Colloidal processing of lead lanthanum zirconate titanate ceramics

Well-dispersed aqueous slurries of fine ceramic powders with high solids loading are often required for various shape forming techniques such as slip and tape casting in order to fabricate advanced ceramics with a dense and uniform microstructure. Colloidal processing of lead lanthanum zirconate titanate (PLZT) powders was conducted at various pH using ammonium polymethacrylate as a dispersant. Suspensions were characterized by viscosity and zeta-potential measurements. The effect of pH on polymer adsorption and the rheological behavior of the slurries were investigated and stabilization mechanisms discussed. Through optimization of the dispersant concentration and pH, solids loadings of the suspensions up to 50 vol.% with a relatively low viscosity were obtained.     

Characterization and microstructure of porous lead zirconate titanate ceramics

Porous lead zirconate titanate (PZT) ceramics are widely used because of their low acoustic impedance, high figure of merit and high hydrostatic sensitivity. In the present work, porous PZT ceramics were fabricated by incorporating polyethylene oxide (PEO) as pore-forming agent. Both PZT powder and PEO were mixed with a binder at different ratios and compaction was carried out. The samples were slowly heated to remove the pore-forming agent and binder without cracks, followed by controlled sintering and electrode forming. Samples were poled using corona poling technique. The ferroelectric properties and microstructure of the prepared ceramics were characterized. The correlation of porosity with microstructure and ferroelectric properties were discussed.     

Thermally stimulated surface autosegregation in lead zirconate titanate ceramics

Thermally stimulated segregation on grain surfaces in lead zirconate titanate ceramics has been shown for the first time to be selective, as a result of which atoms occupying the same crystallographic position accumulate in the surface layer in a ratio differing from that in the bulk. The phase precipitating on the surface of unoriented parent grains may have preferential orientation owing to the orienting effect of single-crystal micrograins. Surface segregation markedly changes the composition of the solid solution toward disproportionation, leading to the formation of TiO₂ and PbZrO₃ instead of PbTi_0.6Zr_0.4O₃.     

Piezoelectric and mechanical properties of ceria-doped lead zirconate titanate ceramics

Phases, microstructures and properties of lead-zirconate-titanate (PZT) ceramics with the compositions Pb(Zr_0.535– Ce Ti_0.465) O₃ where =0.0, 0.001, 0.01, 0.02 and 0.05 were studied. Rhombohedral and tetragonal phases were present at =0.0. The amount of the rhombohedral phase increased with increasing , and only the tetragonal phase was present for >0.001. Thec/a ratio of the tetragonal phase also increases with increasing . Particles of CeO₂ were found to be present in compositions with >0.01, indicating that the solubility of CeO₂ is less than 1a/o on the metals basis. The piezoelectric and electromechanical constants achieved maximum values for =0.001. The hardness increased monotonically with increasing . The modulus of rupture and the fracture toughness, however, went through a minimum and both stayed lower than their values for =0.     

Temperature-dependent ferroelectric hysteresis properties of modified lead zirconate titanate ceramics

Temperature-dependent ferroelectric hysteresis properties of modified lead zirconate titanate ceramics have been investigated in a wide temperature range from 300 to 433 K. It is observed that remnant polarization, saturation polarization, and coercive field are increasing with an increase of the temperature in a low-field region and decreasing in a high-field region. Such behavior is explained by the competition between switching and backswitching mechanisms. A three-stage dependence of the logarithm of the hysteresis loop area on the logarithm of the electric field is identified. The temperature dependence of backswitching properties has been studied. The obtained results indicate that the temperature dependence of the polarization backswitching can be well described by the Arrhenius law. The activation energy for the domain switching determined from the fitting results exhibits decreasing tendency with the increase of the electric field.     

Photoacoustic and X-ray photoelectron spectroscopic studies in reduced lead zirconate titanate ceramics

Lead zirconate titanate (PZT) is known to become a semiconductor after reduction in a hydrogen atmosphere. An attempt is made here to characterize the reduced, as well as the unreduced, PZT system with the help of photoacoustic (PA) spectroscopy and X-ray photoelectron spectroscopy (XPS) and to obtain useful information regarding its electronic behaviour.The band gap of the unreduced PZT is estimated to be 3.56 eV from PA spectra which is observed to remain unaffected after doping with lanthanum, niobium and strontium. XPS results indicate the presence of metallic lead in PZT after hydrogen reduction whereas other elements remain unaffected. This becomes responsible for the change in its conductivity and also for the increased absorption in the visible range which is reflected in the PA spectra. The electronic structure based on PA spectra is also presented for the reduced and unreduced PZT systems.     

