Electric-field-induced phase transitions in <001>-oriented PZN-9PT and PMN-35PT single crystals

Effects of a constant electric field (0 < E < 5 kV/cm) on the optical transmission of 91PbZn_1/3Nb_2/3O₃-9PbTiO₃ (PZN-9PT) and 65PbMg_1/3Nb_2/3O₃-35PbTiO₃ (PMN-35PT) single crystals belonging to the morphotropic regions of these solid solution systems have been studied. At temperatures close that of the morphotropic phase transition, the applied electric field induces two new intermediate monoclinic phases (M_a and M_c) in PZN-9PT and a single intermediate monoclinic phase in PMN-35PT crystals. In PMN-35PT, the new phase is inhomogeneous; in PZN-9PT, the transition from M_a to M_c has a continuous character. The E-T phase diagrams for both crystals are constructed. The results are interpreted within the framework of the Devonshire theory of strongly anharmonic crystals.     

Single crystal growth in PMN-PT and PMN-PZT

Single crystal growth of lead-based piezoelectric ceramics Pb(Mg_1/3Nb_2/3)_0.68Ti_0.32O₃ (PMN-32PT) and Pb(Mg_1/3Nb_2/3)_0.42(Ti_0.638Zr_0.362)_0.58O₃ (PMN-37PT-21PZ) ceramics via templated grain growth (TGG) was investigated. (001)- and (111)-oriented BaTiO₃ (BT) single crystals and (001)-oriented SrTiO₃ (ST) single crystals (of approximately 2.5 × 2.5 × 1 mm) were utilized as seeds for the growth experiments. The piezoelectric single crystals were produced in a process that involves at first hot pressing of single crystal in cold isostatically pressed ceramics followed by subsequent sintering of the samples. Growth of (001)-oriented single crystals with BT seeds was observed in both PMN-32PT and PMN-37PT-21PZ matrices. The measured growth lengths were up to 140 and 65 μm, respectively. The grown (001)-oriented single crystals grown were rectangular. The measured growth lengths of the pyramidal-shaped (111) BT single crystals were up to 1 mm, which is much larger than the growth lengths of the (001) single crystals. Experiments on (001) ST-seeded single crystals were not successful. No single crystal growth was observed due to the dissolution of the ST single crystals in the PMN-PZT matrix. The differences were explained by defect-chemical considerations.     

Impact of Ni dopant on structure and electrical properties of PMN-0.1PT ceramics

The Ni-doped PMN-0.1PT (PMN-0.1PT-xNi) relaxor ferroelectric ceramics were prepared by two-step columbite precursor method, and the effects of Ni dopant on the phase structure, dielectric, ferroelectric and electrostrictive properties were systematically investigated. The introduction of Ni dopant significantly improved the densification and grains size in the ceramics, but also profoundly modified the phase structure. It demonstrated that the substitution of Ni dopant for B-site in PMN-0.1PT lattice could affect electrical properties of PMN-0.1PT binary ceramics. Properly increasing the amount of Ni dopant led to the enhancement of dielectric and ferroelectric and remarkably increased the electrostrictive response. Results in this study indicated that at a composition x of 2.0 mol%, a large strain response could be obtained with maximum strain as high as 0.11% under the low field of 15 kV/mm at room temperature.     

The influence of defects on ferroelectric and pyroelectric properties of Pb(Mg1/3Nb2/3)O3-0.28PbTiO3 single crystals

Relaxor-based ferroelectric single crystals 0.72Pb(Mg_1/3Nb_2/3)O₃-0.28PbTiO₃ (PMN-0.28PT) were grown by a modified Bridgman technique. The direct current (dc) conductivity was investigated and corresponding conduction mechanisms were discussed. V^″Pb−VO defects are dominant from 245 °C to 650 °C. The ferroelectric properties of [1 1 1]-oriented PMN-0.28PT were systematically investigated, with the coercive field (E_c) of 5.2 kV cm⁻¹ and remnant polarization (P_r) of 37.8 μC cm⁻² at room temperature. Moreover, the dielectric and pyroelectric performances of PMN-0.28PT were measured and the integrated pyroelectric performances greatly enhanced after annealing in oxygen at 500 °C for 20 h. This is due to the decrease of oxygen vacancies in the single crystals when being annealed in the oxygen-rich atmosphere. These make [1 1 1]-oriented PMN-0.28PT crystals a promising candidate for infrared detectors and thermal imagers used at room temperature.     

