Perovskite phase formation in the PbMg1/3Nb2/3 O3-PbZrO3-PbTiO3 system by the columbite route

The reaction mechanism of PbMg_1/3Nb_2/3O₃-PbZrO₃-PbTiO₃ (PMN-PZT) perovskite phase prepared by the columbite route has been studied in the temperature range from 600 to 800 °C. The effects of heating and cooling rate during the calcination of 3PbO +MgNb₂O₆+PZT powder mixtures have also been investigated. Nearly pure perovskite phase, 0.9 PMN-0.1 PZTsolid solution with no pyrochlore phase, as determined by X-ray diffraction, could be prepared at 800 °C for 2 H. From DTA/TGA, dilatometry and XRD data the reaction mechanism of PMN-PZT solid solution formation could be divided into three steps: (i) decomposition of columbite (MgNb₂O₆) by reacting with PbO at 350 to 600 °C (ii) the formation of a B-site-deficient pyrochlore phase Pb₂Nb_1.33Mg_0.17O_5.50 at close to 650 °C, and (iii) the formation of perovskite phase PMN-PZT solid solution from the reaction of Pb₂Nb_1.33Mg_0.17O_5.50 pyrochlore phase with MgO and PZT above 650 °C.     

Preparation and phase formation of perovskite Pb(Ni<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>)O<Subscript>3</Subscript> by a reaction-sintering process

Pyrochlore-free Pb(Ni_1/3Nb_2/3)O₃ perovskite ceramics produced by a simple and effective reaction-sintering process were investigated. Without any calcination, the mixture of PbO, Ni(NO₃)₂ and Nb₂O₅ was pressed and sintered directly into PNN ceramics. Density of 98.5% of theoretical value was obtained after sintered at 1230 °C for 2 h in air. 99.3% of theoretical density was obtained after sintered at 1,200 °C for 2 h in PbO compensated atmosphere. PNN ceramic with dielectric constant 1,680 at 25 °C and 1 kHz has been obtained.     

Preparation,microstructural development and dielectric properties of Pb(Mg1/3Nb2/3)O3-Pb(TixZr1−x)O3 multilayer ceramic capacitors

Multilayer ceramic capacitors based on PMN-PZT solid solutions have been prepared using a 70 % Ag-30% Pd alloy as internal electrode. Some interaction of the electrode-dielectric with Ag⁺ diffusion into the dielectric was observed. The Ag⁺ diffusion influenced the normal microstructural development present in the PMN-PZT ceramics. In spite of this, the dielectric behaviour of a five active layers capacitor sintered at 1050 °C for 2 h in air showed a capacitance of 120 nF, an effective dielectric constant maximum of ~200 000 and dielectric losses of about 3% near room temperature and 1 kHz.     

Characterization of lead zirconate titanate thin film deposition onto Pt/Ti/SiO2/Si substrates

Lead zirconate titanate, (Pb(Zr_0.52Ti_0.48)O₃PZT) thin films were deposited onto a Pt/Ti/SiO_2/Si substrate using radio frequency (r.f.) planar magnetron sputtering in this study. The deposited PZT thin films were almost amorphous before the annealing processes and developed a perovskite structure after the annealing process. If the annealing temperature was too low or annealing time too short, pyrochlore would form. However, if the annealing temperature was too high or annealing time too long, the thin film structure would degrade due to the volatilization of PbO. The significant finding in this experiment is that high quality perovskite PZT thin films on Pt/Ti/SiO_2/Si substrates can be obtained by adjusting the annealing temperature to a range of 650 °C to 850 °C and annealing time to a range from 5 to 80 min. In this experiment, the optimal annealing condition was an annealing temperature of 650 °C and time of 20 min. The properties of PZT thin film annealed at 650 °C for 20 min were dielectric constant _r = 869 free dielectric constant ^T ₃₃ = 893 piezoelectric constant d₃₃ = 2.03p m V^-1 piezoelectric constant g₃₃ = 2.57 x 10^-4 V m N^-1, remanent polarization P₁ = 112.5 nC cm^-2 and coercive field E_c= 0.061 kV cm^-1.     

The role of PbO content on the dielectric and piezoelectric properties of PZN-based ceramics

Stoichiometric and nonstoichiometric (with less and excess PbO) PZN based ceramics with the ABO₃ perovskite structure were prepared by the columbite method. The results show that the content of PbO has a great influence on the structure and the electrical properties of PZN based ceramics. In the compositions with less PbO (A/B < 1), the dielectric constant and piezoelectric coefficients decrease due to the appearing of pyrochlore phase. While in the compositions with excess PbO (A/B > 1), the dielectric constants and the piezoelectric coefficients increase to a maximum at 1–2 mol % excess PbO, then decrease with increasing PbO content. This behavior can be attributed to the grain boundary layer caused by excess PbO. The grain boundary layer can be eliminated by thermal annealing and was examined by transmission electron microscopy. After annealing at 1123 K for 4–8 h, a very strong enhancement in the dielectric and piezoelectric properties was observed in the annealed PZN ceramics. In this work, d ₃₃ = 680 pC/N, k _m 27,000, k _p 50 % were achieved in annealed PZN ceramics.     

