Optical properties of (1−<Emphasis Type="Italic">x</Emphasis>)PbZn<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>O<Subscript>3</Subscript>−<Emphasis Type="Italic">x</Emphasis>PbTiO<Subscript>3</Subscript> single crystals

The temperature dependence of the optical transmission and small-angle light scattering with and without applied constant electric field was studied in relaxor single crystals of 0.91PbZn_1/3Nb_2/3O₃-0.09PbTiO₃ (PZN-PT 91/9) and 0.93PbZn_1/3Nb_2/3O₃-0.07PbTiO₃ (PZN-PT 93/7) solid solutions in the region of two phase transitions: (i) from cubic paraelectric to tetragonal ferroelectric phase at T=T _c and (ii) from tetragonal ferroelectric to rhombohedral ferroelectric phase at T=T _rt. In the absence of external electric field, only the phase transition at T _c proceeds in both PZN-PT 91/9 and PZN-PT 93/7 crystals according to a percolation mechanism and is accompanied by the appearance of a sharp maximum in the small-angle light scattering intensity curve. In PZN-PT 93/7 crystals, the application of a relatively weak electric field induces an additional percolation type phase transition at T _rt.     

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.     

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.     

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.     

Heterophase structures and their quantitative characteristics in (1 − x)Pb(Fe1/2Nb1/2)O3 − xPbTiO3 near the morphotropic phase boundary

Features of phase coexistence in solid solutions of (1 − x)Pb(Fe_1/2Nb_1/2)O₃ − xPbTiO₃ with the perovskite-type structure are studied at 0.05 ≤ x ≤ 0.08. The role of elastic matching of the tetragonal P4mm and monoclinic Cm phases of the ferroelectric nature is considered near the morphotropic phase boundary. Model concepts on the stress relief in heterophase structures are developed and applied to interpret the phase content in (1 − x)Pb(Fe_1/2Nb_1/2)O₃ − xPbTiO₃. Good agreement between the calculated and experimental dependences of the volume fraction of the tetragonal phase on x is observed. It is shown that the studied phase coexistence under conditions for the complete stress relief can take place at elastic matching of the single-domain monoclinic phase and the tetragonal phase split into two types of 90° domains.     

Piezoelectric anisotropy: Enhanced piezoelectric response along nonpolar directions in perovskite crystals

This paper discusses the mechanisms that can contribute to the enhanced longitudinal piezoelectric effect along nonpolar directions in perovskite crystals, such as BaTiO₃, PbTiO₃, KNbO₃, Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ and Pb(Zn_1/2Nb_2/3)O₃-PbTiO₃. Piezoelectric anisotropy is discussed in relation to temperature induced phase transitions, compositional variation in solid solutions with morphotropic phase boundaries, applied electric fields, the domain wall structure and domain wall displacement.     

Synthesis of BF–PT perovskite powders by high-energy ball milling

0.7BiFeO₃–0.3PbTiO₃ (BF–PT) powders were synthesized from a mixture of the oxides Bi₂O₃, Fe₂O₃, PbO and TiO₂ using a Fritsch P4™ vario-planetary ball milling system. The perovskite structure of the BF–PT powder can be obtained well and the crystallite size of the powders was greatly reduced to 20–35 nm after milling for 8 h. The pre-calcined course shows a rhombohedral–tetragonal phase transition with the increasing temperature and shows the structure transition near the Curie temperature T_c.     

Effect of CeO<Subscript>2</Subscript> on dielectric,ferroelectric and piezoelectric properties of PMN–PT (67/33) compositions

Lead magnesium niobate–lead titanate [Pb(Mg_1/3Nb_2/3)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.     

Effect of dopants on ageing properties for the PMN-0.1 PT relaxor ferroelectric ceramics

Isothermal ageing properties of the typical ferroelectric relaxor system Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ (abbreviated as PMN-0.1 PT) doped with different kinds of oxides were measured and the effect of dopants on ageing inducing was investigated. The metallic ions of additives were considered to enter sites A or B in the perovskite structure with similar radii and their roles were distinguished as donors, acceptors or equivalent substitutors due to their valences. For the additions of acceptors, dielectric ageing is evident while no obvious ageing was found in the non-doped equivalently substituted or donor-doped PMN-0.1 PT systems.     

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.     

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.     

