Ceramic and Dielectric Properties of Lead Metaniobate Electrical Ceramics

The effect of firing temperature and time on the weight loss, fired porosity, and dielectric properties of lead metaniobate was investigated. The amount of lead oxide lost was found to be a linear function of firing time and in addition increased rapidly as the firing temperature was increased. Specimens fired for 30 minutes at temperatures below 1275°C. had weight losses of less than 1% based on the amount of available PbO present, whereas specimens fired for the same length of time at temperatures greater than 1275°C. had weight losses up to 3.5%. Both a minimum and a maximum point were found in the fired porosity curve of lead metaniobate in the temperature range 1200° to 1350°C. When firing for 30 minutes, the minimum point occurred at about 1225°C. with a porosity value of 8% and the maximum point at 1300°C. with a porosity of 18%. The effect of porosity and weight loss on the dielectric properties of lead metaniobate is presented. The effect of replacing up to 0.7 mole fraction of the lead ion in lead metaniobate by cadmium was investigated. Cadmium additions lowered the Curie temperature and diluted the ferroelectric properties of lead metaniobate.     

Influence of Microstructure on the Dielectric and Piezoelectric Properties of Lead Zirconate-Polymer Composites

Composites with 0–3 connectivity were fabricated from lead zirconate titanate (PZT) and phenolic resin powders. These composites were investigated for dielectric and piezoelectric properties with variations in active particle density and PZT-polymer interface porosity. The dependence of dielectric and piezolectric properties on interface porosity is discussed, especially in terms of porosity factors. The dependence of the piezoelectric constant on interface porosity was greater than that of the dielectric constant. The interface pores play the role of a stress buffer. Thus local stress applied on PZT particles in the composites was remarkably diminished. When particle porosity was high, the dependence of the dielectric and piezoelectric constants on interface porosity decreased.     

氧化锰对偏铌酸铅压电陶瓷性能的影响

本文研究了掺入适量的MnO_2对偏铌酸铅压电陶瓷的影响。实验结果表明,随着MnO_2掺入量的改变,材料的Kt和Qm都发生了变化,当掺入量为0.3Wt％时,Kt达最大,Qm最小,且材料的显微结构也较好。     

Piezoelectric and Dielectric Properties of Acrylonitrile Butadiene Rubber/Lead Magnesio-Niobate Piezoelectric Ceram

A new composite with special piezoelectric property was prepared by using lead magnesio-niobate piezoelectric ceram powders (PMN) as dispersing phase in acrylonitrile butadiene rubber (NBR) matrix. The dielectric and piezoelectric properties of the composite were studied. The result shows that the particle size of 80% of PMN ceram powders was 0.5–2 µm. The piezoelectric constant (d₃₃) of the composite increased with increasing volume fraction of PMN, and the max piezoelectric constant is 33 when the PMN volume fraction is 85%. Appropriate delay of polarizing time with increasing polarizing voltage could be helpful to improve the d₃₃ value. The optional polarizing condition is 25 min, 7–8 kv/mm, and 80°C. The dielectric constant increased with the increasing of the PMN volume fraction. Polarized time, polarized voltage, and polarized temperature have no effect on the dielectric constant.     

Microstructure and Dielectric Properties of Lead Magnesium Niobate-Pyrochlore Diphasic Mixtures

The microstructure and dielectric properties of lead magnesium niobate (PMN) ceramics containing the determental second phase, pyrochlore, have been studied. The pyrochlore phase within PMN was found to be present as isolated grains in the microstructure with a composition of Pb₂(Mg_0.25Nb_1.75)O_6.625 and a preferred octahedral morphology. The amount of pyrochlore second phase can be easily controlled by changing the Mg/Nb ratio on the B-site of the perovskite structure, and a series of diphasic mixtures from near-pure PMN to near-pure pyrochlore were obtained. Its effect on the permittivity follows the isolated Wiener's mixture rule up to a pyrochlore content of 18 vol%.     