Stoichiometric Pb(Mg1/3Nb2/3)O3 perovskite ceramics produced by reaction-sintering process

Stoichiometric lead magnesium niobate, Pb(Mg_1/3Nb_2/3)O₃ (PMN), perovskite ceramics produced by reaction-sintering process were investigated. Without calcination, a mixture of PbO, Nb₂O₅, and Mg(NO₃)₂ was pressed and sintered directly. Stoichiometric PMN ceramics of 100% perovskite phase were obtained for 1, 2, and 4 h sintering at 1250 and 1270 °C. PMN ceramics with density 8.09 g/cm³ (99.5% of theoretical density 8.13 g/cm³) and K_max 19,900 under 1 kHz were obtained.     

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.     

Powders of Pb(ZrxTi1−x)O3 by sol-gel coating of PbO

Powders of lead zirconate titanate (PZT) are prepared by coating a PbO powder with very fine particles containing titanium and zirconium derived from an alkoxide sol. The size of the particles in the coating increases from 10 nm to 100 nm with the increase in the pH during preparation from 3 to 10.5. The powders calcine at low temperature ( 600 °C) to single-phase PZT without the formation of any intermediate phase. The tetragonal and rhombohedral phases are found to coexist betweenx = 0.535 and 0.545. Careful calcination of the powders is needed to ensure removal of residual organics; otherwise the residual carbon reduces PbO to metallic lead leading to high currents during poling. Loss of lead on sintering is significantly lower (1.4 wt%) as compared to samples from conventional powders (6.4 wt%). Successful poling of the sintered samples is achieved when the powders are prepared without using sol stabilizers and are calcined without pelletizing. Washing of the powders is not helpful, perhaps because it leads to change in stoichiometry due to loss of material. A dielectric constant of 950 andd ₃₃ > 190 pCN^–1 are easily achieved.     

Processing and microstructure of porous and dense PZT thick films on Al2O3

The processing of porous PZT thick-film ceramics on Al₂O₃ has been studied. The films were screen-printed from a thixotropic ink of PZT with a 58% solids content. The thick films were sintered between 1000 and 1150°C for 2 h. The sintered films show a 10 m thickness and an average pore diameter ranging from 1–2 m. The PZT forms a continuous skeleton that can be filled with the desired polymer. Dense and continuous PZT films were fabricated by screen-printing PZT ink on previously electroded Al₂O₃ substrates with Ag/Pd 70/30 paste. Densification of the PZT was obtained by sintering near the liquidus temperature of the Ag-Pd system.     

Dielectric and pyroelectric properties of PZFNT/PZT bimorph thin films

Pyroelectric Pb_1,1(Zr_0.58Fe_0.2Nb_0.2Ti_0.02)O₃/Pb_1.1(Zr_0.9Ti_0.1)O₃ (PZFNT/PZT) bimorph thin films are processed via a modified sol-gel method on highly textured (1 1 1)Pt/Ti/SiO₂/Si substrates. XRD and SEM investigations show full pyrochlore to perovskite phase transformation after annealing at 750 °C. XPS depth profiling reveals diffusion of Fe leading to a broad transition layer. The PZT 90/10 bottom layer was shown to be effective for dielectric permittivity control of the bimorph structure. The small signal dielectric constant, , was determined as 580 at 10 kHz. The temperature dependence of is shown to exhibit a single maximum at approximately 195 °C. The C–V characteristics of the bimorph structure show the typical behavior of ferroelectric perovskites. These results are attributed to microstructural effects, particularly the presence of a broad transition layer. The pyroelectric properties are reported in the temperature range from 20 to 60 °C and compared to monomorph PZT and PZFNT films. It is shown that the bimorph thin film has higher pyroelectric coefficient and detectivity than the constituent monomorph films.     

Microwave dielectric properties of Ba5+nTinNb4O15+3n ceramics

New dielectric ceramics Ba_{5 + n}Ti_nNb₄O_{15 + 3n} (n = 1,2,3) with cation-deficient hexagonal perovskite-related structure were prepared by the conventional solid-state reaction route. The phase and structure of the ceramics were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM). The microwave dielectric properties of the ceramics were studied using a network analyzer. These ceramics show dielectric constant (_r) of in the range of 45.1–48.6, _f in the range +59 to +175 ppm°C^{– 1}, and high quality factors with Q×f values up to 22882. The values of _r and _f of the ceramics gradually increase as the number of n increases.     

