Ca-modified Lead Titanate Research Articles

Preparation and Characterization of Ca+2 modified PbTi03 ceramics by HEBM technique

Lead titanate is one of the important member of perovskite materials group having ABO3 type structure. It exhibits piezoelectric as well as pyroelectric properties. It also shows high ferroelectric property. Ca modified lead titanate having stoichemetric formula Pb1-xCaXTiO3 was synthesized by High Energy Ball Milling (HEBM) method at room temperature. Dopant calcium was incorporated in 1 2 and 3 weight percent simultaneously. Structural and electrical properties were studied by taking measurement with standard instruments; results were compared with pure one. Impedance and quality factor analysis of ca modified lead titanate ceramics were done.

Design and simulation of pyroelectric detectors with nanometer size spider-web for low thermal conductance

We report the design and simulation of uncooled pyroelectric detectors which utilizes a nanometer sized mesh or truss to support the suspended detector. Pyroelectric detector is a class of thermal detector in which the change in temperature causes the change in the spontaneous polarization in the sensing material. Ca modified lead titanate (PCT) was selected as the thermometer in the detector because of its high pyroelectric figure of merit. The design and simulation of pyroelectric detectors have been conducted by simulating the structure with Intellisuite™. Finite element method (FEM) was used to simulate the structural and thermal properties of the device. The simulated detectors had a spider web-like structure with each of the strut (ring) of spider web had a width of 100 nm. In the design, the pyroelectric detectors utilized Ni0.8Cr0.2 absorber, PCT sensing layer, Ti electrodes, Al2O3 structural layer to obtain low thermal conductance between the detector and Si substrate. Three different types of pyroelectric detectors were designed and analyzed. The first design had linear electrode and simple spider web support. The value of the thermal conductance of this detector was found to be 3.98 × 10ź8 W/K. The second design had a longer thermal path than the first one and the thermal conductivity of this device was found to be 2.41 × 10ź8 W/K. High detectivity was obtained by reducing the thermal conductance between the sensing layer and the substrate or the heat sink in the third design. The design was optimized for the best result by modifying the shape, dimension and thickness of various layers namely absorber, electrodes, sensing layer, and struts. The thermal conductance between the sensor and the substrate using the third design was found to be as low as 4.57 × 10ź9 W/K which is significantly lower than previously reported values. The thicknesses of the web structure, web support, electrodes, sensing layer, and absorber of the final structure were 2, 1, 0.5, 2, and 0.2 µm respectively for this value of thermal conductance. The absorber diameter was 50 µm and the diameter of the spider web was 200 µm. A total of 80 struts with 100 nm width were used in the design.

Raman scattering study of ca-modified lead titanate

The paraelectric to ferroelectric phase transitions were studied by Raman scattering in Ca-doped lead titanate ceramics. The soft optic modes responsible for the ferroelectric phase transitions were clearly observed. The A(1)(1TO) mode, which softens toward T(c), contains four subpeaks. The frequencies of these subpeaks depend to a great extent on the Ca content and the temperature. These behaviors are discussed on the basis of the anharmonicity of lattice vibrations.

Raman Scattering Study of Ca Modified Lead Titanate

The lattice dynamical properties of (Pb1 − x Ca x )TiO3 ceramics were investigated by Raman scattering. The low-frequency spectra show the strong composition and temperature dependences. The composition dependence of Raman spectra at room temperature is different from the previous work [S.-Y. Kuo, C.-T. Li and W.-F. Hsieh, Phys. Rev. B 69, 184104 (2004).]. This difference is probably attributed to the aging effect of MnO doping. Temperature dependence of Raman spectra of (Pb0.75Ca0.25)TiO3 behaves as expected by the selection rule and the lowest-frequency peak softened and broadened as approaching T c .

