Relaxor PMN Research Articles

Synthesis, structure, dielectric properties and relaxor behavior of a novel solid solution (1-x)Pb(Mg1/3Nb2/3)O3-xBi(Zn2/3Nb1/3)O3

A solid solution of (1-x) Pb(Mg1/3Nb2/3)O3-xBi(Zn2/3Nb1/3)O3 [(1-x)PMN-xBZN)] has been prepared in the form of ceramics with x = 0-0.20 by solid state reaction method. The crystal structure and dielectric properties are investigated. An enhanced relaxor behavior is found when incorporating BZN into canonical relaxor PMN due to the increased chemical disorder. The high temperature slope of dielectric constant as a function of temperature is consistent with the empirical quadratic law. The frequency dependence of the temperature of the dielectric maximum follows the Vogel-Fulcher (V-F) law.

Evidence for anisotropic polar nanoregions in relaxor Pb(Mg1/3Nb2/3)O3: A neutron study of the elastic constants and anomalous TA phonon damping in PMN

We use neutron scattering to characterize the acoustic phonons in the relaxor PMN and demonstrate the presence of an anisotropic damping mechanism directly related to short-range, polar correlations. For a large range of temperatures above Tc ~ 210, K, where dynamic polar correlations exist, acoustic phonons propagating along [1\bar{1}0] and polarized along [110] (TA2 phonons) are overdamped and softened across most of the Brillouin zone. By contrast, acoustic phonons propagating along [100] and polarized along [001] (TA1 phonons) are overdamped and softened for only a limited range of wavevectors. The anisotropy and temperature dependence of the acoustic phonon energy linewidth are directly correlated with the elastic diffuse scattering, indicating that polar nanoregions are the cause of the anomalous behavior. The damping and softening vanish for q -> 0, i.e. for long-wavelength acoustic phonons, which supports the notion that the anomalous damping is a result of the coupling between the relaxational component of the diffuse scattering and the harmonic TA phonons. Therefore, these effects are not due to large changes in the elastic constants with temperature because the elastic constants correspond to the long-wavelength limit. We compare the elastic constants we measure to those from Brillouin scattering and to values reported for pure PT. We show that while the values of C44 are quite similar, those for C11 and C12 are significantly less in PMN and result in a softening of (C11-C12) over PT. There is also an increased elastic anisotropy (2C44/(C11-C12)) versus that in PT. These results suggest an instability to TA2 acoustic fluctuations in relaxors. We discuss our results in the context of the debate over the "waterfall" effect and show that they are inconsistent with TA-TO phonon coupling or other models that invoke the presence of a second optic mode.

Diffuse scattering anisotropy and inhomogeneous lattice deformations in the lead magnoniobate relaxor PMN above the Burns temperature

Neutron diffuse scattering measurements on single crystal PbMg${}_{1/3}$Nb${}_{2/3}$O${}_{3}$ above the Burns temperature are reported. The high temperature elastic diffuse component is highly asymmetric near reciprocal lattice points not corresponding to high-symmetry directions. This asymmetry can be described using Huang scattering formalism assuming that the scattering originates from mesoscopic lattice deformations due to elastic defects. Qualitative agreement between this model and the experimental data is achieved with simple, isotropic defects. It is demonstrated that the weak satellite maxima near Bragg reflections can be interpreted in terms of a finite resolution effect.

Electro-caloric effect in relaxor and ferroelectric compositions of Pb(Mg(1−x)/3Nb2(1−x)/3Zrx)O3 ceramics

Solid solution of relaxor PMN and antiferroelectric PZ, [Pb(Mg(1−x)/3Nb2(1−x)/3Zrx)O3], behaves like ferroelectric with increasing PZ content following a wide composition range of diminishing relaxor properties. Electro-caloric measurements on three relaxor and one ferroelectric composition of this solid solution have been carried out by indirect method. All the compositions give a maximum temperature change of ∼0.33K on application of 1kV/mm electric field. This value is higher than the PLZT or PMN–PT based relaxors. A shift of ∼35°C in the temperature of electro-caloric maximum was observed with application of electric field, for relaxor compositions, attributed to the field induced effect on the transition temperature. Similar shift for ferroelectric composition is significantly lower (∼8°C).

