Double Precursor Solution Coating Approach for Low-Temperature Sintering of [Pb(Mg1/3Nb2/3)O3]0.63[PbTiO3]0.37 Solids

Lead-based piezoelectric ceramics typically require sintering temperatures higher than 1000°C at which significant lead loss can occur. Here, we report a double precursor solution coating (PSC) method for fabricating low-temperature sinterable polycrystalline [Pb(Mg_1/3Nb_2/3)O₃]_0.63-[PbTiO₃]_0.37 (PMN–PT) ceramics. In this method, submicrometer crystalline PMN powder was first obtained by dispersing Mg(OH)₂-coated Nb₂O₅ particles in a lead acetate/ethylene glycol solution (first PSC), followed by calcination at 800°C. The crystalline PMN powder was subsequently suspended in a PT precursor solution containing lead acetate and titanium isopropoxide in ethylene glycol to form the PMN–PT precursor powder (second PSC) that could be sintered at a temperature as low as 900°C. The resultant d ₃₃ for samples sintered at 900°, 1000°, and 1100°C for 2 h were 600, 620, and 700 pm/V, respectively, comparable with the known value. We attributed the low sintering temperature to the reactive sintering nature of the present PMN–PT precursor powder. The reaction between the nanosize PT and the submicrometer-size PMN occurred roughly in the same temperature range as the densification, 850°–900°C, thereby significantly accelerating the sintering process. The present PSC technique is very general and should be readily applicable to other multicomponent systems.     

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.     

Processing and Electrical Properties in Lead-Based (Pb(Mg1/3Nb2/3)O3, Pb(Yb1/2Nb1/2)O3, PbTiO3) Systems

Lead-based ferroelectric (FE) ceramics exhibit superior electromechanical properties; therefore, there has been an increased focus on developing new lead-based FE materials with high Curie temperature ( T _c) and enhanced properties. The aim of this study was to investigate new compositions in the Pb(Mg_1/3Nb_2/3)O₃–Pb(Yb_1/2Nb_1/2)O₃–PbTiO₃ ( PMN–PYbN–PT) system to enhance the electromechanical properties while increasing the T _c and lowering the sintering temperature. The 0.575[0.5PMN–0.5PYbN]–0.425PT composition at PMN/PYbN (50/50) mole ratio were prepared by reactive sintering PMNT and PYbNT powder mixtures at 950°–1200°C for 4 h. PMNT and PYbNT powders were calcined via the columbite method. Samples were prepared by cold isostatic pressing at 80 MPa. Dense and fully perovskite 0.575[0.5PMN–0.5PYbN]–0.425PT ceramics were fabricated at 975°C for 4 h, and these samples displayed a remnant polarization ( P _r) of 32 μ C/cm², coercive field ( E _c) of 17 kV/cm, and a piezoelectric charge coefficient ( d ₃₃) of 475 pC/N. It is proposed that this ternary system can be tailored for various applications.     

Preparation and Characterization of Relaxor Ferroelectric 0.65Pb(Mg1/3Nb2/3)O3–0.35PbTiO3 by a Polymerizable Complex Method

A modified polymerizable complex (PC) method for the preparation of the relaxor ferroelectric 0.65Pb(Mg_1/3Nb_2/3)O₃–0.35PbTiO₃ (PMN–PT) ceramics has been developed using a novel water-soluble Nb precursor. The effects of Pb content and sintering temperature on the structure, morphology, composition, and electrical properties of PMN–PT powders and ceramics were investigated systematically. It was found that the modified PC method could effectively reduce the initial crystallization temperature of the perovskite phase to 500°C. For PMN–PT samples with 15% excess Pb content sintered at 600°C for 2 h, the 87% perovskite phase can be achieved, which is much higher than that in conventional solid-state reactions and other solution-based methods at the same temperature. On further increasing the sintering temperature to 1100°C, the perovskite phase content basically remains constant. This is attributed to the Pb-deficient pyrochlore phase formation. On increasing the sintering temperature to 1250°C, the dielectric constant and remnant polarization of PMN–PT ceramics significantly improved due to the larger grain sizes, enhanced density, and the decreasing pyrochlore phase. PMN–PT ceramics with a 98.5% content of the perovskite phase have been fabricated at 1250°C. It displays typical ferroelectric relaxor characteristics with a remnant polarization of 18 μC/cm², a coercive field of 9.6 kV/cm, a piezoelectric coefficient of d ₃₃=360 pC/N, and room-temperature and maximum dielectric constants of 3600 and 10 500 at 1 kHz, respectively.     

