Synthesis and Dielectric Properties of Solution Sol-Gel-Derived 0.9Pb(Mg1/3Nb2/3)O3–0.1PbTiO3 Ceramics

A solution sol-gel method has been developed to prepare 0.9Pb(Mg_1/3Nb_2/3)O₃-0.1PbTiO₃ (0.9PMN-0.1PT) ceramics. During the processing the gel first converted to cubic pyrochlore phase at a calcination temperature of 600°C followed by the formation of pure perovskite phase at 775°C. The ceramics sintered at 1250°C for 4 h showed ≈98% of the theoretical density. The room-temperature dielectric constant of the pellets sintered at 1250°C showed a maximum value of 25035 at 1 kHz. Sintering studies at different temperatures revealed that the dielectric constant increased with increasing grain size in these ceramics.     

Large Pyroelectric Effect in Relaxor-Based Ferroelectric Pb(Mg1/3Nb2/3)O3–PbTiO3 Single Crystals

The pyroelectric properties of (1− x )Pb(Mg_1/3Nb_2/3)O_{3− x} PbTiO₃ (PMN− x PT) single crystals with various compositions and orientations have been investigated using a dynamic method. Excellent pyroelectric performances can be achieved in 〈111〉-oriented rhombohedral PMN− x PT (0.24≤ x ≤0.30) crystals, where the measurement direction corresponds to the polar axis of the crystal. At room temperature, the pyroelectric coefficient and the detectivity figure of merit ( F _d ) for the 〈111〉-oriented PMN–0.28PT single crystal are 8.55 × 10⁻⁴ C·(m²·K)⁻¹ and 9.89 × 10⁻⁵ Pa^−1/2 (100 Hz), respectively, superior to those of the widely used pyroelectric materials. They are also weak temperature dependent and nearly independent of frequency. These outstanding pyroelectric performances make the single crystals a promising candidate for uncooled infrared detectors and thermal imagers.     

Dielectric and Pyroelectric Properties of 〈111〉-Oriented Fe-Doped 0.62Pb(Mg1/3Nb2/3)O3–0.38PbTiO3 Single Crystals

Fe-doped 0.62Pb(Mg_1/3Nb_2/3)O₃–0.38PbTiO₃ (PMN–0.38PT) single crystals were grown by a modified Bridgman technique. Two kinds of single crystals with different iron ion molar ratios, (i) 0.2 mol% and (ii) 1.0 mol%, were obtained. The effect of doping iron ions on the dielectric and pyroelectric properties of the 〈111〉-oriented PMN–0.38PT single crystals was examined. The temperature of the permittivity maximum ( T _m) exhibits no dispersion behavior and decreases with increasing doping concentration. The dielectric loss of the 0.2 mol% Fe-doped PMN–0.38PT single crystal is much lower than that of the high dopant content crystal (1.0 mol%) and undoped crystal, which makes it possess excellent pyroelectric performance. By a dynamic method, the measured pyroelectric coefficient and detectivity figure of merit ( F _D) of 0.2 mol% Fe-doped PMN–0.38PT single crystal are 439 μC/m²·K and 56.3 μPa^−1/2, respectively, both better than those of widely used pyroelectric single crystal LiTaO₃. The results imply that the single crystal is a promising candidate for infrared detectors and other pyroelectric applications. The mechanism of doping effect was also discussed based on the principles of crystal chemistry.     

Synthesis of 0.4Pb(Mg1/3Nb2/3)O3–0.3Pb(Mg1/2W1/2)O3–0.3PbTiO3 Ceramics by Metal Alkoxide Method, and Its Dielectric Properties

0.4Pb(Mg_1/3Nb_2/3)O₃–0.3Pb(Mg_1/2W_1/2)O₃–0.3PbTiO₃+ x MgO ( x = 0 to 0.04) were prepared by a metal alkoxide method. The percent of perovskite phase of the calcined powders increased with increased calcination temperatures. About 89% of perovskite phase was obtained at 1050°C. The dielectric constant of the pellets fired at 1100°C was increased by the addition of 10 wt% excess Mg(OC₂H₅)₂ and had a maximum value of 7532 at 1 kHz.     

