Lead Magnesium Niobate Relaxor Research Articles

Low-field-driven large strain in lead zirconate titanium-based piezoceramics incorporating relaxor lead magnesium niobate for actuation

Studies on the piezoelectric materials capable of efficiently outputting high electrostrains at low electric fields are driven by the demand for precise actuation in a wide range of applications. Large electrostrains of piezoceramics in operation require high driving fields, which limits their practical application due to undesirable nonlinearities and high energy consumption. Herein, a strategy is developed to enhance the electrostrains of piezoceramics while maintaining low hysteresis by incorporating lead magnesium niobate relaxors into lead zirconate titanium at the morphotropic phase boundary. An ultrahigh inverse piezoelectric coefficient d33*\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${d}_{33}^{*}$$\\end{document} of 1380 pm/V with a reduced hysteresis of 11.5% is achieved under a low electric field of 1 kV/mm, outperforming the major lead-based piezoelectric materials. In situ synchrotron X-ray diffraction and domain wall dynamics characterization with sub-microsecond temporal resolution reveal that the outstanding performances originate from facilitated domain wall movement, which in turn is due to reduced lattice distortion and miniaturized domain structures. These findings not only address the pending challenges of effective actuation under reduced driving conditions but also lay the foundation for a more systematic approach to exploring the origin of large electrostrains.

Bridging the gap between the short-range to long-range structural descriptions of the lead magnesium niobate relaxor

The structure-property relationships on different length scales and their connections to the macroscopic piezoelectric and dielectric properties are one of the most fascinating topics of relaxor ferroelectrics and need to be further explored. Here, we provide structural insights into the gap between the short-range structure and the long-range structure of the classical relaxor ferroelectric lead magnesium niobate (PMN) using a combination of theoretical simulations and pair distribution function (PDF) analysis. Our study shows that PMN exhibits a disordered low-symmetry structure at the smallest length scale (1–10 Å) and a cubic crystallographic average structure at large length scale. A rhombohedral phase is observed at the intermediate length scale (∼ 20–70 Å), resulting from chemical ordered regions with the ordered local electric field and associated quasi-correlated Pb displacements. Our work advances the understanding of the structures of relaxor ferroelectrics at different length scales and the relationships among them.

Effects of Bi(Zn2/3Nb1/3)O3 Modification on the Relaxor Behavior and Piezoelectricity of Pb(Mg1/3Nb2/3)O3-PbTiO3 Ceramics.

Relaxor lead magnesium niobate (PMN)-based materials exhibit complex structures and unusual properties that have been puzzling researchers for decades. In this paper, a new ternary solid solution of Pb(Mg1/3Nb2/3)O3-PbTiO3-Bi(Zn2/3Nb1/3)O3 (PMN-PT-BZN) is prepared in the form of ceramics, and the effects of the incorporation of BZN into the PMN-PT binary system are investigated. The crystal structure favors a pseudocubic symmetry and the relaxor properties are enhanced as the concentration of BZN increases. The relaxor behavior and the related phase transformations are studied by dielectric spectroscopy. A phase diagram mapping out the characteristic temperatures and various states is established. Interestingly, the piezoelectricity of the PMN-PT ceramics is significantly enhanced by the BZN substitution, with an optimal value of d33 reaching 826 pC/N for 0.96[0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3]-0.04Bi(Zn2/3Nb1/3)O3. This paper provides a better understanding of the relaxor ferroelectric behavior, and unveils a new relaxor-based ternary system as piezoelectric materials potentially useful for electromechanical transducer applications.

Anelastic relaxor behavior of Pb(Mg1/3Nb2/3)O3

Elastic storage modulus and loss of relaxor lead magnesium niobate ceramics, Pb(Mg1/3Nb2/3)O3, have been measured with dynamic mechanical analyzer in single cantilever mode in the temperature range from 170 K to 320 K and at frequencies from 0.1 Hz to 50 Hz. The dependence of the elastic susceptibility (inverse modulus) on temperature and frequency of the driving force has characteristics of typical relaxor behavior that can be well described with the Vogel-Fulcher law. The parameters of the Vogel-Fulcher relation exhibit similar values for the dielectric and anelastic relaxations. Similarities and differences between anelastic and dielectric relaxor behaviors are identified.

