Pure PMN Research Articles

Lamellar-like nanostructure in a relaxor ferroelectrics Pb(Mg1/3Nb2/3)O3

The nanostructure of relaxor ferroelectric materials has been a central focus for investigating the microscopic origin of their intriguing physical properties. While it is believed that relaxor ferroelectricity is governed by polar nanostructures, such as polar nanoregions or nanodomains, recent studies have indicated the importance of additional mechanisms, such as the competition of ferroelectric/anti-ferroelectric order and the formation of hierarchical nanodomains. This calls for further investigation on the nanostructure. Here, we used conventional, in situ, and atomic-scale electron microscopy to study prototypic relaxor ferroelectrics, Pb(Mg1/3Nb2/3)O3 (PMN) and Pb(Mg1/3Nb2/3)O3–PbTiO3 (PMN-PT). We found that a lamellar-like nanostructure was present in pure PMN, which had been overlooked in past studies and did not have a strong correlation with the polar nanostructure and the chemically ordered region. Unlike the lamellar-like nanodomains in PMN-PT, the lamellar-like nanostructure in PMN was not coupled with Pb-ion displacement and was not reoriented by the presence of an electric field. The results suggested that the formation of a lamellar-like structure occurs prior to the formation of larger-scale polar order in relaxor ferroelectrics.

Synthesis and investigation of properties of nanostructured cubic PMN ceramics for possible applications in electronics

The pure phase of Pb(Mg1/3Nb2/3)O3 was synthesized by two-stage chemical process at 800 °C. Thermal analysis of precursors was done by TG-DSC. XRD, Raman spectroscopy, FESEM and HRTEM analyses were done to characterize synthesized material and also to observe the microstructure. XRD studies revealed the formation of pure crystalline PMN ceramics (JCPDS PDF# 00-081-0861) having crystallite size around 28 nm. The particle size was examined to be around 19 nm by HRTEM. The nanocrystalline PMN ceramics exhibited a bandgap around 3.28 eV using diffuse reflectance spectroscopy. Dielectric nature was inspected using impedance analyzer between 40 Hz and 110 MHz. Dielectric constant ( $${\epsilon}_{r}$$ ) and $${\text{tan}}\delta$$ were investigated where unusual negative values of $${\epsilon}_{r}$$ were observed beyond 41.26 MHz. A peak in $${\text{tan}}\delta$$ near 41.26 MHz was also obtained.

Improvement in dielectric, piezoelectric and ferroelectric properties of 0.64PMN–0.36PT ceramics by Sb modification

Pure and Sb-doped 0.64PMN–0.36PT (PMN–PT) ceramics near MPB have been prepared using columbite precursor technique. The effects of Sb-doping on microstructure and electrical properties were studied systematically. Powder XRD and SEM exhibited the formation of pure perovskite phase with homogeneous microstructure. As compared to the pure PMN–PT ceramics, enhanced dielectric constant, and reduced transition temperature (Tm) and dielectric loss (tan δ) were observed for Sb-doped PMN–PT ceramics. Displacement–Voltage (D–V) butterfly hysteresis loops and quasi-static d33 meter revealed a higher value of piezoelectric charge coefficient (d33) for Sb-doped sample (644 pm/V and 551 pC/N) as compared to pure ceramic (435 pm/V and 410 pC/N). P–E hysteresis curves showed improved ferroelectric properties after Sb doping. A high value of pyroelectric coefficient (p ∼ −1170.4 µC m−2 °C−1) for Sb-doped PMN–PT ceramic was obtained. Sb-doped PMN–PT ceramic showed an excellent anti-fatigue nature over 107 switching cycles. Small leakage current was evident from J–E analysis for both the ceramics. Therefore, Sb-doped PMN–PT ceramic proved to be a better choice for applications in the electronic ceramic industries.

