PMN-PT Crystals Research Articles

Low-voltage electron emission from thin [Pb(Mg1/3Nb2/3)O3]0.72 [PbTiO3]0.28 single crystals induced by ferroelectric polarization switching

Electron emission from [Pb(Mg1/3Nb2/3)O3]0.72 [PbTiO3]0.28 (PMN–PT) thin ferroelectric single crystals is reported at ultralow voltages down to 20 V per 400 μm thickness, and for up to 109 switching cycles. The PMN–PT samples were prepared with split gold top electrodes exhibiting a 25 μm wide gap region. Applying a sinusoidal voltage between the two top electrodes and the bottom electrode initiated electron emission from the gap region. The emitted electrons were collected under UHV conditions using two single electron counters arranged under an angle of 90°. Two emission regimes have been identified. Both are attributable to weak electron emission, however, clearly separated by the onset of complete ferroelectric polarization switching. This is also confirmed by recording nanoscale ferroelectric hysteresis loops by means of piezoresponse force microscopy. The emitted electrons are found to have a broad energy distribution with the maximum kinetic energies reaching 110 and 50 eV for applied switching voltages of 140 and 110 V, respectively. Our results confirm that polarization reversal is the governing mechanism behind the electron-emission process in the thin PMN–PT samples. Also, the applied electric field strengths needed to trigger electron emission from the PMN–PT crystals are about 10 times lower compared to most other (ferroelectric) materials reported in the literature.

Enhanced magnetoelectric effect in longitudinal-transverse mode Terfenol-D∕Pb(Mg1∕3Nb2∕3)O3–PbTiO3 laminate composites with optimal crystal cut

Magnetoelectric (ME) laminate composite consisting of optimal crystal cut thickness-polarized piezoelectric 0.7Pb(Mg1∕3Nb2∕3)O3–0.3PbTiO3 (PMN-PT) single crystal and the length-magnetized magnetostrictive Tb0.3Dy0.7Fe1.92 (Terfenol-D) alloy has been fabricated. The cut optimization of PMN-PT crystal greatly enhances the longitudinally magnetized-transversely polarized (L-T) mode ME effect, which has a superior ME voltage coefficient αE of ∼3.02V∕cmOe in low frequency band. Near the resonance frequency of 95kHz, the coefficient dramatically increases and reaches the maximized value of 33.2V∕cmOe, which is almost two times larger than the previously reported ⟨001⟩-oriented PMN-PT crystal based L-T mode laminate composite.

Improved stability for piezoelectric crystals grown in the lead indium niobate–lead magnesium niobate–lead titanate system

Higher coercive fields (EC) and depoling temperatures (TR∕T) were obtained for crystals in the Pb(In1∕2Nb1∕2)O3–Pb(Mg1∕3Nb2∕3)O3–PbTiO3 (PIN–PMN–PT) ternary system. Data are given for a crystal boule with starting composition 0.24PIN-0.44PMN-0.32PT, and with chemical distributions along the growth direction. The dielectric, piezoelectric, and elastic properties were determined. Similar to binary PMN–PT, ternary PIN–PMN–PT crystals have outstanding piezoelectric properties (e.g., d33∼900–1900pm∕V, k33∼0.83–0.92). In addition, PIN stabilizes piezoelectric performance by doubling EC (∼6kV∕cm) and increasing TR∕T by ∼20°C. These improvements are advantageous for acoustic transducers used in high-drive applications.

Electric field induced critical points and polarization rotations in relaxor ferroelectrics

The giant electromechanical response in ferroelectric relaxors such as $\mathrm{Pb}({\mathrm{Mg}}_{1∕3}{\mathrm{Nb}}_{2∕3}){\mathrm{O}}_{3}\text{\ensuremath{-}}\mathrm{Pb}\mathrm{Ti}{\mathrm{O}}_{3}$ (PMN-PT) is of great importance for a number of ultrasonic and medical applications as well as in telecommunications. On the basis of the dielectric, heat capacity, and piezoelectric investigations on PMN-PT crystals of various PT compositions and bias fields, we have recently shown the existence of a line of critical points for the paraelectric to ferroelectric transformations in the composition-temperature-electric field $(x\text{\ensuremath{-}}T\text{\ensuremath{-}}E)$ phase diagram. Here, we show the piezobehavior in more detail and present a theoretical evaluation of the Widom line and the critical line. This line effectively terminates a surface of first order transitions. Above this line, supercritical evolution has been observed. On approaching the critical point, both the enthalpy cost to induce the intermediate monoclinic states and thus the barrier for polarization rotations decrease significantly. The maximum of the piezoelectric response is not at $E=0$, but at the critical field values. It is shown that the critical fluctuations in the proximity of the critical points are directly responsible for the observed enhancement of the electromechanical response in the PMN-PT system. In view of the large electric field dependence of the dielectric constant near the critical point, these systems may also be important as electric field tunable elements.