High Pyroelectric Coefficients of Ca-Modified Lead Titanate Sol-Gel Thin Films Obtained by Multiple Deposition and Crystallization

Ferroelectric thin films of (Pb 0.76 Ca 0.24 )TiO 3 nominal composition have been obtained, by multiple spin-on deposition on Si-based substrates and RTP crystallization, from precursor solutions processed by the diol-based sol-gel method. A mixed <001>/<100> or <111> preferential orientations were promoted by appropriate choice of the substrate, as determined by XRD measurements. The effect of substrate annealing and crystallized film annealing on the pyroelectric coefficient of the films was determined and discussed. Poling of the films at room temperature and at 150 °C was tested. The highest pyroelectric coefficient achieved was n ∼ 40.0 2 10 m 9 Ccm m 2 K m 1 .

Fatigue properties and microstructures of (Pb,Ca)TiO3 ceramics

Electric fatigue properties and microstructures of Ca-modified lead titanate (Pb1−xCaxTiO3) ceramics were investigated using polarization-electric field measurements and transmission electron microscopy. Specimens show an extraordinary increasing in remanent the polarization after switching up to 106 cycles for specimens with certain compositions. The coercive fields of specimens with different Ca content exhibit different behavior. The x=0.5 specimens show a decreasing in the coercive field when cyclically loaded. The x=0.4 specimen just shows a decrease and then an increase in Ec while the coercive field of the x=0.3 specimens reveals an increasing trend. Microstructural investigations indicate that when the c/a ratio is large, intersecting domain boundaries are induced under repeated application of electric field. On the other hand, when x=0.5, the number of domain boundaries does not increase significantly, suggesting that domain boundary mobility is higher for Pb0.5Ca0.5TiO3 specimens.

Characterization of Calcium-Modified Lead Titanate Thin Films Derived from a Diol-Based Sol–Gel Process

Polycrystalline thin films of Ca-modified lead titanate (PCT) were deposited on Pt/SiO2/Si substrates using a diol-based sol–gel process. Calcium acetylacetonate hydrate was adopted as a starting material instead of the calcium acetate or calcium nitrate tetrahydrate used conventionally. By changing the Ca content (5–35 mol%) and heating temperature (500–800°C), the influences of various processing parameters on the characteristics of thin films were studied. With the increase of the Ca content, the relative dielectric constant (εr) of PCT thin film increased from 43 to 70 at the heating temperature of 700°C. It was found that the coercive field (Ec) and the remanent polarization (Pr) decreased, but the pyroelectric coefficient (γ) increased with an increase of Ca content. The results reveal that PCT thin film with a Ca content of 25 mol% exhibits the largest figures of merit for the voltage responsivity and the specific detectivity at a heating temperature of 700°C.

Quantitative texture analysis applied to the study of preferential orientations in ferroelectric thin films

The occurrence of preferred crystallographic orientations, or texture, is a determinant factor of the behaviour of polar materials, like ferroelectric thin films. This is the reason why numerous works have been focused in the preparation of highly oriented films for pyroelectric sensors and electromechanical applications. Traditionally, preferred orientations were determined by the analysis of the main reflections obtained by X-ray diffraction, which only in some cases are characteristic of the texture of the material. Regardless of the interest of this subject, the quantitative texture analysis of ferroelectric thin films has not been systematically applied. This consists in the measurement of pole figures with a goniometer, and the determination of the orientation distribution function. In this work we summarise briefly the principles of the quantitative texture analysis and we demonstrate its application to the study of different ferroelectric thin films: La and Ca modified lead titanate (PTL and PTC) and lead zirconate titanate (PZT). This method allows the study of the characteristics of the type of texture and the identification of the different components that contribute to the final texture of the material. An indicative value of the texture strength is also obtained for both the ferroelectric film and the substrate layers. This information allows us the study of the process that leads to the orientation in thin films, and to obtain correlations between texture and physical properties.

