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.     

Effect of Lead Content on the Structure and Electrical Properties of Pb((Zn1/3Nb2/3)0.5(Zr0.47Ti0.53)0.5)O3 Ceramics

The effects of lead content on the structure and electrical properties of Pb((Zn_1/3Nb_2/3)_0.5(Zr_0.47Ti_0.53)_0.5)O₃ ceramics were investigated. Specimens with various lead concentrations were prepared by the conventional oxide-mixing method. When the lead concentration was slightly less than the stoichiometric amount, a large amount of pyrochlore phase was formed along with the perovskite phase. On the other hand, excessive amounts of lead led to the formation of PbO on the surface of the specimen. These second phases were seriously detrimental to electromechanical properties. The highest piezoelectric properties were observed when an excess of 1 mol% lead was added. By optimizing the specimen composition, excellent piezoelectric and dielectric properties ( k _p= 0.7, d ₃₃= 490 pC/N, and ɛ_m= 15000) were obtained.     

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.     

Pyrolysis of Pb(Zr05Ti05)O3 Precursors: Avoiding Lead Partitioning

Three different chemical precursor routes were investigated to synthesize Pb(Zr₀₅Ti₀₅)O₃: mixing hexanoates, acetate complexing of alkoxides, and the synthesis of a mixed alkoxide by the reaction of titanium alkoxide and zirconium alkoxide with lead acetate. For each, elemental Pb and PbO were the first crystalline phase observed during pyrolysis conditions that involved rapid heating (e.g., to 400°C). The formation of Pb (and PbO) could be avoided by first heattreating hydrolyzed, mixed alkoxide precursor powders at 300°C for 1 h. This treatment was not effective for the two other precursors. It is concluded that both the carbonaceous content of the precursor (lowest for the hydrolyzed, mixed alkoxides) and the rate of hydrocarbon release during pyrolysis are critical to avoid the formation of elemental Pb during pyrolysis.     

Crystal Structure and Ferroelectric Properties of (Bi0.5Na0.5)TiO3–Ba(Zr0.05Ti0.95)O3 Piezoelectric Ceramics

The crystal structure and ferroelectric properties of (1− x )(Bi_0.5Na_0.5)TiO₃– x Ba(Zr_0.05Ti_0.95)O₃ (BNBZT x, x ≤12%) lead-free piezoelectric ceramics were studied. The distance between the centers of cations and anions ( d _c–a) as well as the lattice parameters was carefully investigated by Rietveld refinement on X-ray diffraction patterns. It was found that the crystal phase was determined by the amount of Ba(Zr_0.05Ti_0.95)O₃ added, whereas the pure rhombohedral and tetragonal phases are observed in compositions containing x ≤4 and x ≥8%, respectively. A rhombohedral–tetragonal morphotropic phase boundary (MPB) was found at around BNBZT6, which showed a maximum and minimum d _c–a at its rhombohedral and tetragonal phases, respectively. According to the present study, the ferroelectric properties show a strong dependence on their crystal phases. For the single-phase compositions, the remanent polarization ( P _r) generally increased with the value of d _c–a while their coercive fields ( E _c) were determined by their lattice parameters. Nevertheless, the behavior in P _r and E _c for MPB compositions is related to not only the lattice parameter but also the composed phases.     

Sol—Gel Fabrication of Pb(Zr0.52 Ti0.48)O3 Thin Films Using Lead Acetylacetonate as the Lead Source

Lead zirconium titanate (PZT) thin films of the morphotropic phase boundary composition [Pb(Zr_0.52Ti_0.43)O₃] were deposited on platinum-coated silicon by a modified sol-gel process using lead acetylacetonate as the lead source. The precursor solution for spin coating was prepared from lead acetylacetonate, zirconium n -butoxide, and titanium isopropoxide. The use of lead acetylacetonate instead of the widely used lead acetate trihydrate provided more stability to the PZT precursor solution. Films annealed at 700°C for 12 min formed well-crystallized perovskite phase of Pb(Zr_0.52Ti_0.48)O₃. Microstructures of these films indicated the presence of submicrometer grains (0.1 to 0.2 μm). The dielectric constant and loss values of these films measured at 10 kHz were approximately 1200 and 0.04, respectively, while the remanent polarization and coercive field were ∼ 13 μC/cm² and ∼ 35 kV/cm. Aging of the solution had almost no effect on the dielectric and ferroelectric properties of these films.     

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.     

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.     

