PbMg1/3Nb2/3O3 Research Articles

X-ray-induced piezoresponse during X-ray photon correlation spectroscopy of PbMg1/3Nb2/3O3.

X-ray photon correlation spectroscopy (XPCS) holds strong promise for observing atomic-scale dynamics in materials, both at equilibrium and during non-equilibrium transitions. Here an in situ XPCS study of the relaxor ferroelectric PbMg1/3Nb2/3O3 (PMN) is reported. A weak applied AC electric field generates strong response in the speckle of the diffuse scattering from the polar nanodomains, which is captured using the two-time correlation function. Correlated motions of the Bragg peak are also observed, which indicate dynamic tilting of the illuminated volume. This tilting quantitatively accounts for the observed two-time speckle correlations. The magnitude of the tilting would not be expected solely from the modest applied field, since PMN is an electrostrictive material with no linear strain response to the field. A model is developed based on non-uniform static charging of the illuminated surface spot by the incident micrometre-scale X-ray beam and the electrostrictive material response to the combination of static and dynamic fields. The model qualitatively explains the direction and magnitude of the observed tilting, and predicts that X-ray-induced piezoresponse could be an important factor in correctly interpreting results from XPCS and nanodiffraction studies of other insulating materials under applied AC field or varying X-ray illumination.

Quasielastic Light Scattering in the Broadband Brillouin Spectra of Relaxor Ferroelectric PbMg1/3Nb2/3O3

In this paper, the behavior of quasielastic light scattering (QELS) in a PbMg1/3Nb2/3O3 (PMN) crystal under broadband Brillouin light scattering in a temperature range from 750 K to 80 K was studied. It was shown that QELS consists of two components: narrow (0.9 GHz to 11 GHz) and wide (80 GHz to 600 GHz). The dependencies of the intensity, I, of these components on the frequency, ν, are well described by the power law I ~ eνα, with different α, and are determined by the distribution of the relaxation times. The analysis of the Brillouin spectra showed that the behavior of the relaxation time of both the components of QELS with temperature change is well described by the Arrhenius law. Additionally, in the vicinity of the intermediate temperature T* ≈ 380 K, a critical relaxation time behavior for the narrow component of QELS was detected. In the vicinity of the same temperature, a maximum in the integral intensity of both the components of QELS was observed, which is adjacent to another maximum in the region of the Vogel-Fulcher temperature TVF ≈ 250 K corresponding to the transformation of the crystal to a nonergodic state.

Non-linearity in engineered lead magnesium niobate (PbMg1/3Nb2/3O3) thin films

The local compositional heterogeneity associated with the lack of long-range ordering of Mg2+ and Nb5+ in PbMg1/3Nb2/3O3 (PMN) is correlated with its characteristic “relaxor” ferroelectric behavior. Earlier work [Shetty et al., Adv. Funct. Mater. 29, 1804258 (2019)] examined the relaxor behavior in PMN thin films grown at temperatures below 1073 K by artificially reducing the degree of disorder via synthesis of heterostructures with alternate layers of Pb(Mg2/3Nb1/3)O3 and PbNbO3, as suggested by the “random-site model.” This work confirmed the development of ferroelectric domains below 150 K in long-range-ordered films, epitaxially grown on (111) SrTiO3 substrates using alternate target timed pulsed-laser deposition of Pb(Mg2/3Nb1/3)O3 and PbNbO3 targets with 20% excess Pb. In this work, the first through third-harmonic dielectric charge displacement densities and complex dielectric susceptibilities were analyzed as a function of temperature and frequency in zero-field-cooled PMN films with short- and long-range ordering. The long-range ordering decreased the dispersion in the first- and third-harmonic dielectric charge displacement densities relative to short-range-ordered films. It was found that the one-dimensional ordering achieved in the long-range-ordered film is insufficient to achieve a fully normal ferroelectric state. In the presence of quenched random electric fields, these films require a small ac field to facilitate percolation of the polar nano-regions, enabling normal ferroelectric-like behavior at lower temperature (T < 240 K). The films behave like a typical relaxor near room temperature. With reduced ordering, the short-range films exhibit greater dispersion in linear and higher order harmonic dielectric charge displacement density.