Characterization of All the Elastic, Piezoelectric, and Dielectric Constants of Tetragonal Pb(Mg1/3Nb2/3)O3–PbTiO3 Single Crystals

Pb(Mg1/3Nb2/3)O3–PbTiO3 (PMN–PT) single crystals have a tetragonal 4 mm symmetry. In this paper, the elastic, piezoelectric, and dielectric constants of PMN–PT single crystals were measured by the resonance method. A total of eleven independent material constants were measured including six elastic compliance constants at a constant electric field, two dielectric constants at constant stress, and three piezoelectric constants d. Four crystal sample sets of different geometries were prepared in order to measure the length–thickness extensional, thickness extensional, length extensional and thickness shear modes of vibrations, respectively. The experimental impedance spectrum of the PMN–PT crystals was compared with a numerical impedance spectrum calculated with the measured material constants. Good agreement between the two spectra confirmed the validity of the characterization method. In addition, the piezoelectric constant d33, which was determined by the resonance method, was also compared with that measured by a commercial d33 meter. This further confirmed the validity of the resonance measurements.

Dynamic strain in magnetic films on piezoelectric crystals

Reversible biaxial strain has been induced in ferromagnetic films of several lanthanum manganites which have been epitaxially grown on the (0 0 1) face of high-strain piezoelectric crystals of Pb(Mg 1/3Nb 2/3) 0.72Ti 0.28O 3 (PMN-PT). The strain-induced changes of the Curie temperature and the remanent magnetization have been observed. PMN-PT(0 0 1) crystals used as substrates are characterized with respect to their lattice parameters, domain-related surface topology and electric relaxation behavior. A sample consisting of a magnetic film on a piezo-crystal forms a simple and well-defined model system for strain-mediated magnetoelectric coupling.

Dielectric and piezoelectric properties of [0 0 1] and [0 1 1]-poled relaxor ferroelectric PZN–PT and PMN–PT single crystals

The properties of PZN–PT and PMN–PT single crystals of varying compositions and orientations have been investigated. Among the various compositions studied, [0 0 1]-optimally poled PZN-(6–7)%PT and PMN-30%PT exhibit superior dielectric and piezoelectric properties, with K T ≈ 6800–8000, d 33 ≈ 2800 pC/N, d 31 ≈ −(1200–1800) pC/N for PZN-(6–7)%PT; and K T = 7500–9000, d 33 = 2200–2500 pC/N and d 31 = −(1100–1400) pC/N for PMN-30%PT. These two compositions are also fairly resistant to over-poling. The [0 0 1]-poled electromechanical coupling factors ( k 33, k 31 and k t ) are relatively insensitive to crystal composition. [0 1 1]-optimally poled PZN-7%PT single crystal also exhibits extremely high d 31 values of up to −4000 pC/N with k 31 ≈ 0.90–0.96. While [0 1 1]-poled PZN-7%PT single crystal becomes over-poled with much degraded properties when poled at and above 0.6 kV/mm, PZN-6%PT crystal shows no signs of over-poling even when poled to 2.0 kV/mm. The presence of a certain amount (i.e., 10–15%) of orthorhombic phase in a rhombohedral matrix has been found to be responsible for the superior transverse piezoelectric properties of [0 1 1]-optimally poled PZN-(6–7)%PT. The present work shows that flux-grown PZN–PT crystals exhibit superior and consistent properties and improved over-poling resistance to flux-grown PMN–PT crystals and that, for or a given crystal composition, flux-grown PMN–PT crystals exhibit superior over-poling resistance to their melt-grown counterparts.

One-Dimensional Crystal Growth Near Morphotropic Phase Boundary (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 Crystal Fibers

Ferroelectric perovskite (1−x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 single crystals of near morphotropic phase boundary composition in rhombohedral phase, were successfully grown by a laser heated pedestal growth (LHPG) technique. The LHPG technique is a novel one-dimensional crystal growth method that requires no crucible for growth, allows compositions gradient adjustment during growth, and of high growth speed. The growth of highly volatile Pb-containing perovskite crystals was accomplished by an approach that uses excess PbO and boron oxide in the feed material that act as traveling flux in the molten zone during the growth. Controlling of growth orientation and composition homogeneity was studied. Dielectric, ferroelectric and piezoelectric properties of LHPG grown PMN-PT crystals were obtained and reported in this paper.