Growth of High-Quality Pb((Zn1/3Nb2/3)0.91Ti0.09)O3 Single Crystals by Excess ZnO Addition

A high-quality single crystal of Pb((Zn_1/3Nb_2/3)_0.91Ti_0.09)O₃ (PZNT 91/9), 40 mm in diameter and 20 mm in length, was successfully grown using the solution Bridgman method with a slight excess amount of ZnO. High-quality wafers were sliced from the light-brown single crystal. No PbO inclusions or opaque areas were observed in the transparent wafers. An array probe for echocardiography was constructed with the single-crystal wafer, and its superior performance was demonstrated.     

Effect of Mn on Aging of (Pb0.63Ba0.37)(Zr0.7Ti0.3)O3 Dielectric Ceramics

An aging model for relaxors is suggested on the basis of the transformation of a supercooled cubic lattice into a tetragonal lattice. Manganese ions distort the crystal lattice, and the distortion affects the phase transformation rate. As a result, the aging rate may be expected to change. The lattice constant of (Pb_0.63Ba_0.37)(Zr_0.7Ti_0.3)O₃+χ MnO mol% dielectric ceramics was used as a measure of the degree of the distortion. As the lattice constant decreased up to 0.5 MnO mol%, the aging rate increased, justifying the proposed model.     

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.     

Preparation of Lead Zirconate Titanate (Pb(Zr0.52Ti0.48)O3) by Homogeneous Precipitation and Calcination

Preparation of phase-pure PZT (Pb(Zr_0.52Ti_0.48)O₃) powders was achieved, in the presence of urea (CH₄N₂O), by homogeneous precipitation. Aqueous solutions of PbCl₂, ZrOCl₂·8H₂O, and TiCl₄ were used as the starting materials in the synthesis of phase-pure PZT powders. Phase evolution behavior of precursor powders was studied by powder X-ray diffraction (XRD) in air, over the temperature range of 90° to 750°C. The morphology of the formed powders was studied by scanning electron microscopy (SEM). Semiquantitative chemical analyses of the samples were performed by energy-dispersive X-ray spectroscopy (EDXS).     

Structure–Property Relationship in Mn-Doped (Pb0.94Sr0.06)(Zr0.53Ti0.47)O3

Hard piezoelectrics based on PZT with a composition near the morphotropic phase boundary (Pb_0.94Sr_0.06)(Zr_0.53Ti_0.47)O₃ [PSZT] have been synthesized by the sol–gel method. The influence of B site aliovalent dopant Mn³⁺ on the crystal structure and electrical properties has been investigated. Mn³⁺ions ( d ⁴) are found to change the crystal structure from tetragonal to rhombohedral as a result of Jahn–Teller distortion of the MnO₆ octahedra and are therefore found to impart donor characteristics to PSZT.     

Substrate Effect on the Magnetoelectric Behavior of Pb(Zr0.52Ti0.48)O3 Film-On-CoFe2O4 Bulk Ceramic Composites Prepared by Direct Solution Spin Coating

Magnetoelectric (ME) composite structures of Pb(Zr_0.52Ti_0.48)O₃ (PZT) and CoFe₂O₄ (CFO) were prepared by directly growing PZT films on highly dense CFO ceramics via a simple solution spin coating, rather than by conventional high-temperature cofiring. An obvious ME response, which had the same bias-dependent trend as the piezomagnetic coefficient of CFO ceramics, was observed in such film-on-bulk ceramic composites. It was found that the PZT films showed a good ferroelectric feature, and the ME response of the composites strongly depended on the resistivity of the CFO ceramics as both a substrate and a bottom electrode. The results suggest plenty of room for further enhancing the ME response of such films-on-ceramic substrate composites.     

Fatigue of Field-Induced Strain in Antiferroelectric Pb0.97La0.02(Zr0.77Sn0.14Ti0.09)O3 Ceramics

The fatigue of mechanical strain induced by electric fields was investigated for antiferroelectric Pb_0.97La_0.02(Zr_0.77Sn_0.14Ti_0.09)O₃ ceramics. The material shows a high resistance to fatigue owing to bipolar electric cycling up to 10⁸ cycles. The strain hysteresis loop is still fairly symmetric, whereas the maximum field-induced strain decreases by only 30% of its initial value. The fatigued samples show a damaged microstructure with dendritic macrocracks and microcrack clouds. The fatigue is attributed to a combination of electrochemical and mechanical mechanisms.     

Structure-Property Phase Diagram of BaZrxTi1−xO3 System

In the course of searching environmental friendly lead-free relaxor ferroelectrics a complete phase diagram of barium zirconate titanate, Ba(Zr _x Ti_{1− x} )O₃ system with compositions 0.00≤ x ≤1.00 has been developed based on their dielectric behavior. It has been shown that BaZr _x Ti_{1− x} O₃ system depending on the composition, successively depicts the properties extending from simple dielectric (pure BaZrO₃) to polar cluster dielectric, relaxor ferroelectric, second order like diffuse phase transition, ferroelectric with pinched phase transitions and then to a proper ferroelectric (pure BaTiO₃). A comprehensive structure–property correlation of BaZr _x Ti_{1− x} O₃ ceramics has been studied to understand the various ferroelectric phenomena in the whole phase diagram.     