Relaxor (Pb0.7Bi0.3)(Mg0.231Nb0.462Fe0.3)O3 electronic compound for magnetoelectric field sensor applications

A solid solution between relaxor ferroelectric PbMg1/3Nb2/3O3 (PMN) and multiferroic BiFeO3 (BFO) has been synthesized by a solid-state chemical reaction route. The comprehensive x-ray diffraction studies of (1 − x)PbMg1/3Nb2/3O3–xBiFeO3 [(1 − x)PMN–xBFO] confirm the realization of stable and orthorhombic crystal systems. From the dielectric study, relaxor behavior has been observed, which is corroborated by a broadened peak and diffusive phase transition. The magnetoelectric (ME) properties have been explored through P–E loop, M–H loop, and magnetoelectric coefficient analyses. The simultaneous occurrence of polarization and magnetization reveals the ME coupling response of the PMN–BFO compounds. Excellent values of PS = 15.94 μc/cm2, Pr = 7.68 μc/cm2, MS = 12.96 emu/g, Mr = 1.25 emu/g, and ME coefficient value of 220 mV/cm Oe for x = 0.3 are obtained, which is helpful for magnetoelectric field sensor applications. To ascertain its sensing capability, a prototype has been developed, and the sensing behavior of the device has been established by placing it near a designed helical coil electromagnetic field generator structure.

Polymorphic and morphotropic phase transitions in Pb(Mg1/3Nb2/3)O3–PbTiO3 solid solutions

Study of evolution of ferroelectric correlations in a system which intrinsically exhibits short range polar order in the form of polar-nano regions (PNRs), is the goal of the present work. For this purpose, well-known Relaxor ferroelectric i.e. PbMg1/3Nb2/3O3(PMN) and its solid solutions with PbTiO3(PT) has been systemically synthesized by varying composition, precursors and synthesis parameters. Dynamics associated with the PNRs and structural phase transitions of various polymorphs have been traced through temperature and frequency dependent dielectric permittivity profile. Formation of solid solutions with PT generates ferroelectric correlations associated with the tetragonal polymorphs, suppresses thermal fluctuations, overcomes diffused character of phase transition, effects polarization switching, stabilizes ferroelectric hysteresis characteristics and shifts dielectric permittivity maxima toward higher temperatures. Addition of PT led to relaxation dynamics associated with the multiple polymorphic phase transitions for T < 500 K, where system exhibits intrinsic character. Polymorphs with low symmetries lies below freezing temperature, where structural phase transition generates polar order. Diffusivity and activation energy of phase transitions, and freezing temperatures of polar regions of various processes have been quantified and compared as a function of PT. Excellent ferroelectric response of the compositions lying in the vicinity of the Morphotropic phase boundary composition has been observed.

Relaxor ferroelectrics and related superglasses

Mesoscopic ferroic glasses such as martensitic strain glass Ti50−x Ni50+x, magnetic cluster glass La0.7Ca0.3Mn0.7Cd0.3O3, and superdipolar relaxor PbMg1/3Nb2/3O3 (PMN) undergo glass transitions preceded by mesoscopic precursor patterns – elastic or magnetic tweed or polar nanoregions (PNR), respectively. In PMN the PNR glass transition at Tg ≈ 240 K reveals glassy dynamic criticality and non-ergodicity of the field-induced low-T phase similar to that of a superspin glass of fixed magnetic nanoparticles in a diamagnetic environment. A final ferroelectric domain state is reached at Tp ≈ 213 K via PNR percolation, which is absent in weak relaxors like BaTi0.65 Zr0.35O3 (BTZ35).

Local atomic order and hierarchical polar nanoregions in a classical relaxor ferroelectric

The development of useful structure-function relationships for materials that exhibit correlated nanoscale disorder requires adequately large atomistic models which today are obtained mainly via theoretical simulations. Here, we exploit our recent advances in structure-refinement methodology to demonstrate how such models can be derived directly from simultaneous fitting of 3D diffuse- and total-scattering data, and we use this approach to elucidate the complex nanoscale atomic correlations in the classical relaxor ferroelectric PbMg1/3Nb2/3O3 (PMN). Our results uncover details of ordering of Mg and Nb and reveal a hierarchical structure of polar nanoregions associated with the Pb and Nb displacements. The magnitudes of these displacements and their alignment vary smoothly across the nanoregion boundaries. No spatial correlations were found between the chemical ordering and the polar nanoregions. This work highlights a broadly applicable nanoscale structure-refinement method and provides insights into the structure of PMN that require rethinking its existing contentious models.