Dielectric, Piezoelectric, and Pyroelectric Properties of Lead Zirconate—Lead Zinc Niobate Ceramics

New piezoelectric and pyroelectric ceramics consisting of antiferroelectric lead zirconate (PZ) and relaxor ferroelectric lead zinc niobate (PZN) are studied from an application view-point of the field-induced antiferroelectric-to-ferroelectric phase transition. An antiferroelectric-ferroelectric phase boundary exists in PbZr_x(Zn_1/3Nb_2/3)_1−xO₃ (PZZN-1000x) close to x = 0.93 to 0.94 at room temperature. A new ferroelectric rhombohedral phase change, F_α–F'_α, at low temperature is found and studied by the temperature dependence of the pyroelectric coefficient. Electrical poling in these ceramics is easy, and the coercive field E_c∼8 to kV/cm is rather low. Samples with compositions in the range PZZN-86 to PZZN-92 have a large electromechanical coupling constant, k (k_t and k₁₅∼50% to 60%), and a low dielectric constant, ɛ_s (ɛ^T₃₃/ɛ₀= 260 to 320, ɛ^T₁₁/ɛ₀= 380). PZZN ceramics appear to be potential candidates for high-frequency ultrasonic transducers used in the thickness shear mode. The pyroelectric figure of merit (F_v) of these ceramics is comparable to the values published for the PZT-based or PbTiO₃-based materials.     

Relationships between Sintering Conditions,Microstructure and Dielectric Properties of Lead Iron Niobate

Lead iron niobate, Pb(Fe_1/2Nb_1/2)O₃ (PFN) ceramics have been produced by sintering PFN powders synthesized from lead oxide (PbO) and iron niobate (FeNbO₄), with an effective method developed for minimising the level of PbO loss during sintering. Attention has been focused on relationships between sintering conditions, phase formation, density, microstructural development and dielectric properties. The sintering temperature has been found to have a pronounced effect on the density, grain growth and dielectric properties of the sintered PFN ceramics, with maximum density and relative permittivity values obtained under sintering conditions of 1175°C for 2 h. The origin of the strong dependence of values of ε_r and tan δ on frequency is discussed. ©     

Tailoring of the Lead Metaniobate Ceramic Processing

The processing of a PbNb₂O₆ (PN) ceramic was investigated and optimized. Through thermal gravimetric and X-ray diffraction analysis the optimal calcination condition and the starting firing temperature were estimated. The powders were submitted to thermal treatments to obtain PN ceramic powders with an orthorhombic ferroelectric phase. The effect of PbO excess addition to compensate the PbO losses, during the calcination and the firing, was also studied. The highest density value was found to be 96% of the theoretical density. The temperature dependence of the dielectric properties, for samples sintered at different temperatures, allowed the study of the sintering kinetic.     

Effects of Zirconia on Microstructure and Dielectric Properties of Barium Titanate Ceramics

Dielectric properties and structural characteristics of BaTiO₃ ceramics are significantly influenced by small addition (2 wt%) of ZrO₂. SEM and TEM observations revealed enhanced microstructural uniformity and retarded grain growth depending on sintering temperature. Above 1320°C, Zr diffusion into the BaTiO₃ lattice resulted in a chemical modification of the tetragonal structure and the development of core–shell grains. Below 1320°C, TEM analysis showed ZrO₂ at the grain boundaries as discrete particles (∼0.03μm). X-ray diffraction analysis revealed a decrease in the axial (c/a) ratio with decreasing grain size. A corresponding decrease in the spontaneous polarization, and twinned domain structures, were also observed in the fine-grained ceramics. These samples also showed a flattened permittivity response with temperature and significantly lower losses.     