Structural and electrical studies of CeO2 modified lead zirconate titanate ceramics

The present study is an investigation of the structural and electrical properties of solid solution processed lead zirconate titanate (PZT) ceramics modified by CeO₂. The PZT composition studied is Pb(Zr_0.535Ti_0.465)O₃ modified with 0.0–0.2 mol % CeO₂. Studies of the loss of lead oxide during sintering have been performed. The lead loss increases with increasing Ce in the sample up to 0.1 mol % Ce and becomes nearly constant on further addition of Ce. The lattice parameters and cell volume of the tetragonal phase of PZT also increase with addition of Ce up to 0.1 mol % Ce. The lead loss and X-ray data indicate that Ce is being reduced to Ce³⁺ and is going onto the A-site of the PZT perovskite system. The study concludes that controlled modification of the MPB composition of PZT using 0.1 mol % CeO₂ results in substantial enhancement of piezoelectric strain coefficients, dielectric constant and electromechanical coupling coefficients.     

Dielectric and pyroelectric properties of Ba-modified lead lanthanum zirconate stannate titanate ceramics

(Pb_0.97−xLa_0.02Ba_x)(Zr_0.75Sn_0.12Ti_0.13)O₃ ceramics in the composition range 0.1 ≤ x ≤ 0.16 were prepared by conventional solid state reaction process. On increasing Ba content from 0.1 to 0.16 mol, the specimens underwent phase transition from the first order to the second order and the Curie temperature decreased from 85 to 35 °C. With x = 0.16, the specimen showed good pyroelectric properties for practical applications. When a 500 V/mm dc bias field was applied, the specimen showed the maximum pyroelectric coefficient of 5800 μC/m² K and figure of merit of 58 × 10⁻⁵ Pa^−0.5 at Curie temperature.     

Dielectric and piezoelectric properties of neodymium oxide doped lead zirconate titanate ceramics

The dielectric and electromechanical properties of lead zirconate titanate [Pb(Zr, Ti)O₃] ceramic added with neodymium oxide have been systematically studied employing the vector impedance spectroscopic (VIS) technique. The specimens were prepared using the mixed oxide route by adding different mol% of Nd2O₃ (01 to 7mol%) in [Pb(Zr, Ti)O₃] near morphotropic phase boundary. Piezoelectric equivalent circuit parameters R, L, C_a in series and C_b in parallel have been determined by simulating /Z/ and Θ plots. Electromechanical coupling coefficients and strain constants for the radial modes show a peak at about 3 mol%, the dielectric constant peaks at about 1 mol% and voltage constants peak at about 0–75 mol% of Nd₂O₃.     

Improvement of sintering and piezoelectric properties of soft lead zirconate titanate ceramics

Niobium-doped Pb(Zr_0.53Ti_0.47)O₃ (PZTN) ceramics were prepared by the conventional(mixed oxides) method, modified by the addition of a PZT colloid of the same composition. The colloidal precursor was prepared using a coprecipitation method. Such an addition produced a significant improvement in the sinterability of a conventionally prepared PZTN powder and the sintering temperature was reduced, achieving a density 98% theoretical density at 1075 °C for 2 h. The measured piezoelectric properties were as high ask _p = 0.62 andd ₃₃ = 330 ×10^–12CN^–1.     

Crystal structure of lead zirconate titanate ceramics prepared using ultrasonic processing

We have studied how the duration of ultrasonic processing of presynthesized lead zirconate titanate powders influences the crystal structure and physical properties of ceramics produced from such powders. The effect of the ultrasonication time on the sintering temperature, the formation of crystalline phases in the ceramics, and their Curie temperature has been assessed.     