Synthesis of Pyrochlore-Free 0.9Pb(Mg1/3Nb2/3)O3-0.1PbTiO3 Ceramics via a Soft Mechanochemical Route

Single-phase perovskite 0.9Pb(Mg_1/3Nb_2/3)O₃-0.1PbTiO₃ (0.9PMN–0.1 PT) from a stoichiometric mixture of starting materials was synthesized by applying a mechanochemical technique to the stage of a precursor. A stoichiometric mixture of PbO, TiO₂, Mg(OH)₂, and Nb₂O₅ was milled for 60 min and heated at temperatures as low as 850°C for 4 h to obtain a single phase. The maximum dielectric constant of the samples from the milled mixture increased as the sintering temperature increased, with the remarkable grain growth, and attained 24600 at 1200°C. In contrast, poor densification and coexistence of the pyrochlore phase were observed on the samples from the nonmilled mixture. Further observation suggested that the pyrochlore phase concentrated near the surface during sintering and then migrated into the PbZrO₃ packing powder, leading to a pyrochlore–free phase at 1250°C. The dielectric constant of the latter ceramics was explained by the series mixing rule for the dielectric constant of a diphasic solid.     

Synthesis of Pb(Mg1/3Nb2/3)O3 in Excess Lead Oxide by Mechanical Activation

Twenty hours of mechanical activation of mixed oxides at room temperature led to the formation of Pb(Mg_1/3Nb_2/3)O₃ (PMN) in excess PbO. The crystallinity of the activation-derived perovskite PMN phase was further established when the activated PMN–PbO phase mixture was subjected to calcination at 800°C. Pyrochlores, such as Pb₃Nb₄O₁₃ and Pb₂Nb₂O₇, were not observed as transitional phases on mechanical activation and subsequent calcination, although 50% excess PbO was deliberately added. The perovskite PMN phase was recovered by washing off excess PbO using acetic acid solution at room temperature. It was sintered to a relative density of 98.9% of theoretical at 1200°C for 1 h and the sintered PMN exhibited a dielectric constant of ∼14 000 at 100 Hz and a Curie temperature of −11°C.     

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.     

Mechanochemical Synthesis of 0.9[0.6Pb(Zn1/3Nb2/3)O3·0.4Pb(Mg1/3Nb2/3)O3]·0.1PbTiO3

Lead zinc niobate–lead magnesium niobate–lead titanate (PZN–PMN–PT) ceramic powders of perovskite structure have been prepared via a mechanochemical processing route. A single-phase perovskite powder of ultrafine particles in the nanometer range was successfully synthesized when a MZN powder (columbite precursor) was mechanically activated for 10 h together with mixed lead and titanium oxides. The following steps are involved when the ternary oxide mixture is subjected to an increasing degree of mechanical activation. First, the starting materials are significantly refined in particle size as a result of the continuous deformation, fragmentation and then partially amorphized at the initial stage of mechanical activation. This is followed by the formation of perovskite nuclei and subsequent growth of these nuclei in the activated oxide matrix with increasing activation time. When calcined at various temperatures in the range of 500–800°C, pyrochlore phase was not detected by XRD phase analysis in the mechanochemically synthesized powder. Only a minor amount (∼2%) of pyrochlore phase was observed when the calcination temperature was raised to 850°C. The PZN–PMN–PT derived from the mechanochemically synthesized powder can be sintered to ∼98% relative density at a sintering temperature of 950°C. The PZN–PMN–PT sintered at 1100°C for 1 h exhibits a dielectric constant of ∼18 600 and a dielectric loss of 0.015 at the Curie temperature of 112°C when measured at a frequency of 0.1 kHz, together with a d ₃₃ value of 323 ×10⁻¹² pC/N.     