Impact of the Electric Field on the Freezing Dynamics of Pb(Mg1/3Nb2/3)O3

The dielectric response of canonical relaxor PMN single crystal oriented in [111] direction was investigated under the influence of various dc bias electric fields. The behavior of the Vogel-Fulcher temperature obtained from the characteristic relaxation times determined from the peaks of the imaginary component ϵ″(T) of the complex dielectric constant ϵ*(T) was studied as a function of the dc bias electric field. The observed results reveal nonmonotonous behavior of the Vogel-Fulcher temperature as a function of the strength of the dc bias electric field. We show that such a behavior can be well interpreted in terms of nonlinear dielectric susceptibility as a dominant factor in the dielectric dynamic of relaxors in dc bias electric fields.

Polar nanoregions in Pb(Mg1/3Nb2/3)O3 (PMN): insights from a supercell approach

Abstract We report construction of a model of polar nanoregions in the PMN relaxor ferroelectric based on first-principles lattice dynamics for chemically ordered supercells [S.A. Prosandeev et al., Phys. Rev. B 70, 134110 (2004)], combined with invariance under permutations and dipole-dipole interaction as a source supporting randomly oriented residual polarization. Representative analytical estimates of polar nanore-gion — supercell mapping reproduce both nonzero local and zero macroscopic polarization of the structure, as well as the temperature change of the supercell anisotropy at cooling and field cooling.

Ferroelectric Phase Transitions Viewed Via Nonlinear Dielectric Response

Experimental data on the nonlinear dynamic responses of barium titanate (discontinuous ferroelectric phase transition, PT), triglycine sulphate (continuous PT), as well as the prototype relaxor lead magnoniobate, and the weakly doped quantum paraelectric K0.995Li0.005TaO3 are presented. The classic ferroelectrics display all features of the third order dielectric susceptibility, χ 3 , as predicted by mean-field theory (including the change of sign of χ 3 at the continuous PT). On the other hand, the positive sign of χ 3 measured on the relaxor PMN is due to the presence of polar nanoregions and their specific contribution to the dielectric response measured at enhanced electric field.

RelaxorPb(Mg1/3Nb2/3)O3: A Ferroelectric with Multiple Inhomogeneities

Despite intensive studies on Pb(Mg(1/3)Nb(2/3))O(3) (PMN) relaxor, understanding the exact nature of its giant dielectric response and of its physical ground state is a fundamental issue that has remained unresolved for decades. Here, we report a comprehensive study of PMN relaxor crystal, and show that (i) its anomalous dielectric behavior in a broad temperature range results from the reorientation of polarization in the crystal, and (ii) the PMN relaxor is essentially a nanosized ferroelectric material with multiscale inhomogeneities of domain structure in addition to the well-known inhomogeneities of chemical composition and local symmetry. Such inhomogeneities are believed to play a crucial role in producing the huge and enigmatic physical effects in relaxor system, and may be used to design other new systems with giant effects such as a relaxor system.

Tunability properties in the paraelectric state of the Pb(Mg 1/3Nb 2/3)O 3 ceramics

Pb(Mg 1/3Nb 2/3)O 3 ceramics prepared via columbite method exhibit high crystallinity and high density after sintering at 1200 °C. Typical relaxor behavior are demonstrated by the dielectric data. Although showing a diffuse phase transition, at room temperature the system is in its paraelectric state, i.e. the PMN structure is fully cubic. The dc-tunability was investigated above the room temperature, when other field-induced contributions than ferroelectric polarization might cause non-linearity. A random non-interacting dipolar unit in a double well potential was employed to describe the ɛ( E) non-linearity. The temperature-dependence of the average polarization corresponding to the polar nanoregions in the paraelectric state of the PMN relaxor was calculated from the ɛ( E) data at various temperatures above T m. A similar trend of decreasing as increasing temperature shows the spin-glass local order parameter determined from the dielectric constant data in the paraelectric state. The local order parameter in the paraelectric state is determined by the nanopolar domains size and correlations.

The Three Characteristic Temperatures of Relaxor Dynamics and Their Meaning

In this report, we compare the temperature evolution of several physical properties of the relaxor systems, PZN, PMN and KTN. We show that three rather than two characteristic temperatures can be identified, T B , T* and T f , and discuss their meaning in light of dielectric, Raman and neutron scattering experimental results.