Growth and electrical performance of Pb(Mg1/3Nb2/3)O3-PbTiO3-Pb(Fe1/2Nb1/2)O3 single crystals

For the first time, we have grown ferroelectric single crystals Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃-Pb(Fe_1/2Nb_1/2)O₃ (PMN-PT-PFN) from the melt by the simple slow cooling process. The chemical composition of the single crystals PMN-PT-PFN (0.59/0.31/0.10) is near the morphotropic phase boundary (MPB). X-ray diffraction (XRD) was used to study phase structure of the as-grown crystals, energy dispersive X-ray spectrometer (EDS) and electron probe micro-analyzer (EPMA) were employed to confirm the chemical composition and element distribution of the as-grown crystals, respectively. The ferroelectric, dielectric and piezoelectric properties of the as-grown PMN-PT-PFN (0.59/0.31/0.10) single crystal oriented along the (0 0 1) axis were measured, which showed that the remnant polarization (P_r), coercive electric fields (E_c), the Curie temperature (T_c) and the piezoelectric coefficient (d₃₃) were 50.2 μC/cm², 13.9 kV/cm, 158 °C and about 1800 pC/N, respectively. All the results indicated that the PMN-PT-PFN (0.59/0.31/0.10) single crystals are promising for applying to field of high frequency.     

Processing and electrical properties of (1 − x)[(1 − y)(Pb(Mg1/3Nb2/3)O3)–y(Pb(Yb1/2Nb1/2)O3)]–xPbTiO3 ceramics

Ferroelectric ceramics in the vicinity of morphotropic phase boundary (MPB) with compositions represented as (1 ? x)[(1 ? y)(Pb(Mg_1/3Nb_2/3)O₃)–y(Pb(Yb_1/2Nb_1/2)O₃)]–xPbTiO₃ were prepared by solid state reaction. The addition of PYbN to PMN–PT decreased the sintering temperature from 1200 °C (y = 0.25) to 1000 °C (y = 0.75). The PT content, where the MPB was observed, increased with the PYbN addition. A remanent polarization value of 28.5 µC/cm² and a coercive field value of 11 kV/cm were measured from 0.62[0.25PMN–0.75PYbN]–0.38PT ceramics, which were close to the ones measured from PMN–0.32PT ceramics. In addition, the Curie temperature was found to increase with PYbN additions.     

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.     

Ferroelectricity of Pb(Zn1/3Nb2/3)O3-BaTiO3-PbTiO3 ceramics in the vicinity of morphotropic phase boundary

The morphotropic phase boundary (MPB) in the (0.85 – x)Pb(Zn_1/3Nb_2/3)O₃ – 0.15BaTiO₃ – xPbTiO₃(0 < x < 0.2) ceramic system was delineated by x-ray diffraction analysis. Polarization hysteresis loop measurements at room temperature were performed for compositions in the vicinity of the MPB. Experimental results demonstrate that the MPB, by its definition the rhombohedral and tetragonal phase coexist in the present system, is a broad composition region where the value of x ranges from 0.12 to 0.18. The remanent polarization, P _r, increases with PbTiO₃(PT) reaching a maximum value of 18 C/cm² at 15 mol%PT, then decreases remarkably with further PT addition, whereas the variation of coercive field, E _c, with PT content shows the opposite trend. The effect of PT incorporation on P _r is more pronounced than on E _c. Correlation between the degree of lattice distortion, instead of the maximization of the polarization orientations inherent to both phases, and P _r is attained to account for the observed phenomenon. The dependence of E _c upon PT content, however, reflects the transition from typical relaxor ferroelectrics to weak normal ferroelectrics, as confirmed by the results of the dielectric measurement.     

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.     

Phase boundary of an LMN-PZ-PT three-component system

Piezoelectric ceramics of Pb(Zr,Ti)O₃ (PZT) were added to a third component La(Mg_2/3Nb_1/3)O₃ (LMN) to form an LMN-PZ-PT three-component system. The morphotropic phase boundary (between the tetragonal phase and rhombohedral phase) was close to the PbZrO₃ site. The phase boundary between the tetragonal and cubic phase was close to the PbTiO₃ site, and the composition 9/62/29 was the three-phase point. The grain size could be reduced by increasing the amount of LMN in the PZT system. Replacing lead ions with lanthanum ions would induce a strain in the lattice because the diameter of the lanthanum ion is smaller than that of the lead ion. The best electromechanical coupling coefficient (K_p) found was 53.7 and the component was close to the morphotropic phase boundary.     

