In-Plane Polarized 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 Thin Films

Ferroelectric 0.7Pb(Mg_1/3Nb_2/3)O₃–0.3PbTiO₃ (PMN-PT) thin films were deposited on ZrO₂/SiO₂/silicon substrates using a chemical-solution-deposition method. Using a thin PZT film as a seed layer for the PMN-PT films, phase-pure perovskite PMN-PT could be obtained via rapid thermal annealing at 750°C for 60 s. The electrical properties of in-plane polarized thin films were characterized using interdigitated electrode arrays on the film surface. Ferroelectric hysteresis loops are observed with much larger remanent polarizations (∼24 μC/cm²) than for through-the-thickness polarized PMN-PT thin films (10–12 μC/cm²) deposited on Pt/Ti/Si substrates. For a finger spacing of 20 μm, the piezoelectric voltage sensitivity of in–plane polarized PMN-PT thin films was ∼20 times higher than that of through-the-thickness polarized PMN-PT thin films.     

Sequential Combination of Constituent Oxides in the Synthesis of Pb(Fe1/2Nb1/2)O3by Mechanical Activation

Pb(Fe_1/2Nb_1/2)O₃(PFN) has been successfully synthesized via a novel mechanical activation of mixed oxides and columbite precursor consisting of lead oxide and FeNbO₄. A nanocrystalline perovskite phase 5–15 nm in crystallite size was formed after 30 h of mechanical activation at room temperature for both types of starting materials. However, the nanocrystalline PFN phase derived from the mixed oxides of PbO, Fe₂O₃, and Nb₂O₅is unstable, and develops pyrochlore phases when calcined at 500°–900°C, while no pyrochlore phase is observed for the material derived from the columbite precursor consisting of PbO and FeNbO₅. Different sintering behavior and dielectric properties were also observed between the two types of PFN. These differences are accounted for by the compositional inhomogeneity in the material derived from the mixed oxides, as was revealed by Raman spectroscopic studies. This suggests that mechanical activation is analogous to thermal activation, where the phase development is strongly dependent on the sequence of combining the constituent oxides.     

Direct Compositional Analysis of Ordered Domains in Pure and La-Doped Pb(Mg1/3Nb2/3)O3 by Analytical Electron Microscopy Techniques

The ordered domain structures in Pb(Mg_1/3Nb_2/3)O₃(PMN) and Pb_{1– x} La _x (Mg_1/3Nb_2/3)O₃ are identified using high-resolution transmission electron microscopy (HRTEM) and nanobeam diffractometry (NBD). The chemical compositions in the ordered domains and in the disordered matrices are also acquired using energy-dispersive spectroscopy (EDS). The best matching computer-simulated HRTEM image has a Mg²⁺/Nb²⁺ ratio of return ½. There is no obvious chemical composition difference between the ordered domains and the disordered matrices. The number of the normalized total positive valence electrons remains almost constant in the ordered domains and in the disordered matrices for all the samples. The reason for the growth of the ordered domains in La-doped PMN also is discussed.     

Analysis of Ferroelectric Domain Switching in 0.7Pb(Mg1/3Nb2/3)O3·0.3PbTiO3: Heterogeneous Nucleation

Polarization reversal and domain dynamics were investigated in 0.7Pb(Mg_1/3Nb_2/3)O₃·0.3PbTiO₃ using a method of current transients. Investigations were performed as a function of applied electric field. The kinetics of the transients were modeled to a stretched exponential-type function.     

Dielectric-State Analysis in Solid-Solution Pb(Yb1/2Ta1/2)O3–Pb(Lu1/2Nb1/2)O3

The structure and temperature dependence of complex lead perovskite dielectrics were investigated for the system (1 − x )Pb(Yb_1/2Ta_1/2)O₃– x Pb(Lu_1/2Nb_1/2)O₃. Superlattice reflections for the compositions 0.8 < x < 1.0 were observed by X-ray diffractometry, and the temperature-composition dielectric-state diagram was determined. In the present study, the disordered middle composition, with 0.2 < x < 0.8, showed a diffuse paraelectric–ferroelectric phase transition, whereas the ordered end compositions, with 0 ≤ x < 0.2 and 0.8 < x ≤ 1.0, revealed successive sharp paraelectric–antiferroelectric and weak antiferroelectric–ferroelectric phase transitions. The dielectric state was confirmed by examining the variation of polarization ( P ) with electric field ( E ).     

Short-Range Ordering in Pb(B'1/3B2/3)O3-Type Relaxor Ferroelectrics

The formation of nonstoichiometric 1:1 ordered nanodomains, which promote B-site microcompositional fluctuation, is known to be one of the most-efficient ways of enhancing diffuse phase transition (DPT) characteristics. A new theory regarding the 1:1 short-range ordering has been developed to account for the observed inability to grow ordered domains beyond the nanometer scale. The dispersion entropy associated with the formation of negatively charged ultrafine domains and the mode of the counter-ion distribution at the domain/matrix interface both have a significant role in controlling the equilibrium ordered domain size.     

