溶胶-凝胶法制备的高压电常数（Bi0.5Na0.5）1－xBaxTiO3系无铅压电陶瓷

测量了使用溶胶-凝胶工艺制备的(Bi0.5Na0.5)1-xBaxTiO3(x=0.00，0.04，0.06，0.08,0.12)系陶瓷的介电、压电、铁电和热释电性能.由于使用了溶胶-凝胶工艺制备的粉料，因此所有样品的压电性能都得到了较大提高.其中(Bi0.5Na0.5)0.94Ba0.06TiO.3系陶瓷具有该系列最大的压电常数，d33=173×10-12C/N，与传统工艺相比，d33提高了近40%.同时，在一定范围内，随Ba含量的增加，材料的剩余极化Pr和矫顽场Ec逐渐减小，退极化温度逐渐降低.对于(Bi0.5Na0.5)0.94Ba0.06TiO.3系陶瓷，剩余极化和矫顽场分别为25μC/cm2和28kV/cm，退极化温度约为80℃. 关键词： 溶胶-凝胶 压电常数 剩余极化 矫顽场     

孔隙率及晶粒尺寸对多孔PZT陶瓷介电和压电性能的影响及机理研究

采用添加造孔剂的方法制备多孔锆钛酸铅(PZT)陶瓷，并研究了孔隙率和晶粒尺寸对多孔PZT陶瓷介电和压电性能的影响及机理.研究表明：孔隙率的增加降低了多孔PZT陶瓷的介电常数，提高了静水压优值，并证明在一定条件下孔隙率与介电常数关系可由Okazaki经验公式及Banno模型预测；晶粒尺寸增加，多孔PZT陶瓷的介电常数、压电系数和优值增加，并可用Okazaki空间电荷理论解释晶粒尺寸对试样介电和压电性能的影响.对于添加重量百分数为10%造孔剂的多孔PZT陶瓷，当烧结温度为1300℃时，孔隙率为34%，d关键词： 多孔PZT陶瓷 静水压优值 压电性能 介电性能     

Measurements of the thermal, dielectric, piezoelectric, pyroelectric and elastic properties of porous PZT samples

The introduction of porosity into ferroelectric ceramics has been of great interest in recent years. In particular, studies of porous lead-zirconate-titanate ceramic (PZT) have been made. In the research reported, samples of Ferroperm Pz27 with porosities of 20, 25 and 30% were studied. Very complete measurements were made of all of the physical properties relevant for ferroelectric applications including thermal conductivity and diffusivity, heat capacity, dielectric, pyroelectric, piezoelectric and elastic properties. Scanning electron micrographs indicated a change from 3-0 to 3-3 connectivity with increasing porosity. Although most of the physical properties are degraded by the presence of porosity, both piezoelectric and pyroelectric figures-of-merit are improved because of the markedly reduced relative permittivity. Porous ferroelectric ceramics are very promising materials for a number of applications.     

Potentiality of SBN textured ceramics for pyroelectric applications

Textured Sr_xBa_1−xNb₂O₆ (SBN) ferroelectric ceramics with x = 0.53 and 0.63 were fabricated by hot forging process. The objective was to obtain, in the ceramic form, the strong anisotropy of the electric properties that these materials possess in the single crystal form. Properties such as electric permittivity, pyroelectric coefficient and dielectric loss showed an anisotropy between the perpendicular and parallel direction with respect to the pressure axis (applied pressure during the forging of the ceramics). A high pyroelectric coefficient, comparable with these published for SBN single crystal with the same composition, was obtained for the SBN53/47 ceramic, when measured in the perpendicular direction to the pressing axis. From the calculus of the pyroelectric figures of merit, it was possible to conclude that the textured SBN53/47 ceramic has a high potential to be used as pyroelectric elements. This ceramic, cut in the perpendicular direction to the pressing axis, possess high potential as fast pulse detector but the same ceramic, cut in the parallel direction to the pressing axis, has better properties to be used as large area and point detectors.     

