Intrinsic Nonstoichiometry in Single-Phase Pb(Zr0.5Ti0.5)O3

Two-phase crucibles made of Pb(Zr,Ti)O₃ with small additions of either PbO or (Zr _x Ti _1-x )O₂, which provide atmospheres of constant PbO activity, permit study of intrinsic nonstoichiometry by thermogravimetry. The width of the single-phase region can be determined by alternate equilibration of a sample with crucible atmospheres of high and low PbO activity. The width of this region for Pb(Zr_0.5Ti_0.5)O₃ is 2.48 mol% PbO at 1100°C.     

Phase Equilibrium in the System PbO-TiO2–ZrO2

Phase equilibrium relations in the system PbO–TiO₂–ZrO₂ were studied by quenching in the range where the PbO content is 50 mole % and more. Isotherms were examined at 1100°, 1200°, and 1300°C and tie lines were determined between the liquid and solid solution in equilibrium. The incongruent melting point of PbZrO₃ was 1570°C and the equilibrium between liquid, PbO-type solid, and PbZrO₃ is peritectic. Pb(Zr,Ti)O₃ solid solutions containing more than 14 mole % PbZrO₃ decomposed to liquid, ZrO₂, and Pb(Zr,Ti)O₃ and the decomposition temperature rises from 1340° to 1570°C with increasing PbZrO₃ content. The system PbTiO₃–PbZrO₃ should not be treated as a binary, but as a section of the ternary system.     

High Piezoelectric and Dielectric Properties of La-Doped 0.3Pb(Zn1/3Nb2/3)O3–0.7Pb(ZrxTi1−x)O3 Ceramics Near Morphotropic Phase Boundary

La-doped 0.3Pb(Zn_1/3Nb_2/3)O₃–0.7Pb(Zr _x Ti_{1− x} )O₃ ( x =0.5–0.53) piezoelectric ceramics with pure perovskite phase were synthesized by a two-step hot-pressing route. The piezoelectric properties of various compositions near the morphotropic phase boundary (MPB) were systematically investigated. Not only was the exact MPB of this system determined via X-ray diffractometry analysis, but also the peak of piezoelectric properties was found near the MPB. The optimum piezoelectric properties of this series were observed in the specimen with Zr/Ti=51/49. The piezoelectric coefficient ( d ₃₃) and electromechanical coupling factor ( k _p) were 845 pC/N and 0.70, respectively, which have not been reported in this system so far. Large permittivity (ɛ_r=4088) and permittivity maximum (ɛ_m=29 500) were also obtained for the poled specimens. The temperatures ( T _max) of the permittivity maxima ranged from 206° to 213°C with various Zr/Ti ratios.     

Reaction Sequence in the Formation of Lead Zirconate-Lead Titanate Solid Solution: Role of Raw Materials

The reaction sequence in the formation of Pb(Zr_0.6Ti_0.4)O₃ (PZT 60/40) was investigated as a function of PbO and ZrO₂ raw material variations, using powder X-ray diffraction. Particular emphasis was placed on the final stages of reaction in the formation of PZT solid solution. Based on the present work, a more detailed reaction sequence is being proposed for Pb(Zr_0.6Ti_0.4)O₃ and similar compositions. This reaction sequence is believed to account for many of the apparent discrepancies which have appeared in the literature.     

Novel Route to Lead-Based Ferroelectric Compounds via Tetragonal Lead(II) Oxide Intermediates

Single-phase perovskite lead-based ferroelectric powders—Pb(Mg_1/3Nb_2/3)O₃(PMN) or 0.9Pb(Mg_1/3Nb_2/3)O₃–0.1PbTiO₃(0.9PMN–0.1PT)—were prepared using Mg(NO₃)₂, instead of MgO or MgCO₃, via a mixed-oxide method and one-step calcination. The reaction proceeded via the formation of 3Pb(NO₃)₂·7PbO, Pb(OH)₂, tetragonal PbO, and then 2PbO–Nb₂O₅(P₂N) for PMN or 3PbO–Nb₂O₅(P₃N) for PMN–PT; a mixture of PMN and Pb₂(Mg _x Nb_1.33)O_{5.33+ x} then formed, followed finally by the formation of single-phase PMN or 0.9PMN–0.1PT. Such prepared powder showed excellent room-temperature dielectric constants—13800 for PMN or 22600 for 0.9PMN–0.1PT—by sintering at a temperature of 900°C for 2 h.     