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.     

Morphotropic Phase Boundary in the Pb(Zn1/3Nb2/3O3)-BaTiO3-PbTiO3 System

The morphotropic phase boundary (MPB) in the relaxor ferroelectric system Pb(Zn_1/3Nb_2/3O₃)-BaTiO₃-PbTiO₃ (PZN-BT-PT) with 15 mol% BT was investigated through dielectric permittivity and high-temperature X-ray diffraction measurements. It was revealed that MPB is a broad composition region extending from 12 to 18 mol% PT, within which the temperatures of the permittivity maximum are close to the ending temperatures for the phase transformation from coexisting rhombohedral and tetragonal phases to cubic phase on heating. When the specimen is cooled, the starting temperatures for the rhombohedral-to-tetragonal phase transition increase with increasing PT content. The large thermal hysteresis observed by X-ray diffraction is caused by the phase transformation between rhombohedral and tetragonal phases. On cooling, the MPB curves toward the PT-rich side, so that ceramics within this composition range undergoe successive phase transitions from cubic to rhombohedral and from rhombohedral to tetragonal phase. The diffuseness of the paraelectric-to-ferroelectric phase transition is remarkably decreased by the addition of PT. The enhanced dielectric permittivity peak values for the MPB compositions are correlated with the reduced lattice distortion and phase coexistence.     

Mechanical Activation-Assisted Synthesis of Pb(Fe2/3W1/3)O3

Perovskite Pb(Fe_2/3W_1/3)O₃ (PFW) was prepared via a mechanical activation-assisted synthesis route from mixed oxides of PbO, Fe₂O₃, and WO₃. The mechanically activated oxide mixture, which exhibited a specific area of >10 m²/g, underwent phase conversion from nanocrystalline lead tungstate (PbWO₄) and pyrochlore (Pb₂FeWO_6.5) phases on sintering to yield perovskite PFW, although the formation of perovskite phase was not triggered by mechanical activation. When heated to 700°C, >98% perovskite phase was formed in the mechanically activated oxide mixture. The perovskite phase was sintered to a density of ∼99% of theoretical density at 870°C for 2 h. The sintered PFW exhibited a dielectric constant of 9800 at 10 kHz, which was ∼30% higher than that of the PFW derived from the oxide mixture that was not subjected to mechanical activation.     

A-Site and B-Site Order in (Na1/2La1/2)(Mg1/3Nb2/3)O3 Perovskite

(Na_1/2La_1/2)(Mg_1/3Nb_2/3)O₃ undergoes a series of phase transitions that involve cation order on the A- and B-sites of the parent perovskite structure. At high temperatures both sites contain a random distribution of cations; below 1275°C a 〈111〉 layering of Mg and Nb leads to the formation of a 1:2 ordered structure with a monoclinic supercell. A second transition was observed at 925°C, where the Na and La cations order onto alternate A-site positions along the 〈001〉 direction of the parent subcell. By quenching samples from above 1275°C to preserve the disorder on the B-site, a fourth variant of this compound was obtained by inducing A-site order through a subsequent anneal at 900°C. Although the changes in structure do not produce significant alterations in the relative permittivity (ɛ_r∼ 35), they do have a significant effect on the value of the temperature coefficient of the capacitance.     

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.     

Unique Dielectric Behavior of 0.6Pb(Ni1/2W1/2)O3·0.4PbTiO3 Derived from Mechanical Activation

0.6Pb(Ni_1/2W_1/2)O₃·0.4PbTiO₃(0.6PNW·0.4PT) of complex perovskite structure is successfully synthesized by mechanical activation of mixed oxide composition, followed by sintering at 950°C. It exhibits a considerably stable temperature dependence of dielectric constant over the wide temperature range of −120° to 20°C, although there occurs a dielectric peak at around 74°C. Raman spectroscopic studies show the coexistence of tetragonal and pseudocubic perovskite phases on sintering at 950°C, which are attributed to the inhomogeneous distribution of PbTiO₃ arising from mechanical activation. The dielectric behavior can be fine tuned by thermal annealing at 750°C, leading to phase redistribution in PNW-PT.     

Preparation of Dense Lead Magnesium Niobate–Lead Titanate (Pb(Mg1/3Nb2/3)O3–PbTiO3) Ceramics by Spark Plasma Sintering

The effect of spark plasma sintering (SPS) on the densification behavior of Pb(Mg_1/3Nb_2/3)O₃–PbTiO₃ ceramics has been investigated. Specimens with a density of >99% of the theoretical density (TD) were obtained using SPS treatment at 900°C. Through normal sintering at 1200°C, however, the density of the specimen was only ∼92% of TD.     

