Ferroelectric and dielectric properties of ferroelectromagnet Pb(Fe1/2Nb1/2)O3 ceramics and thin films

The ferroelectric and dielectric properties of ferroelectromagnet Pb(Fe_1/2Nb_1/2)O₃ (PFN) ceramics and thin films prepared by pulsed laser deposition (PLD) have been investigated systematically. PFN ceramics experienced a para-ferroelectric transition and a para-antiferromagnetic transition at 380 K and 145 K, respectively. At room temperature, it has an electrical remnant polarization of 11.5 C/cm² and a coercive field of 4.04 kV/cm. The dielectric behaviors show characteristics of diffusive phase transition at a wide temperature range around 380 K. Anomalies in the dielectric constant and loss tangent have been observed near the Neel temperature of 145 K, indicating a coupling between the ferroelectric and antiferromagnetic orders in PFN ceramics. At room temperature, the PFN films exhibited a remnant electric polarization of 7.4 C/cm², a coercive field of 10.5 kV/cm, and a dielectric constant of 486 at frequency of 10 kHz, indicating their potential applications in memory devices.     

Fabrication and optical properties of Pb(Mg(1/3)Nb(2/3))O(3)-PbTiO(3) thin films on Si substrates using the PLD method.

Epitaxial 0.67Pb(Mg(1/3)Nb(2/3))O(3)-PbTiO(3)-0.33PbTiO(3) (PMN-PT) thin films with electro-optic effects were fabricated on (PMN-PT) thin films with electro-optic effects were fabricated on (La0(0.5)Sr0(0.5))CoO(3) (LSCO)/CeO(2)/YSZ-buffered Si(001) substrates using double-pulse excitation pulsed laser deposition (PLD) method with a mask placed between the target and the substrate. Epitaxial growth of PMN-PT thin films was undertaken using the two-step growth method of PMN-PT film. The PMN-PT seed layer was deposited at 500 degrees C on the LSCO/CeO(2)/YSZ/Si, which temperature was the same as that used for LSCO deposition. The PMN-PT thin films were deposited on the PMN-PT seed layer at 600 degrees C, which enables growth of high-crystallinity PMN-PT films with smooth surfaces. We obtained optimum fabrication conditions of PMNPT film with micrometer-order thickness. Resultant films showed high crystallinity with full width at half maximum (FWHM) = 0.73 deg and 1.6 mum thickness. Electro-optic properties and the refractive index value were measured at 633 nm wavelength using the prism coupling method. The obtained refractive index was 2.59. The electro-optic coefficients r(13) and r(33) were determined by applying the electrical field between a semitransparent, thin top electrode of Pt and a bottom LSCO electrode. The electro-optic coefficient was r(13) = 17 pm/V at transverse electric field (TE) mode and r(33) = 55 pm/V at transverse magnetic field (TM) mode.     

Dielectric properties of low-fitting Pb(Mg1/3Nb2/3)1−xTixO3-Bi2O3/Li2O ceramics

Dielectric properties of low-firing Pb(Mg_1/3Nb_2/3)_1–x Ti _x O₃-Bi₂O₃/Li₂O ceramics are studied in this work. With the addition of Bi₂O₃/Li₂O eutectic composition, the sintering temperature of PMN_1–x PT _x could be lowered to 900° C. Relaxor behaviour of PMN_1–x PT _x is enhanced by the incorporation of Bi₂O₃/Li₂O due to the substitution of Bi⁺³/Li⁺ into the PMN_1–x PT _x framework. Bi₂O₃/Li₂O eutectic composition is used as a fluxing agent, Curie shifter and depressor. Evaporation of Bi₂O₃/Li₂O and PbO during firing is checked and examined via energy dispersive spectrometry (EDS) and X-ray diffraction (XRD) is used to clarify the Curie shifting and depressing effect of Bi₂O₃/Li₂O.     

High dielectric non-linear properties of the Pb[(Mg1/3Nb2/3)0.8(Sc1/2Nb1/2)0.2]O3 ceramics

Pure perovskite Pb[(Mg_1/3Nb_2/3)_0.8(Sc_1/2Nb_1/2)_0.2]O₃ (PMNSN) ceramics were prepared via a modified ‘columbite-type’ method. The 1:1 B-site ordered structure was detected by X-ray diffraction and transmission electron microscopy. The dielectric relaxation behavior was described by a Lorentz relation and a small polaron over the Curie temperature range. The dielectric tunability properties were investigated at 300 K and 10 kHz. A high dielectric tunability (～ 75% at 30 kV/cm), low dielectric loss (～ 0.003) and high figure of merit (～ 250) of PMNSN, indicate that PMNSN is a promising dielectric tunable material. The high dielectric non-linear behavior of PMNSN was further discussed in terms of the Landau–Ginsberg–Devonshire thermodynamic theory completed with a Langevin term that describes the contribution of the re-orientation of the polar nanoclusters to the non-linear ?(E) dependences.     