Conventionally Prepared Submicrometer Lead-Based Perovskite Powders by Reactive Calcination

Submicrometer powders of various Pb-based perovskites, including PbTiO₃, PbZrO₃, Pb(Zr_0.53Ti_0.47)O₃, and Pb(Mg_1/3Nb_2/3)O₃ were prepared by a reactive calcination process. Using only reagent-grade raw materials and conventional processing techniques, highly reactive powders were produced by reacting the materials near the temperature of maximum volumetric expansion. At this point, the morphological development results in a skeletal-type structure consisting of ultrafine particulates that can be readily broken down further by milling. Powder sizes less than 0.3 μm and as small as 70 nm generally only achievable using chemical processing techniques were achieved. The highly reactive powders allowed densification to occur at temperatures as low as ∼900°C with correspondingly small grain sizes. A model describing the physiochemical behavior and associated morphological development of Pb-based perovskites was herein proposed.     

Thick Film Patterned Ceramics Using UV-Curable Pastes

Screen-printed layers of Al₂O₃, BaTiO₃, 0.90Pb(Mg_1/3Nb_2/3)-0₃–0.10PbTiO₃, Pb(Zr,Ti)O₃, ZnO, and glass alumina pastes have been patterned using photoprinting techniques. Curability of each paste by ultraviolet light and formation of holes with various diameters were studied for application as a production method for very small-sized vias. The dependence of hole diameters on various experimental parameters is presented and discussed. Wall slopes were found to depend on the transmission of the powders used in the pastes.     

Effects of Sintering Atmosphere on Densification Behavior and Piezoelectric Properties of Pb(Ni1/3Nb2/3)O3–PbZrO3 Ceramics

Densification of polycrystalline Pb(Ni_1/3Nb_2/3)O₃–PbTiO₃–PbZrO₃ (PNN–PT–PZ) specimens was enhanced as the partial pressure of O₂ in the sintering atmosphere was increased. This observation was attributed to the increase in the internal pressure of a closed pore due to the thermal decomposition of PbO at a low partial pressure of O₂. The relative dielectric permittivity (ε_r), d ₃₃, k _p, and grain size of sintered specimens were also increased as the partial pressure of O₂ in the sintering atmosphere was increased. The observed dependence of piezoelectric properties on the partial pressure of O₂ was discussed in terms of the enhanced formation of the A-site vacancy ( V "_Pb) or the suppression of the B-site defect ( V ¨_O) as the oxygen potential increased.     

Temperature–Time Texture Transition of Pb(Zr1−xTix)O3 Thin Films: I, Role of Pb-rich Intermediate Phases

Lead-rich intermediate phases, in particular Pt_5–7Pb and PbO, are found to form on Pt(111) atop Ti–buffered Si substrates prior to formation of Pb(Zr_{1− x} Ti _x )O₃ (PZT) thin films. Pt_5–7Pb is a [111] textured transient intermetallic phase that nucleates PZT[111] texture. PbO is a [001] textured layer compound that nucleates PZT[100] texture. The formation conditions and lattice matching of these intermediate phases have been examined. The presence of other possible intermediate phases, such as pyrochlore and Zr and Ti-rich phases, has also been investigated but found unrelated to the texture selection of perovskite PZT.     

Low Temperature Coefficient of Resonance Frequency Composition in the System Pb(Zr,Ti)O3—Pb(Mn1/3 Nb2/3)O3

Pb(Zr,Ti)O₃–Pb(Mn_1/3 Nb_2/3)O₃ (PZT–PMnN) system has been studied for high-power piezoelectric applications. This study investigates this system to find out the composition with high-power density piezoelectric characteristics and low tem-perature coefficient of resonance frequency (TCF). It was found that the composition 0.9PZT–0.1PMnN (Zr/Ti = 0.51/0.49) modified with 6 mol% Sr exhibits a TCF of −8 ppm/°C (−20 to +80°C). Further, the dielectric and piezoelectric properties of this composition are as follows: k _p= 0.53; Q _m= 800; d ₃₃= 274; ε₃₃/ε₀= 1290 and tan δ=1.1%, which shows the suitability of this composition for ultrasonic devices used under fluctuating thermal environment.     