Relaxor Behavior in Ordered Lead Magnesium Niobate (PbMg1/3Nb2/3O3) Thin Films

AbstractThe local compositional heterogeneity associated with the short‐range ordering of Mg and Nb in PbMg1/3Nb2/3O3 (PMN) is correlated with its characteristic relaxor ferroelectric behavior. Fully ordered PMN is not prepared as a bulk material. This work examines the relaxor behavior in PMN thin films grown at temperatures below 1073 K by artificially reducing the degree of disorder via synthesis of heterostructures with alternate layers of Pb(Mg2/3Nb1/3)O3 and PbNbO3, as suggested by the random‐site model. 100 nm thick, phase‐pure films are grown epitaxially on (111) SrTiO3 substrates using alternate target timed pulsed‐laser deposition of Pb(Mg2/3Nb1/3)O3 and PbNbO3 targets with 20% excess Pb. Selected area electron diffraction confirms the emergence of (1/2, 1/2, 1/2) superlattice spots with randomly distributed ordered domains as large as ≈150 nm. These heterostructures exhibit a dielectric constant of 800, loss tangents of ≈0.03 and 2× remanent polarization of ≈11 µC cm−2 at room temperature. Polarization–electric field hysteresis loops, Rayleigh data, and optical second‐harmonic generation measurements are consistent with the development of ferroelectric domains below 140 K. Temperature‐dependent permittivity measurements demonstrate reduced frequency dispersion compared to short range ordered PMN films. This work suggests a continuum between normal and relaxor ferroelectric behavior in the engineered PMN thin films.

Depth dependant element analysis of PbMg1/3Nb2/3O3 using muonic x-rays

The relaxor PbMg1/3Nb2/3O3 (PMN) has received attention due to its potential applications as a piezoelectric when doped with PbTiO3 (PT). Previous results have found that there are two phases existing in the system, one linked to the near-surface regions of the sample, the other in the bulk. However, the exact origin of these two phases is unclear. In this paper, depth dependant analysis results from negative muon implantation experiments are presented. It is shown that the Pb content is constant throughout all depths probed in the sample, but the Mg and Nb content changes in the near-surface region below 100 μm. At an implantation depth of 60 μm, it is found that there is a 25% increase in Mg content, with a simultaneous 5% decrease in Nb content in order to maintain charge neutrality. These results show that the previously observed skin effects in PMN are due to a change in concentration and unit cell.

Superdipole glass ground state of relaxor ferroelectrics

ABSTRACTQuenched random fields (RFs) are well-known to be a basic driving force of the peculiar behavior of relaxor ferroelectrics such as PbMg1/3Nb2/3O3 (PMN), SrxBa1-xNb2O6 (SBN), and BaTi1-xZrxO3 (BTZ), hence, giving rise to strong frequency dispersion of the dielectric response, an apparent lack of macroscopic symmetry breaking at low temperatures, and the formation of polar nanoregions (PNRs) thus creating random ‘domain states’. A fundamental completion of relaxor physics toward a superdipolar cluster glass ground state of the randomly interacting PNRs appears necessary as evidenced by dynamic criticality and non-ergodic aging and rejuvenation processes.

Broadband dielectric spectra in PbMg1/3Nb2/3O3 crystals with chemical order modified by La doping

PbMg1/3Nb2/3O3 (PMN) is a well known ferroelectric relaxor. PMN crystal doped with La3+ has greatly enlarged chemically ordered regions (CORs) in the structure. It is interesting to know how the development of CORs influences physical properties of PMN crystal. In this work, dielectric properties and distribution of relaxation times of PMN and 0.98Pb(Mg1/3Nb2/3)O3–0.02La(Mg2/3Nb1/3)O3 (PLMN) crystals are studied. The experiment was performed in 120–500 K temperature range and wide frequency range—up to 46 GHz. The results demonstrate that the relaxor behaviour of PMN and PLMN is qualitatively the same in spite of the fact that chemical ordering is very different.

The cluster glass route of relaxor ferroelectrics

Relaxor ferroelectrics such as PbMg1/3Nb2/3O3 (PMN), Sr0.75Ba0.25Nb2O6 (SBN75) and BaTi0.65Zr0.35O3 (BTZ35) are disordered ferroelectric solids, in which polar nanoregions (PNRs) are stabilized on cooling by random electric fields due to either charge or structural disorder prior to their cluster glass transitions at Tg. This two-step process is clearly distinct from conventional (atomic) spin glass transitions. Decisive features of the mesoscopic cluster glass ground states are critical glass dynamics at Tg and stretched exponential relaxation, memory and rejuvenation upon aging below Tg.

