Sawyer-Tower Circuit Research Articles

Changes in Ferroelectric Properties of 0.7PMN–0.3PT Ceramic with Compressive Stress

In this work, effects of compressive stress on the ferroelectric properties of 0.7PMN–0.3PT ceramics were investigated. The ceramics with the formula (0.7)Pb(Mg1/3Nb2/3)O3-(0.3)PbTiO were prepared by a conventional mixed-oxide method. The ferroelectric properties under compressive stress were observed at stress up to 80 MPa using a compressometer in conjunction with a modified Sawyer-Tower circuit. The results showed that applied stress had a significant influence on the ferroelectric properties of 0.7PMN–0.3PT ceramics. Ferroelectric characteristics, i.e. the area of the ferroelectric hysteresis (P-E) loop, the saturation polarization (Psat), the remanent polarization (Pr) and loop squareness (Rsq), decreased with increasing compressive stress, while the coercive field (Ec) remained relatively constant. Stress-induced domain wall motion suppression and non-180oC ferroelectric domain switching processes are responsible for the changes observed.

Ferroelectric properties of Pb(Zr1/2Ti1/2)O3–Pb(Zn1/3Nb2/3)O3 ceramics under compressive stress

Effects of compressive stress on the ferroelectric properties of ceramics in PZT–PZN system were investigated. The ceramics with a formula (1− x )Pb(Zr 1/2 Ti 1/2 )O 3 – x Pb(Zn 1/3 Nb 2/3 )O 3 or (1− x )PZT–( x )PZN ( x = 0.1–0.5) were prepared by a conventional mixed-oxide method. The ferroelectric properties under the compressive stress of the PZT–PZN ceramics were observed at the stress levels up to 170 MPa using a compressometer in conjunction with a modified Sawyer–Tower circuit. It was found that with increasing compressive stress the area of the ferroelectric hysteresis ( P – E ) loops, the saturation polarization ( P sat ), the remnant polarization ( P r ), and the coercive field ( E c ) decreased. These results were interpreted through the non-180° ferroelastic domain switching processes.

Stress-dependent ferroelectric properties of Pb(Zr1/2Ti1/2)O3–Pb(Zn1/3Nb2/3)O3 ceramic systems

Abstract Effects of compressive stress on the ferroelectric properties of ceramics in PZT–PZN systems were investigated. (1 − x )Pb(Zr 1/2 Ti 1/2 )O 3 ( x Pb(Zn 1/3 Nb 2/3 )O 3 or (1 − x )PZT–( x )PZN ( x = 0.1–0.5) ceramics were prepared by a conventional mixed-oxide method. The ferroelectric properties under compressive stress of the PZT–PZN ceramics were observed at stress levels up to 170 MPa using a compressometer in conjunction with a modified Sawyer–Tower circuit. It was found that with increasing compressive stress the area of the ferroelectric hysteresis (P–E) loops, the saturation polarization ( P sat ), the remanent polarization ( P r ), and the coercive field ( E c ) decreased. These results were interpreted through the non-180° ferroelectric domain switching processes.

Influence of space-charge on hysteresis loop characteristics of ferroelectric thin films

Hysteresis loops of Pb(Zr, Ti)O3 (PZT) thin films obtained by using a Sawyer-Tower (ST) circuit are affected by many factors. This paper investigated the influence of space charge on the hysteresis loop of thin-film ferroelectrics, based on the model that polarization consists of two parts: linear and switching polarization. It is found that the space charge affects both the shape and offset of the ideal hysteresis loop. Further investigation shows that the practical hysteresis loop has a close relationship with the equivalent ST circuit parameters: the leakage resistance of the FE film, the equivalent input impedance of the measurement equipment, the signal source, and other similar parameters. The normally assumed symmetric hysteresis loop without any offset is obtained with an ST circuit when the output becomes stable. The hysteresis loop obtained at the initial stage of applied signal depends on the initial status of the FE film, and remnant polarization causes an initial offset that gradually disappears.

Bright, low voltage europium doped gallium oxide thin film electroluminescent devices

Europium doped gallium oxide thin film electroluminescent devices with bright, red emission (611nm) and relatively low threshold voltages of 60V were produced using pulsed laser deposition. The use of transparent conducting electrodes of amorphous InGaZnO on transparent aluminum titanium oxide/indium tin oxide/7059 Corning glass substrates resulted in a device that is transparent throughout the visible spectrum. At 100V, with 1kHz excitation, the luminance was 221cd∕m2. The Sawyer-Tower circuit analysis and time dependent emission measurements suggest that the charge trapping at the aluminum titanium oxide/Ga2O3:Eu interface plays an important role in producing efficient emission.