Direct measurement of oxygen in lead-based ceramics using the ζ-factor method in an analytical electron microscope

X-ray absorption of oxygen is significant in thin specimens of Pb(Mg_1/3Nb_2/3)O₃-35 mol% PbTiO₃ [PMN-35PT] due to the presence of heavy elements such as Pb and Nb. Therefore, direct measurement of the oxygen concentration in these types of systems can be difficult. Furthermore, assumption of the composition from stoichiometric considerations may not be feasible, particularly if the valence state of one or more of the cation species is variable. Using only XEDS data, the -factor method provides absorption corrected compositional information. In the present study, it was shown that such data were in very good agreement with the nominal values for PMN-35 PT, whereas the uncorrected data underestimated the oxygen content by 300%. In previous work, it was theorized that the swelling of samples containing excess PbO was linked to changes in the composition of the intergranular liquid phase. The -factor technique was used to show that the oxygen to lead ratio of this second phase changes upon annealing.     

Electromechanical coupling properties of [001], [011] and [111] poled Pb(Mg1/3Nb2/3)O3-0.32PbTiO3 single crystals

The electric field induced “butterfly” curves and polarization loops, and the stress induced strain and polarization responses of [001], [011] and [111] oriented Pb(Mg_1/3Nb_2/3)O₃-0.32PbTiO₃ (PMN-0.32 PT) relaxor ferroelectric single crystals have been systematically investigated by experiment study. The focus is on the effect of constant compressive bias stress on the electromechanical coupling behavior along three crystallographic directions of PMN-0.32 PT single crystals. Dependence of the coercive field, remnant polarization, dielectric constant, and piezoelectric coefficient on the bias stress has been quantified for PMN-0.32 PT single crystals oriented in three different directions. Obtained results show that the large piezoelectric responses under zero compressive stress in [001] and [011] orientation are dominated by intrinsic crystal lattice while the engineered domain structure has a relatively minor effect. It is found that observed responses under stress cycle for [001] oriented crystals are due to polarization rotation and phase transformations. However, those for [011] and [111] oriented crystals are due to domain switching. The “butterfly” curves and polarization loops driven by electric field under different bias compression are described by two non-180° domain switching.     

Theoretical modelling of one dimensional photonic crystal based optical demultiplexer

An optical demultiplexer through one-dimensional Si–SiO₂ photonic crystal structure in the presence of air cavity with a single crystal PMN-0.38PT material is presented. The transmittance of this structure is obtained using the transfer matrix method. The transmittance of this structure shows a sharp passband in the band gap region. It is observed that by introducing PMN-0.38PT layer in both sides of the air cavity, the existing band gap region of Si–SiO₂ structure is slightly increased. Here, PMN-0.38PT material is working as a tunable element for passband. By applying some external potential on PMN-0.38PT crystal, the thickness of cavity layer can be tuned and the passband can be placed at any desired wavelength in the band gap region. Since the photonic band gap region contains a range of wavelengths which are not allowed to pass through the structure can be considered as a multiplex signal for the proposed demultiplexer. Therefore, any optical signal that lies in the band gap region of the structure can be separated into its components as a pass band. Hence, the proposed structure will work as an optical demultiplexer.     

Rapid formation of lead magnesium niobate-based ferroelectric ceramics via a high-energy ball milling process

Pyrochlore-free nano-sized 0.90Pb(Mg_1/3Nb_2/3)O₃(PMN)-0.10PbTiO₃(PT) and 0.65PMN-0.35PT powders were synthesized from oxides via a high-energy ball milling process. Single perovskite phase PMN-PT were readily formed from the oxide mixture after milling for only 2 h. The grain size calculated from X-ray diffraction (XRD) patterns of all samples is about 20 nm, which is in agreement with the observation from scanning electron microscopy (SEM) (20-50 nm). PMN-PT ceramics were obtained by sintering the milled powders at temperature from 1000 to 1100°C for 2 h. The dielectric, ferroelectric properties of the PMN-PT ceramics derived from the synthesized powders were comparable with the reported results in the literature.     