Characteristics of High-Q Microwave Dielectric Ceramics Nd(Co1/2Ti1/2)O3 With CuO Addition

We report the microwave dielectric properties and the microstructures of Nd(Co_1/2Ti_1/2)O₃ ceramics prepared by the conventional solid-state route. The prepared Nd(Co_1/2Ti_1/2)O₃ exhibits a mixture of Co and Ti showing a 1:1 order in the B site. Lowering the sintering temperature (as low as 1260°C) and promoting the densification of Nd(Co_1/2Ti_1/2)O₃ ceramics could be effectively achieved by adding CuO (up to 0.75 wt%). At 1350°C, Nd(Co_1/2Ti_1/2)O₃ ceramics with 0.5 wt% CuO addition possess a dielectric constant (ɛ_r) of 27.6, a Q × f value of 165 000 GHz (at 9 GHz), and a temperature coefficient of resonant frequency (τ_f) of −20 ppm/°C. By comparing with pure Nd(Co_1/2Ti_1/2)O₃ ceramics, incorporating additional CuO helps to render a dielectric material with a higher dielectric constant, a smaller τ_f value, and a 20% dielectric loss reduction, which makes it a very promising candidate for applications requiring low microwave dielectric loss.     

Control of Leakage Resistance in Pb(Zr,Ti)O3 Thin Films by Donor Doping

Donor doping, with La and Nb, has been used successfully to improve the leakage resistance of Pb(Zr,Ti)O₃ (PZT) films. Donor doping of Pb(Zr_0.5Ti_0.5)O₃ films has led to an improvement in the leakage resistance of over 2 1/2 orders of magnitude at elevated temperatures (T 100°C). The effect on leakage resistance is the same for the A-site (La) and B-site (Nb) dopants. However, the improvement is only about 1 order of magnitude near room temperature. This temperature effect is due to an increase in the transition temperature from a low activation energy mechanism to a higher activation energy mechanism. Similar improvements in leakage resistance have also been obtained by increasing the Pb concentration in the starting solution, which implies that Pb vacancies are the dominant acceptor species in the undoped films. In addition, donor doping has been effective in improving the electrical breakdown strength at elevated temperatures. Consequently, donor-doped PZT films have been shown to be superior to undoped films for applications requiring high leakage resistance, such as decoupling capacitors.     

Effect of Excess PbO on the Sintering Characteristics and Dielectric Properties of Pb(Mg1/3Nb2/3)O3–PbTiO3-Based Ceramics

Additions of excess PbO to the perovskite Pb[(Mg_1/3Nb_2/3)_0.92Ti_0.08]O₃ solid solution enhanced the formation of a liquid phase at 840°C, which served as a densification aid for the ceramics. The liquid phase allowed elimination of pores and promoted grain growth during sintering. With additions of 1 to 2 wt% excess PbO, densities in excess of 97% of theoretical were obtained at a sintering temperature of 950°C. The peak dielectric constants of the resulting ceramics were over 18 000 at 30°C and dissipation factors less than 1%. Additions of PbO in excess of 2 wt% resulted in inferior dielectric properties due mainly to the dilution of the ferroelectric phase.     

Piezoelectric Properties of Pb[Zr0.45Ti0.5-xLux(Mn1/3Sb2/3)0.05]O3 Ceramics

The piezoelectric properties of Pb[Zr_0.45Ti_{0.5- x} Lu _x (Mn_1/3-Sb_2/3)_0.05]O₃ ceramics, with 0 lessthan equal to x lessthan equal to 0.03, have been investigated. The partial substitution of Ti⁴⁺ with Lu³⁺ permitted improvement of the electromechanical coupling factor ( k _p), the dielectric constant (epsilon^T₃₃), and the piezoelectric constant ( d ₃₃), while the dielectric loss (tan delta) increased and the mechanical quality factor ( Q _m) decreased with an increase of x . A pertinent piezoelectric material for actuator applications was Pb[Zr_0.45Ti_0.48Lu_0.02(Mn_1/3Sb_2/3)_0.05]O₃, and the piezoelectric properties were k _p = (58.5 ± 0.5)%, epsilon^T₃₃ = 32 ± 25, d ₃₃ = (373 ± 6) 10^-12 C/N, Q _m = 714 ± 22, and tan delta = (0.98 ± 0.03)%.