Annealing effect of platinum-based electrodes on physical properties of PZT thin films

This study examined the crystal structure and surface morphology, including the Ti segregation mechanism on the surface due to the inter-diffusion between Pt, Ti and TiOx as a glue layer, according to the annealing temperature and growth orientation of a Pt film. In addition, the fatigue mechanism of ferroelectric PZT thin films deposited on a Pt-based electrode was also investigated. The nano-structure, orientation mapping, and micro-morphologies of the triangular Pt hillocks were investigated by scanning electron microscopy with an electron backscatter diffraction (EBSD) function. The D–E hysteresis loop of the ferroelectric films was measured using a Sawyer–Tower circuit at 1 kHz to obtain the remanent polarization and coercive field.

Changes in ferroelectric properties of barium titanate ceramic with compressive stress

In this work, barium titanate (BT) ceramic was prepared using a conventional mixed oxide method. The effect of uniaxial compressive stress on the ferroelectric properties of BT ceramics were investigated. The changes in ferroelectric properties were observed at stress up to 60 MPa using a compressometer in conjunction with a modified Sawyer–Tower circuit. The results showed that applied stress had a significant influence on the ferroelectric properties of BT ceramics. Ferroelectric characteristics, i.e. the area of the ferroelectric hysteresis (P–E) loop, the saturation polarization (Psat), the remanent polarization (Pr) and the loop squareness (Rsq), decreased with increasing compressive stress, while the coercive field (Ec) remained constant. Stress-induced domain wall motion suppression and non-180° ferroelectric domain switching processes are responsible for the changes observed.

Dielectric nonlinear properties of pyridinium tetrafluoroborate single crystal near the ferroelectric phase transition

AbstractPyridinium tetrafluoroborate (PyBF4) single crystals have been grown and their dielectric properties around the ferroelectric phase transition at 237.3 K were studied. The electric permittivity was measured as a function of temperature as the dc electric field ranged between 0 and 1100 kV/m. The electric permittivity was also measured at constant temperature as a function of the electric field intensity, which was changed slowly in the range 0–650 kV/m. Detailed measurements of spontaneous polarization were done by means of a Sawyer–Tower circuit and a pyroelectric method. The results of the experimental studies were analyzed in the framework of the classical dielectric state equation and the nonlinearity coefficient B was estimated. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

A poling study of lead zirconate titanate∕polyurethane 0–3 composites

0–3 composites of lead zirconate titanate particles dispersed in a thermoplastic elastomer polyurethane matrix were fabricated. The dielectric permittivity and loss of the composite film were measured and compared to the theoretical values. The composites were polarized by the ac fields at different frequencies. With the application of the Sawyer-Tower circuit, the D-E hysteresis loops of the composites can be measured during the poling process. By decreasing the poling frequency, the composite sample shows a larger “remanent” polarization at the same poling field. To evaluate the poling effectiveness, the pyroelectric coefficients of the poled composite samples were measured by a dynamic method.

Stress‐Biased Cymbals Using Shape Memory Alloys

Cymbals and other flextensional transducers demonstrate high effective displacements due to the amplifying nature of the metal endcaps, while stress‐biased RAINBOW actuators display high displacements due to enhanced 90° domain wall translational processes that result from the tensile stress in the surface region of the lead zirconate titanate (PZT) layer created during manufacturing. A new class of transducers, called stress‐biased cymbals (SBC), was developed that couples the operational principles of cymbal and stress‐biased actuators. Pre‐stressing the PZT in the cymbal was accomplished using a flat‐trained shape memory alloy endcap. Hysteresis loops were measured using a Sawyer–Tower circuit for different pre‐stress levels. Enhancements in the differential dielectric constant of more than 70% and the effective d33 of the cymbal by ∼57% were observed, suggesting greater 90° domain wall motion in the SBC compared with the standard cymbal device. The stresses developed during the fabrication process were measured and compared with theoretical models. Additional performance characteristics including dynamic dielectric constant, loss, and radial resonance frequency of the devices are also reported.