Dielectric Properties and Relaxation in (1−x)BiScO3–xBa(Mg1/3Nb2/3)O3 Solid Solutions

The dielectric properties and frequency dispersion associated with a dielectric relaxation were evaluated within the perovskite (1− x )BiScO₃– x Ba(Mg_1/3Nb_2/3)O₃ solid solution systems (0.7 ≤ x ≤ 1). With increasing BiScO₃, the room-temperature dielectric permittivity at low frequency (100 Hz) increased up to 115 at x = 0.7, and a dielectric relaxation phenomenon was evident. Relaxation parameters were analyzed using several Arrhenius-type equations, and the microwave dielectric property measurement using rectangular wave-guide method enabled confirmation of the extrapolated value of the Arrhenius plot. The result of the microwave dielectric property measurement was also checked with J -function fitting based on the frequency-dependent Gaussian distribution of the associated dielectric loss data at low frequency.     

Mechanosynthesis and Thermal Stability of Piezoelectric Perovskite 0.92Pb(Zn1/3Nb2/3)O3–0.08PbTiO3 Powders

The mechanosynthesis of piezoelectric perovskite 0.92Pb(Zn_1/3Nb_2/3)O₃–0.08PbTiO₃ (PZN–PT) by direct mechanochemical activation of the constituent oxides has been studied by X-ray diffraction (XRD) and transmission electron microscopy (TEM). This and the PbO flux method are the only two procedures that have succeeded in synthesizing this phase, which has recently been shown to present very high electromechanical response. The thermal stability of the single perovskite phase powders has been studied by differential thermal analysis/thermogravimetry and by high-temperature XRD as a function of mechanical activation time and pressure. The phase was found to transform into a pyrochlore type structure at temperatures above 400°C. The transformation presented a significant time dependence, and it was slowed down by increasing mechanical activation time and by the application of pressures by hot pressing. Sintering experiments were accomplished and 85% density, 77% perovskite-phase ceramics were obtained after heating at 1000°C for 1 h. Hot pressing at this temperature failed to increase the percentage of perovskite phase. Results are discussed, and procedures for obtaining dense single-phase PZN–PT-based ceramics with ultrahigh piezoelectricity are proposed.     

Relaxor Behavior of the 0.9BaTiO3–0.1La(Mg1/2Ti1/2)O3 Solid Solution

Low-frequency dielectric response of air- and oxygen-sintered ceramics with the composition 0.9BaTiO₃–0.1La(Mg_1/2Ti_1/2) O₃ (0.9BT–0.1LMT) has been studied in the temperature range of 12–550 K. In comparison with pure BT, in 0.9BT–0.1LMT the dielectric permittivity maximum is shifted by almost 300 K toward lower temperatures. Both real and imaginary parts of dielectric permittivity of the solid solution, in the range 12–150 K, show a strong frequency-dependent behavior, which is typical of relaxors. On the basis of the model of exponential cluster size distribution and the Cole–Cole equation, the degree of interaction between the polar clusters was estimated. It was shown that the oxygen vacancies arising during sintering at high temperatures did not affect noticeably the relaxor properties of the material. The role of heterovalent La³⁺/Ba²⁺ and Mg²⁺/Ti⁴⁺ substitutions in the relaxor behavior formation is discussed.     

(Bi1/2Na1/2)TiO3–Ba(Cu1/2W1/2)O3 Lead-Free Piezoelectric Ceramics

(Bi_1/2Na_1/2)TiO₃ with 0–6 mol% Ba(Cu_1/2W_1/2)O₃ (BNT-BCW), a new member of the BNT-based group, has been prepared following the conventional mixed oxide route. The compacted bodies were sintered at 1130°C for 2 h to get dense ceramics. The addition of BCW into BNT ceramics facilitated the poling process because of a reduction in leakage current. 0.995BNT·0.005BCW ceramics exhibit a relatively high piezoelectric constant ( d ₃₃= 80 × 10⁻¹² C/N) and a relatively low dielectric loss (tan δ= 1.5%). Increased amount of BCW was found to increase the dielectric constant and loss of BNT-BCW ceramics and to suppress the grain growth. During sintering, some BCW diffuses into the lattice of BNT to form a solid solution and some remains on the grain boundaries.     

Structure–Property Relations in xBaTiO3–(1−x)La(Mg1/2Ti1/2)O3 Solid Solutions

The microwave dielectric properties and microstructures of compounds in the solid solution series x BaTiO₃–(1− x )La(Mg_1/2Ti_1/2)O₃ (BTLMT) have been investigated. The structural phase transitions that occur as a function of x have been studied and are related to changes in the dielectric properties. For compounds where x ≤ 0.1, X-ray diffraction (XRD) showed evidence of 1:1 ordering between Mg and Ti cations. For x ≤ 0.3, XRD and electron diffraction revealed that compounds were tilted in both antiphase and in-phase. However, for 0.3 < x < 0.7, only antiphase tilting was present. The temperature coefficient of resonant frequency (τ_f) vs the relative permittivity (ɛ_r) was linear until x = 0.5 at which point in the solid solution the transition to a nontilted structure resulted in nonlinear behavior. τ_f values close to zero (−2 ppm/°C) were achieved at x = 0.5 (ɛ_r∼ 60), which had a quality factor ( Q · f _o) of 9600 GHz.