Lead Calcium Titanate Ceramics Research Articles

Ferroelectric Properties of Laser Ablated Sm Modified PCT Thin Films

Crystallized thin films of samarium modified lead calcium titanate ceramics with composition; Pb0.66Sm0.08Ca0.24Mn0.02Ti0.98O3 were deposited under different annealing and laser energy conditions. Thin films deposited at these conditions show a surface roughness, coercive field and remnant polarization in the range of 1.9–6.0 nm, 120–220 kV/cm and 4–11.5 μC/cm2, respectively. I-V and C-V measurements were also performed in order to study the electrical behaviour of the films.

Microstructure and electron properties of Sm modified lead calcium titanate ceramics

Abstract Lead calcium titanate ceramics modified by partial substitution of rare earths for lead, particularly, (Pb, Sm, Ca)(Ti, Mn)O 3 ceramics, were explored for their structural, dielectric and piezoelectric properties. These modified ceramics with a composition of Pb 0.76−3 x /2 Sm x Ca 0.24 Ti 0.98 Mn 0.02 O 3 ( x = 0 − 0.08) were prepared by solid state reaction route. The XRD study showed single-phase formation with tetragonal structure. Lattice anisotropy ( c / a ) was found to decrease from 1.057 to 1.023 with increase in Sm substitution from 0 to 8 mol%, respectively. Microstructural study revealed the average grain size between 1.2 and 2.2 μm. The relative density was found to increase from 95% to 98.4% with increase in samarium substitution from 0 to 8 mol%, respectively. Detailed dilatometric study was performed in order to study the shrinkage behaviour during the sintering schedule. The maximum shrinkage was found to occur between 900 °C and 1100 °C. The dielectric constant ( ɛ ′) and loss (tan δ ) for all the compositions were investigated over a wide frequency (100 Hz to 1 MHz) and temperature (25–450 °C) range. The room temperature (25 °C) dielectric constant was found to increase from 130 (at 10 kHz) for pure lead calcium titanate sample to 380 (at 10 kHz) for 8 mol% samarium substituted sample and also showed a decreasing trend with increase in the frequency for all the substitutions (0–8 mol% Sm). Curie temperature, T C (determined from the plot of ɛ ′ vs. temperature) and tan δ were found to decrease with increasing samarium content. The Curie temperature was found to decrease from 348 °C to 192 °C for 0–8 mol% Sm substitutions, respectively. Piezoelectric coefficients were also measured at room temperature. Electromechanical anisotropy ( k t / k p ) was observed to increase from 11.7 (0 mol% Sm) to 27 (8 mol% Sm). Piezoelectric anisotropy ( d 33 / d 31 ) was also observed to increase from 22.5 for un-substituted sample to 28 for the sample substituted with 8 mol% samarium. The experimental results successfully showed that samarium substitution not only reduces the lattice anisotropy but also helps in improving piezoelectric properties.

Comparison of piezoelectricity in Ta 5+ and La 3+ substituted lead calcium titanate ceramics

This paper reports the experimental investigations on the effect of La 3+ and Ta 5+ substitution on the structural characteristics and dielectric and piezoelectric properties of lead calcium titanate (PCT) ceramic. The PCT samples with A-site and B-site substitution having the composition formula Pb 0.76− x /2La x Ca 0.24(Ti 0.98Mn 0.02) 1− x /2O 3 and Pb 0.76Ca 0.24Mn 0.02Ti 0.98−5 x /4Ta x O 3, x=0 and 0.02, respectively , were prepared using conventional solid-state reaction method. Phase formation and structural analysis were studied using X-ray diffraction and scanning electron microscopy, respectively. Dielectric constant ( ε′) and loss tangent (tan δ) as a function of frequency were measured at room temperature as well as elevated temperature. Both ε′ and tan δ decreased with increase in frequency at room temperature. Curie temperature decreased with La and Ta doping in PCT ceramics due to a decrease in the tetragonality of PCT ceramics. Piezoelectric charge coefficients ( d 33, d 31) increased with La 3+ substitution due to reorientation of the grains and decreased with Ta 5+ substitution because of the increase in porosity. Figure of merit d h g h increased and decreased with La and Ta substitution, respectively. A good ferroelectric behaviour is obtained for La substitution, while no hysteresis is obtained for Ta substitution.