Large piezoelectric strain observed in sol–gel derived BZT–BCT ceramics

High performance lead (Pb)-free piezoelectric ceramics with excellent piezoelectric properties is in great demand for sensor and actuator applications. Barium zirconate titanate–barium calcium titanate [xBZT–(1 − x)BCT] (x = 0.5) is one such lead free system, which exhibits high piezoelectric properties similar to lead zirconate titanate (PZT). In this study we report the synthesis and characterization of this lead free [xBZT–(1 − x)BCT] (x = 0.5) via wet chemical sol–gel method. Calcination of the BZT–BCT precursor only at 1000 °C (against 1300 °C reported in the literature) for 4 h resulted in formation of single phase nanoparticles (<50 nm) as confirmed by X-ray diffraction (XRD) and transmission electron microscopy (TEM) studies. Highly dense and homogenous microstructure with 95% of the theoretical density was obtained by solid-state sintering of the green pellets at 1550 °C. Remanent polarization (Pr) of 11.55 μC/cm² and relative permittivity of 20,020 at the Curie temperature of 95 °C were obtained. Electrically poled BZT–BCT ceramics samples exhibited high piezoelectric charge coefficients, d₃₃ ∼ 530 pC/N, d₃₃* ∼ 942 pm/V, large electromechanical coupling coefficient k_p ∼ 0.45 and a large strain of 0.15%, which are comparable to those of lead based piezoelectric ceramics. The excellent piezoelectric properties of this sol–gel derived BZT–BCT system has been analyzed and correlated to its structure in this report.     

Ferroelectric domain structures in (Pb,La)(Zr,Ti)O<Subscript>3</Subscript> ceramics observed by scanning force microscopy in acoustic mode

Ferroelectric domain structures of transparent (Pb,La)(Zr,Ti)O₃ (PLZT) ceramics were investigated by scanning force microscopy (SFM) in the acoustic mode. The antiparallel domain configuration with a periodic distribution and local inhomogeneity in PLZT ceramics were clearly revealed with this new domain-imaging technique. The imaging mechanism of ferroelectric domains in SFM acoustic mode is discussed in terms of a local piezoelectric vibrator model. PACS 77.84.Dy; 77.80.Dj; 77.65.-j; 77.22.Ej; 07.79.-v     

In-plane dielectric characterization of sol–gel derived PLZT (9/65/35) thin films using an interdigital electrode configuration

Lead lanthanum zirconate titanate (PLZT 9/65/35) thin films were deposited on MgO (00l) substrates using a sol–gel method. X-ray diffraction measurements reveal that the PLZT film has epitaxially grown on the substrate and has a pure perovskite structure. Using gold interdigital electrodes the in-plane dielectric properties of the films were measured as a function of frequency (1 kHz to 10 GHz), temperature (293–435 K) and dc electric field (0–20 MV/m). The PLZT (9/65/35) thin film exhibits a diffuse phase transition, which indicates a relaxor-like ferroelectric behavior. The temperature dependence of the characteristic relaxation time was analyzed in terms of the Vögel–Fulcher relation. The relative permittivity has a high tunability of 34–42% in the frequency range of 10 MHz to 1 GHz.     

The physics of pyroelectric infrared devices

The absorption of radiation with pyroelectric detectors and the thermal properties of these devices are discussed using a simple physical picture — the physics of waves. Considered are the reflection, transmission and interference of electromagnetic and of thermal waves within the pyroelectric sensor arrangement. In particular, thin metal films, quarter wavelength structures, and anti-reflection coatings on metal films as absorber structures are discussed. The effect of the substrate on the pyroelectric response is treated and new figures of merit are introduced for the comparison of sensor materials which are mounted on a heat sink.     