Low-level Laser Therapy to the Mouse Femur Enhances the Fungicidal Response of Neutrophils against Paracoccidioides brasiliensis

Neutrophils (PMN) play a central role in host defense against the neglected fungal infection paracoccidioidomycosis (PCM), which is caused by the dimorphic fungus Paracoccidioides brasiliensis (Pb). PCM is of major importance, especially in Latin America, and its treatment relies on the use of antifungal drugs. However, the course of treatment is lengthy, leading to side effects and even development of fungal resistance. The goal of the study was to use low-level laser therapy (LLLT) to stimulate PMN to fight Pb in vivo. Swiss mice with subcutaneous air pouches were inoculated with a virulent strain of Pb or fungal cell wall components (Zymosan), and then received LLLT (780 nm; 50 mW; 12.5 J/cm2; 30 seconds per point, giving a total energy of 0.5 J per point) on alternate days at two points on each hind leg. The aim was to reach the bone marrow in the femur with light. Non-irradiated animals were used as controls. The number and viability of the PMN that migrated to the inoculation site was assessed, as well as their ability to synthesize proteins, produce reactive oxygen species (ROS) and their fungicidal activity. The highly pure PMN populations obtained after 10 days of infection were also subsequently cultured in the presence of Pb for trials of protein production, evaluation of mitochondrial activity, ROS production and quantification of viable fungi growth. PMN from mice that received LLLT were more active metabolically, had higher fungicidal activity against Pb in vivo and also in vitro. The kinetics of neutrophil protein production also correlated with a more activated state. LLLT may be a safe and non-invasive approach to deal with PCM infection.

Effective dielectric function of porousPb(Mg1/3Nb2/3)O3ceramics

A set of $\mathrm{Pb}({\mathrm{Mg}}_{1/3}{\mathrm{Nb}}_{2/3}){\mathrm{O}}_{3}$ (PMN) relaxor ceramics with different porosities (66--96% of theoretical density) was processed from the pure perovskite PMN powder by varying the sintering temperature (930--980 K) and isostatic pressure. The effective room temperature permittivity at 100 Hz varied correspondingly from \ensuremath{\sim}4000 to \ensuremath{\sim}15 000. We measured and fitted the room temperature infrared (IR) reflectivity of corresponding polished ceramics, from which the effective dielectric function was obtained. The results were compared with the low-frequency permittivity data and discussed using several effective medium models. The best results were obtained using the Lichtenecker model (with the exponent \ensuremath{\alpha} \ensuremath{\approx} 0.2), which fits quite well the IR spectra as well as the static permittivity for all the porosity values. Also the simulation using the finite element method supported the same model. It allows us to conclude that the samples show quite complex shape and topology of the pores, but all of the pores show similarity with a weak nonzero percolation (open porosity).

Dielectric and ferroelectric properties of PMN–PT–PZ ceramics prepared via combustion technique

The fabrication of 0·53Pb (Mg1/3Nb2/3)O3–0·37PbTiO3–0·10PbZrO3 (PMN–PT–PZ) ferroelectric ceramics using the combustion technique and the effects of firing conditions on the phase structure, microstructure and electrical properties of the powders and ceramics were studied. Glycine was used as a fuel to reduce the reaction temperature. It was found that a single perovskite phase of PMN–PT–PZ powders was obtained from the sample calcined at 900°C for 2 h. The conventional technique uses two steps in the calcination process. The use of glycine in the combustion technique reduced the process to one step. The morphology of the PMN–PT–PZ powders showed an almost spherical shape and the average particle size increased from 0·12 to 2·51 μm when the calcination temperature was increased from 700 to 1000°C. The pure PMN–PT–PZ ceramics exhibited coexistant phases of the rhombohedral and the tetragonal perovskite phase in the samples sintered at a temperature lower than 1100°C. A second phase of pyrochlore was found in the samples sintered at temperatures higher than 1150°C. The PMN-PT-PZ ceramics sintered at 1100°C for 2 h exhibited the highest density, highest linear shrinkage and highest dielectric constant at Tc of 7·72 g cm−3, 16·13% and 18337 respectively. The densest PMN-PT-PZ ceramic exhibited good ferroelectric properties of (using an electric field at 30 kV cm−1) Pr = 26·9 μC cm−2 and Ec = 4·5 kV cm−1.