Structural and electrical properties of lanthanum-substituted lead titanate ceramics

The effect of lanthanum substitution on the structural, dielectric and piezoelectric properties of lead calcium titanate (PCT) ceramics is studied. Samples with compositional formula Pb0.76− x La x Ca0.24Ti0.98Mn0.02O3 (PLCT) (x = 0–0.08, in steps of 0.02) were prepared by the conventional dry ceramic technique. Phase and structural analysis was carried out using XRD and SEM respectively. X-ray analysis confirmed the formation of single-phase compound with tetragonal crystal structure. Dielectric properties were studied in detail as a function of frequency and temperature. The Curie temperature (T C) and tetragonality (c/a) was found to decrease with increase in lanthanum content. The Curie temperature was also confirmed from the thermal-expansion behaviour of the sintered samples. Piezoelectric coefficients (d 33, d 31, g 33, g 31, g h, d h, k t and k p) were measured at room temperature. From this study it is found that La3+ substitution helps in the improvement of electro-mechanical anisotropy.

Improved piezoelectric properties via mechano-chemical activation in modified PCT ceramics

High-density samarium modified lead calcium titanate ceramics were successfully prepared by using a novel mechano-chemical activation technique, which skips the calcinations steps at an intermediate temperature that is always required in the normal conventional technique. Better densification could be achieved by activation process. XRD study showed single-phase formation with tetragonal structure and microstructural study revealed almost uniform grain size of 1.4μm. Dielectric study demonstrated sharp peak in dielectric versus temperature plots and slightly low value of the Tc as compared to that observed for samples prepared by conventional technique. The mechanical alloying technique rendered drastic improvement in piezoelectric properties. The ratio of electromechanical anisotropy (kt/kp) was obtained to be ∼62 as compared to 52 in the case of samples by conventional process. Comparison in the structural and electrical properties is discussed in detail for conventional versus mechano-chemical alloying process.

Dielectric and piezoelectric properties of microwave processed Sm substituted PCT ceramics

The effect of samarium substitution on the structural, dielectric and piezoelectric properties of lead calcium titanate ceramics was investigated. Dense ceramics with nominal composition Pb0.76−3x/2SmxCa0.24Ti0.98Mn0.02O3 (x = 0–0.08) were fabricated by a novel, simple, energy and time efficient, and environment friendly microwave sintering process. The samples were sintered at 1100°C for 30 min. All the compositions show single phase with tetragonal structure. Tetragonality decreases and relative density increases with increase in samarium substitution. The variation of the dielectric constant with temperature shows a ferroelectric phase transition and the transition temperature decreases with increase in the amount of samarium. Diffusivity increases with samarium substitution. All the compositions show well-defined ferroelectric behaviour. The electromechanical thickness coupling coefficient (kt) and piezoelectric longitudinal coefficient (d33) showed an increasing trend whereas the electromechanical planar coupling coefficient (kp) and the magnitude of the piezoelectric transverse longitudinal coefficient (d31) showed a decreasing trend with increase in samarium substitution level, which in turn results in an increase in electromechanical anisotropy.

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.

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.

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.

Local polarization in Lead-Calcium Titanate ceramics

Calcium-modified Lead Titanate ceramics Pb 0.76 Ca 0.24 [(Co 0.5 W 0.5) 0.05 Ti 0.95O 3] are studied by means of dielectric and thermal expansion measurements as a function of temperature. Results show that the phase transition has a diffusive character with an exponent τ that decreases when temperature increases. Above the transition temperature, Tc, the electrical conductivity of samples affects the thermal behaviour of the dielectric constant. From thermal expansion measurements, results show that the thermal elongation and thermal expansion coefficient separate from their normal behaviour at a temperature Td = 460° C, much higher than Tc and close to the phase transition temperature of PbTiO 3. The difference Δα = α − α 0 (anomalous part of the thermal expansion coefficient) decreases to zero when the temperature increases from Tc, following a logarithmic law Δα = F( logΔT). Thermal expansion results may be ascribed to some type of local polarization in the crystalline grains, which disappears near the phase transition temperature of PbTiO 3.