Fabrication of textured KNNT ceramics by reactive template grain growth using NN templates

Lead-free non-stoichiometric (K_0.470Na_0.545)(Nb_0.55Ta_0.45)O₃ (KNNT) textured ceramics were prepared by a reactive templated grain growth method using NaNbO₃ (NN) templates. The Plate-like NaNbO₃ (NN) templates were synthesized from bismuth layer-structured Bi_2.5Na_3.5Nb₅O₁₈ (BNN) particles by a topochemical microcrystal conversion (TMC) method. Using 5 wt% of NN templates, textured KNNT ceramics were fabricated, and their crystal structure, microstructure, dielectric and piezoelectric properties were compared with non-textured KNNT ceramics prepared by a conventional solid state reaction method. The textured KNNT ceramics exhibited high grain orientation and high dielectric constant. In addition, piezoelectric properties of textured KNNT ceramics were improved, giving a high piezoelectric coefficient d₃₃ = 390 pC/N and piezoelectric coupling coefficient k_p = 0.60.     

Large pyroelectric response in (Pb0.87La0.02Ba0.1)(Zr0.7Sn0.3−x Ti x )O3 antiferroelectric ceramics under DC bias field

(Pb_0.87La_0.02Ba_0.1)(Zr_0.7Sn_0.3−x Ti _x )O₃ (PLBZST, 0.06≤x≤0.09) antiferroelectric ceramics were fabricated by conventional solid state reaction process, and their ferroelectric, dielectric, and pyroelectric properties were systemically investigated. PLBZST with different Ti content were all confirmed to be in an antiferroelectric phase at T=50°C, which is close to the lowest phase transition temperature. Compared with conventional FE ceramics, PLBZST antiferroelectric ceramics exhibited higher electric field induced pyroelectric coefficient (p). As the content of Ti increased from 0.06 to 0.09, the pyroelectric coefficient increased from 1000 to 6500 μC/m²K under a 500 V/mm DC bias field. The maximum pyroelectric coefficient of 8400 μC/m²K was obtained at x=0.09 when an 850 V/mm DC bias field was applied, which is far larger than that of conventional phase transition pyroelectric materials. Large pyroelectric response is beneficial for the development of infrared detectors and thermal imaging sensors.     

有序组装超薄膜热释电性能的优化研究

报道两亲性染料半花菁(DAEP)与隔层材料氮冠醚(NC)交替LB膜的热释电效应以及掺杂金属离子（Ba2+）对LB膜热释电性能的影响.发现所测样品的热释电系数p高达58μCm-2K-1；在频率为1kHz—100kHz的范围内，其εr和tanδ的数值分别为2.34—1.96和0.08—0.04.并讨论了不同成膜方式和掺杂金属离子Ba2+对LB膜热释电性能影响的物理机理.     

Microstructure,dielectric, and piezoelectric properties of Ce‐modified Na0.5Bi4.5Ti4O15 high temperature piezoceramics

The cerium modified sodium bismuth titanate (Na_0.5Bi_4.5Ti₄O₁₅, NBT) piezoelectric ceramics have been prepared by using the conventional mixed oxide method. X‐ray diffraction analysis revealed that the cerium modified NBT ceramics have a pure four‐layer Aurivillius phase structure. The piezoelectric activity of NBT ceramics was found significantly improved by the modification of cerium. The Curie temperature T_c, and piezoelectric coefficient d₃₃ for the NBT ceramics with 0.50 wt% cerium modification were found to be 655 °C, and 28 pC/N respectively. The Curie temperature gradually decreased from 668 °C to 653 °C with the increase of cerium modification. The dielectric spectroscopy showed that the samples possess stable piezoelectric properties, demonstrating practical potential that for high temperature applications. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Relationship between the microstructure and the microscopic piezoelectric response of the <Emphasis Type="Italic">α</Emphasis>- and <Emphasis Type="Italic">β</Emphasis>-phases of poly(vinylidene fluoride)

The piezoelectric and pyroelectric properties of PVDF mainly depend on its β-phase. This work reports the study by scanning force microscopy in a piezoresponse mode of the variations in the topological morphology and piezoelectric surface response of β-PVDF prepared by the main preparation methods of this phase. Clear differences in the poled region distribution and size, as well as in the local piezoactivity, have been identified. The piezoelectric activity at a mesoscale reflects the semicrystalline phase of the polymer.     

