈111〉 constant increased up to 0.453±0.104 after 105 cycles in 〈111〉 oriented crystals that show fatigue. However, much less change is observed in β〈001〉 as a function of cycling for 〈001〉 crystals. Characteristic time constants for relaxation (τ〈hkl〉) were calculated for 〈001〉 and 〈111〉 orientations as 0.401±0.048 s and 57.46±0.10 s, respectively. These results suggest a faster polarization relaxation in 〈001〉 than in the 〈111〉 orientation of rhombohedral PZN-PT ferroelectric crystals.

Adaptive ferroelectric states in systems with low domain wall energy: Tetragonal microdomains

Ferroelectric and ferroelastic phases with very low domain wall energies have been shown to form miniaturized microdomain structures. A theory of an adaptive ferroelectric phase has been developed to predict the microdomain-averaged crystal lattice parameters of this structurally inhomogeneous state. The theory is an extension of conventional martensite theory, applied to ferroelectric systems with very low domain wall energies. The case of ferroelectric microdomains of tetragonal symmetry is considered. It is shown for such a case that a nanoscale coherent mixture of microdomains can be interpreted as an adaptive ferroelectric phase, whose microdomain-averaged crystal lattice is monoclinic. The crystal lattice parameters of this monoclinic phase are self-adjusting parameters, which minimize the transformation stress. Self-adjustment is achieved by application of the invariant plane strain to the parent cubic lattice, and the value of the self-adjusted parameters is a linear superposition of the lattice constants of the parent and product phases. Experimental investigations of Pb(Mg1/3Nb2/3)O3–PbTiO3 and Pb(Zn1/3Nb2/3)O3–PbTiO3 single crystals confirm many of the predictions of this theory.

Fe-substituted 0.92Pb(Zn1/3Nb2/3)O3–0.08PbTiO3 single crystals: A “hard” piezocrystal

The dielectric and electrically induced strain characteristics of Fe-substituted Pb(Zn1/3Nb2/3)O3–PbTiO3 single crystals have been investigated. These investigations have shown that Fe substitution results in: (i) a lowering of the field level required to obtain large strains, (ii) an increased squareness in the ε−E response indicative of “hard” piezoelectric properties, and (iii) enhanced linearity in the region where saturation is approached at high field levels. Interestingly, the hard characteristics occur along with an enhanced stability of an intermediate ferroelectric orthorhombic state.

Phase stabilities of “morphotropic” phases in Pb(Zn1/3Nb2/3)O3–PbTiO3 single crystals

Based on the optic and dielectric data acquired under different mechanical and electric conditions and temperature, we show that an orthorhombic phase exists near the morphotropic phase boundary (MPB) (on both the rhombohedral and tetragonal sides of MPB). Because of the proximity of the free energy of this phase to the two other morphotropic phases, i.e., the rhombohedral and tetragonal phases, the experimentally observed phases and phase diagrams near MPB depend crucially on the mechanical and electric conditions as well as the sample history.

Mechanical aging behavior of oriented Pb(Mg1/3Nb2/3)O3–PbTiO3 and Pb(Zn1/3Nb2/3)O3–PbTiO3 single crystals

The aging characteristics of 〈001〉-oriented Pb(Zn1/3Nb2/3)O3–PbTiO3 (PZN-PT) and Pb(Mg1/3Nb2/3)O3–PbTiO3 (PMN-PT) single crystals have been studied under electrical and mechanical drive. A significant increase in hysteretic loss and decrease in piezoelectric constant were observed under continuous excitation. Systematic investigations of piezoelectric aging were then performed using a novel mechanical fatigue method. Piezocrystals were placed between two magnetostrictive plates and clamped. Periodic longitudinal compressive stresses were generated by applying magnetic fields. At both short and long times, the piezoelectric constant was found to decrease slowly. However, in an intermediate range, a pronounced decrease was observed over a narrow time range. The dynamics of aging have been shown to scale to a hierarchical relaxation process, typical of disordered systems such as random field and glassy states.

Photoelastic effects in tetragonal Pb(Zn1/3Nb2/3)O3–PbTiO3 single crystals near the morphotropic phase boundary

In order to explore the photoelastic effects of the ferroelectric single crystal Pb(Zn1/3Nb2/3)O3–PbTiO3 (PZN–PT), the piezo-optical coefficients π were characterized for 0.9PZN–0.1PT and 0.88PZN–0.12PT under uniaxial stress using an interferometer method. The results show that the crystal exhibits very large π values (for example, π33 can reach 19.8×10−12 m2/N), indicating that this material is a good candidate for stress sensors and acousto-optic modulators.