Dielectric and Electrical Conductivity Properties of PMS–PZT Ceramics

The dielectric and electrical conductivity properties of x Pb(Mn_1/3Sb_2/3)O₃–(1− x )Pb(Zr_0.52Ti_0.48)O₃ (PMS–PZT) ceramics were studied. X-ray diffraction indicated that all samples exhibit a single-phase perovskite structure. Dielectric study revealed that the dielectric relaxor behavior was induced by co-doping Mn²⁺ and Sb⁵⁺ into Pb(Zr_0.52Ti_0.48)O₃ ceramics. Electrical conductivity measurements showed that the concentration of carriers are increased with the increase in PMS contents. After annealing in an oxygen atmosphere for 30 h, the direct current conductivity of PMSZ15 was much lower than that of the as-sintered sample. The reason why this phenomenon occurs may be the reduction of oxygen-vacancy concentration.     

Temperature–Time Texture Transition of Pb(Zr1−xTix)O3 Thin Films: II, Heat Treatment and Compositional Effects

Texture transition of Pb(Zr_1−xTi_x)O₃ thin films grown from a metallo–organic solution onto Pt/Ti/SiO₂/Si substrates has been studied. The orientation obtained depends on the crystallization temperature and time and can be drastically altered by modifying the heat treatment schedule. A [100] texture requires an initial seeding treatment in the intermediate temperature range. This is attributed to a nucieation advantage associated with the formation of an intermediate PbO[001] texture that tends to form at intermediate temperature over time. A [111] texture develops at higher temperature during rapid heating and can be rationalized by the formation of an epitaxial intermetallic phase Pt_5–7Pb, at the PZT/Pt interface that provides lattice matching between PZT(lll), Pt_5–7Pb(lll), and Pt(lll). Temperature–time transformation texture (TTT) diagrams of PZT texture have been constructed for seeding various orientations. The effect of composition (Pb excess and Zr/Ti ratio) and the possible manipulation of these texture selection relations by combining compositional tailoring and heat treatment schedules are illustrated.     

Effect of Simultaneous Addition of BiFeO3 and Ba(Cu0.5W0.5)O3 on Lowering of Sintering Temperature of Pb(Zr,Ti)O3 Ceramics

Sintering of 0.5-wt%-MnO₂-added Pb(Zr_0.53Ti_0.47)O₃ ceramics progresses at 935°C for 50 min by the addition of complex oxides of perovskite-type crystal structure, BiFeO₃ and Ba(Cu_0.5W_0.5)O₃. In order to elucidate the low-temperature sintering mechanism of Pb(Zr,Ti)O₃ ceramics, the shrinkage and the evolution of the microstructure of a compacted body during heating were studied. It has been shown that the densification process was separated into the following three stages: the rearrangement of grains, the grain boundary diffusion of atoms, and then grain growth. Also, microstructural and elemental analyses of the ceramics revealed the existence of an amorphous phase at the grain boundaries predominantly composed of lead and copper oxides. Consequently, this process can be facilitated by the occurrence of a transient liquid phase corresponding to the above amorphous phase.     

Effect of Grain Coalescence on the Abnormal Grain Growth of Pb(Mg1/3Nb2/3)O3-35 mol% PbTiO3 Ceramics

Abnormal grain growth (AGG), which occurred during the heat treatment of Pb(Mg_1/3Nb_2/3)O₃-35 mol% PbTiO₃ (PMN-35PT) with excess PbO, was investigated. AGG has been suggested to be the consequence of grain coalescence that results in the formation of Σ3 coincidence site lattice and low angle grain boundaries. Because of reentrant edges appearing at the ends of these boundaries, the coarsening rate of grains was significantly enhanced and AGG occurred.     

Structure and Dielectric Properties of Pb(Sc2/3W1/3)O3–Pb(Zr/Ti)O3 Relaxors

The structure and dielectric properties of (1− x )Pb(Sc_2/3W_1/3)O₃–( x )Pb(Zr/Ti)O₃ ceramics have been investigated over a full substitution range. All compositions with x < 0.5 adopt a cubic perovskite structure; however, for x ≤ 0.25 a doubled cell results from a 1:1 ordered distribution of the B-site cations. The structural order in Pb(Sc_2/3W_1/3)O₃ (PSW) can be described by a random-site model with one cation site occupied by Sc³⁺ and the other by a random distribution of (Sc_1/3³⁺W_2/3⁶⁺). The ordering is destabilized in solid solutions of PSW with PbZrO₃ (PSW–PZ), but stabilized by PbTiO₃ in the (1− x )PSW–( x )PT system. The changes in order are accompanied by alterations in the dielectric response of the two systems. For PSW–PZ the temperature of the permittivity maximum ( T _ɛ,max) increases linearly with x ; however, for PSW–PT T _ɛ,max decreases in the ordered region (up to x = 0.25) and then increases rapidly as the order is lost. Similar effects were produced by modifying the degree of order of (0.75)PSW–(0.25)PT; when the order parameter was reduced from ∼1.0 to ∼0.65, T _ɛ,max increased by more than 60°C.     