Diffuse scattering in relaxor ferroelectrics: true three-dimensional mapping, experimental artefacts and modelling

The available body of experimental data in terms of the relaxor-specific component of diffuse scattering is critically analysed and a collection of related models is reviewed; the sources of experimental artefacts and consequent failures of modelling efforts are enumerated. Furthermore, it is shown that the widely used concept of polar nanoregions as individual static entities is incompatible with the experimental diffuse scattering results. Based on the synchrotron diffuse scattering three-dimensional data set taken for the prototypical ferroelectric relaxor lead magnesium niobate-lead titanate (PMN-PT), a new parameterization of diffuse scattering in relaxors is presented and a simple phenomenological picture is proposed to explain the unusual properties of the relaxor behaviour. The model assumes a specific slowly changing displacement pattern, which is indirectly controlled by the low-energy acoustic phonons of the system. The model provides a qualitative but rather detailed explanation of temperature, pressure and electric-field dependence of diffuse neutron and X-ray scattering, as well as of the existence of a hierarchy in the relaxation times of these materials.

Revisit of the Vögel–Fulcher freezing in lead magnesium niobate relaxors

The Vögel–Fulcher (VF) equation ω=ω0 exp[−Ea/kB(Tm−Tf)] was frequently used to describe the dielectric relaxation of relaxor ferroelectrics where ω is the probe frequency at the peak temperature Tm of either the real or imaginary parts of the dielectric constant. We revisited this relation in a typical relaxor lead magnesium niobate and found that the parameters obtained were not physically meaningful. Meaningful results can only be obtained by fitting the VF relation on the characteristic relaxation time τc, whose temperature dependence can be obtained from the Cole–Cole model. The freezing temperature we obtained is 230 K, below which τc becomes temperature independent.

High transition temperature lead magnesium niobate–lead zirconate titanate single crystals

Recently developed relaxor lead magnesium niobate–ferroelectric lead zirconate titanate single crystals exhibit large length extensional k33 coupling, improved thermal stability, and a higher coercive field compared to morphotropic lead magnesium niobate–lead titanate single crystals. Experimental results and implications for sound projectors are presented and discussed in terms of the morphotropic phase boundary slope and width. Spontaneous polarizations derived from the calculated atom shifts in both crystals compared favorably with experimental values.

Evolution of a nonspontaneous, high piezoelectric coupling symmetry axis in relaxor-ferroelectric single crystals

A nonspontaneous, high permittivity, “dielectrically soft” symmetry axis possessing large piezoelectric activity was found to exist for predominantly ferroelectric tetragonal FT compositions in the relaxor lead magnesium niobate–ferroelectric lead titanate, (1−x)Pb(Mg1∕3Nb2∕3)O3–(x)PbTiO3, single crystal system. The symmetry axis is not unique. It is a function of the lead titanate concentration x. It becomes the [011] for tetragonal compositions with x>0.35 and the [001] for rhombohedral compositions with 0.30⩽x⩽0.34. The two axial systems are degenerate for x∼0.35 and likely to converge at x∼0.29. Domain engineering for maximum piezoelectric response is easily accomplished for electric fields applied along this axis. The observations were confirmed by (1) isothermal resonance-antiresonance experiments on length extensional bars fabricated from multidomain (1−x)Pb(Mg1∕3Nb2∕3)O3–(x)PTiO3 single crystals and (2) numerical computation using Devonshire’s theory. The results are discussed in terms of recent field-temperature-composition phase diagram and lattice fluctuations along the four equivalent ⟨111⟩ directions. Implications for improved sound projector performance and the influence of dc fields on the domain states are discussed.

Electrostrictive effect in lead-free relaxor K0.5Na0.5NbO3–SrTiO3 ceramic system

The elastic strain of lead-free relaxor K0.5Na0.5NbO3–SrTiO3 ceramic system, induced by applied electric fields with amplitudes up to 40kV∕cm, has been investigated. The strain response, being similarly low (order of 10−5) as in the classical lead magnesium niobate relaxor, is shown to be of solely electrostrictive origin, as a pure quadratic relation holds between induced strain and electric polarization. The strain dependence on the SrTiO3 content is presented and discussed. Furthermore, electrostrictive coefficients are shown to be constant over a broad temperature range and, similar to dielectric properties, independent of electric-field cycles, which suggests possible applications of this translucent, high-dielectric constant, and environmental-friendly ceramic system.