Effects of Thickness on Piezoelectric Properties of Highly Oriented Lead Zirconate Titanate Films

Lead zirconate titanate (PZT) films were deposited on platinized silicon substrates by spin coating using PZT sols containing polyvinylpyrrolidone (PVP) as an additive. PZT films with a 60/40 composition and a thickness of up to 8 μm were fabricated by repeating the deposition process 15 times on highly oriented (100) and (111) seed layers with the same composition. The films grew well in the direction of the seed layers and had a uniform and smooth surface without any cracks. As the thickness of the films increased, the grain size remained almost the same, but the effective d ₃₃ value increased steadily. The thickness dependence of the piezoelectric properties was attributed to the residual stress of the films.     

Structure and Dielectric Properties of Lead Pyrochlores

This work investigates the structure and stability of the pyrochlore solid solution Pb _n Nb₂O_{5+ n} using a combination of high-resolution electron microscopy and electron diffraction. The microwave dielectric properties of the series 1.5 ≤ n ≤3.0 have been established, and the effect of the substitution of Ta⁵⁺ for Nb⁵⁺ on dielectric properties has also been investigated for n = 1.5 and 2.0. Single-phase cubic pyrochlore was obtained for n = 1.5. Compositions for which n > 1.5 showed discreet PbO-rich layers on {111}_cubic planes between alternating slabs of pyrochlore, similar in appearance to Ruddlesden–Popper phases. The occurrence of these layers results in a lowering of the overall symmetry to trigonal, and their presence was found to have a profound effect on the microwave dielectric properties.     

Mg~(2+)掺杂对PZT陶瓷材料介电性能的影响

系统地研究了Mg2+掺杂对PZT材料相结构及介电性能的影响,结果表明:Mg2+的添加阻止了陶瓷晶粒的过分长大,起到了细化晶粒的作用,改善其烧结性能,降低了烧结温度;由于晶格发生畸变,体系的相结构由三方相向四方相过渡;Mg2+的引入使PZT陶瓷材料的红外光谱图明显向高波数的方向移动,并且显著提高了材料的介电常数,有效降低了其介电损耗,使材料的介电性能得到了明显优化。     

Chemical Heterogeneity in PMN–35PT Ceramics and Effects on Dielectric and Piezoelectric Properties

Pb[(Mg_1/3Nb_2/3)_0.65Ti_0.35]O₃ (PMN–35PT) powder was prepared using the columbite precursor method. Fully dense compacts were formed by hot-pressing the powder at 950°C, and then the compacts were annealed at 1150°C for 5 and 10 h, respectively. Dielectric and piezoelectric properties of the as-hot-pressed and annealed samples were measured and correlated with microstructure. The as-hot-pressed material exhibited relaxor–ferroelectric-like behavior, with a relatively low dielectric constant maximum measured at 1 kHz ( K _m@1kHz) of 8160. Annealing resulted in a transition to weak normal-ferroelectric behavior, a shift in the dielectric maximum temperature from 190°C to 169°C, and a dramatic increase of K _m@1kHz to a maximum value of 41 720 for the longer anneal. The as-hot-pressed microstructure was chemically heterogeneous, characterized by submicrometer-sized regions of varying magnesium, niobium, and titanium content that likely originated from chemical heterogeneities that were present in the as-prepared PMN-PT powder. The as-hot-pressed properties have been explained as being the integrated response of many discrete ferroelectric responses as dictated for each of these regions by the local chemistry. The transition on annealing has been explained in terms of chemical homogenization to a near-morphotropic phase-boundary composition that is intrinsically weak normal-ferroelectric. Differences in polarization-versus-electric-field and strain-versus-electric-field behavior between the hot-pressed and annealed materials have been discussed in terms of differences in domain mobility.     

Dielectric and Piezoelectric Properties of PZT Substituted with Samarium

The paper reports influence of samarium substitution on the properties of a PZT composition near MPB. Samarium (Sm) was varied from 0 to 0.02/FU. The samples were prepared by standard double sintering ceramic method. XRD analysis showed all samples to be of single phase. Dielectric properties were studied as a function of temperature and frequency. All the samples show well defined ferroelectric behaviour. Remanence ratio ( P r / P s ) was found to increase with increasing Sm concentration. Piezoelectric change coefficient d 33 decreases with increase in Sm.     

