Lead Calcium Titanate Research Articles

X-ray characterisation of chemical solution deposited PbTiO 3 films with high Ca doping

Single crystalline phase lead calcium titanate (Pb 1− x Ca x TiO 3) (PCT) thin films, with Ca 2+ contents between 24 and 50 at.%, have been prepared onto Pt/(1 0 0)MgO by chemical solution deposition and rapid thermal processing. The sol–gel process used enables the synthesis of air-stable and precipitate-free solutions with high Ca 2+ contents (up to 50 at.% of substitution of Pb 2+ by Ca 2+ in the PbTiO 3 perovskite has been tested). Structure and texture of the crystalline films have been determined by X-ray diffraction (XRD), using the Bragg–Brentano geometry. Strain of the films structure has been calculated by the variance method using the 1 1 1 perovskite peak of the grazing incidence XRD patterns. Data obtained by XRD and dielectric properties measured in the PCT films are compared with those reported for bulk ceramics.

Leakage current and relaxation characteristics of highly (111)-oriented lead calcium titanate thin films

Highly (111)-oriented (Pb0.76Ca0.24)TiO3 (PCT) thin films were grown on Pt/Ti/SiO2/Si substrates by a sol–gel process. The Au/PCT/Pt metal–insulator–metal film capacitor showed well-saturated hysteresis loops at an applied field of 800 kV/cm with remanent polarization (Pr) and coercive electric field (Ec) values of 18.2 μC/cm2 and 210 kV/cm, respectively. The leakage current depended on the voltage polarity. At low electrical field and with Pt electrode biased negatively, the Pt/PCT interface exhibits a Schottky emission characteristics. The Au/PCT interface forms an ohmic contact. The conduction current when the Au electrode is biased negatively shows a space-charge-limited behavior. The dielectric relaxation current behavior of Au/PCT/Pt capacitor obeys the well-known Curie–von Schweidler law at low electric field. At higher fields, the currents have contributions to both dielectric relaxation current and leakage current.

Electrical properties of compositionally graded lead calcium titanate thin films

The compositional gradient (Pb 1− x Ca x )TiO 3 (PCT) thin films of x=0 and 24 mol% were fabricated on Pt/Ti/SiO 2/Si substrates by using a modified sol–gel process. The final structure consists of two layers, up-graded films starting from PbTiO 3 on the Pt electrode to the top PCT(24) layer, whereas films with opposite gradient are called down-graded films. Highly (100)-oriented graded PCT thin films have been obtained when the graded PCT thin films were annealed at 600 °C. At 100 kHz, the dielectric constants were 79 and 128, respectively, for the up-graded and down-graded PCT films. The pyroelectric coefficient ( p) of the graded films was measured by a dynamic technique. At room temperature, the values of p and figure-of-merits ( F D) of the up-graded and down-graded PCT films are 95 μC/m 2 K and 9.1×10 −6 Pa −0.5, 112 μC/m 2 K and 8.6×10 −6 Pa −0.5, respectively.

Characterization of sol-gel synthesized lead calcium titanate (PCT) thin films for pyro-sensors

Thin films of Pb 0.80Ca 0.20TiO 3 and Pb 0.76Ca 0.24TiO 3 are prepared using the sol-gel technique on ITO coated corning 7059 glass. X-ray diffraction studies on these films show perovskite structure with tetragonal phase. Dielectric, pyroelectric and ferroelectric studies are carried out on these films. Results suggest that PCT76/24 with pyrocoefficient (∼43 nC cm −2 K −1) and voltage responsivity (∼2340 V cm −2 J −1) is a promising pyrosensor material.

Nanoscale imaging of elastic and piezoelectric properties of nanocrystalline lead calcium titanate

In this study the influence of the annealing conditions on the surface morphology and the elastic and piezoelectric properties of thin-film lead calcium titanate samples were investigated with enhanced atomic force microscopy techniques like tapping mode, atomic force acoustic microscopy and ultrasonic piezo-mode. The morphology of the thin-films can serve as an indicator of their properties, whether they are in an amorphous, polycrystalline and/or nanocrystalline state proving the imaging capability of dynamic force microscopy techniques.

Effects of excess PbO on the preparation process of modified lead–calcium titanate ceramics

The effects of excess PbO on the preparation process of modified lead–calcium titanate ceramics were studied. The sintering period were divided into two stages: the initial sintering stage and the grain growth stage, at which the temperatures were chosen to be 980 and 1000 °C, respectively. In this study, an excess amount of PbO was added before the calcining stage and the initial sintering stage. The changes in the ceramic performance due to the excess amount of PbO were investigated. The figures of merit were the electromechanical coupling coefficients and mechanical quality factors. We observed that 1 mol% excess of PbO added at the calcining stage and 2.5 mol% excess of PbO added at the sintering stage would lead to a better performance and a smaller weight loss. By using the XRD and SEM results, the effects caused by the excess of PbO in the material processing were discussed.