Processing and properties of Pb(Mg1/3Nb2/3)O3-PbZrO3-PbTiO3 ceramic relaxors

The shrinkage phenomenon during the reaction-sintering of PMN-PZT from low-temperature pre-reacted 3PbO + MgNb₂O₆ + PZT powder mixtures has been studied. It was assumed that the pre-reaction treatment leads to the formation of a pyrochlore phase containing very active MgO small particles, and that the strong shrinkage occurring up to 800 °C took place by the diffusion of Mg²⁺ cations into the pyrochlore phase particles, thus controlling the reaction-sintering shrinkage phenomenon. Above that temperature the densification was enhanced by a liquid-phase sintering process. The ceramics sintered at 1050 °C for 2 h showed 96% of the theoretical density, and the dielectric constant of such a sintered ceramic showed a maximum value of 17 000 at 1 kHz. It was also found that the dielectric constant decreased with increasing grain size. Although the role of PZT in enhancing the dielectric constant of otherwise low-purity PMN ceramics is not clear, the increase in K is assumed to be a solid-solution effect. The presence of impurities and the PbO stoichiometry could be influencing the not too high dielectric constant value of PMN-PZT ceramics.     

Preparation of Pb(Mg1/3Nb2/3)O3–Pb(Zn1/3Nb2/3)O3 ceramics by the B-site precursor method and dielectric characteristics

Powders in the Pb(Mg1/3Nb2/3)O3–Pb(Zn1/3Nb2/3)O3 system, with a high perovskite yield, were prepared by a B-site precursor method. PbO was added to pre-reacted B-site components of Mg1-xZnxNb2O6 solid solution, which was further calcined to form a perovskite structure. Perovskite phase contents and lattice parameters were obtained from X-ray analyses. Weak-field low-frequency dielectric constants and losses of sintered pellets were measured as functions of composition, temperature and frequency. Dielectric relaxation behaviours were investigated in terms of diffuseness coefficients. Microstructures were observed to correlate with other characteristics. © 1998 Chapman & Hall     

不同镁源反应物对反应烧结制备Pb（Mg1/3Nb2/3）O3陶瓷的影响

采用MgO和(MgCO3)4·Mg(OH)2·5H2O为不同镁源反应物,通过高温反应烧结工艺制备Pb(Mg1/3Nb2/3)O0.(PMN)陶瓷,研究不同Mg源反应物对PMN陶瓷物相组成、相对密度及组织形貌的影响.结果表明:以MgO为前驱体时.由于其反应活性差,扩散和反应不均匀,导致烧结样品中有焦绿石相残留,且焦绿石相对晶界的钉扎阻碍作用使得致密化过程进行相对较慢,所得PMN样品致密度相对较低;而以(MgCO3)4·Mg(OH)2·5H2O为前驱体时,因其受热分解可以得到大比表面积、高反应活性的MgO,从而可以制得高致密度且具有单一钙钛矿相组成的PMN陶瓷材料.     

Determination of nonlinear electromechanical energy conversion and the field-dependent elastic modulus of Pb(Mg(1/3)Nb(2/3 ))O(3)-based electrostrictors

Energy conversion efficiency is a critical parameter for all electromechanical materials. Although excellent techniques are available for linear materials, nonlinearities complicate the determination of conversion efficiency in electrostrictive Pb(Mg(1/3)Nb(2/3 ))O(3) (PMN). The field dependence of the elastic modulus presents additional problems. A technique combining pulse-echo ultrasound has been developed to approximate the change in the Young's modulus with applied field. A 30% decrease was observed at 1 MV/m (from ~100 to ~70 GPa). The boundary condition for these measurements was a constant electric field as opposed to constant dielectric displacement. In combination with the results from harmonic analysis, the modulus data may be used to determine the electromechanical conversion efficiency. This has been accomplished using an energy balance criterion for a PMN-based composition (with and without dc bias). The resulting longitudinal coupling values are >0.5 for practical electric fields (<1 MV/m peak).     