Cymbal actuators fabricated using PMN-PT single crystal

Cymbal actuators with very high displacement have been fabricated and tested. A cymbal actuator consists of a piezoelectric disc sandwiched between two truncated conical metal endcaps. Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) single crystal is used as the piezoelectric driving element of the cymbal actuator. The influence of the piezoelectric coefficient of the driving element on the actuator performance has been studied. Due to its high piezoelectric d33 and d31 coefficients, a PMN-PT single crystal actuator gives a much higher displacement than a PZT actuator.

Direct observations of electric field-induced domain boundary cracking in 〈001〉 oriented piezoelectric Pb(Mg1/3Nb2/3)O3–PbTiO3 single crystal

In situ transmission electron microscopy study of electric field-induced cracking has been conducted on 〈001〉 oriented 0.65Pb(Mg1/3Nb2/3)O3–0.35PbTiO3 crystal. Fracture of the 90° domain boundary was directly observed in the tetragonal area under both static and alternating electric fields. The field strength required to induce domain boundary cracking was lower for alternating electric field than for static field.

Composition, temperature, and crystal orientation dependence of the linear electro-optic properties of Pb(Zn1/3Nb2/3)O3–PbTiO3 single crystals

The linear electro-optic (EO) coefficients of Pb(Zn1/3Nb2/3)O3–PbTiO3 single crystals over a broad composition range were investigated at temperatures from −20 to 80 °C. The orientation effect on the EO coefficients was also examined. For crystals poled in the 〈001〉 direction, a large r33 was observed near the morphotropic phase boundary (MPB). More importantly, r33 was found to be independent of temperature for the crystals on the tetragonal side of the MPB. In contrast, r13 was nearly zero for all compositions examined at all the temperatures. The large r33 near the MPB and the observed crystal orientation effect of the EO coefficients were also analyzed.

Growth, characterization and properties of relaxor ferroelectric PMN-PT single crystals

The present paper reviews the recent progress of studies on growth, characterization and properties of relaxor ferroelectric Pb(Mg1/3Nb2/3)O3-PbTiO3 single crystals in Shanghai Institute of Ceramics. Their chemical compositions were selected near the rhombohedral-tetragonal morphotropic phase boundary, more favorable in the rhombohedral phase. The dominant method used for growing the single crystals was the modified Bridgman technique, by which the single crystal boules with the size larger than 25mm diameter and 50 mm long were grown. Different orientation thin plates with thickness less than 1mm were cut from the boules and their domain structures, morphology and properties were characterized. Their phase transition were discussed as well.

Cryogenic behavior of perovskite materials

Dielectric and piezoelectric properties of perovskite materials such as La modified Pb(Zr,Ti)O3 ceramics and Pb(Zn1/3Nb2/3)O3-PbTiO3 single crystals were investigated for cryogenic capacitor and actuator applications. Enhanced extrinsic contributions resulted in piezoelectric coefficient (d33) as high as 250 pC/N at 30 K, superior to that of PZT (d33 ∼ 100 pC/N). This cryogenic property enhancement was associated with retuning the MPB for cryogenic temperatures. PZN-PT single crystals exhibited dramatic property improvements such as d33 > 500 pC/N at 30 K as a result of an engineered domain state.

Dielectric and piezoelectric properties of perovskite materials at cryogenic temperatures

Dielectric and piezoelectric properties of perovskite materials including La modified Pb(Zr, Ti)O3 (PZT's), (Ba, Sr)TiO3 (BST) polycrystalline ceramics and Pb(Zn1/3 Nb2/3)O3-PbTiO3 (PZN-PT) single crystals were investigated for capacitor and actuator applications at cryogenic temperatures. PZTs were compositionally engineered to have decreased Curie temperatures (Tc) by La and Sn doping in order to compensate for the loss of extrinsic contributions to piezoelectricity at cryogenic temperatures. Enhanced extrinsic contributions resulted in piezoelectric coefficients (d33) as high as 250 pC/N at 30 K, superior to that of conventional DOD Type PZT's (d33~100 pC/N). This property enhancement was associated with retuning to the MPB at cryogenic temperatures. 5/95 BST with a dielectric maximum at 57 K was investigated to obtain high electrostrictive properties or E-field induced piezoelectricity. Coupling coefficients (k31) 25% comparable to those of the cryogenic PLZT piezoelectrics were observed at d.c. bias of 1.5 kV/cm and 50 K. Though significantly lower than the room temperature values, PZN-PT rhombohedral single crystals exhibited d33> 500 pC/N at 30 K.

Phase transitions in the Pb (Zn1/3Nb2/3)O3-PbTiO3system

Abstract Two successive phase transitions, changing the crystal symmetry from rhombohedral to tetragonal, and then to cubic on a heating process, have been investigated in the Pb(Zn1/3Nb2/3)O3-PbTiO3 single crystals with the composition near the morphotropic phase boundary. The existence of the morphotropic phase boundary has been confirmed by measuring the dielectric, piezoelectric and pyroelectric constant. Anomalously large electromechanical and piezoelectric constants are observed on the morphotropic phase boundary.