First principles studies of the born effective charges and electronic dielectric tensors for the relaxor PMN (PbMg 1/3Nb 2/3O 3)

We report first principles density functional calculations of the Born effective charges and electronic dielectric tensors for the relaxor PMN (PbMg 1/3Nb 2/3O 3). Visualization of the Born charge tensors as “charge ellipsoids” have provided microscopic insights on the factors governing piezoelectric enhancements with polarization rotation. Several 15 and 30-atom ferroelectric and antiferroelectric supercells of PMN involving 1:2 and 1:1 chemical ordering have been studied. A cascading set of ferroelectric phonon instabilities lead to several low symmetry monoclinic structures. We find a ground state with a 15-atom unit cell with 1:2 chemical ordering along [1 1 1] with a monoclinic C2 structure.

Damped soft phonons and diffuse scattering in40%Pb(Mg1∕3Nb2∕3)O3−60%PbTiO3

Using neutron elastic and inelastic scattering and high-energy x-ray diffraction, we present a comparison of 40% Pb(Mg$_{1/3}$Nb$_{2/3}$)O$_{3}$-60% PbTiO$_{3}$ (PMN-60PT) with pure Pb(Mg$_{1/3}$Nb$_{2/3}$)O$_{3}$ (PMN) and PbTiO$_{3}$ (PT). We measure the structural properties of PMN-60PT to be identical to pure PT, however, the lattice dynamics are exactly that previously found in relaxors PMN and PZN. PMN-60PT displays a well-defined macroscopic structural transition from a cubic to tetragonal unit cell at 550 K. The diffuse scattering is shown to be weak indicating that the structural distortion is long-range in PMN-60PT and short-range polar correlations (polar nanoregions) are not present. Even though polar nanoregions are absent, the soft optic mode is short-lived for wavevectors near the zone-centre. Therefore, PMN-60PT displays the same waterfall effect as prototypical relaxors PMN and PZN. We conclude that it is random fields resulting from the intrinsic chemical disorder which is the reason for the broad transverse optic mode observed in PMN and PMN-60PT near the zone centre and not due to the formation of short-ranged polar correlations. Through our comparison of PMN, PMN-60PT, and pure PT, we interpret the dynamic and static properties of the PMN-xPT system in terms of a random field model in which the cubic anisotropy term dominates with increasing doping of PbTiO$_{3}$.

Recent study of nanomaterials prepared by inert gas condensation using ultra high vacuum chamber

The ultra high vacuum chamber was developed in the Department of Nuclear Physics, University of Madras with the funding from DST, India. This UHV chamber is used to prepare nanocrystalline materials by inert gas condensation technique (IGCT). Nanocrystalline materials such as PbF2, Mn2+-doped PbF2, Sn-doped In2O3 (ITO), ZnO, Al2O3, Ag2O, CdO, CuO, ZnSe:ZnO etc., were prepared by this technique and characterized. Results of some of these materials will be presented in this paper. In solid-state207Pb NMR on PbF2 a separate signal due to the presence of grain boundary has been observed. The structural phase transition pressure during the phase transformation from the cubic phase to orthorhombic phase under high pressure shows an increase with the decrease in grain size. Presence of electronic centres in nanocrystalline PbF2 is observed from Raman studies and the same has been confirmed by photoluminescence studies. Al2O3 was prepared and56Fe ions were implanted. After implantation segregation of56Fe ions was examined by SEM. The oxidation properties of ITO were studied by HRTEM. As against the expectation of oxide coating on individual nanograins of In-Sn alloy, ITO nanograins grew into faceted nanograins on heat treatment in air and O2 atmosphere. The growth of ITO under O2 atmosphere showed pentagon symmetry. The PMN was initially prepared by solid-state reaction. Further, this PMN relaxor material will be used to convert into nanocrystalline PMN by IGCT with sputtering and will be studied

Comparison of the Dielectric Response of Relaxor PbMg1/3 Nb2/3O3 Ceramics and Single Crystals

Dielectric response of relaxor PMN ceramics (standard and textured) was investigated in the high-frequency range (1 MHz–1.8 GHz) and compared with the broad-band response of PMN single crystals. Similar to PMN crystals, dielectric response of PMN ceramics was found to be mainly defined by the polar nanocluster dynamics. Mesoscopic structure and imperfections of ceramics do not result in the remarkable contribution of the additional mechanisms, but influence the dynamics of polar nanoclusters and lead to the weakening of the cluster flipping mechanism contribution. The freezing temperature seems to be the same ( T f ∼ 200 K).