Low- and infralow-frequency dielectric properties of the Pb(Mg1/3Nb2/3)O3 + 2 wt % Li2O ceramics

A dielectric response of the Pb(Mg1/3Nb2/3)O3 ferroelectric ceramics with impurity of 2 wt % Li has been studied. The phase transition has been found to exhibit a relaxor character, as is the case in PMN without Li. However, unlike pure PMN, the dielectric response dispersion in PMN + 2 wt % Li2O has been described by the Cole-Cole equation at temperatures below the temperature of the low-frequency maximum of the permittivity. An analysis of the dispersion parameters in a wide temperature range has demonstrated that it can be due to the relaxation of domain walls in PMN + 2 wt % Li2O that appear most likely because of the existence of anomalously coarse grains in PMN + 2 wt % Li2O.

Processing Optimization of Lead Magnesium Niobate‐Lead Titanate Thin Films for Piezoelectric MEMS Application

We report processing conditions and electromechanical properties of highly textured, 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 (PMN–PT) films, processed via chemical solution deposition on platinized silicon substrates. Textured perovskite seed layers, optimization of heat treatment conditions and Pb content control were studied to obtain pure perovskite PMN–PT films with dense, columnar grains. Highly (100)‐ and (111)‐oriented films, with Lotgering factors between 91% and 97%, and average grain size up to ~430 nm were synthesized on thin PbTiO3 and Pb(Zr,Ti)O3 seed layers. Overall, (100)‐textured films showed higher dielectric permittivity and saturated d33,f piezoelectric coefficients. Dense, submicron‐thick, (100)‐oriented films showed low‐field, relative dielectric permittivity of up to ~2850 (tan δ = 0.02) at 1 kHz, and remnant polarization values up to 17.5 μC/cm2. The films showed saturated d33,f piezoelectric coefficients as high as 210 pm/V.

Synthesis of Pb(Mg1/3Nb2/3)O3 by Self‐Assembled Colloidal Aggregates

We developed a new, simple method to prepare pure perovskite Pb(Mg1/3Nb2/3)O3 (PMN) from an aqueous suspension in a single annealing step. In this synthesis it is crucial to suppress the reaction between PbO and Nb2O5, which leads to secondary pyrochlore PbxNbyOz phases. Our method is based on the designed arrangement of particles of the starting compounds. The self‐assembly of the colloidal aggregates was governed by particle surface charge, which was adjusted by the suspension pH. At pH below 11.8 particle–particle interactions lead to close contacts between lead oxide and niobium oxide particles in the suspension as well as in the dried powders, whereas at pH above 11.8 close contacts between lead and niobium oxide particles are avoided. The suspensions of the starting powders were prepared at pH 10.0, 11.4, 12.5, and in acetone. After heating of the dried suspension with the pH set at 12.5 at 900°C, a pure perovskite PMN powder was obtained. On the contrary, the powders prepared from the pH 11.4, 10.0, and acetone suspensions still contained the detrimental pyrochlore phase after heating at 900°C. The properties of the ceramics prepared from the pH 12.5 suspension are superior in comparison with the other samples.

Effect of chemically ordered regions on the acoustic behaviors in Pb(Mg1/3Nb2/3)O3 studied by Brillouin scattering

The longitudinal acoustic phonon modes of Pb(Mg1/3Nb2/3)O3 (PMN) and La-doped PMN were investigated by using Brillouin spectroscopy and compared. The acoustic behaviors of La-doped PMN were very similar to those of pure PMN in spite of its much larger size of the chemically ordered regions induced by La-doping. The relaxation times of La-doped PMN in the ergodic relaxor phase were almost the same to those of PMN. This result shows that the temperature evolution of dynamic polar nanoregions and the related high-frequency dynamics of PMN-based crystals in the gigahertz range are not affected by the size of the B-site cation-ordered regions.