Fluorine-oxygen substitution in MgO-doped lead zirconate titanate ceramics: diffractometric and dielectric studies

A fluorine-oxygen substitution has been realized in a PZT material with a composition Pb_0.89(Ba, Sr)_0.11(Zr_0.52Ti_0.48)O₃ thanks to the introduction of Mg²⁺ ions in the B-site of the perovskite. Oxygen vacancies may exist in the anionic sublattice if the fluorine rate is lower than the required one for a stoichiometric PZT-type ABO₃. The F–O substitution makes the relative amount of rhombohedral phase in the MgO and F-doped PZT samples decrease and a drastic increase of the Curie temperature is observed. Minimum values of dielectric constant, high level dielectric losses and piezoelectric coefficient are obtained for a fluorine concentration close to the stoichoimetric PZT one.     

锆钛酸铅压电陶瓷PZT7的形状记忆效应研究

提出了一种新的方法可以使锆钛酸铅压电陶瓷PZT7具有形状记忆效应.用自制的sawyer-Tower电路测试得到PZT7方形样品发生极化反转对应的电场强度大约为130kV/cm.当施加对称的饱和极化电压370V时,PZT7/Si(109/146μm)悬臂梁端部的变形一电场曲线呈现典型的"蝴蝶"形状.在外电场为0时,悬臂梁端部的变形为0.如果施加不对称的极化电压,悬臂梁端部的变形--电场曲线发生明显的变化.不同的反向极化电压使悬臂梁端部产生不同的变形,而且,电压和变形是一一对应的.因此,在外电场为零时,PZT7/Si悬臂梁可以具有多个不同的稳定位置,表现出明显的形状记忆效应.实验表明,对于长度为15.5mm的PZT7/Si悬臂梁而言,当施加的反向极化电压从120V回到0时,悬臂梁端部产生的变形最大,为68.5μm.     

Effect of Gd-substitution on dielectric and transport properties of lead zirconate titanate ceramics

The gadolinium (Gd)-modified lead zirconate titanate (i.e., Pb_1?xGd_x (Zr_0.65Ti_0.35)_1?x/4O₃; x = 0, 0.07, 0.10 and 0.12) ceramics have been synthesized using a high-temperature (~1,100 °C) solid-state reaction route. Preliminary X-ray structural studies show the formation of single-phase compounds in the tetragonal crystal system. Scanning electron micrographs of the surface of pellet samples show uniform distribution of grains of different shape and size with few voids. It is interesting to observe the significant effect of Gd-substitution on the nature, size, and distribution of grains, and the density of samples. Detailed analysis of dielectric properties of the materials indicates that the materials are non-relaxor but have diffused ferroelectric phase transition. The temperature and frequency dependence of conductivity follows Jonscher’s universal power law.     

Dip-coating conditions and modifications of lead titanate and lead zirconate titanate films

The modifications of dip-coated lead titanate (PT) and lead zirconate titanate (PZT) films strongly depend on the film thickness and the substrate in addition to the heat-treatment temperature. At 500 to 600 ° C, metastable paraelectric pyrochlore grew on glass plates (amorphous plates) when the thickness of the coated films produced by one coating cycle was below 100 nm, while ferroelectric perovskite formed on crystalline substrates or when thick films were coated on amorphous plates. This tendency is discussed in terms of an inhomogeneous reaction and the epitaxial effect. The perovskite PT films coated on single-crystal SrTiO₃ plate at 700 ° C were strongly oriented to thec-axis.     

Laser reflectometry in situ measurement of lead zirconate titanate film growth

A convenient method is described for optical characterization of thin films during growth. The method has been demonstrated on lead zirconate titanate (PZT) films deposited by pulsed laser ablation for various temperatures. The optical constants of the PZT films as well as the film growth rate were determined in situ by fitting (with three free parameters) the calculated reflectance as a function of film thickness to the experimental reflectance curve as a function of deposition time, as obtained by unpolarized laser reflectometry. The fitted parameters are the uniform complex PZT refractive index and the layer thickness (assumed proportional to time), with the complex refractive index of the platinum substrate being measured previously. These results compare well with the subsequent ellipsometric measurements made to assess the precision of the reflectometry technique.     

A fracture-mechanical theory of subcritical crack growth in ceramics

An interpretation is proposed of the power law describing the relation between subcritical crack growth rate and stress intensity factor. It is based on the idea that thermal transients both break and re-establish bonds. The effects, which occur during these processes are mathematically described using a Morse potential. Already the rough model employed provides enough information on bond breaking to understand the principle of subcritical crack growth.