Central-Peak Components and Polar Soft Mode in Relaxor PbMg1/3Nb2/3O3 Crystals

Dielectric response of relaxor PMN single crystals was investigated in a broad frequency range 100 Hz–100 THz by a combination of dielectric spectroscopy (100 Hz–1 GHz, 10–700 K), time-domain THz spectroscopy and infrared (IR) reflectivity (5–3000 cm−1, 10–300 K). Polar TO1 phonon (soft mode) is resolved in THz and IR spectra at all temperatures studied, follows the Cochran law and softens towards the Burns temperature on heating. The central mode (dielectric relaxation) splits below room temperature into two components. First one appears in the THz range and is assigned as IR activated phonon density of states due to the breaking of local symmetry as a consequence of polar nano-clusters. Second relaxation originates from cluster breathing and flipping. It anomalously broadens on cooling and leads to frequency-independent dielectric loss between 100 Hz–100 GHz below 200 K in the non-ergodic phase.

Field cooled and zero field cooled 207Pb NMR and the local structure of relaxor PbMg1/3Nb2/3O3.

An isotropic 207Pb NMR spectrum corresponding to the glassy matrix with spherical shell type Pb shifts from the cubic sites, as well as an anisotropic spectral component corresponding to polar nanoclusters with a Pb shift parallel to the [111] direction, have been observed in a PbMg(1/3)Nb(2/3)O3 (PMN) single crystal. This represents a microscopic confirmation of the model of relaxors first proposed by Burns and Dacol. A sudden increase in the intensity of the anisotropic cluster line is seen for electric fields larger than the critical field around 210 K. This demonstrates the occurrence of an orientational percolation type transition to the field-induced ferroelectric phase with about 50% of the Pb nuclei still remaining in the spherical glass matrix. A similar though smaller increase of the intensity of this line is also seen in the zero field cooled data, demonstrating that relaxor PMN is an incipient ferroelectric.

Manifestation of Polaronic States in Ferroelectric Relaxor PMN

Small polaron states in the model ferroelectric relaxor PMN were confirmed in this work by detection of the characteristic IR-absorption accompanied by light-induced polaron transport. The mechanism of an influence of mobile polaronic clusters on the polar cluster reorientations and, as a result, on the co-operative phenomena in relaxor is developed. Here mobile polaronic clusters can move on the interfaces of polar clusters with carrying of their polarizations. The latter are moving self-consistently with polaronic clusters, and are involved to the reorientation-like motion. The polar cluster-polar cluster interaction between such type reorienting polarizations of different clusters can be a possible origin of phase transitions in PMN-like relaxors. Semi-empirical Hartree-Fock calculations of electronic polaron states in some model ABO 3 -systems performed are in a good agreement with the experiment.

Polaronic States in Ferroelectric Relaxor PMN

Small polaron states in the model ferroelectric relaxor PMN were confirmed by detection of the characteristic IR-absorption accompanied by light-induced polaron transport.

Non-linear dielectric dispersion in PMN relaxor system

In PbMg 1/3Nb 2/3O 3 (PMN) single crystals the first ε 1 * and the third harmonic complex dielectric constant ε 3 * were measured along the 〈0 0 1〉 and 〈1 1 1〉 axes as a function of frequency and temperature in a small electric field. In the temperature interval between 270 and 220 K the first ε 1 * and the third harmonic complex dielectric constant ε 3 *, and the dielectric non-linearity β= ε 3/ ε 1 4 ε 0 3 show prominent dielectric dispersion. It is also shown that the dielectric non-linearity β shows a crossover from a decreasing paraelectric-like to a rapidly increasing glass-like temperature behaviour which was predicted by the spherical random bond random field model for relaxors.

Quasistatic Field-Cooled Dielectric Response in Relaxor Materials

Quasistatic dielectric response in PMN relaxor system was studied as a function of the dc electric field by utilizing a charge accumulation technique in a field-cooled experiment. An anomaly associated with the onset of spontaneous polarization was observed in the linear field-cooled dielectric response when crossing electric field threshold line E T (T) separating the relaxor and ferroelectric phases in an E-T phase diagram. Evidences were found that the E T (T) first order phase transition line may end in an isolated critical point at higher electric fields.