Structure and electrical properties of (111)-oriented Pb(Mg1/3Nb2/3)O3-PbZrO3-PbTiO3 thin film for ultra-high-frequency transducer applications

Ternary lead magnesium niobate-lead zirconate titanate system 0.4Pb(Mg(1/3)Nb(2/3))O(3)-0.25PbZrO(3)-0.35PbTiO(3) (40PMN-25PZ-35PT) thin film with a thickness of 1.5 μm was grown on Pt(111)/Ti/SiO(2)/Si substrate via chemical solution deposition. X-ray diffraction and transmission electron microscopy results suggested the film obtained was highly (111)-oriented. The remanent polarization and coercive electric field of the film were found to be 25.5 μC/cm(2) and 51 kV/cm, respectively. In addition, at 1 kHz, the dielectric constant was measured to be 1960 and the dielectric loss 0.036. The film was observed to undergo a diffuse ferroelectric-to-paraelectric phase transition at around 209°C. The leakage current appeared to depend on the voltage polarity. If the Au electrode was biased positively, the leakage current was dominated by the Schottky emission mechanism. When the Pt electrode was biased positively, the conduction current curve showed an ohmic behavior at a low electric field and space-charge-limited current characteristics at a high electric field.     

New preparation method of low-temperature sinterable Pb(Mg1/3Nb2/3)O3 powder and its dielectric properties

A relaxor ferroelectric material, Pb(Mg_1/3Nb_2/3)O₃(PMN) with perovskite phase was prepared by one-step calcination in the present study. The PMN powder with >99% perovskite phase was prepared successfully by adding an aqueous Mg(NO₃)₂ solution rather than MgO to the alcoholic slurry of PbO and Nb₂O₅, followed by calcination at 950°C for 2 h. The DSC and XRD analysis showed that the pathway in the one-step calcination was different from those of the known columbite or solution processes. The PMN powder sintered to 95.6% of the theoretical density at even 900°C for 2 h. Its room temperature dielectric constant showed 13800 at 1 kHz, the loss of dielectric constant of 0.05% and the specific resistivity of 2.4 × 10¹⁰ ·cm.     

Temperature stable dielectric properties for Pb(Mg1/3Nb2/3)O3-BaTiO3-PbTiO3 system ceramics

Abstracts are not published in this journal This revised version was published online in November 2006 with corrections to the Cover Date.     

Pb(Mg1/3Nb2/3)O3-PbTiO3晶体组分对结构与性能的影响

用熔体Modified Brdgman法生长出尺寸直径40 mm长度80 mm的弛豫铁电单晶PMNT90/10,表明该方法不仅适合在准同型相界(MPB)附近生长PMNT单晶,也适合生长PT含量很低的PMNT单晶.在生长出的PMNT90/10晶体中,铁电相与顺电相两相共存,并呈现亚微畴结构特征.随着晶体组分由PMN组元变化到MPB组分附近,PMNT的电畴结构呈现微畴-亚微畴-不规则宏畴-规则宏畴演化系列,而介电弛豫特性则逐步弱化.PMNT固熔体的电学性能依赖于晶体组分,(001)切型PMNT90/10晶体的压电常数d33约80 pC/N,显著低于MPB附近组分,但其介电常数ε达到12600,明显高于后者.     

Synthesis of Pb(Mg1/3Nb2/3) O3 perovskite by an alkoxide method

Pb(Mg_1/3Nb_2/3)O₃ materials have been synthesized using sol-gel, freeze-drying or spray-pyrolysis techniques. The as-prepared powders were of an amorphous form which could be converted into a crystalline form by calcination. The pyrochlore phase was inevitably formed with an accompanying perovskite phase. As the calcining temperature increased, greater proportions of the desired perovskite phase occurred. The residual pyrochlore phase could be completely transformed into the perovskite phase when the powders were prepared via freeze-drying or by a spray-pyrolysis method. The maximum proportion of the pyrochlore phase was, however, only 92% when the powders were synthesized by a sol-gel route. Thermal gravimetric analysis/differential thermal analysis (TGA/DTA) and infrared transmission spectroscopy (FTIR) indicated that Mg(OEt)₂ and Nb(OEt)₅ formed a double alkoxide but Pb(OAc)₂ formed separate clusters during the hydrolysis of the solution in the sol-gel process. Inhomogeneous mixing meant that the intermediate phase formed was rather difficult to eliminate completely. Homogeneous mixing was preserved when the solution was directly freeze dried or spray pyrolysed. The size of the preferentially formed pyrochlore phase was very fine and further transformation was feasible. Pb(Mg_1/3Nb_2/3)O₃ materials, free of the pyrochlore phase, could therefore be obtained.