Transmission Electron Microscopy of Pb(Zr0.52Ti0.48)O3

Transmission electron microscopy of Pb(Zr_0.52Ti_0.48)O₃ sintered with 3 wt% excess PbO indicates that there is an amorphous grain-boundary phase 10 nm thick. The grain-boundary phase has a higher Pb content than the bulk material. Influence of such a phase on sintering is discussed.     

Fabrication and Properties of Sol–Gel-Derived BiScO3–PbTiO3 Thin Films

BiScO₃–PbTiO₃ (BSPT) thin films near the morphotropic phase boundary were successfully fabricated on Pt(111)/Ti/SiO₂/Si substrates via an aqueous sol–gel method. The thin films exhibited good crystalline quality and dense, uniform microstructures with an average grain size of 50 nm. The dielectric, ferroelectric, and piezoelectric properties of the sol–gel-derived BSPT thin films were investigated. A remanent polarization of 74 μC/cm² and a coercive field of 177 kV/cm were obtained. The local effective piezoelectric coefficient d ^*₃₃ was 23 pC/N at 2 V, measured by a scanning probe microscopy system. The dielectric peak appeared at 435°C, which was 80°C higher than that of Pb(Ti, Zr)O₃ thin films.     

Coarsening Process of Penetration-Twinned Grains in PMN-35 mol% PT Ceramics

In a Pb(Mg_1/3Nb_2/3)O₃-35 mol% PbTiO₃ (PMN-35PT) specimen with 5 mol% excess PbO, the pores trapped inside grains by heat treatment in a double cycle at 1150°3C have revealed the coarsening pattern of the grains. Using this technique, the coarsening process of abnormal large grains with typical characteristics of penetration twins could be determined. The results suggest that two-dimensional nucleation and lateral growth enhanced at the reentrant edges are the cause of zigzag-shaped σ3 incoherent twin boundaries.     

Substitution of Bi and Nb Ions in Lead Zirconate-Titanate

Solid-state substitution of Bi and Nb ions in the perovskite crystal structure of Pb(Ti_0.47Zr_0.53)O₃ was investigated by sample weight changes at 1150°C in an "equilibrium" PbO atmosphere. A model is discussed that includes the effect of charge neutralization, requiring weight losses for A-site substitutions and weight gains for B-site substitutions. Experiments support the substitution of Bi as Bi³⁺ on the Pb²⁺ A site and Nb as Nb⁵⁺ on the (Ti,Zr)⁴⁺ B site of lead zirconate-titanate. For each mole of BiO_1.5 added to a specimen, 1.5 moles of PbO are lost; for each mole of NbO_2.5 added, 0.5 moles of PbO are gained. These results agree with the proposed model and with ionic size arguments. The weight changes were time-dependent during the first 30 to 40 h at 1150°C. This behavior is accounted for by the presence of transient second phases.     

Lanthanum-Modified (1 – x)(Bi0.8La0.2)(Ga0.05Fe0.95)O3·xPbTiO3 Crystalline Solutions: Novel Morphotropic Phase-Boundary Lead-Reduced Piezoelectrics

(1 – x )(Bi_0.8La_0.2)(Ga_0.05Fe_0.95)O₃· x PbTiO₃ (BLGF-PT) crystalline solutions have been fabricated by solid-state reactions. BLGF-PT has single perovskite phase structure with a rhombohedral–tetragonal (FE_r-FE_t) morphotropic phase boundary (MPB) at a PT content of x = 0.43. Lanthanum substitution has been found to increase the insulation resistance and decrease the coercive field down to 20 kV/cm, which results in significant improvements in dielectric and piezoelectric properties of BLGF-PT. The dielectric constant, loss tangent, Curie temperature, remnant polarization, piezoelectric d ₃₃ constant, and planar coupling factor of 1760, 0.05, 264°C, 33 μC/cm², 295 pC/N, and 0.36, respectively, have been achieved for BLFG-PT in the vicinity of the MPB. Compared with conventional Pb(Zr,Ti)O₃ (PZT) piezoelectric ceramics, the BLGF-PT is a competitive alternative piezoelectric material with decreased lead content.