Composites of 0.9Pb(Mg1/3Nb2/3)O3-0.1PbTiO3 prepared by a sol-gel method: effect of atmosphere powders

Dielectric and electrical properties of relaxor ferroelectric 0.9PMN-0.1PT ceramics prepared by a sol-gel method were investigated as a function of PbZrO₃ atmosphere powders. The proper amount of atmosphere powders led to better properties of dielectric constant, polarization, and strain by preventing PbO volatilization from ceramics. Excessive amount of atmosphere powder, however, resulted in aging characteristics such as decreases in dielectric constant and loss exhibiting saddle-shaped dielectric constant and loss vs. temperature curves. A propeller-shaped P-E hysteresis curve indicating aging characteristics was also observed when an excessive amount of atmosphere powder was used during sintering. The aging of ceramics caused by absorption of PbO into the ceramics resulted in decreased polarization and strain. These aging characteristics associated with defects by excessive PbO absorption could not be reversed even though the aged ceramics underwent a heat-treatment above the dielectric maximum temperature.     

Microwave dielectric properties of B2O3 doped LaAlO3 ceramics at low sintering temperature

The microwave dielectric properties and the microstructures of LaAlO₃ ceramics with B₂O₃ additions (0.25–1 wt%) prepared with conventional solid-state route have been investigated. Doping with B₂O₃ (up to 0.5 wt%) can effectively promote the densification of LaAlO₃ ceramics. It is found that LaAlO₃ ceramics can be sintered at 1400°C due to the liquid phase effect of B₂O₃ addition. The Q × f value as well as the dielectric constant decreases at higher B₂O₃ doping level (1 wt%) due to the increase of boundary phases. At 1460°C, LaAlO₃ ceramics with 0.5 wt% B₂O₃ addition possesses a dielectric constant ( _r ) of 22.9, a Q × f value of 44700 (at 9 GHz) and a temperature coefficients of resonant frequency ( _f ) of –36 ppm/°C. The B₂O₃-doped LaAlO₃ ceramics can find applications in microwave devices requiring low sintering temperature.     

铅欠缺对PZN基陶瓷有序微区、介电和电致应变性能的影响

研究了初始粉体中氧化铅欠缺对PZN基陶瓷的相组成、有序微区、介电和电致应变性能的影响.研究发现,随着氧化铅欠缺量的增大,预烧粉体和陶瓷的焦绿石相含量逐渐增大、钙钛矿相含量逐渐减少.当铅欠缺小于1%时,随着铅欠缺量的增大, PZN基陶瓷的有序微区、介电常数和电致应变大幅度增大;而当铅欠缺大于1%时,铅欠缺会使介电和电致应变性能下降.而铅欠缺对介电损耗影响很小.铅欠缺使介电和电致应变性能增加的原因主要是由于"有效有序微区"尺寸的增大和晶界间过量氧化铅层的消除.     

Dielectric characteristics of Ba(Mg1/3Ta2/3)O3 ceramics sintered at low temperatures

Dielectric characteristics of Ba(Mg_1/3Ta_2/3)O₃ ceramics (BMT ceramics) sintered at low temperatures with 2–3 wt% NaF additives were determined. A dielectric constant of 25 and extremely low dielectric loss (< 0.0001) were measured at 100 kHz and 1 MHz in BMT ceramics sintered under these conditions, and no frequency dependence of the dielectric constant was observed. This suggested that NaF as sintering additive had no harmful influence on the dielectric properties of the ceramics.     

Microstructure and ferroelectric properties of soft-doped sol–gel derived PZT/SKN fibers

Sol–gel derived PZT/SKN fibers with a final composition of 0.98(PbO)_1+z (Zr_0.53Ti_0.47)O₂-0.02Sr(K_0.25Nb_0.75)O₃ and a PbO content of z = +0.04 and +0.14 in the spinning sol were sintered at different temperatures. Fiber stoichiometry, phase content and microstructure as well as the physical properties of the fibers were investigated. A fully densified microstructure independent from the initial PbO content was obtained for fibers sintered at 950 °C or higher. Enhanced porosity was found only for fibers sintered at 900 °C. The densification of the fiber batches at the lower temperatures is dominated by solid state sintering, while liquid phase sintering is promoted by sintering at temperatures above 900 °C. TEM investigations confirmed the homogeneous nature of the PZT/SKN fibers devoid of compositional gradients. Typical dielectric permittivity is in the range of 650–1000. The ferroelectric hysteresis loops are well pronounced showing typical soft-doped behavior with remanent polarization values in the range of 15 and 34 μC/cm² and coercivities of about 1.9 V/μm.     