Piezoelectric properties of niobium-doped 18PMN-41PZ-41PT ceramics

The effects of various amounts of excess niobium ions added to the 18PMN-41PZ-41PT three-component ceramics system on the crystal structure, microstructure, polarization versus electric field, strain versus electric field and piezoelectric properties, have been studied. It was found that addition of niobium ions to 18PMN-41PZ-41PT induced a change in the crystal structure from rhombohedral to tetragonal phase. The excessive niobium ions also formed a micro-second phase which existed in the grain boundary, which could refine and uniform the grain. The refined and uniformed microstructure was found to increase the remanent polarization, saturation strain, planar coupling coefficient, K _p, and mechanical quality factor, the best value of K _p being 69%.     

Electrical properties of Pb(Mg1/3Nb2/3)O3-PbTiO3 ceramics modified with WO3

Ferroelectrics 0.67Pb (Mg_1/3Nb_2/3)O₃-0.33PbTiO₃ (PMN-PT) + x mol% WO₃ (x=0.1, 0.5, 1, 2) were prepared by columbite precursor method. Electrical properties of WO₃-modified ferroelectrics were investigated. X-ray diffraction (XRD) was used to identify crystal structure, and pyrochlore phase were observed in 0.67Pb (Mg_1/3Nb_2/3)O₃-0.33PbTiO₃+2 mol% WO₃. Dielectric peak temperature decreased with WO₃ doping, indicating that W⁶⁺ incorporated into PMN-PT lattice. Lattice constant, pyrochlore phase and grain size contribute to the variation of K_max. Both piezoelectric constant (d₃₃) and electromechanical coupling factors (k_p) were enhanced by doping 0.1 mol% WO₃, which results from the introduction of “soft” characteristics into PMN-PT, while further WO₃ addition was detrimental. We consider that the two factors, introduction of “soft” characteristics and the formation of pyrochlore phase, appear to act together to cause the variation of piezoelectric properties of 0.67PMN-0.33PT ceramics doping with WO₃.     

掺杂对0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3陶瓷结构和电学性能的影响

用传统的固相反应法、通过铌铁矿预合成路线制备了1mol%ZnO、MnO2和CuO掺杂的0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3(0.7PMN-0.3PT)陶瓷。XRD分析表明掺杂的0.7PMN-0.3PT陶瓷都呈现纯三方钙钛矿结构。烧成的陶瓷具有较高的致密度,其中CuO掺杂的0.7PMN-0.3PT陶瓷达到理论密度的93.79%。掺杂的0.7PMN-0.3PT陶瓷都呈现宽化、弥散的介电响应峰,然而介电常数的频率色散现象明显减弱。CuO掺杂的0.7PMN-0.3PT陶瓷呈现优良的综合电学性能:介电常数最大值εm达到21000左右,剩余极化强度Pr达到27.49μC/cm2,压电应变常量d33达到548pC/N。     

Composites of 0.9Pb(Mg1/3Nb2/3)O3-0.1PbTiO3 prepared by a sol-gel method: effect of atmosphere powders

Dielectric and electrical properties of relaxor ferroelectric 0.9PMN-0.1PT ceramics prepared by a sol-gel method were investigated as a function of PbZrO₃ atmosphere powders. The proper amount of atmosphere powders led to better properties of dielectric constant, polarization, and strain by preventing PbO volatilization from ceramics. Excessive amount of atmosphere powder, however, resulted in aging characteristics such as decreases in dielectric constant and loss exhibiting saddle-shaped dielectric constant and loss vs. temperature curves. A propeller-shaped P-E hysteresis curve indicating aging characteristics was also observed when an excessive amount of atmosphere powder was used during sintering. The aging of ceramics caused by absorption of PbO into the ceramics resulted in decreased polarization and strain. These aging characteristics associated with defects by excessive PbO absorption could not be reversed even though the aged ceramics underwent a heat-treatment above the dielectric maximum temperature.     