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.     

Piezoelectric Resonances, Linear Coefficients and Losses of Morphotropic Phase Boundary Pb(Mg1/3Nb2/3)O3–PbTiO3 Ceramics

A method based on the use of four piezoelectric resonances for three sample geometries that allows obtaining the full set of linear electric, mechanical, and electromechanical coefficients, and all related losses of a piezoelectric ceramic has been applied to Mn-doped 0.655Pb(Mg_1/3Nb_2/3)O₃–0.345PbTiO₃ at the morphotropic phase boundary (MPB PMN–PT). Length-poled MPB PMN–PT ceramic plates presented piezoelectric shear double resonances associated with a thickness gradient of tetragonal and rhombohedral (or monoclinic) phases that originated during poling. The versatility of the method still allowed addressing these double resonances and obtaining all the linear coefficients and losses of the well-poled material. These are given for MPB PMN–PT and compared with those of a Navy type II Pb(Zr,Ti)O₃ (PZT) ceramic. MPB PMN–PT presents piezoelectric coefficients as high as soft PZT but significantly lower losses, and so less overheating and hysteresis under high driving fields. Its thermal stability has been studied up to 100°C, and the temperature dependence of a number of linear coefficients and of the thickness and planar coupling factors and frequency constants of disks has been obtained. The latter thickness parameters hardly changed with temperature, while planar ones showed a relative variation of 10%.     

Effects of Silver and Palladium Doping on the Dielectric Properties of 0.9Pb(Mg1/3Nb2/3)O3–0.1 PbTiO3 Ceramic

The doping of silver and palladium into a 0.9Pb-(Mg_1/3Nb_2/3)O₃–0.1PbTiO₃ (PMN–PT) ceramic has been investigated. It was found that Ag could be incorporated into the PMN–PT lattice, though this was almost impossible with Pd. Doping at up to 0.2 mol% of Ag and Pd reduced the maximum dielectric constant ( K _max) from 21000 to 14000 without any conspicuous change in physical properties. Order–disorder transitions in the perovskite structure contributed to the decrease in K _max, since the diffuseness parameter, δ, which represents the degree of the order-disorder relationship, increased with Ag doping. However, addition of more than 0.2 mol% increased K _max. Increases in grain size and in the perovskite ratio contributed to this increase. The dielectric properties of Ag/Pd-doped samples were intermediate between the Ag- and Pd-doped samples.     

Single-Calcination Synthesis of Pyrochlore-Free 0.9Pb(Mg1/3Nb2/3)O3–0.1PbTiO3 and Pb(Mg1/3Nb2/3)O3 Ceramics Using a Coating Method

A coating approach for synthesizing 0.9Pb(Mg_1/3Nb_2/3)O₃–0.1PbTiO₃ (0.9PMN–0.1PT) and PMN using a single calcination step was demonstrated. The pyrochlore phase was prevented by coating Mg(OH)₂ on Nb₂O₅ particles. Coating of Mg(OH)₂ on Nb₂O₅ was done by precipitating Mg(OH)₂ in an aqueous Nb₂O₅ suspension at pH 10. The coating was confirmed using optical micrographs and zeta-potential measurements. A single calcination treatment of the Mg(OH)₂-coated Nb₂O₅ particles mixed with appropriate amounts of PbO and PbTiO₃ powders at 900°C for 2 h produced pyrochlore-free perovskite 0.9PMN–0.1PT and PMN powders. The elimination of the pyrochlore phase was attributed to the separation of PbO and Nb₂O₅ by the Mg(OH)₂ coating. The Mg(OH)₂ coating on the Nb₂O₅ improved the mixing of Mg(OH)₂ and Nb₂O₅ and decreased the temperature for complete columbite conversion to ∼850°C. The pyrochlore-free perovskite 0.9PMN–0.1PT powders were sintered to 97% density at 1150°C. The sintered 0.9PMN–0.1PT ceramics exhibited a dielectric constant maximum of ∼24 660 at 45°C at a frequency of 1 kHz.     