English

The processing conditions, microstructure, and dielectric properties of strontium bismuthtitanate (SBT) were systematically studied. The specimen was synthesised by a mechano-chemicalprocessing route using a planetary ball mill. It is important that the action is vigorous enoughto break up loose aggregates and a fine particle size is obtained. The specimen was calcinedat 800 oC for 4 h. The calcined samples were subjected to cold isostatic pressing (CIP) processand finally sintered at 1200 oC for 2 h. A relative density 90 per cent of the theoretical densitywas obtained. Pellets having a diameter of 1cm and thickness of 1 mm were prepared from thesintered compacts for electrical measurements. X-ray diffraction showed that a single phase withthe layered perovskite structure of SBT was formed. Morphological studies were carried out bySEM analysis. Frequency dependence of impedance can provide additional insight intomechanisms controlling the electrical response. Resonance studies were made on poled samplein the frequency range 100 kHz – 20 MHz using an impedance analyser (HP-4294A) interfacedto a computer at room temperature. Dielectric measurements in the frequency range 100 Hz–1 MHz were made using an impedance analyser (HP-4192A) interfaced to a computer and themeasurements were carried out from room temperature to 550 oC. The ferroelectric hysteresis loopwas measured using a standard ferroelectric analyser based on Sawyer-tower circuit. Elasticcompliance (s33, s11) coupling factor (k33, k31)were also obtained. These materials can be utilisedin practical applications as substitutes for lead titanate and lead zirconate titanate (PZT)-basedceramics, where high temperature applications are foreseen.

Non-linear behavior of multilayer ceramic capacitors with a new equivalent circuit under AC-fields

The electrical properties were investigated to understand better the non-linear behavior of multilayer ceramic capacitors (MLCCs). The electrical properties of the capacitors with a new equivalent circuit were simulated by a Sawyer-Tower circuit system under a high AC-field using B 2 spice software, the simulated results were then compared with the experimental results. The experimental Q-V curves showed the non-linearity of ferroelectricity in the applied AC-fields. The predicted Q-V curves using B 2 spice software under various AC-fields also showed the non-linearity of ferroelectricity in high AC-fields. As a result, the nonlinear dielectricity of the MLCCs was successfully simulated by the new circuit model.

Dielectric properties of doped polystyrene and polymethylmethacrylate

About 1 μm thick films of polystyrene (PS) and polymethylmethacrylate (PMMA) doped with diphenylsulfoxide (DS) up to 40 wt.% were prepared from solutions using spin-coating method. Glass transition temperature (T g) of doped polymer films was determined by DSC technique. The depth profile and surface concentration of DS dopant were measured by RBS and XPS methods, respectively. The temperature dependence of relative permittivity of the films was determined from capacitance measurement. The dependence of polarization (P) on electric field (E) was measured using a standard Sawyer–Tower circuit. The glass transition temperature T g of both composites was found to be decreasing function of the DS concentration. The DS doping leads to an increase of relative permittivity of the PS and PMMA films. RBS and XPS measurements reveal an outward diffusion of DS dopant in PS/DS films at elevated temperature. No such effect was observed in PMMA/DS films. PMMA/DS layers were found to be more thermally stable comparing to PS/DS.

Poling of soft piezoceramic PZT

The properties of piezoelectric ceramic materials are strongly dependent on the degree of polarization as set by the poling process. In the present work a soft piezoceramic PZT material was polarized at different poling conditions. The hysteresis loop, the polarization current and pyroelectric current measurements were used to evaluate the polarization state of the material. The hysteresis loop was monitored using a home-made computer controlled Sawyer–Tower circuit. The polarization current was recorded during the poling process at different applied electric fields, poling time and temperature. The pyroelectric coefficient and the polarization were calculated from the pyroelectric current. The polarization calculated from these data was in excellent agreement with the polarization as calculated from the poling current. The relative permittivity and loss factor were measured as a function of temperature after different poling conditions. The effects of the various poling conditions on the dielectric and ferroelectric properties of the soft PZT are discussed. It is shown that, contrary to common practice, poling at a field slightly larger than the coercive field is adequate to reach full polarization at room temperature.

Study on ZnGa 2O 4:Cr 3+ a.c. powder electroluminescent device

An a.c. powder electroluminescent (EL) device using ZnGa 2O 4:Cr 3+ phosphor was fabricated by the screen printing method. Optical and electrical properties of the device were investigated. The fabricated device shows a red emission at 695 nm driven by the a.c. voltage. The emission is attributed to the energy transfer from hot electrons to Cr 3+ centers via self-activated Ga–O groups. Luminance ( L) versus voltage ( V) matches the well-known equation of L = L 0exp(− bV − 1 / 2 ) and luminance increases proportionally with frequency due to the increase of excitation probability of host lattice or Cr 3+ centers. The diagram of the charge density ( Q) versus applied voltage ( V) is based on a conventional Sawyer–Tower circuit. At 280 V and 1000 Hz, the luminance and the luminous efficiency of the fabricated powder EL device are about 1.0 cd/m 2 and 13 lm/W, respectively. And under the high field, the device fabricated with the oxide-based phosphor of ZnGa 2O 4:Cr 3+ shows excellent stability in comparison with the conventional sulfide powder EL device.