Structure and Electrical Properties of Lead Calcium Titanate Nanocrystalline Thin Films Prepared by a Sol-Gel Process with Rapid Thermal Annealing

Nanocystalline (Pb 0.76 Ca 0.24 )TiO 3 (PCT) thin films were grown on Pt/Ti/SiO 2 /Si(100) substrates by a modified sol-gel process. Randomly oriented tetragonal PCT thin films have been obtained. Atomic force microscopy reveals that the films are dense, have a smooth surface, and the grain size is about 40 nm for polycrystalline PCT film on a Pt/Ti/SiO 2 /Si(100) substrate annealed at 650 °C by rapid thermal annealing. The electrical measurements were conducted on PCT films in metal-ferroelectric-metal (MFM) capacitor configuration. The results show that the film exhibited good ferroelectrity with remanent polarization and coercive electric field of 36 μC/cm 2 and 240 kV/cm, respectively. At 100 kHz, the dielectric constant and dielectric loss of the film are 295 and 0.027, respectively, for thin films of 200 nm thickness.

Diffuse phase transition and relaxor properties of nanocrystalline lead calcium titanate

Recently the question arised, how the physical properties of a ferroelectric change when the grain size is reduced to the nanometer range. We have produced amorphous Lead Calcium Titanate (PTC) films by rf-sputtering onto Pt/Ti/Si substrates. We then prepared different grain sizes by two different types of annealing processes. To investigate the dielectric properties the temperature and frequency dependence of the dielectric constant was recorded and temperature dependent Raman spectroscopy was used to look for phase transitions and symmetries. Independent of the annealing method all nanocn stalline samples showed a significant diffusivity of the phase transition. The dielectric properties also changed from classical ferroelectric to relaxor behaviour with a large frequency dependence of the dielectric constant.

Growth of lead calcium titanate single crystals and their characterisationxs

Single crystals of perovskite ferroelectric solid solutions Pb1-x Ca x TiO3 with different Ca content were grown from high temperature solutions by Remeikas technique using KF as a flux. The crystals were nearly equidimensional in morphology and slightly bigger size crystals were obtained for 10 mole% of Ca content. Two dimensional layer growth patterns have been found on the (100) surface. Marked influence of Ca substitution on lattice parameter values and curie temperature has been found using X-ray diffraction and differential scanning calorimetry studies.

Seeding acceleration of perovskite crystallization in lead calcium titanate thin films

Seeding to enhance the kinetics of phase transformation was demonstrated with a special seeding process using crystallized ultrafine lead titanate powder to lower the temperature of perovskite formation of the modified lead calcium titanate thin films. X-ray diffraction and scanning electron microscopy show that the pyrochlore-to-perovskite phase transformation temperature of the seeded lead calcium titanate film can be lowered by as much as 50°C when compared with the unseeded lead calcium titanate film. This is most likely related to the decrease of activation energies of nucleation which, in turn, increases the kinetics of the perovskite formation, since numerous nucleation sites are provided. The similarity, or small lattice mismatch of crystal structure between the lead titanate and perovskite of the modified lead calcium titanate film supports these explanations.

A-site cation ordering and dielectric behavior of lead-calcium titanate

The microstructure and dielectric behavior of lead-calcium thanate (Pb0.5Ca0.5)TiO3 ceramics were investigated Three types of ordering—1/2{111}, 1/2{110} and 1/2{100} are found to be coexisted in (Pb0.5Ca0.5)TiO3 and the ordering degree can be intensified by long time annealing. The effects of ordering degree on the dielectric behavior were studied, which showed a less strong frequency dispersion (ΔTo), but a more diffused FE → PE phase transition (5) with the ordering degree increased.

Polytype structures in lead-calcium titanate ceramics

Abstract High resolution transmission electron microscopy (HRTEM) was used to investigate the ion ordering structures of lead-calcium titanate (Pb 0.5 Ca 0.5 )TiO 3 . The results show that apart from the presence of 1 2 “111”, 1 2 “110” and 1 2 “100” superstructures, there is a 1 4 “110” modulation structure coexisting in (Pb 0.5 Ca 0.5 )TiO 3 . The characteristics of the 1 4 “110” modulation structure were determined at the lattice level. Probable arrangements of the atoms in the atomic layers in the modulation structure were suggested.

High-resolution electron microscope study of the ordered lead-calcium titanate ceramics

High-resolution electron microscopy (HREM) has been used to demonstrate the structural characteristics of ordered (Pb0.5Ca0.5) TiO3. The fine structure of both ordered and disordered domains was exposed in lattice level. It was shown that there are 1/2 {111}, 1/2 {110} and 1/2 {111} ordering coexisted in (Pb0.5Ca0.5) TiO3 and all of them are chemical ordering due to the layers of Pb2+ and Ca2+ cations align alternatively along different directions. For 1/2 {111} chemical ordering, a special type of boundary defined as “vernier boundary” was introduced.