C-Axis oriented sol–gel (Pb,Ca)TiO3 ferroelectric thin films on Pt/MgO

Ca-modified lead titanate thin films were prepared on (111)Pt/(100)MgO substrates by spin-on sol–gel process. Two layers of 0.3 mol/l solution were deposited on the substrate and each of them subjected to drying and rapid thermal processing (RTP) for crystallization, which reduces tensile strains. Single perovskite films with a preferred orientation in the direction perpendicular to the plane of the substrate were obtained as measured by X-ray diffraction analysis. Pyroelectricity of these films was measured before and after a polarization process being the pyroelectric coefficient close to ≈2.5×10−8 C cm−2 K−1. Ferroelectric properties were also measured, obtaining values of PR of ≈25 μC cm−2 and Ec of ≈110 kV.cm−1. Compressive strains resulting from the differences between thermal expansion coefficients of the substrate and the film cause the (001) orientation of the (Pb,Ca)TiO3 perovskite layer, that is very convenient for pyroelectric devices.

The mechanical and electromechanical properties of calcium-modified lead titanate/poly(vinylidene fluoride-trifluoroethylene) 0-3 composites

Thin film composite sensors have been fabricated which incorporate piezoelectric ceramic particles in a polymer matrix. Such composites are more compliant than pure piezoelectric ceramics and can be embedded in thick structures to monitor internal mechanical conditions such as the evolution of damage. The mechanical properties and electromechanical interaction of composite films consisting of Ca-modified lead titanate particles in a poly(vinylidene fluoride-trifluoroethylene) matrix are examined in this paper. The viscoelastic properties of these composites (with various volume fractions, up to 60% ceramic) have been measured over a range of frequencies (0.01 to 100 rad ). These composite properties are primarily controlled by the viscoelastic properties of the polymer matrix, and are shown to depend greatly on frequency and ceramic content. The complex piezoelectric coefficients and have been measured for these composites for various volume fractions and over a frequency range from 5 to 100 rad . The magnitudes and phase angles of the piezoelectric coefficients are also shown to be highly frequency dependent.

Anomalous elastic and dielectric behavior in nanocrystalline Ca-modified lead titanate (PTC) films

Thin amorphous PTC-films of 1 μm thickness were produced by rf-sputtering at room temperature. A subsequent annealing process enabled us to prepare different grain sizes which have been characterised by x-ray powder diffraction. At the transition from the amorphous to the nanocrystalline state the elastic modulus c 11 measured by HR-Brillouin spectroscopy exhibited a surprising instability. The dielectric constant showed not only the expected increase with increasing grain size but also a significant relaxor behavior.

Ferroelectric improvements of (Pb,Ca)TiO3 thin films

Ca-modified lead titanate thin films of nominal composition Pb 0.76 Ca 0.24 TiO 3 , deposited on Pt/TiO 2 /(100)Si substrates, have been prepared by sol-gel spin-on process. Crystallization of the samples was promoted by Rapid Thermal Processing (RTP). Different PbO excesses in the precursor solution and different heating rates during the RTP have been tested. Hysteresis loops improve and switching currents increase when films are deposited from solutions with a 10 mole% PbO excess and are crystallized with a heating rate of 30°C/sec. These improvements are associated to a good fit of the film stoichiometry and to a reduction of the substrate-ferroelectric interface. Postannealing of the crystallized (Pb,Ca)TiO 3 films, leads to a favourable distribution of the charged defects liberating domains and facilitating their switching.

The low-frequency Young modulus and internal friction in Pb-Ca and Pb-Zr titanate ceramics

Measurements of the elastic moduli of Ca-modified lead titanate ceramics, as a function of temperature, have been made for frequencies in the range 0.2-20 Hz and for poling fields in the range , using the three-point bending method. The results indicate that there are extrinsic contributions to the elastic modulus due to microstructure and polarization processes in the samples, with the contribution of microstructure greater than that of the polarization state. We found a relaxational behaviour of the elastic modulus due to thermal fluctuations with large relaxation times induced by order-parameter fluctuations in the phase transition and to the diffusive character of the ferro-paraelectric transitions that take place in materials of these compositions. Comparisons with very low-frequency behaviour of PZT ceramics are made and the results are discussed on the basis of the existent theoretical models dealing with thermal fluctuations at the ferro-paraelectric phase transition.