Fabrication and Characterization of Single Crystal Cymbals

Cymbal transducers are made using single crystal relaxor ferroelectric PMN-PT. An electrically conductive adhesive film with uniform geometry and thickness is used to bond the metal cymbal caps to the single crystal. Upon curing, the bond exhibits good mechanical strength under both static and dynamic test conditions. It is found that the capacitance and d 33 of the cymbal drop markedly upon curing as compared to the single crystal disk. It is demonstrated that this is not due to depoling during the adhesive cure stage but rather clamping of the single crystal disk by the stiff metal cymbal caps.

A-4 Poled domain structure with a surface electrode pair on PMN-PT crystal

A-4 Poled domain structure with a surface electrode pair on PMN-PT crystal

Nontrivial dependence of dielectric stiffness on bias field in relaxors and dipole glasses

Dielectric permittivity studies in the field-cooled mode show a linear dependence of dielectric stiffness (inverse dielectric permittivity) on the dc bias in (1−x)PbMg1∕3Nb2∕3O3−xPbTiO3 crystals. We explain this unusual result in the framework of a theory of transverse, hydrodynamic-type instability of local polarization.

Cut directions for the optimization of piezoelectric coefficients of lead magnesium niobate–lead titanate ferroelectric crystals

The representation surfaces of the piezoelectric strain coefficient (d) were calculated for [011], [001], and [111] poled lead magnesium niobate–lead titanate (PMN–PT) crystals with ∼31% PT. It was discovered that the zxt±45° cut (rotation around z axis ±45°) for [011] poled PMN–PT crystal gives a unique repolable shear piezoelectric coefficient d36 up to 2600 pC/N. The zxt 0° cut (without rotation) d31 up to −1750 pC/N was obtained for the [011] poled crystals. It was also found that an extraordinarily high shear piezoelectric coefficient d15 up to 5190 pC/N for the single-domain crystal (3 m) occurred in the zxt−22.5 cut (22.5° clockwise rotation about the x axis). These calculated results were experimentally verified.

Composition and orientation dependence of phase configuration and dielectric constant tunability inpoled Pb(Mg1/3Nb2/3)O3–PbTiO3 single crystals

The composition and orientation dependence of the room temperature piezoelectric constantd33 and the dielectric constant tunability was investigated in poled single crystals of(1−x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 (PMN–PT)with x varying from 0.24 to 0.38. The temperature, frequency, orientation and compositiondependence of the dielectric constant in the poled crystals shows that domainconfigurations and phase transitions in the poled crystals strongly depend on bothcomposition and orientation. Poled polydomain crystals near the morphotropic phaseboundary, especially for -poled 0.70PMN–0.30PT crystals with a critical composition for the relaxor state, possess a large piezoelectricconstant d33 = 2210 pC N−1 and a high dielectric constant tunability of 40.6% (at a dc bias of1 kV mm−1). The largetunability of εr in PMN–PT crystals is expected to be the most promising candidate for potentialapplications in continuously adjustable capacitors and dielectric amplifiers.

Reaction of platinum crucible and melt during PMN-PT crystal growth

PMN-PT crystals have been of considerable interest in recent years due to their excellent ferroelectric, piezoelectric, photoelectric properties and promising applications in various electric and electric–optical devices. However, the crucible leakage is usually a fetal limitation during preparation of the crystal. In this work, the PMN-PT crystals were prepared by Bridgman-accelerated crucible rotation technique (ACRT) method. The morphologies of the bottom surface of the PMN-PT crystal and the inner surface of the platinum crucible, in which the crystal grew, were examined by scanning electronic microscope (JSM-840). The local composition was analyzed by EDAX spectrometer attached to the scanning unit. Investigated results indicated that there are evident reaction between the platinum crucible and PbO–MgO–Nb 2O 5–TiO 2 melt during PMN-PT crystal growth, which is the main cause of crucible leakage. Another cause of the crucible leakage is due to the unequally distorted platinum grain boundary.