ChemInform Abstract: Modified Lead Calcium Titanate Ceramics with a Relatively Large Dielectric Constant for Hydrophone Applications.

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Modified Lead Calcium Titanate Ceramics with a Relatively Large Dielectric Constant for Hydrophone Applications

Modified lead titanate of the base composition (Pb,Ca)Ti‐(Co,W)O3+ 0.01 mol% MnO was doped with 2 to 6 mol% strontium and barium to increase the dielectric constant, K, while preserving a high piezoelectric anisotropy (d33/d31). K was increased above 500 and a d33/d31 ratio of 34/1 was achieved when the composition Pb0.65Ca0.31Sr0.04Ti0.09‐(CO0.5W0.5)0.06O3+ 0.01 mol% MnO was fabricated. The large d33/d31 resulted in an impressive hydrostatic piezoelectric coefficient (dh= 81 × 10—12 m2/V). The relatively low transition temperature (Tc= 120°C) did not result in an increased aging rate when samples were tested at 40°C and 99% humidity for 120 h after poling. A small tetragonality ratio (1.008) enabled saturation of ceramic properties at poling fields as low as 30 kV/cm at 100°C.

Thin-film semiconductor electrodes deposited on pyroelectric ceramics: Application to compact spectrally selective pyroelectric IR sensors

Abstract Ferroelectric materials like lead calcium titanate ceramics have been demonstrated to be excellent materials for pyroelectric detectors. They are usually covered with electroded black gold. This material is extensively used to obtain both a fair IR absorption and a good electrical contact. Spectrally selective compact IR sensors for specific applications could be obtained by means of vacuum deposition on the pyroelectric substrate of the specific multilayer IR filter. However, very smooth substrates are required for proper adhesion of the multilayer, which is not the case for black gold layers. Besides, these layers do not possess the optical properties required in the filter's design and development process. Semiconductors like germanium or silicon are typical IR optical materials widely used in optical multilayers. Vacuum-evaporated Ge thin films have been deposited onto pyroelectric lead calcium titanate ceramics. In this work, a new system to improve the performance of lead calcium titanate ceramics for an infrared sensor is proposed. Studies have also been performed in order to establish the behaviour of this material as both an electrode and first layer. The feasibility of obtaining compact spectrally selective pyroelectric IR sensors has also been proved.

Study of the piezoelectric properties of 1-3 composites as a function of the mechanical characteristics of the phases

The behaviour of the electromechanical parameters (d31, Kp) of biphasic composite materials has been studied as a function of the relative elastic compliances of the phases and the volumetric fraction of the piezoelectrically active phase, a ferroelectric ceramic in the systems under consideration. The mathematical expressions for the dielectric and piezoelectric parameters obtained from models of 1-3 connectivity composites were the starting point for this study.1,2The discussion has taken into consideration different values of d,31 and d33. Values for lead titanatezirconate and lead-calcium titanate, the latter having a high piezoelectric anisotropy, have been considered.The results show that the low coupling of the planar mode of the resonance in the composite disk is strongly dependent on the relative elastic compliances of the component phases, as well as on the d3l/d33 ratio of the ceramic phase. Additionally, this analysis reveals that it is possible to get a value of Kp of the composite, which is virtually zero, simply by varying the ratio between the elastic compliances of the phases, even when the composite exhibits a nonzero value of the d31 coefficient. A high ratio between elastic compliances of the matrix and the ceramic SMij/SEij will result in values of Kp of the composite very close to zero.

Piezoelectric properties of modified lead calcium titanate and an epoxy resin composites

Abstract Composites of 1–3 connectivity made from Ca-modified lead titanate ceramic pellets and extruded fibers and an epoxy resin were prepared and characterized as ultrasonic transducers. Although the properties of the two types of ceramics present differences, composites have uniquely a thickness resonance mode. Frequency numbers close to the ceramic values are observed.

90° Domain reorientation in Lead-Calcium Titanate ceramics

Abstract The 90° domains reorientation is studied by thermal expansion on Lead-Calcium Titanate ceramics that were poled by the usual procedure at different values of the poling electric field. The reorientation of 90° domains under dinamic conditions is also studied through measurements of lateral switching strain at different temperatures of the samples. The results show good agreement on the percentage of 90° domains that remain oriented in the electric field direction for both procedures. The results also suggest a poling procedure that provides a remanent polarization 10–15% higher than that obtained by usual poling methods.

Anisotropy in hot-pressed lead-calcium Titanate

Abstract The anisotropic behaviour of hot-pressed calcium Lead Titanate (Pb/Ca=76/24) well densified (>95%) and porous, poorly densified (<90%) ceramic is studied by means of dielectric and thermal measurements. The results clearly show the influence of internal mechanical stresses and proportion of the gel component on dielectric and thermal expansion behaviour. The porosity drastically modifies the anisotropic behaviour of hot-pressed ceramics.