Evidence of an Elastic Instability between the Amorphous and the Microcrystalline State of Ca-modified Lead Titanate as revealed by Brillouin Spectroscopy

Evidence of an Elastic Instability between the Amorphous and the Microcrystalline State of Ca-modified Lead Titanate as revealed by Brillouin Spectroscopy

Elastic moduli in modified lead titanate ceramics

Abstract Measurements have been made of the elastic modulus as a function of temperature in Sm or Ca modified lead titanate ceramics, for a frequency of 0.5 Hz and poling fields between zero and 90 kV/cm, using the three bending points procedure. The results show the existence of extrinsic contributions due to the state of the microstructure and the poling processes of the samples, the contribution from the microstructure being greater than that from the polarization state. The variation with tetragonal distortion, c/a - 1, must be attributed to differences in longitudinal and transversal electrostriction coefficients.

Sol—gel processing of Pb 1 − xCa xTiO 3 thin films

Thin films of Ca-modified lead titanate were fabricated by sol—gel processing. The complex alkoxides were prepared by reacting lead acetate and calcium chloride with titanium tri-isopropoxide mono-acetylacetonate. Titanium tri-isopropoxide mono-acetylacetonate was synthesized by addition of acetylacetone to titanium tetra-isopropoxide as a chelating agent. Thin films were deposited on Si(100), MgO(100) and Pt/MgO(100) substrates by dip-coating. X-ray diffraction analyses were carried out for thin films to investigate crystalline phases, crystallographic orientation and lattice parameters. Thin films deposited on all the substrates used exhibited perovskite single phase. Conditions for obtaining homogeneous crack-free thin films were determined.

Influence of thermal treatment on the properties of Ca-modified lead titanate thin films

Results are presented on the influence of thermal treatment on the final properties of CA-modified lead titanate thin films, obtained by a sol-gel method and spin coating. X-ray diffractometry, electron microscopy, Auger spectroscopy, and electrical measurements have been used to characterize samples. Films obtained by rapidly heating (> 500°C min −1) the deposits show a lower than expected tetragonal distortion, but are free from pyrochlores and have better ferroelectric properties.

Mechanical characterization of calcium-modified lead titanate ceramics by indentation methods

The microstructural dependence of the mechanical properties of Ca-modified lead titanate piezoelectric ceramics were studied. To this end, a combination of the Vickers and Knoop indentation techniques at different applied loads was used as simple method for mechanical characterization of these ceramics. The influence of porosity, grain size and tetragonal distortion on hardness, Young's modulus and toughness is discussed. An attempt to obtain internal stresses from toughness variation reveals the limitations of the method.

Thickness dependence of ferroelectric properties of modified lead titanate ceramics

Abstract Using a pulse sequence method, switching currents in Ca modified lead titanate ceramics have been measured. Slices in the hundred micron range were used. It has been found that the threshold switching voltage depends on thickness as dn, with n 0). The asymmetric effect found in the switching currents has been explained as due to the internal field produced by space charge, which should be dependent on the ratio vB/vG (volume of grain boundary / volume of grain). The amount of 90° domains back-switched after the first pulse has been calculated and the dynamic of relaxation has also been established.

PmP113. Frequency dependence of the piezoelectric d31coefficient as a function of ceramic tetragonality

Abstract Measurements have been made of the complex piezoelectric coefficient (d31), by a quasistatic method, so as to determine its real and imaginary components as a function of frequency (f = 10−3 - 103 Hz) and temperature. Results obtained with Ca-modified lead titanate and lead lanthanum titanate-zirconate ceramic samples reveal the existence of relaxations at a very low frequency for the former and at frequencies of tens of hertzs for the latter. Tetragonal distortion and polar microregions could be considered as the respective causes of such relaxation processes.