Effect of Phase Transformation on the Sintering of Lead Barium Metaniobate Solid Solutions

The densiflcation behavior and microstructure development were examined for Pb_1-xBa_xNb₂O₆ (x = 0.0, 0.15, and 0.30) with the low-temperature rhombohedral form. The rhombohedral form transformed to the high-temperature tetragonal form during sintering. The phase transformation increased the rate of grain growth, which influenced the microstructure development and densiflcation. The densiflcation proceeded partly before the phase transformation occurred, and the microstructure changed by the sequential formation of necks, chainlike grains, and equiaxed grains. The microstructure just after the phase transformation was determined by the microstructure just before the phase transformation. The chainlike and equiaxed grains changed to elongated and large equiaxed grains, respectively. Pore shape also changed.     

Microstructure and Magnetic Properties of Lead Ferrite

Unoriented lead ferrite specimens were prepared by calcining and sintering techniques. Specimens having an initial composition of Pb0.5Fe₂O₃ had the best permanent magnet properties (for nondoped material). The effects of small amounts of added oxides on the microstructure and magnetic properties were also determined. Silica and boria were most effective in raising the (B_aH^a)_max to over 1.4 × 10⁶ G.Oe as compared to 0.9 to 1.1 × 10⁵ G.Oe for commercial un oriented barium ferrite magnets. Optical and electron microscopy revealed that silica and boria form low melting phases as the specimens are sintered, which, acting as fluxes (probably by a solution-precipitation mechanism), enhance the densification of the magnets, thereby raising the B_r, and (B_aH_a)_max, values. On cooling, these nonmagnetic low-melting phases are retained at the ferrite grain boundaries where they inhibit domain wall motion which would otherwise lead to a reduction in coercive force. Although these magnets are termed "un oriented" to distinguish them from "oriented" ferrites which are purposely aligned before sintering, a slight orientation is imparted to the polycrystalline compact during the pressing operation before sintering. The silica and boria additions increase the degree of orientation by accelerating the rate of densification. The increase in orientation accounts for part of the increase in B_r, and (B_a, H_a)_max.     

钛酸铅微晶玻璃介电性能研究

主要对钛酸铅系铁电性微晶玻璃的介电性能做了研究,研制的微晶玻璃初始组成由形成主晶相的氧化物和形成玻璃相的氧化物构成,经过熔融、热处理可以得到以钛酸铅为主晶相的微晶玻璃,分析了不同组成情况下微晶玻璃的介电性能.     

Microwave Dielectric Properties of Antiferroelectric Lead Zirconate

The dielectric properties of ceramic lead zirconate and rutile are presented at microwave frequencies. Several techniques are required to span the frequency range from 100 Hz to 26 GHz, and rutile is utilized as a reference material to determine the consistency between measurement methods. A significant relaxation was seen for lead zirconate. At 10 GHz, the dielectric constant decreased 20% from the 1-MHz value of 160, and the dielectric loss increased by more than 3 times the low-frequency value of 0.007.     

铅粉对防辐射砂浆水化性能和微观结构与组成的影响

利用XRD,SEM,TG-DSC和压汞仪研究了铅粉对砂浆水化性能和微观结构与组成的影响.实验表明,当铅粉掺量较低时,粒度较小的铅粉在砂浆体系中起细集料填充效应,能够改善孔结构,增强砂浆的力学性能.如果铅粉掺量过多则会破坏水泥的水化过程,并且会产生大量的Pb3(CO3)2(OH)2从而导致砂浆的表面结构被破坏,严重影响了砂浆的耐久性.由于铅本身对伽马射线具有优异的屏蔽性能,因此可以增强砂浆的防辐射性能.