Aperiodic atomic ordering in PMN recovered from the anomalous x-ray scattering

Various imaging techniques with atomic resolutions have been developed to study 3D arrangement of atoms in sub-nanometer and nanometer scale. The method presented is based on the measurement of the anomalous portion of x-ray scattering in large volume of the reciprocal space. It can be shown that, by analogy to x-ray holography with atomic resolution, the anomalous diffuse scattering provides information on both the amplitude and the phase of the scattered wave. The sample was PbMg1/3Nb2/3O3 (PMN), which belongs to relaxor ferroelectrics. Although the short and intermediate range chemical ordering is responsible for its relaxor behaviour, the real arrangement of cations remains unclear so far. The intensities of x-ray scattering in a large 3D volume of the reciprocal space were measured using an intense x-ray radiation generated by the synchrotron facility. Anomalous x-ray scattering has been obtained as a difference of intensity maps collected at two energies. The energy E1 just below the Nb K absorption edge was chosen in order to get a strong anomalous component in the scattering from Nb atoms. The data acquired at the energy E2 far from the absorption edge were used as the reference. The measured 3D pattern of anomalous scattering, including both discrete diffraction peaks and continuous x-ray diffuse scattering, allows us to reconstruct numerically an average environment around Nb atoms. The reconstructed real-space images clearly show a systematic local ordering of Mg2+ and Nb5+ cations. This ordering is more significant close to the central reference Nb atom but it is still apparent at the distance of about 3 nm giving thus an idea on the average size of ordered regions. More distant sites are occupied randomly with probabilities of occurrence of Mg2+ and Nb5+ cations given by their relative fraction in the sample. It is possible to determine conditioned probabilities of site occupancies by the given type of atom provided that the central site is occupied by Nb and to get information on the structure model of the ordered regions in the crystal.

Size effects in a relaxor: further insights into PMN

Dielectric measurements of PbMg1/3Nb2/3O3 (PMN) powder and dense ceramics with grain sizes between 15 nm and two microns were carried out in a broad frequency range (20 Hz–1 GHz). Clear grain size dependence of relaxor behavior was evidenced. A progressive transformation from Vogel-Fulcher behavior towards the Arrhenius process in the PMN with reduction of grain size in both ceramics and powder was observed. In the case of ceramics we were able to extract deeper information from the distributions of relaxation times and an analysis using the Vogel-Fulcher law, revealing two main contributions: a fast part of distribution of relaxation times with a maximum close to 10−11 s, which is almost grain-size independent and has a non-polar origin; whereas, a process with long relaxation times (in the time range of 10−8 to 10−5 s) is associated with the dynamics of the polar nanoregions and is strongly suppressed with reduction of grain size. The results of dielectric investigations are confirmed by Nuclear Magnetic Resonance experiments.

Optical Interferometric Technique for Induced Strain Ferroelectric Loop Study at Low Frequency

Michelson interferometric technique was modified in the setup and used to measure very small changes in optical path length for electric field induced-strain phenomena. Induced-strain is established in the sample when the beam of light propagating through the sample surface undergoes a shift in phase, which in turn leads to a change in the intensity of the interference pattern formed where the reference and probing beams recombine. In this work the electric field induced-strain was measured as a function of electric field (s-E loop) and polarization (s-P loop) of PbMg1/3Nb2/3O3(PMN) and 0.7PbMg1/3Nb2/3O3-0.3PbZr0.52Ti0.48O3(0.7PMN-0.3PZT) ceramics, which showed electrostrictive (quadratic shape curve) and piezoelectric (butterfly shape curve) behavior at various frequency (0.01-1Hz).

Theoretical investigations on electrocaloric properties of (111)-oriented PbMg1/3Nb2/3O3 single crystal

The electrocaloric (EC) effect accompanied with the ferroelectric to paraelectric phase transition in (111)-oriented PbMg1/3Nb2/3O3 (PMN) is investigated. It is shown that the largest change ΔT is 0.37 K in 3 kV/cm electric field shift near the Curie temperature of 221 K; that is, the cooling ΔT per unit field (MV/m) is 1.23×10−6 m·K/V. This value is significantly larger, and comparable with the value of 0.254×10−6 m·K/V for PbZr0.95Ti0.05O3 thin film under larger electric field shift ΔE = 30 kV/cm. Thus, the EC effect of (111) PMN single crystal provides cooling solutions at low temperatures, and opens more opportunities for practical application in cooling systems.