Nature of thermally stimulated acoustic emission from PbMg1/3Nb2/3O3–PbTiO3 solid solutions

We discuss the nature of the thermally stimulated acoustic emission (AE) in single crystals of PbMg1/3Nb2/3O3–PbTiO3 (PMN-PT). In particular, we derive an expression describing the efficiency of AE and we discuss in this connection AE from pure PMN. We have carried out original experiments revealing the dependence of AE in PMN-PT on the electric bias fields, and we found that the AE efficiency of PMN-PT can be heavily enhanced in a certain temperature interval by applying an electric bias field.

Effect of two-stage sintering on phase formation, microstructure and dielectric properties of perovskite PMN ceramics derived from a corundum Mg 4Nb 2O 9 precursor

Pure and dense relaxor perovskite ceramics of lead magnesium niobate (PMN) have been successfully fabricated by using a combination between a corundum Mg 4Nb 2O 9 B-site precursor and a two-stage sintering techniques. Effect of doubly sintering on phase formation, microstructure and dielectric properties of the PMN ceramics was determined via XRD, SEM and dielectric measurement. It has been found that under suitable two-stage sintering schemes, dense and pure perovskite PMN ceramics derived from a corundum B-site precursor route can be successfully achieved with better dielectric properties than those of ceramics from either a conventional or a two-stage sintered columbite B-site precursor methods.

Temperature characteristics and development of field-induced phase transition in relaxor ferroelectric Pb(Mg1/3Nb2/3)0.87Ti0.13O3 ceramics

Ferroelectric phase inducing threshold electric field Eth and its temperature dependence were determined in relaxor ferroelectric 0.87Pb(Mg1/3Nb2/3)O3−0.13PbTiO3 (PMN–13PT) ceramics by measuring dielectric response on a dc field pulse. Evolution of the induced ferroelectricity was observed by means of polarization measurements. An inducing threshold field was found to have a minimum of Eth,min=1.55 kV/cm at T=−5 °C. In contrast to pure PMN, which shows a minimum threshold field near the depolarization temperature, the temperature of the minimum threshold field differs by an amount of ΔT=23 °C from the depolarization temperature Tdp=18 °C in PMN-13PT.

Dynamic origin of the morphotropic phase boundary: Soft modes and phase instability in0.68Pb(Mg1/3Nb2/3O3)−0.32PbTiO3

We report neutron inelastic scattering and high-resolution x-ray diffraction measurements on single crystal $0.68\text{Pb}({\text{Mg}}_{1/3}{\text{Nb}}_{2/3}{\text{O}}_{3})\text{\ensuremath{-}}0.32{\text{PbTiO}}_{3}$ (PMN-0.32PT), a relaxor ferroelectric material that lies within the compositional range of the morphotropic phase boundary (MPB) where the piezoelectric properties of $\text{PMN-}x\text{PT}$ compounds are close to maximal. Data were obtained between 100 and 600 K under zero and nonzero electric field applied along the cubic [001] direction. The lowest-energy, zone-center, transverse optic phonon is strongly damped and softens slowly at high temperature; however, the square of the soft-mode energy begins to increase linearly with temperature as in a conventional ferroelectric, which we term the soft-mode ``recovery,'' upon cooling into the tetragonal phase at ${T}_{C}$. Our data show that the soft mode in PMN-0.32PT behaves almost identically to that in pure PMN, exhibiting the same temperature dependence and recovery temperature even though PMN exhibits no well-defined structural transition (no ${T}_{C}$). The temperature dependence of the soft mode in PMN-0.32PT is also similar to that in PMN-0.60PT; however, in PMN-0.60PT the recovery temperature equals ${T}_{C}$. These results suggest that the temperature dependence and the energy scale of the soft-mode dynamics in $\text{PMN-}x\text{PT}$ are independent of concentration on the Ti-poor side of the MPB, but scale with ${T}_{C}$ for Ti-rich compositions. Thus the MPB may be defined in lattice dynamical terms as the concentration where ${T}_{C}$ first matches the recovery temperature of the soft mode. High-resolution x-ray studies show that the cubic-to-ferroelectric phase boundary shifts to higher temperatures by an abnormal amount within the MPB region in the presence of an electric field. This suggests that an unusual instability exists within the apparently cubic phase at the MPB.

