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.     

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.     

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.     

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).     

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.     

Sintering Behavior of Cadmium-Doped Pb(Ni1/3Nb2/3)O3–PbZrO3–PbTiO3 Ceramics

Substituting Cd²⁺ ions into the A and B sites in a Pb(Ni_1/3Nb_2/3)O₃PbZrO₃PbTiO₃ (PNNPZPT) ternary perovskite material made it possible to determine the effects of the Cd²⁺ ion substitution site on sintering behavior. The substitution site of the Cd²⁺ ion was identified by using X-ray photoelectron spectroscopy spectra. Although Cd²⁺ ions were substituted into the A and B sites in PNNPZPT, the Cd²⁺ ions preferred the A site over the B site. When Cd²⁺ ions replaced Pb²⁺ ions, a weight gain was observed during sintering. On the other hand, replacing Ni2 ions with Cd²⁺ ions promoted weight loss. Those weight changes indicated that Cd²⁺ ions change the bonding strength between the B-site cations and the oxygen of the octahedron in a perovskite structure. Density was influenced by the Cd²⁺ ion substitution site, and the A-site-doped compositions had higher densities than the B-site-doped compositions.     

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.     

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.     

Electromechanical Properties of Some Pb (Mg1/3Nb2/3–PbTiO3–(Ba,Sr)TiO3 Ceramics: I

Compositional variation within the Pb(Mg_1/3Nb_2/3) O₃–PbTiO₃–(Ba, Sr)TiO₃ (hereafter PMN–PT–BT,ST) ternary (6.4% PT% 14.1%, 1.25% BT,ST% 2.5%) results in major changes in induced strain and hysteresis. For the 1.25% BT family, the increase in strain correlates with an increase in T _max, while the dielectric loss is uncorrelated with hysteresis and strain. In addition, weak field aging (which is not reset by application of field) shows little effect on strain and hysteresis for drive fields of > 0.2 MV/m. The vary narrow polarization-fields loops (virgin curvesnearly indistinguishable from subsequent cycles) show that weak-field permittivity is a good approximation to the high-field permittivity. is a good approximation to the high-field Permittivity. Although these data clarify the frequency ( T _max is linearly dependent on the logarithm of the frequency) effect on weak-field dielectric behavior, they do not directly address the question of meaningful extrapolation of high-field strain with frequency. In particular, the question remains as to whether the high-field permittivity and strain are frequency dependent. In future papers we will address this question by a combination of measurement techniques as functions of frequency.     

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.     

Effects of La2O3 Addition and PbO Excess on the Transmittance of PbZrO3–PbTiO3–Pb(Zn1/3Nb2/3)O3 Ceramics by Spark Plasma Sintering

The effects of La₂O₃ addition and PbO excess on the microstructures and optical properties of PbZrO₃–PbTiO₃–Pb(Zn_1/3Nb_2/3)O₃ (PZ–PT–PZN) ceramics prepared by spark plasma sintering were investigated. When 1 mol% La₂O₃ was added, the highest transmittance of 35% at 700 nm for PZ–PT–PZN ceramics was obtained. The improved transmittance was attributed to the increased relative density and the decreased optical anisotropy. The samples containing more than 1 mol% La₂O₃ showed decreased transmittance, due to the appearance of secondary phases. The transmittance of PZ–PT–PZN ceramics increased slightly to 29% at 700 nm with increasing amount of excess PbO up to 10 mol% and thereafter decreased rapidly.     

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%.     

Dielectric Properties of Pb(Fe2/3W1/3)O3–PbTiO3 Solid-Solution Ceramics

The dielectric properties of (1− x )Pb(Fe_2/3W_1/3)O₃· x PbTiO₃ solid solutions were investigated from 10² to 10⁶ Hz in the temperature range 150–600 K. The phase transition of Pb(Fe_2/3W_1/3)O₃ (PFW) was shifted by PbTiO₃ (PT) additions to higher temperatures at a rate of 6.3 K/mol% of PT. The temperature dependence of dielectric permittivity showed a sharper transition as the PT content increased. Dielectric measurements in a wide temperature range showed the presence of a second set of dielectric peaks at higher temperatures (350–600 K), besides the ferroelectric–paraelectric phase transition. This second set of peaks vanished when the samples were annealed in nitrogen. The activation energy values for the second relaxation varied between 0.50 and 0.63 eV, in agreement with the conduction activation energy determined for each sample. This relaxation is apparently related to electron holes.     

Influence of Excess PbO Additions on {111} Single-Crystal Growth of Pb(Mg1/3Nb2/3)O3–35 mol% PbTiO3 by Seeded Polycrystal Conversion

The influence of additions of excess PbO to Pb(Mg_1/3Nb_2/3)O₃–35 mol% PbTiO₃ (PMN–35PT) on {111} single-crystal growth by seeded polycrystal conversion was studied in the range of 0–5 vol% PbO. PbO volatilization and hence weight loss during annealing was controlled effectively by a double-crucible type of arrangement. PbO additions increased boundary mobility significantly in PMN–35PT, thus facilitating single-crystal growth by seeded polycrystal conversion (SPC). This is attributed to the formation of a boundary wetting PbO-based liquid phase. The growth process occurs very rapidly initially, after which it slows down. This is presumably due to both a decrease in the driving force for boundary migration because of an increase in matrix grain size, and a transition to lower mobility facets. It is also shown that for a given annealing time, the size of the grown crystal scales with the lateral dimensions of the seed crystal.     

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.     

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.     

Dielectric Characteristics of Bi- and Ti-Substituted Pb(Mg1/3Nb2/3)O3

Pb[Mg_1/3Nb_2/3]O₃ was gradually substituted by Bi[Mg_2/3Nb_1/3]O₃ (BiMN) up to 30 mol%, with an overall modification by a constant fraction of PbTiO₃ (10 mol%). Monophasic perovskite powders could be prepared via the B-site precursor route. Ceramic samples of the system showed a typical relaxor behavior of frequency-dependent dielectric dispersion. Values of the maximum dielectric constant decreased substantially with increasing BiMN concentration, whereas corresponding temperatures changed only moderately.