Hyper-Raman and Raman scattering from the polar modes of PbMg1/3Nb2/3O3

Microhyper-Raman spectroscopy of PbMg1/3Nb2/3O3 (PMN) single crystal is performed at room temperature. The use of an optical microscope working in backscattering geometry significantly reduces the LO signal, highlighting thereby the weak contributions underneath. We clearly identify the highest frequency transverse optic mode (TO3) in addition to the previously observed soft TO-doublet at low frequency and TO2 at intermediate frequency. TO3 exhibits strong inhomogeneous broadening but perfectly fulfils the hyper-Raman cubic selection rules. The analysis shows that hyper-Raman spectroscopy is sensitive to all the vibrations of the average cubic symmetry group of PMN, the three polar F1u- and the silent F2u-symmetry modes. All these vibrations can be identified in the Raman spectra alongside other vibrational bands likely arising from symmetry breaking in polar nanoregions.

Ferroelectric and Relaxor Ferroelectric to Paralectric Transition Based on Lead Magnesium Niobate (PMN) Materials

First ferroelectric materials were found in Rochelle salt was in a perovskite structure. Lead Magnesium Niobate (PMN) is a perovskites with a formula of PbMg1/3Nb2/3O3 (PMN) and are typical representatives for most of all ferroelectrics materials with relaxor characteristic. It posses high dielectric permittivity which nearly ~ 20,000[ with a broad dielectric permittivity characteristic, known as relaxor ferroelectric below room temperature. Some of the researcher might think that the transition from relaxor ferroelectric to paraelectric is similar to the characteristic as observed from ferroelectric to paraelectric, but it is not necessary. The puzzling is how do we categorise them. How is the domain structure look like typically in ceramic materials.

Local Ordering in Lead-Based Relaxor Ferroelectrics

Lead-based ferroelectric materials are both well-studied and widely used and have a wide range of applications from ultrasonics to energy harvesting and beyond. However, the use of Pb-containing materials is environmentally undesirable, due to the toxicity of lead. This is particularly highlighted by the disposal of Pb-based devices when their lifespan is through. Because of this large drawback, chemists have been searching for Pb-free ferroic materials that can replace PZN (PbZn1/3Nb2/3O3), PMN (PbMg1/3Nb2/3O3), PZT (PbZr1-xTixO3), and all their derivatives. Underlying much of materials chemistry is the idea that function arises from structure, so if we can determine the structure of a material, we can understand how its useful properties arise. This understanding can then lead to the tuning of these properties and the development of new materials. However, the question arises: What is meant by structure? Conventionally, structure is determined by X-ray or neutron diffraction, in which the Bragg peak intensities are measured and a unit cell is determined. In many materials, local ordering, order that persists only for few unit cells or nanometers, is important in determining the physical properties. This is very much the case in the relaxor ferroelectrics, an important class of functional oxides. Indeed, disorder, randomness, and short-range order (SRO) are all invoked to help explain many of the key properties. The local order in Pb-based ferroelectrics has been extensively studied, with the most definitive probe being single-crystal diffuse scattering. In this Account, I outline the current debate on the nature of the local order and explore how this information can inform the search for lead-free materials. Local order, as distinct from the overall average order revealed by conventional techniques, relates more closely to the crystal chemistry of the individual ions and so appears to give a better insight into how the crystal chemistry leads to the ferroelectric properties.

Kinetics and thermodynamics of the ferroelectric transitions in PbMg1/3Nb2/3O3 and PbMg1/3Nb2/3O3-12% PbTiO3 crystals

The two-step freezing and melting of the field-induced ferroelectric order in PbMg1/3Nb2/3O3 (PMN) and (PbMg1/3Nb2/3O3)0.88(PbTiO3)0.12 (PMN-PT) is investigated. In PMN-PT, direct microscopic images show that both steps occur in the same spatial regions. The higher temperature freezing corresponds to the higher temperature melting, indicating that the stages are not just kinetically but also thermodynamically distinct. The higher-T melting step shows several indications of being a sharp first-order transition near an equilibrium temperature. The lower-T melting step shows more kinetic dependence. Partially poled PMN also spontaneously approaches saturation polarization on zero-field aging, indicating that the true equilibrium state is ferroelectric below ∼200 K. In PMN-PT, a variety of kinetic measurements on the ferroelectric state indicate that the kinetics are governed by a glassy matrix showing aging effects.