Direct and simultaneous observation of ferroelectric and magnetic domains

The ferroelectric/magnetic domain structure in a magnetoelectric binding BaTiO₃/Fe₈₁Ga₁₉ and the ferroelectric/crystallographic domain structure in a magnetoelectric binding PMN-34PT/Mn₅₀Ni₂₈Ga₂₂ were observed successfully by scanning electron acoustic microscopy (SEAM). Both the stripe ferroelectric domains in single crystals and the stripe magnetic domains in polycrystalline grains are obtained simultaneously, which exhibits that the scanning electron acoustic microscopy is a unique imaging technique. In addition, the experimental results show that the SEAM technique may be used in multiferroics to character two or more ferroic domains simultaneously. The imaging mechanisms of ferroelectric domains, magnetic domains, and crystallographic domains are attributed to piezoelectric coupling mechanism, magneto–elastic coupling mechanism, and thermo–wave coupling mechanism, respectively.     

Phase-modulated ellipsometry for probing the temperature-induced phase transition in ruthenium-doped lead zinc niobate-lead titanate single crystal

Phase-modulated ellipsometry was applied to measure changes in the refractive index of pure and ruthenium (Ru)-doped 0.9Pb (Zn_1/3Nb_2/3)O₃ (PZN)-0.1PbTiO₃ (PT) during the heating process in real time. Both samples were heated from room temperature to 200 °C in a thermally insulated chamber. In both samples, the phase transitions were observed to change from tetragonal to cubic. The temperature region at which the phase transition (Curie region) of Ru-doped 0.9PZN-0.1PT occurred not only broadened but also shifted to a lower temperature. The refractive indices were extremely stable in this region, meaning that Ru-doped 0.9PZN-0.1PT is a more favorable medium for the fabrication of optical memories.     

Time dependence of dielectric constants of Pb(Mg1/3Nb2/3)O3-BaTiO3-PbTiO3 ferroelectric ceramics for X7R MLCs

The isothermal ageing behaviour of Pb(Mg_1/3Nb_2/3)O₃-BaTiO₃-PbTiO₃ ceramics, promising high dielectric (ε_25°C = 4574) materials for X7R multilayer ceramic capacitors (MLCs) was studied over a wide range of frequencies. During ageing, the dielectric constants and loss tangents decreased linearly with the logarithm of ageing time. The ageing rates were evidently influenced by the test frequencies. The maximum value, within the range 0.1 to 1000 kHz, was about 1.7% per decade (time) and meets the corresponding ageing specifications for X7R ceramic dielectrics. This revised version was published online in July 2006 with corrections to the Cover Date.     

Piezoelectric properties of hot-pressed 18PMN-41PZ-41PT ceramics

Piezoelectric ceramics of 18PMN-41PZ-41PT were sintered by hot-pressing and normal sintering methods. The microstructure, density, P-E curve and S-E curve were also compared. The best hot-pressing condition for 18PMN-41PZ-41PT material was obtained at a temperature of 1000 °C and a pressure of 700 kg cm⁻²; it could achieve 99.66% theoretical density and a fine, uniform microstructure as a result of a 200–300 °C decrease in the sintering temperature. A higher coercivity was attained with the density increase. The fine, uniform microstructure also enhanced the increase in polarization and strain.     

Electromechanical properties of fine-grain, 0.7 Pb(Mg(1/3)Nb(2/3))O3-0.3PbTiO3 ceramics

A fine grain, relaxor-based piezoelectric ceramic 0.7 Pb(Mg(1/3)Nb(2/3))O3-0.3PbTiO3 (PMN-30% PT) has been investigated, which was fabricated using the columbite precursor method. The complete set of electromechanical properties of the piezoceramic at room temperature is determined using a combination of ultrasonic and resonance techniques. This fine-grain ceramic (grain size < or = 2.5 microm) exhibits ultra-high dielectric permittivity (epsilon33(T)/epsilon0 approximately 7000) and a high coupling coefficient k(33) (= 0.78). Ultrasonic spectroscopy was used to measure the dispersion of the phase velocity and attenuation for the longitudinal wave propagating in the poling direction. Lower attenuation and smaller velocity dispersion were observed compared to modified Pb(Zr(x)Ti(1-x)O3 (PZT-5H) ceramics. The measurement results show that this fine-grain PMN-30% PT ceramic is a very good material for making ultrasonic array transducers.     