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%.     

New Preparation Method of Low-Temperature-Sinterable Perovskite 0.9Pb(Mg1/3Nb2/3)O3-0.1PbTiO3 Powder and Its Dielectric Properties

A relaxor ferroelectric material, 0.9Pb(Mg_1/3Nb_2/3)O₃-0.1PbTiO₃ (0.9PMN-0.1PT) with a pyrochlore-free phase, was prepared by using one-step calcination in the present study. The 0.9PMN-0.1PT powder with the pure perovskite phase was prepared successfully from a mixture of the PMN precursor and the crystalline PT by heating for 2 h at temperatures greaterthan equal to750°C. The PMN precursor was synthesized by adding an aqueous Mg(NO₃)₂ solution, rather than MgO, to the alcoholic slurry of PbO and Nb₂O₅. The 0.9PMN-0.1PT powder sintered to >96% relative density via heat treatment for 2 h at temperatures of 900°-1200°C. The highest room-temperature dielectric constant (epsilon_rt) was 24700 at 1 kHz for the samples that were sintered at 1100°C; however, the samples that were sintered at 900°C still had epsilon_rt values of 22600 at 1 kHz.     

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.     

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.     

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.     

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.     

Single-Calcination Synthesis of Pyrochlore Free Pb(Mg1/3Nb2/3)O3 Powders Using Particle-Coating Method

Using two-step particle-coating method, pyrochlore-free Pb(Mg_1/3Nb_2/3)O₃ (PMN) powders have been successfully synthesized by a single calcination step at a relatively lower calcined temperature of 850°C. The XRD and EDS results confirmed that the Mg–citric acid polymeric complex coatings effectively prevent direct contact between PbO and Nb₂O₅ and thus avoid the formation of pyrochlore phase. The coated powders were calcined directly without the ball-milling procedure at 850°C. The pyrochlore-free PMN powders obtained showed uniform and even grain size. The results showed that this method is an attractive method for the synthesis of PMN-based composite powders.     

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).     

Grain Growth Control and Solid-State Crystal Growth by Li2O/PbO Addition and Dislocation Introduction in the PMN–35PT System

Grain growth behavior and solid-state single crystal growth (SSCG) in the Pb(Mg_1/3Nb_2/3)O₃–35 mol% PbTiO₃ (PMN–35PT) system have been investigated with varying Li₂O/PbO ratios. The effect of dislocation density on crystal growth has also been studied. For SSCG, a BaTiO₃ single-crystal seed was embedded in a polycrystalline PMN–PT matrix. During annealing, a PMN–PT single crystal grew from the seed at the cost of the small matrix grains. Addition of Li₂O dopant first enhanced and then reduced abnormal grain growth in the matrix. In the 2 mol% Li₂O and 6 mol% PbO excess PMN–PT samples annealed at 1200°C, considerable single-crystal growth occurred without formation of abnormally large grains in the matrix. Increasing the dislocation density in the BaTiO₃ seed crystal resulted in enhanced growth of single crystals. These results were explained in terms of interface reaction-controlled nucleation and growth, based on crystal growth theories.     

Phase Equilibria in the Ga2O3In2O3 System

Subsolidus phase relationships in the Ga₂O₃–In₂O₃ system were studied by X-ray diffraction and electron probe microanalysis (EPMA) for the temperature range of 800°–1400°C. The solubility limit of In₂O₃ in the β-gallia structure decreases with increasing temperature from 44.1 ± 0.5 mol% at 1000°C to 41.4 ± 0.5 mol% at 1400°C. The solubility limit of Ga₂O₃ in cubic In₂O₃ increases with temperature from 4.X ± 0.5 mol% at 1000°C to 10.0 ± 0.5 mol% at 1400°C. The previously reported transparent conducting oxide phase in the Ga-In-O system cannot be GaInO₃, which is not stable, but is likely the In-doped β-Ga₂O₃ solid solution.     

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.