Local phenomena of(1−x)PbMg1/3Nb2/3O3−xPbTiO3single crystals(0≤x≤0.38)studied by Raman scattering

The study of $(1\ensuremath{-}x){\text{PbMg}}_{1/3}{\text{Nb}}_{2/3}{\text{O}}_{3}\text{\ensuremath{-}}x{\text{PbTiO}}_{3}$ (PMN-PT) single crystals where $x$ is 0, 0.09, 0.21, 0.28, 0.32, 0.35, and 0.38 was carried out with the use of x-ray, dielectric, and Raman scattering techniques in a wide temperature range. In this work, special attention was paid to the analysis of the Raman spectra. However, the results of the structural and dielectric studies were used to better interpret the Raman features. On the basis of the results of these studies, a phase diagram is given. The investigations confirmed that with the increase in the ${\text{PbTiO}}_{3}$ (PT) content the relaxor behavior becomes ferroelectric and that structural phase transitions of different types are observed. Raman studies were performed in a broad temperature range for all concentrations to understand the complex behavior of the PMN-PT system. The origin of the high temperature Raman spectra is considered in the whole concentration range and an origin of these spectra is proposed. For pure PMN and the solid solutions with a Ti content lower than 0.21, the 1:1 chemical order in the $B$-ion sublattice leads to the appearance of clusters with $Fm\overline{3}m$ symmetry. For higher PT contents, the high temperature Raman spectra seem to originate from the polar nanoregions of rhombohedral or tetragonal symmetry. All of the obtained Raman results are interpreted with the use of the group theory analysis. These results confirmed that the symmetries determined from the x-ray diffraction are average ones and play the role of a matrix in which nanoregions with a distinct local symmetry (generally monoclinic) are embedded. The analysis of the Raman spectra allowed us to determine the temperature and composition dependences of the Raman line frequencies, the reduced intensities, and the widths, providing clear evidence for the occurrence of the phase transitions. The anomalous behavior of the line width of some Raman lines related to the Pb ion vibrations pointed to the special role of Pb ion dynamics in the mechanism of phase transitions in the PMN-PT system.

Enhanced ordered structure and relaxor behaviour of0.98Pb(Mg1/3Nb2/3)O3–0.02La(Mg2/3Nb1/3)O3 single crystals

High quality Pb(Mg1/3Nb2/3)O3 (PMN) and La-doped PMN (PLMN) single crystals were grown via a top-seededsolution growth method. At a doping level as low as 2 at.% of La, the 1:1 B-sitecation (chemical) order was significantly enhanced as revealed by the presenceof superlattice peaks in the x-ray diffraction pattern and comparatively large(∼100 nm) chemically ordered regions (CORs) in the transmission electron microscopy dark field images.The average chemical order parameter was calculated (from the intensity of superlattice peaks) tobe S≈0.44. Besides, x-ray diffraction revealed the presence of a low-symmetry (presumablyrhombohedral) phase. The effect of La doping on the dielectric relaxation was notsubstantial. Though the magnitude of the dielectric constant peak in PLMN was reducedby half as compared to pure PMN, the peak temperature and diffuseness as well as theshape of the dielectric relaxation spectra remained almost unchanged. The analysis of thetemperature dependence of the characteristic time for the main relaxation process in termsof the Vögel–Fulcher law revealed the freezing of dipole dynamics at temperatureTf = 192 K, which was onlyslightly lower than the Tf = 213 K in PMN. To reconcile the structural and dielectric data we suggest that therhombohedral phase forms inside CORs while the chemically disordered matrix remainscubic and is populated by dynamic polar nanoregions that give rise to the characteristicdielectric response.