Dielectric and elastic properties of 0.70Pb(Mg1/3Nb2/3)O3–0.30PbTiO3 single crystal and their electric-field dependence

The dielectric and elastic properties of [001]_c-oriented 0.7Pb(Mg_1/3Nb_2/3)O₃–0.3PbTiO₃ (PMN–0.3PT) crystal were investigated as a function of poling field at 300 and 360 K, respectively. At 300 K, the dielectric constant and elastic compliance of rhombohedral PMN–0.3PT crystal change drastically at a critical field corresponding to an electric-induced ferroelectric phase transition. At 360 K, the PMN–0.3PT crystal is tetragonal, its dielectric constant and elastic compliance change drastically at two critical fields, which indicates an intermediate phase. Furthermore, much small dielectric loss factors and mechanical loss factors are observed in mono-domain state, which indicates that losses mainly come from domain wall contributions.     

Piezoelectric properties of (Pb,Sr) (Zr,Ti, Mn,Zn, Nb)O3 piezoelectric ceramic

In this paper, the aim is to study the piezoelectric properties of (Pb, Sr)[(Zr, Ti)(Zn_1/3Nb_2/3) (Mn_1/3Nb_2/3)]O₃ ceramic with compositions close to the morphotropic phase boundary. The dielectric and piezoelectric properties of this system were investigated by way of changed contents of two main compounds, TiO₂ and Mn_1/3Nb_2/3. There are two phases existing in this system, one tetragonal and the other pseudocubic. With a constant amount of 4 mol% Pb(Mn_1/3Nb_2/3)O₃ and 8 mol% Pb(Zn_1/3Nb_2/3)O₃, the morphotropic phase boundary exists when the amount of PbTiO₃ is nearly equal to 44 mol%. The structure is perovskite with pseudocubic symmetry for PbTiO₃ less than 44 mol%, but it is tetragonal symmetry for higher PbTiO₃ concentrations. The planar coupling factor and piezoelectric constant are higher for compositions near the morphotropic phase boundary, but the mechanical quality factor and longitudinal velocity are lowest. As far as the dielectric constant of poled material is concerned, its maximum in the multicomponent system is displaced into the tetragonal phase and does not coincide with the maximum of electromechanical quality factor. The variation of remanent polarization with composition is the same as that of the coupling factor. Thus, compositions with the tetragonal phase are ferroelectrically harder and those with the pseudocubic phase are ferroelectrically softer than compositions close to the morphotropic phase boundary. Besides the influence of Ti, the effect of Mn_1/3Nb_2/3 is also studied in this paper. The planar coupling factor increases with increasing Mn_1/3Nb_2/3 and reaches a maximum at 5 mol% Mn_1/3Nb_2/3, and then decreases for higher Mn_1/3Nb_2/3 values. The mechanical quality factor increases, but the dielectric constant decreases, with increasing Mn_1/3Nb_2/3.     

Relaxor based ferroelectric single crystals for electro-mechanical actuators

 The piezoelectric properties of relaxor based ferroelectric single crystals, such as Pb(Zn_1/3Nb_2/3)O3−PbTiO₃ (PZN-PT) and Pb(Mg_1/3Nb_2/3)O₃−PbTiO₃ (PMN-PT) were investigated for electromechanical actuators. In contrast to polycrystalline materials such as Pb(Zr,Ti)O₃ (PZTs), morphotropic phase boundary (MPB) compositions were not essential for high piezoelectric strain. Piezoelectric coefficients (d₃₃’s ) >2200 pC/N and subsequent strain levels up to >0.5% with minimal hysteresis were observed. Crystallographically, high strains are achieved for <001> oriented rhombohedral crystals, though <111> is the polar direction. Ultrahigh strain levels up to 1.7%, an order of magnitude larger than those available from conventional piezoelectric and electrostrictive ceramics could be achieved, possibly being related to an E-field induced phase transformation. High electromechanical coupling (k₃₃) >90% and low dielectric loss <1%, along with large strain make these crystals promising candidates for high performance solid state actuators. Received: 2 January 1997 / Accepted: 27 March 1997