Effects of Fe2O3 doping on the microstructure and piezoelectric properties of 0.55Pb(Ni1/3Nb2/3)O3-0.45Pb(Zr0.3Ti0.7)O3 ceramics

0.55Pb(Ni_1/3Nb_2/3)O₃-0.45Pb(Zr_0.3Ti_0.7)O₃(PNN-PZT) ceramics with different concentration of xFe₂O₃ doping (where x = 0.0, 0.8, 1.2, 1.6 mol%) were synthesized by the conventional solid state sintering technique. X-ray diffraction analysis reveals that all specimens are a pure perovskite phase without pyrochlore phase. The density and grain size of Fe-doped ceramics tend to increase slightly with increasing concentration of Fe₂O₃. Comparing with the undoped ceramics, the piezoelectric, ferroelectric and dielectric properties of the Fe-doped PNN-PZT specimens are significantly improved. Properties of the piezoelectric constant as high as d₃₃ ~ 956 pC/N, the electromechanical coupling factor k_p ~ 0.74, and the dielectric constant ε_r ~ 6095 are achieved for the specimen with 1.2 mol% Fe₂O₃ doping sintered at 1200 °C for 2 h.     

Effect of Pb(Fe1/2Nb1/2)O3 modification on dielectric and piezoelectric properties of Pb(Mg1/3Nb2/3)O3-PbZr0.52Ti0.48O3 ceramics

10 mol% Pb(Fe_1/2Nb_1/2)O₃ (PFN) modified Pb(Mg_1/3Nb_2/3)O₃-PbZr_0.52Ti_0.48O₃ (PMN-PZT) relaxor ferroelectric ceramics with compositions of (0.9 − x)PMN-0.1PFN-xPZT (x = 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8 and 0.9) were prepared. X-ray diffraction investigations indicated that as-prepared ceramics were of pure perovskite phase and the sample with composition of x = 0.8 was close to morphotropic phase boundary (MPB) between rhombohedral and tetragonal phase. Dielectric properties of the as-prepared ceramics were measured, and the Curie temperature (T_c) increased sharply with increasing PZT content and could be higher than 300 °C around morphotropic phase boundary (MPB) area. At 1 kHz, the sample with composition of x = 0.1 had the largest room temperature dielectric constant ?_r = 3519 and maximum dielectric constant ?_m = 20,475 at T_m, while the sample with composition of x = 0.3 possessed the maximum dielectric relaxor factor of γ = 1.94. The largest d₃₃ = 318 pC/N could be obtained from as-prepared ceramics at x = 0.9. The maximum remnant polarization (P_r = 28.3 μC/cm²) was obtained from as-prepared ceramics at x = 0.4.     

Influence of lead oxide addition on LnTiTaO<Subscript>6</Subscript> (Ln = Ce,Pr and Nd) microwave ceramics

The effect of PbO addition on the structural, processing and microwave dielectric properties of LnTiTaO₆ (Ln = Ce, Pr and Nd) ceramics are reported. Conventional solid state ceramic route was used for the preparation of samples. Phase pure LnTiTaO₆ (Ln = Ce, Pr and Nd) ceramics are prepared at a calcination temperature of 1300°C. The samples are sintered at optimized temperatures. Addition of PbO reduces the sintering temperature. The crystal structure of the materials was analysed using X-ray diffraction techniques and the surface morphology of the sintered samples was analysed using scanning electron microscopy. The dielectric constant at microwave frequency range decreases for higher PbO addition for all the samples but the quality factor improves on small PbO addition. The thermal stability of resonant frequency was also improved with PbO addition on all the systems. A number of samples with improved microwave dielectric properties were obtained on all the systems suitable for practical applications.     

Properties of fluorine-doped PbMg<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>O<Subscript>3</Subscript> ceramics

We report the first fluorine doping of lead magnesium niobate in the PbMg _{(1 + x)/3}Nb_{(2 ? x)/3}O_{3 ? x} F _x system in a wide composition range, x = 0.025 to 0.625. The fluorine content of the samples is shown to be substantially lower than the intended one because of the fluorine volatilization in the form of HF during synthesis and sintering in air. The ceramics consist of magnesium and lead oxides undetectable by x-ray diffraction, and a perovskite phase whose composition can be represented by the formula PbMg_{(1 + m)/3}Nb_{(2 ? m)/3}O_{3 ? m} F _m , where the fluorine content after sintering is m ≤ 0.12. The PbO and MgO contents of the ceramics depend on the starting mixture composition (x) and heat-treatment conditions (hydrogen fluoride and lead oxide volatilization). As a result of the low fluorine content, the diffraction patterns of the samples show no superlattice reflections, and their lattice parameter varies insignificantly with x. Data are presented on the temperaturedependent dielectric permittivity of ceramic samples sintered and annealed under different conditions.