Application of Fourier harmonic analysis to the electromechanical response of an electroactive material

Signal decomposition through Fourier analysis can aid quantification of the electromechanical properties (induced strain and polarization) of electroactive materials. Spectral analysis of the strain and polarization, obtained from the Fourier transform, provides a unique characterization tool that better conveys material response than can be accomplished with polynomial fitting. The derived coefficients can be mapped onto those in the Devonshire phenomenology. The technique is demonstrated by analysis of a lead magnesium niobate relaxor ferroelectric [0.9875(0.935PMN–0.065PT)–0.0125BT or 0.9233PMN–0.06419PT–0.0125BT] operating in the electrostrictive regime. Fourier analysis, applied to a materials response, provides the first quantitative linkage to materials coefficients. A generalized mathematical approach has been derived that equates a Fourier series expression, from the transform of a time-domain electromechanical response, to the basic underlying physics developed in Devonshire theory. Thus, the electrostrictive strain and polarization coefficients are calculated directly from the harmonic spectrum of the response. A benefit of the Fourier transform approach is the direct calculation of electrostrictive (and piezoelectric) coefficients with quantitative criterion for truncation and a “goodness of fit” criterion related to the zero frequency component. The real strength of the approach lies in its ability to accommodate electromechanical hysteresis and provide a distinct quantification of a given strain response. This is accomplished while faithfully describing the true harmonic content of the signal. The coefficients provide a descriptive fingerprint for use of the material under varying conditions.

Experimental Determination of Instantaneous Ionic-Pair Displacement-Correlation Functions of Relaxor PMN

Ionic-pair equal-time displacement correlations in relaxor lead magnesium niobate, PbMg 1/3 Nb 2/3 O 3 (PMN), were investigated at 300 and 270K in terms of an x-ray diffuse scattering technique. Functions of the distinct correlations were determined quantitatively. The results show the significantly strong rhombohedral-polar correlations regarding Pb-O, Mg/Nb-O, and O-O' pairs. Their spatial distribution at 300K forms an ellipse or a sphere with the diameters of 30-80A, and the sizes are reduced to 30-40A on cooling through local condensation of thermal lattice fluctuations. This direct observation of local structure in the system proves presence of the polar microregions in the paraelectric state which leads to the dielectric dispersion.

Chemical ordering in lanthanum-doped lead magnesium niobate relaxor ferroelectrics probed by A1g Raman mode

Chemical ordering of the B-site cations in undoped, 5, 10, 20, and 30 mol % La3+-doped Pb(Mg1/3Nb2/3)O3 (PMN) ceramics with perovskite structure, has been examined by Raman scattering. Two B-site chemical ordering models, the space-charge model, and the random layer model assume a space group of Fm3̄m for the ordered nanoregions. It is found that A1g Raman mode around 780 cm−1 from the B-site ordered nanoregions with a space group Fm3̄m, is very sensitive to the delicate changes of the chemical order at B site. Frequency changes of this A1g characteristic mode with La3+ doping, are analyzed according to the lattice parameters and chemical order effects. The present results provide stronge evidence supporting the random layer model in La-doped PMN.

The use of harmonic analysis of the strain response in Pb(Mg(1/3)Nb(2/3)) O3-based ceramics to calculate electrostrictive coefficients.

The electromechanical response of ceramics has long been described with Landau Devonshire phenomenology, wherein the strain response is linked to a polynomial expansion in electric field or dielectric displacement. Consequently, the electromechanical response has been modeled with a variety of basis functions. However, these models have failed to accommodate hysteresis and the harmonic response that arises with saturation phenomena. In addition, no quantitative criterion has been used to truncate the expansion. By implementing a discrete Fourier transform in conjunction with Devonshire phenomenology, these three problems can be overcome as demonstrated with a dielectrically aged, lead magnesium niobate relaxor ferroelectric well above its Tmax, i.e., operating in the electrostrictive regime.

X-ray diffuse scattering study on ionic-pair displacement correlations in relaxor lead magnesium niobate

Ionic-pair equal-time displacement correlations in relaxor lead magnesium niobate, $Pb(Mg_{1/3}Nb_{2/3})O_{3}$, have been investigated at room temperature in terms of an x-ray diffuse scattering technique. Functions of the distinct correlations have been determined quantitatively. The results show the significantly strong rhombohedral-polar correlations regarding Pb-O, Mg/Nb-O, and O-O' pairs. Their spatial distribution forms an ellipse or a sphere with the radii of 30-80$\AA$. This observation of local structure in the system proves precursory presence of the polar microregions in the paraelectric state which leads to the dielectric dispersion.

Reaction sintering and characterization of lead magnesium niobate relaxor ferroelectric ceramics

The formation and densification of Pb(Mg1/3Nb2/3)O3 ceramics prepared by reaction sintering have been investigated. Two kinds of lead sources. PbO and Pb3O4 are used as the starting materials for Pb(Mg1/3Nb2/3)O3. During heating processes, the specimens first expand while the pyrochlore phase is formed. At elevated temperatures, the formation and rapid sintering of Pb(Mg1/3\Nb2/3)O3 occur simultaneously. The starting materials of the Pb3\O4 system exhibit better reactivity and sinterability than those of the PbO system. With Pb3\O4 as the starting material, monophasic Pb(Mg1/3\Nb2/3)O3 ceramics with high sintering density are successfully achieved by reaction sintering at as low as 900 °C. While for the PbO system, pure perovskite phase could not be synthesized because of the existence of residual pyrochlore phase, and the ceramics obtained have low sintering density. The dielectric permittivity of the Pb(Mg1/3Nb2/3)O3 ceramics obtained in the Pb3O4 system is higher than that in the PbO system. This is attributed to the formation of pure perovskite phase and high sintering density in the former system.