High Strain, 〈001〉 Textured 0.675Pb(Mg1/3Nb2/3)O3–0.325PbTiO3 Ceramics: Templated Grain Growth and Piezoelectric Properties

Lead magnesium niobate–lead titanate, 0.675Pb(Mg_1/3Nb_2/3)O₃–0.325PbTiO₃ (PMN–32.5PT) ceramics were textured (grain-oriented) in the 〈001〉-crystallographic direction by the templated grain growth process. The textured PMN–32.5PT ceramics were produced by orienting {001}-SrTiO₃ (ST) platelets (∼10 μm in diameter and ∼2-μm thickness) in a submicron PMN–32.5PT matrix. The templated growth of 〈001〉-oriented PMN–32.5PT grains on the ST platelets resulted in textured ceramics with ∼70% Lotgering factor and >98% theoretical density. Unlike most lead-based ceramics, excess PbO was not needed for sintering or grain growth. Based on unipolar stain-field measurements at 0.2 Hz, the textured samples displayed >0.3% strain at 50 kV/cm. Low-field d ₃₃-coefficients of >1600 pC/N (<5 kV/cm) were measured directly from unipolar measurements. The low drive field d ₃₃-piezoelectric coefficient of the highly textured samples is two times greater than polycrystalline PMN–32.5PT.     

Piezoelectric Properties of Pb(Mg1/3Nb2/3)O3—PbTiO3—PbZrO3 Solid Solution Ceramics

Ceramic and electrical properties and crystal structures of the system Pb(Mg_l/3Nb_2/3- PbTiO₃-PbZrO₃ are described. The system is composed of three crystal phases at room temperature: pseudocubic, tetragonal, and rhombohedral. A high dielectric constant and radial coupling coefficient and low resonant resistance were obtained for the compositions near the morphotropic transformation. The composition Pb(Mg_l/3Nb_2/3)_0.4375Ti_0.4375Zr_0.125O₃ had the lowest temperature coefficient of resonant frequency.     

Ferroelectric 90° Domain Evaluation in Tetragonal Pb(Mg1/3Nb2/3)O3–PbTiO3 Ceramics

The domain structure of ferroelectrics changes during poling has a direct influence on the macroscopic properties of the materials. The intensity variation of the different X-ray diffraction (XRD) pattern profiles was used to identify the percentage of 90° domain reorientation in the tetragonal phase of Pb(Mg_1/3Nb_2/3)O₃–PbTiO₃ (PMN–PT) ceramics after poling. The results are consistent with the change of piezoelectric properties. In addition, by using XRD patterns, a spatial distribution of polarization in a well-poled 0.62PMN–0.38PT ceramics has been determined and was found to be best described by the Cauchy function W _00l (φ)=1/(1+0.023φ²).     

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.     

Single Crystals of Pb(Mg1/3Nb2/3)O3—35 mol% PbTiO3 from Polycrystalline Precursors

A potentially more cost-efficient method of growing single-crystal relaxor-based ferroelectric materials has been investigated. Seed single crystals of Pb(Mg_1/3Nb_2/3)O₃(PMN)—;35 mol% PbTiO₃(PT) were embedded within polycrystalline powders and annealed at temperatures from 900° to 1200°C. The boundary of the single crystal migrated through the polycrystal matrix under the influence of grain boundary curvature; growth distances of several millimeters were observed, verifying the feasibility of the approach. The grown single crystals exhibited macroscopic cubic growth morphologies with (100) faces. Strain levels as high as 0.68% under an electric field of 30 kV/cm were observed in initial measurements.     