Preparation of nanocrystalline ferroelectric CaBi 4Ti 4O 15 by citrate gel method

A gel was formed when an aqueous solution of CaCl 2, BiNO 3, TiOCl 2 and citric acid in stoichiometric ratio is heated on a water bath. This gel on decomposition at 700 °C produced nano crystallites of the ternary oxide, CaBi 4Ti 4O 15 (CBT). The phase contents and lattice parameters were studied by the powder X-ray diffraction (XRD). Particle size and morphology was studied by transmission electron spectroscopy (TEM). The room temperature dielectric constant at 1 kHz is 390. The ferroelectric hysteresis loop parameters of these samples were also studied by a home-built Sawyer-tower circuit.

Effect of uniaxial compressive pre-stress on ferroelectric properties of soft PZT ceramics

The effect of uniaxial compressive pre-stress on the ferroelectric properties of commercial soft PZT ceramics is investigated. The ferroelectric properties under the uniaxial compressive pre-stress of the ceramics are observed at stress up to 24 MPa using a compressometer in conjunction with a modified Sawyer–Tower circuit. The results show that the ferroelectric characteristics, i.e. the area of the ferroelectric hysteresis (P–E) loops, the saturation polarization (Psat), the remanent polarization (Pr), and the loop squareness (Rsq) decrease with increasing compressive pre-stress, while the coercive field (Ec) is virtually unaffected by the applied stress. The stress-induced domain wall motion suppression and non-180° ferroelectric domain switching processes are responsible for the changes observed. In addition, a significant decrease in these parameters after a full cycle of stress application has been observed and attributed to the stress-induced decrease in the switchable part of the spontaneous polarization at high stress. Furthermore, the permittivity calculated from the P–E loops is found to decrease with increasing applied pre-stress. This finding differs considerably from the results in the low-field experimental condition. Finally, this study clearly shows that the applied stress has a significant influence on the ferroelectric properties of soft PZT ceramics.

Improving ferroelectric properties of Pb(Zr 0.44Ti 0.56)O 3 ceramics by Pb(Mg 1/3Nb 2/3)O 3 addition

Ceramics in PMN–PZT system with formula ( x)Pb(Mg 1/3Nb 2/3)O 3–(1 − x)Pb(Zr 0.44Ti 0.56)O 3 (when x = 0.0, 0.1, 0.3, 0.5, 0.7) are prepared by a solid-state mixed-oxide technique. The phase formation behavior and microstructure are studied using X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The ferroelectric properties are measured by a simple Sawyer–Tower circuit. XRD analysis shows that the possible morphotropic phase boundary (MPB) between the tetragonal and pseudo-cubic phases is identified near the 0.3PMN–0.7PZT composition. In addition, ferroelectric properties of PMN–PZT ceramics are found to enhance at the ceramic composition with x = 0.3. This clearly implies that the MPB of this PMN–PZT system lies near the x = 0.3 composition. Most importantly, this study shows that the addition of PMN can improve the ferroelectric behavior in PZT ceramics.

Preparation of nanocrystalline ferroelectric BaBi 4Ti 4O 15 by Pechini method

A gel was formed when an aqueous solution of BaCl 2, BiNO 3, TiOCl 2 and citric acid in stoichiometric ratio is heated on a water bath. This gel on decomposition at 600 °C produced the nano crystallites of ternary oxide, BaBi 4Ti 4O 15 (BBT). The phase contents and lattice parameters were studied by the powder X-ray diffraction (XRD). Particle size and morphology was studied by transmission electron spectroscopy (TEM). The room temperature dielectric constant at 1 kHz is 90. The ferroelectric hysteresis loop parameters of these samples were also studied by a home built Sawyer-tower circuit.

Uniaxial stress dependence of ferroelectric properties of xPMN-(1–x)PZT ceramic systems

Effects of uniaxial compressive pre-stress on the ferroelectric properties of ceramics in the PMN-PZT system are investigated. The ceramics with a formula xPb(Mg1/3Nb2/3)O3-(1-x)Pb(Zr0.52Ti0.48)O3 or xPMN-(1-x)PZT when x=0.0, 0.1, 0.3, 0.5, 0.7, 0.9, and 1.0 are prepared by a conventional mixed-oxide method. The ferroelectric properties under the uniaxial compressive pre-stress of the PMN-PZT ceramics are observed at the stress levels up to 13 MPa using a compressometer in conjunction with a modified Sawyer–Tower circuit. It is found that with increasing compressive pre-stress levels the area of the ferroelectric hysteresis (P–E) loops, the saturation polarization (Psat), the remanent polarization (Pr), and the coercive field (Ec) decrease. These results are interpreted through the non-180° ferroelastic domain-switching processes. Finally, the calculated differential permittivity for all the xPMN-(1-x)PZT ceramics, except for 0.5 PMN-0.5 PZT, decreases with increasing applied stress.