High-performance PMN-PT thick films

This article describes some of our work on ?.??Pb(Mg?/?Nb(?/?)O?-?.??PbTiO? (0.65PMN-0.35PT) thick films printed on alumina substrates. These thick films, with the nominal composition ?.??Pb(Mg?/?Nb(?/?)O?-?.??PbTiO?, were produced by screen-printing and firing a paste prepared from an organic vehicle and pre-reacted fine particles of avery chemically homogeneous powder. To improve the adhesion of the 0.65PMN-0.35PT to the platinized alumina substrate,a Pb(Zr?.??Ti?.??)O? layer was deposited between the electrode and the substrate. The samples were then sintered at 950 °C for 2 h with various amounts of packing powder on the alumina (Al?O?) substrates. The sintering procedure was optimized to obtain dense 0.65PMN-0.35PT films. The films were then characterized using scanning electron microscopy as well as measurements of the dielectric and piezoelectric constants.The electrostrictive behavior of the 0.65PMN-0.35PT thick films was investigated using an atomic force microscope(AFM). Finally, substrate-free, large-displacement bending type actuators were prepared and characterized, and the normalized displacement (i.e., the displacement per unit length) of the actuators was determined to be 55 μm/cm at 3.6 kV/cm.     

A finite element computational framework for enhanced photostrictive performance in 0–3 composites

Photostriction is a multiphysics phenomenon comprising of both photovoltaic effect and converse piezoelectric effect. The extensively researched photostrictive material is lead lanthanum zirconate titanate, i.e., Pb_0.92La_0.08(Zr_0.65Ti_0.35)_0.98O₃ (PLZT) ceramic. In contrast to the traditional approaches of improving deflection response, the current study proposes a 0–3 composite model to substantially enhance the effective material properties, which in turn significantly improves the deflection response. A computational framework based on finite element analysis is employed to 0–3 photostrictive composite of PLZT as matrix and Pb(Mg_1/3Nb_2/3)O₃-0.35PbTiO₃ (PMN-35PT) as the inclusions. The representative volume element (RVE) or unit cell technique is used to incorporate the local variation of constituent properties and to calculate photostrictive properties such as effective elastic, dielectric, piezoelectric, and pyroelectric properties. An opto-electro-thermo-mechanical finite element formulation was engaged to get the actuation response of photostrictive material bonded to cantilever and simply supported beam. The maximum deflection for cantilever beam attached to photostrictive composite patch having 25% inclusions volume fraction in 0–3 composite is found to be 38% more in comparison to pure PLZT material. It is established that the opto-electro-mechanical 0–3 composite actuators possess high potential in lightweight, compact and wireless actuation applications.

     

Characterization of lead-based relaxor ferroelectric crystals by acoustic emission

The acoustic emission (AE) method is presented as a useful complementary tool for nondestructive characterization of selective relaxor ferroelectrics. Combined measurements of the dielectric permittivity and AE activity as a function of temperature and externally applied electric fields have been carried out using Pb(Mg_1/3Nb_2/3)O₃–33%PbTiO₃ (PMN-0.33PT) single crystals and Pb(Sc_0.5Ta_0.5)O₃ (PST) single crystals. Anomalous behavior in the electric field dependencies of the characteristic temperatures, T_m (diffuse permittivity maximum in PMN-PT) and T_n (formation of incommensurate antiferroelectric domains in PST), and the associated AE intensities has been observed. Both T_m and T_n exhibit minima coinciding with the AE activities maxima at critical values of the applied dc electric fields, 0.5 and 0.13 kV respectively. These phenomena are discussed mainly in terms of the interaction of the external field with the random electric fields originating from the polar nanoregions in relaxor ferroelectrics.