Pyroelectric properties of BiFeO3 ceramics prepared by a modified solid-state-reaction method

BiFeO₃ (BFO) ceramics were prepared by a modified solid-state-reaction method which adopts a higher heating/cooling rate during the sintering process than usually used. It was found that the calcination temperature T _cal (from 400 to 750°C) does not influence the BFO phase formation, while the sintering temperature T _sin (from 815 to 845°C) dominates the phase purity. The optimum sintering temperature was in the range from 825 to 835°C. The optimized samples exhibit saturated ferroelectric hysteresis loops with a remnant polarization of 13.2 μC/cm². The measured piezoelectric coefficient d ₃₃ was 45 pC/N. No remnant magnetization was observed in all of the samples. The pyroelectric properties were studied as a function of temperature and frequency. A pyroelectric coefficient as high as 90 μC/m² K was obtained at room temperature in the optimized sample. An abrupt decrease of the pyroelectric coefficient was observed at temperatures between 70 and 80°C. On the basis of our results, BFO may have the potential for pyroelectric applications.     

Preparation and dielectric study of high-quality PLZT x/65/35 (x = 6,7,8) ferroelectric ceramics

Ferroelectric ceramics are an important class of solid-state materials as they exhibit a wide range of applications. Various compositions of the ferroelectric ceramic (Pb,La)(Zr,Ti)O₃ (known as PLZT) were prepared and their dielectric properties were studied. It is difficult to prepare phase-pure PLZT compounds by the direct solid-state reaction method. Its preparation required the use of a special 'covering method' adopted to facilitate phase formation using the solid-state reaction method. High-quality PLZT samples of different compositions (x/65/35, x=6,7,8) prepared using the 'covering method' without adding any excess PbO (to avoid PbO loss) resulted in single-phase formation. The 8/65/35 composition has yielded a dielectric constant of 11273 at T_C, which is in good agreement with the literature value [1, 2]. Also, as the lanthanum content x was varied from 6 to 8 mole %, T_C decreased and the low-frequency (1 kHz) room-temperature dielectric constant value increased. The present publication gives a detailed account of the evolution of the phase-pure PLZT compositions and their physical properties.     

Contribution of oxygen vacancies to the giant dielectric response in Sm1.5Sr0.5NiO4−δ ceramics

The dielectric properties of Sm_1.5Sr_0.5NiO_4?δ ceramics with different concentrations of oxygen vacancies were characterized. The ceramics with lower concentration of oxygen vacancies were prepared by directly sintering the sol–gel derived powders in air, while the higher one could be obtained by annealing the as-sintered ceramics in the flow of nitrogen. The post-densification annealing in the flow of nitrogen decreased the dielectric constant at low temperature and increased it at high temperature, while the dielectric loss increased in overall temperature range. The activation energy of low-temperature dielectric relaxation decreased with increasing the concentration of oxygen vacancies, and so did that of bulk electrical resistances although the values of resistances increased, while the activation energy of electrical resistances for grain boundary increased though the values of resistances decreased. The giant dielectric response in the as-sintered Sm_1.5Sr_0.5NiO_4?δ ceramics should be mainly attributed to the small polaronic hopping process, while that of annealed ceramics should be directly linked to the oxygen vacancies.     

Enhanced ferroelectric and piezoelectric properties in La-modified PZT ceramics

The effect of lanthanum (La) doping on ferroelectric and piezoelectric properties of lead zirconate titanate (PZT) sample has been investigated. Pb_1?x La _x Zr_0.52Ti_0.48O₃ ceramics with x = 0.00, 0.02, 0.04, 0.06 and 0.10 were prepared by the sol–gel technique. Raman and Fourier transforms infrared spectroscopy have been employed to understand the structural modification due to ionic size mismatch. Raman spectra show the existence of both rhombohedral and tetragonal crystal symmetries. It also shows the dielectric relaxation with increase in La concentration in the sample. The increase in lattice strain due to La doping increases the remnant polarization and coercive field. The linear piezoelectric coefficient increases with the increase in La concentration. It reveals that La-substituted PZT is a better candidate for piezoelectric sensor applications as compared to that of PZT.     