Lattice Dynamics and Central-Mode Phenomena in the Dielectric Response of Ferroelectrics and Related Materials

In this review we describe and discuss recent results on the linear dielectric response of high-permittivity dielectric crystals and ceramics in the wide frequency range 102–1014Hz. Our attention is paid to materials which exhibit some interesting low-frequency polar-phonon anomalies in combination with some additional dielectric dispersion below the polar phonon region. The following compounds are discussed: microwave ceramics Bi1.5Zn1.0Nb1.5O7, antiferroelectric PbZrO3ceramics and AgNbO3crystals, ferroelectric LiNaGe4O9, LaBGeO5, Cd2Nb2O7and SrBi2Ta2O9crystals, incommensurate ferroelectric Sr2Nb2O7, Ba2NaNb5O15and BCCD crystals, dipolar-glass crystal of Rb1/2(ND4)1/2D2PO4, relaxor ferroelectric Pb(Sc1/2Ta1/2)O3and PLZT ceramics and PMN crystals, antiferroelectric PLZT 2/95/5 ceramics and relaxor-based PMN-PT, PZN-PT and BiScO3-PT crystals and ceramics. For these materials the polar phonon spectra are discussed together with their flow-frequency dielectric response and dispersion regions in between, in the 10–300 K or higher temperature range, depending on the existing phase transitions of interest. Some universal features of the disorder and anharmonicities are pointed out: central-mode phenomena near displacive phase transitions and polar nano-clusters which appear at rather high temperatures and remain present down to low temperatures if the material remains structurally disordered. The manifestation of the latter in the dielectric spectra consists in extreme broadening of the relaxation region on cooling which at low temperatures results in constant loss spectra (1/fnoise).

공진법을 이용한 PMN-PT 단결정의 탄성, 유전, 압전상수 측정

PMN-PT, a piezoelectric single crystal, has many useful applications such as sensors and actuators. In this paper, all the elastic, piezoelectric, and dielectric constants of the PMN-32％PT single crystals were measured by the resonance method. For the rhombohedral symmetry, a total of twelve independent material constants were measured such as six elastic compliance constants at constant electric field, two dielectric constants at constant stress, and four piezoelectric constants d. Seven sets of crystal samples of each different geometry were prepared for the measurement of length-thickness extensional, thickness extensional, radial, length extensional and thickness shear modes of vibration, respectively. In order to check the validity of the measurement, experimental impedance spectrum of the PMN-PT crystal was compared with numerical data spectrum calculated with the measured material constants. The good agreement between the two spectra confirmed validity of the results in this paper.

An investigation of large fatigue rate in cub-oriented Pb(Mg1/3Nb2/3)O3–PbTiO3 single crystal

Domain structures in <111>cub-oriented 0.70Pb(Mg1/3Nb2/3)O3–0.30PbTiO3 (PMN–PT) single crystal have been investigated by both optical microscopy and transmission electron microscopy (all of the orientations below will be given in terms of the prototype cubic axes, denoted by the subscript cub). Microcracking in the fatigued PMN–PT crystal samples has been observed and its forming mechanism have been analyzed in terms of domain configurations. The contribution of microcracking to the large fatigue rate in <111>cub-oriented PMN–PT single crystal has been identified. A new approach that is based on observed domain configuration and microcracking has been proposed to explain the large fatigue rate in the <111>cub-oriented PMN–PT single crystal.

Abnormal piezoresponse behavior of Pb(Mg 1/3Nb 2/3)O 3–30%PbTiO 3 single crystal studied by high-vacuum scanning force microscope

The effect of vacuum level on the piezoresponse behavior of Pb(Mg 1/3Nb 2/3)O 3–30%PbTiO 3 (PMN–30%PT) single crystal has been investigated by scanning force microscopy (SFM) in the piezoresponse mode under high vacuum. Unusual piezoresponse behavior related to the screening charges compensation mechanism was observed on the surface of (1 1 1)-oriented crystal. The low piezoresponse signal detected by high-vacuum SFM is attributed to the instability of the polarization state that is caused by the insufficient compensation of the minor intrinsic screening charges for the polarization charges in PMN–30%PT single crystal under high vacuum condition. The high domain contrast of the sample at an ambient pressure is due to the dominant surface screening charges resulted from surface adsorption, which plays an important role in determining the stability of the domain behavior and in achieving the optimal properties for PMN–PT crystal with the composition near the morphotropic phase boundary.

Importance of structural irregularity on dielectric loss in (1−x)Pb(Mg1/3Nb2/3)O3−(x)PbTiO3 crystals

The dielectric properties of (1−x)Pb(Mg1/3Nb2/3)O3−(x)PbTiO3 (PMN–PT) crystals have been investigated over a temperature range of 4 to 450 K at various frequencies. At low temperatures, an unusual frequency dependent plateau region in the absorption was observed between 75 and 175 K. At both higher and lower temperatures, the absorption was frequency independent. Analysis of the relaxation time constant revealed power-law divergence, typical of fractal behavior in disordered magnetic systems. The results demonstrate the importance of structural irregularities on the dielectric loss mechanism in poled oriented PMN–PT crystals.