Effect of sintering conditions on the pyrochlore phase content in PMN–PFN ceramics prepared by sol–gel process

Lead magnesium niobate–lead iron niobate [(1 − x)Pb(Mg 1/3Nb 2/3)O 3– xPb(Fe 1/2Nb 1/2)O 3, (1 − x)PMN– xPFN] system, where x = 0.0–1.0, was prepared using sol–gel synthesis by mixing acetates Pb, Mg and Fe with Nb-ethylene glycol-tartarate complex at 80 °C. Single pyrochlore phase (Pb 1.83Mg 0.29Nb 1.71O 6.39 or Pb 3Nb 4O 13) was formed by the calcination of gels at 600 °C. Average particle sizes of pure PMN and PFN powders were ∼80 and 150 nm. The pyrochlore phases were partially decomposed to perovskite phase at sintering temperatures of 1150 and 1250 °C. The maximum bulk density in ceramic samples increased with both sintering temperature and the content of PFN phase in samples but despite these facts—the volume fractions of porosity were too high in all prepared samples. From the point of view of perovskite phase content, the optimum sintering temperature of PMN–PFN is shifted from 1200 to 1150 °C in comparison with the sample with PMN stoichiometry. Low values of ɛ r were measured in low density samples with high pyrochlore content and this characteristic is probably the main factor affecting ɛ r in prepared ceramics. In microstructures of PMN–PFN ceramics sintered at 1150 °C at different times, the bimodal grain size distribution was observed with small grains of globular shape and larger grains of regular or octahedral shape. The results of EDX and XRD analysis showed that the more complex types of pyrochlore phases were present in ceramics.

An investigation on 1–3 cement based piezoelectric composites

1–3 cement based piezoelectric composites which had good compatibility with civil engineeringstructural materials were fabricated by the cut–fill technique. The piezoelectric, dielectricand ferroelectric properties of the composites were studied. The acoustic impedance of thecomposites was also investigated. The results show that the piezoelectric strain constantd33 and the dielectricconstant ε of the composites increase linearly with the increase of PMNvolume fraction, while the piezoelectric voltage constantg33 presents theopposite trend. The g33 values of the composites are much higher than those of pure PMN. The remnant polarizationPr and thecoercive field Ec of the composite with 27.26% volume fraction of PMN are4.12 µC cm−2 and 4.01 kV mm−1, respectively. By enhancing the PMN volume fraction, the acoustic impedance of thecomposites can be tailored to match that of the civil engineering structural material, i.e.concrete. Therefore, this new kind of composite has potential to be used in civil structurehealth monitoring.

Anomalous Broad Distribution of Relaxation Times in Mixed PMN-PSN Ceramics

Dielectric permittivity of 0.8PMN-0.2PSN ceramic was measured in the frequency range from 20 Hz to 3 GHz. The typical ferroelectrics relaxor dielectric dispersion was observed. From the frequency dependence of complex dielectric permittivity, the distribution of relaxation times was calculated. The low frequency limit of the distribution of relaxation times diverges according to the Vogel–Fulcher law with the freezing temperature T f = 226 K which is lower than in PMN ceramics, obtained previously. The comparison of distributions of relaxation times between 0.8PMN-0.2PSN and pure PMN tends to the conclusion about smaller polar nano regions in 0.8PMN-0.2PSN ceramic.

Effect of CeO2 on dielectric, ferroelectric and piezoelectric properties of PMN–PT (67/33) compositions

Lead magnesium niobate–lead titanate [Pb(Mg1/3Nb2/3)O3–PbTiO3] powders doped with different mole % of CeO2 were prepared by a modified columbite route with compositions corresponding to morphotropic phase boundary (MPB) region. These powders were calcined at 800 °C for 4 h and circular test specimens were prepared by uniaxial pressing. The specimens were sintered at 1150 °C/2 h, poled at 2 kV/mm d.c. voltage and were characterized for dielectric, ferroelectric and piezoelectric properties. It was observed that the piezoelectric and ferroelectric properties initially increase up to 2 mol% of ceria addition and then decrease with increase in ceria concentration. The diffusivity of the dielectric curves increases with increase in ceria concentration. The decrease in Curie temperature was observed from 173 °C corresponding to pure PMN–PT to a temperature of 138 °C for 10 mol% of ceria addition.