A Polyethylene Glycol-Modified Solid-State Reaction Route to Synthesize Relaxor Ferroelectric Pb(Mg1/3Nb2/3)O3–PbTiO3 (PMN–PT)

By introducing polyethylene glycol (PEG) to the conventional simultaneously mixed oxide reaction route, the 0.65Pb(Mg_1/3Nb_2/3)–0.35PbTiO₃ (0.65PMN–0.35PT) powders and ceramics with pure perovskite phase have been successfully synthesized. It is found that PEG interacts with PbO oxide in a way favoring the formation of the desired perovskite phase. As a result, pyrochlore-free 0.65PMN–0.35PT powders are synthesized at a low temperature of 850°C. The ceramics sintered at 1000°C show uniform grains with the size ranging from 1 to 3 μm. The room temperature dielectric constant is 3440. The maximum dielectric constant is 16 220 at 1 kHz. This method can be applied to the synthesis of other Pb-containing and Bi-containing ferroelectric materials, especially the relaxor-type ferroelectrics in which the pyrochlore phase is difficult to eliminate.     

Preparation of 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 Thin Films Via a Polyvinylpyrrolidone-Assisted Aqueous Sol–Gel Process and Dielectric Properties

Pb(Mg_1/3Nb_2/3)O₃–PbTiO₃ (PMN–PT) thin films were prepared by spin coating using aqueous solutions of metal salts containing polyvinylpyrrolidone, where niobium oxide layers and lead—magnesium–titanium oxide layers were laminated on Pt(111)/TiO _x /SiO₂/Si(100) substrates and fired at 750° or 800°C. 250 ± 20 nm thick 0.7PMN–0.3PT thin films of a single-phase perovskite could be prepared, and the film fired at 750°C had dielectric constants and dielectric loss of 1900 ± 350 and 0.13 ± 0.03, respectively, exhibiting polarization-electric field hysteresis with a remanent polarization of 5.1 μC/cm² and a coercive field of 21 kV/cm.     

Kinetics of {001} Pb(Mg1/3Nb2/3)O3–35 mol% PbTiO3 Single Crystals Grown by Seeded Polycrystal Conversion

The kinetics of {001}-oriented Pb(Mg_1/3Nb_2/3)O₃–35 mol% PbTiO₃ (PMN–35PT) single crystals grown by seeded polycrystal conversion were systematically quantified as a function of excess PbO liquid phase. The coarsening behavior of the corresponding matrix grains was similarly quantified. Single-crystal seed plates were embedded in a matrix of PMN-35PT with varying amounts of liquid phase (PbO) content in the range of 0 to 5 vol% and annealed at 1150°C for 0–10 h. Apparent maxima in the growth rates were observed at a PbO content of ∼3 vol% for both the single crystal and matrix grains. In both cases, the growth data were found to most closely follow cubic growth kinetics. Implications regarding the effect of PbO volume fraction on the matrix and single-crystal growth mechanisms are discussed.     

Phase Transitions in Pb(Mg1/3Nb2/3)O3–PbTiO3 Studied by Low-Frequency Internal Friction Measurement

The low-frequency internal friction (0.1 Hz< f <10 Hz) of (100− x %)Pb(Mg_1/3Nb_2/3)O₃− x %PbTiO₃ ( x =0, 13, 23, 33) ceramics has been measured in the temperature range between 90 and 500 K. All of the internal friction peaks show a height that is inversely proportional to the measurement frequency, thus they can be attributed to first-order phase transitions. The phase transitions between rhombohedral, monoclinic, and tetragonal phases in ceramics with x =33 occur over a very broad temperature range from 150 to 400 K, indicating that the giant piezoelectric effect in this material may be attributed to a field-induced phase transition process.     

Texture Control of Sol-Gel Derived Pb(Mg1/3Nb2/3)O3–PbTiO3 Thin Films Using Seeding Layer

Lead magnesium niobium titanate (PMNT) thin films with a composition near the morphotropic phase boundary were prepared on conventional Pt(111)/Ti/SiO₂/Si substrates using a modified sol-gel process. A PbO seeding layer was introduced to the interface between the PMNT layer and the substrate to enhance the [001]-preferential orientation of the PMNT film. Single-phase perovskite PMNT films with highly [001]-preferential orientation were obtained at reduced annealing temperatures compared with the PMNT films directly deposited on the same substrates. The dielectric and ferroelectric properties of the prepared PMNT films were evaluated as a function of annealing temperature.