Slow dynamics and ergodicity breaking in a lanthanum-modified lead zirconate titanate relaxor system

The freezing of the dynamic process in a 9/65/35 lanthanum lead zirconate-titanate (PLZT) ceramics has been investigated by measurements of the frequency-dependent complex dielectric constant and the quasistatic field-cooled (FC) and zero-field-cooled (ZFC) dielectric susceptibilities. It was found that the aging process is responsible for the difference in temperature variations of the FC static dielectric constant and the static dielectric constant determined in the dynamic ZFC experiment. Analysis of the complex dielectric susceptibility by a temperature-frequency plot has revealed that for an aged PLZT sample the ergodicity is broken due to the divergence of the longest relaxation time in the vicinity of 249 K, i.e., the temperature where the ferroelectric phase can also be induced by applying sufficiently high electric field. However, the bulk of the distribution of relaxation times was found to remain finite even below the freezing temperature. It is shown that the behavior of the relaxation spectrum and the splitting between the field-cooled and zero-field-cooled dielectric constants in PLZT relaxor is qualitatively similar to what was observed in the lead magnesium niobate (PMN) relaxor and is reminiscent of the nonergodic behavior reported in various spin glasses. Moreover, the temperature dependence of the third order nonlinear susceptibility indicates a glassy rather than ferroelectric multidomain nature of the nonergodic relaxor state in both PMN and PLZT systems.

Polarization changes in the ferroelectric relaxor lead magnesium niobate

A study is reported of the polarization and depolarization processes in the model ferroelectric relaxor, lead magnesium niobate (PMN), in pulsed and sine electric fields applied along the pseudocubic direction (001) above Td (Td is the phase transition temperature between the induced macrodomain ferroelectric and the nonpolar phases). The study was made by the electroluminescence and polarization-switching current hysteresis techniques. Pulsed electricfield measurements revealed the influence of pulse duration on electroluminescence intensity under polarization and depolarization of a sample, as well as a decrease of delay in the onset of depolarization for pulses shorter than the time required for the polarization to set in. A delay of depolarization in a sine electric field was observed to exist within a certain instantaneous fieldstrength interval. A study has also been made of the increase of the depolarization delay induced by simultaneous application of a sine electric field and a dc bias, or of an axial mechanical stress varying in phase with the electric field. The results obtained indicate the onset and persistence of field-induced local ferroelectric regions within a certain interval of instantaneous electric-field strengths. The effect of domain and domain-like processes on these phenomena is discussed.

Low temperature synthesis of Mg4Nb2O9

Abstract Magnesium niobate, Mg4Nb2O9, which is a room temperature photoluminescent material and a precursor for the synthesis of relaxor lead magnesium niobate, is prepared at a very low temperature of 550 °C by a precipitation method, compared to the conventional ceramic method of synthesis at 1300 °C. The compound is characterized by powder X-ray studies.

Comparison of DC and AC field effects on dielectric properties of lead magnesium niobate relaxor: Study of single crystals and ceramics

Dielectric permittivity of PbMg1/3Nb2/3O3 (PMN) relaxor was investigated as a function of DC bias and AC driving field. In single crystals, DC and AC field effects exhibited very different behavior, including anisotropy and sign of the effect. It was shown that the model of PMN, in which the dielectric response of the material to the AC field was controlled by a side-way motion of the interphase boundaries of the polar regions, provided a good qualitative interpretation of the observed phenomena. Comparison of the DC and AC field effects measured in ceramics and single crystals demonstrated that the data obtained for ceramics correspond to the averaging of the non-linear effects over random orientations of the grains.

A new glass model for lead magnesium niobate relaxors

The dielectric behavior of a solid solution, 10 mol% lead titanate in lead magnesium niobate(0.1PT-0.9PMN), was studied. The resemblance between the relaxor ferroelectrics and glasses was discussed. A more reasonable new function was introduced to characterize the relation between the frequency and the temperature of dielectric constant maximum of relaxor ferroelectrics. It was found that the activation energy of 0.1PT-0.9PMN is 0.037ev.