Technology of PLZT ceramics microfibers for multiferroics composites

Compactness and large energy conversion capacity are the main reasons of development of sophisticated ceramics materials in microfibers form, which are prepared for high-speed multiferroic systems and devices. These multifunctional composite applications are owing to coupling of electrical and magnetic properties, as well as additional thermal and mechanical properties. So that, they are suitable for magnetic sensors, electrically tunable non-linear transducers, and non-volatile memories. In our experiment, the thin fibers ceramics have been produced using special environmental chamber where the high temperature sintering can be protected by controlling such parameters as temperature and sintering atmosphere. Consequently, for these purposes structural and physical properties, preparation and thermal synthesis of micrometer sized lead lanthanum zirconate titanate (PLZT) fibers were investigated thoroughly. Since the phase transition properties of PLZT fibers differ much, the production process of fibers suffers from lack of proper high temperature control. Consequently, our experiments should help to eliminate this drawback, so that various technological conditions, parameters, and subsequent sintering atmosphere with different mixtures of PbO and ZrO were experimentally tested. Final conclusions include comparative analysis of obtained PLZT fibers ferroelectric phase transition properties to specific sintering atmosphere.     

Microstructure and dielectric properties of PMN–PT ceramics prepared by the molten salts method

The sintering characteristic and dielectric properties of 0.67PMN–0.33PT ceramics prepared by the molten salt synthesis (MSS) method were investigated. PMN–PT particles synthesized by MSS with smaller grain size and good dispersion could lower the sintering temperature of ceramics; PMN–PT ceramics with relative density above 96% could be obtained in the range 1150–1180 °C. The molten salts species could significantly affect the microstructure and properties of MPN-PT ceramics. In the range 1100–1200 °C, PMN–PT ceramics from the sulfate flux MSS powders showed intergranular fracture, but that from the chloride flux MSS powder showed transgranular fracture. At the same sintering condition, the properties of PMN–PT ceramics from the powders prepared in the chloride flux are better than that from the powders prepared in the sulfate flux, their maximum dielectric constant ε_max≈29,385 and piezoelectric constant d₃₃≈660 pC/N. The above results demonstrated that PMN–PT ceramics prepared by the molten salts method possessed excellent piezoelectric and dielectric properties.     

多孔钛酸钡陶瓷制备及其增强的压电灵敏性

在压电陶瓷中增加孔洞数量,可以有效改善陶瓷的静水压优值,提高其压电灵敏性.考虑到铅基压电陶瓷对环境和人体的危害,本文以糊精为造孔剂,采用传统固相烧结法制备无铅钛酸钡(BaTiO_3)多孔压电陶瓷.研究烧结温度(1250,1280,1300℃)和糊精含量(5%,10%,15%)对BaTiO_3陶瓷晶体结构、孔隙率以及孔形貌特征的影响,探索孔隙率与BaTiO_3陶瓷介电、压电、声阻抗以及静水压优值等性能之间的相关性.结果表明:所有多孔陶瓷表现出三维贯通的开气孔,尺寸约为1—7μm.烧结温度强烈影响BaTiO_3陶瓷的孔隙率,加入10%低沸点的糊精时,1250℃和1280℃烧结均获得孔隙率高达58%的多孔BaTiO_3陶瓷;然而1300℃烧结,陶瓷孔隙率急速下降到13%.1250℃烧结10%糊精含量的陶瓷表现出高的静水压优值(约8376×10~/(-15)Pa~(-1))和低的声阻抗(约2.84MRrayls(1Rayl=10Pa·s/m)).与1250℃相比,1280℃烧结的陶瓷晶粒之间的结合力明显增强,有利于提高陶瓷的力学强度.这些优异的性能预示着多孔钛酸钡陶瓷在传感器和水听器领域有着潜在的应用前景.