Papers by Keyword: Ferroelectric

Abstract: Lead-free powders of Bi(Na_0.81K_0.19)O₃ doped 0.3 wt.% CoO were prepared by a conventional mixed oxide technique. The sintering process was controlled with various rate up and down temperature. The samples were sintered at 1,050 °C for 4 h which difference heating rate controlled i.e. 100, 300, and 600 °C/h. The XRD pattern analysis of all studied samples showed a single phase perovskite structure Dielectric and ferroelectric properties of the ceramics were investigated as a function of rate controlled sintering temperature. The sample heating rate at 600 °C/h showed maximum dielectric constant (~5961) at T_m. In addition, the ferroelectric properties were analyzed and discussed.

Abstract: 0.82NBT-0.18ST and 0.85NBT-0.15ST thin films have been prepared on Si substrates by a modified metalorganic solution deposition process. To achieve films with better ferroelectric properties, three main items have been changed in the process. Then the crystal structures, surface microstructures, hysteresis loops, fatigue curves and capacitance-voltage curves of the films were measured. It can be found that NBT-ST films can crystallize well after annealing at 650 °C for 5 minutes and have smooth surface microstructures. The 0.85NBT-0.15ST thin films exhibit better well-defined hysteresis loops than 0.82NBT-0.18ST, with a remnant polarization of 1.1 mC/cm² and a coercive fields of 44.2 kV/cm. The clockwise C-V curves show that they have a desired polarization-type switching mode. The memory window of 0.82NBT-0.18ST thin film is about 1.8V, and that of 0.85NBT-0.15ST thin film is about 2.5V.

Abstract: Lead free Multiferroic composites that comprise Co_0.6Zn_0.4Fe_1.7Mn_0.3O₄ (CZFMO) and 72.5(Bi_1/2Na_1/2TiO₃)-22.5(Bi_1/2K_1/2TiO₃)-5(BiMg_1/2Ti_1/2O₃) (BNT-BNT-BMgT) were synthesized using sol-gel method and it’s structural, ferroelectric and magnetic properties were studied. The X-ray diffraction displayed the single phase formation of parent phases and the presence of two phases in the composites. The samples showed a well saturated polarization-electric field hysteresis loops. The remnant polarization and saturation polarization values are decreased with increasing ferrite content. Room temperature (RT) magnetic measurements show that composites are soft magnetic. The composite with x = 0.2, showed the enhanced magnetic and ferroelectric properties. Moreover, these ME composites provide a great opportunity as potential lead free systems for multifuntional device applications.

Abstract: In this research, the Bi_0.5(Na_0.80K_0.20)_0.5Ti_0.99Ti_0.10O₃ were prepared via a conventional solid-state reaction method, and their properties were related with calcination temperature. The crystalline structure of BNKTZ ceramics was assessed by X-ray diffraction (XRD) method. Other physical properties, i.e. porosity, density, microstructure, and electrical properties were determined. XRD patterns for all samples showed a pure perovskite, where coexistence between rhombohedral and tetragonal phases was observed for some conditions. The optimum dielectric constant was obtained for the ceramic calcined at 800 °C. The ferroelectric and piezoelectric properties were improved and showed the highest values for the calcination temperature around 900-1000°C. The improvements of ferroelectric and piezoelectric properties were proposed to be due to the ceramics had compositions closed to MPB composition. Furthermore, density also had a contribution for the improvements.

Abstract: In this research, the effect of electrode type on electrical i.e. dielectric and ferroelectric behavior of 0.94BNT-0.06BT ceramics was studies. The ceramics were prepared by conventional mixed oxide method. The sample exhibited a pure perovskite structure with rhombohedral phase. For dielectric measurement, the ceramics with Ag pasted electrodes exhibited very high dielectric constants and good responding with low frequency than Au sputtered electrode.

Abstract: In this research, the effects of sintering temperature on phase structure, densification, microstructure, mechanical and electrical properties of modified-PZT ceramics were investigated. All ceramics were prepared by a conventional mixed oxide amend sintered at various temperatures from 1150 - 1250°C. XRD pattern indicated that completely solid solution occurred for all samples and the ceramics exhibited a single perovskite without any secondary phases. At lower sintering temperature, the dominant phase was rhombohedral while tetragonal phase became dominant at higher temperature. Grain size tended to increase with increasing sintering temperature. The dielectric, ferroelectric and piezoelectric properties were also increased with increasing sintering temperature. In addition, the highest low field d₃₃ of 620 pC/N of was observed for the 1250°C sample.

Abstract: In this paper, we study the electrical properties and breakdown phenomena of PZT ferroelectric thin film in electrowetting systems. The experimental results indicate that irreversible charge trapping occurred with repeated voltage actuation, resulting in contact angle relaxation and reduction of the ferroelectric film breakdown strength. The breakdown voltage depends on DC voltage polarity, and this polarity dependence was found to be related to the thickness of the ferroelectric layer. When AC voltage was applied, the breakdown voltage increased directly with voltage frequency. These phenomena are interpreted in terms of electrochemical reactions at the liquid/solid interface, an empirical model was used to estimate the amount of trapped charge in the ferroelectric film.

Abstract: Pure BiFeO₃ (BFO), Ca-doped and Eu/Ca-codoped BFO nanoparticles were prepared by using a sol–gel method. The effects of Eu/Ca-codoped on the structural, magnetic and ferroelectric properties of the samples were studied. The X-ray diffraction (XRD) analysis reveals a structure transition in the codoped samples. Co-doped samples were obtained with the best ferromagnetic properties, with the largest remaining magnetization Mr = 0.20 emμ/g. The structure transition may be the main cause for the origin of improved magnetic properties, which destroys the space modulated spin structure of BFO and releases the locked magnetic. In addition, the doping of Eu into BFO can reduce the leakage current and enhance the ferroelectric properties.

Abstract: Structure–property relationship has been performed in the lanthanum-modified lead–zirconate–titanate (PLZT) with a lanthanum content 8 and Zr/Ti ratio 40/60. The X-ray diffraction analysis, scanning electron microscopy, and sintering behavior have evidently demonstrated that it is possible to tailor the structural properties of PLZT 8/40/60. Structure of PLZT 8/40/60 had pure perovskite with tetragonal without secondary phase. Tetragonality (c/a) was observed in the range of 1.01093-1.02095. SEM micrographs were shown a development of mean grain size to clarify the development of grain after sintering processing. The result shows that increasing of sintering temperature resulted in mean grain size increasing from 1.70 to 3.08 μm. Ferroelectricity of PLZT ceramics were normal ferroelectric and dielectric constant increased with the increasing sintering temperature.

Abstract: In this study, leadbased ferroelectric ceramics Pb_0.91La_0.09Zr_0.65Ti_0.35O₃ PLZT (9/65/35) were fabricated by solid solution method. The electrical and mechanical properties were measured by modified Michelson interferometer and Sawyer-Tower circuit to investigate electric field induced strain and polarization (s-P-E) of PLZT (9/65/35) at 30-70 °C. The induced strain and polarization were changed when the temperature was increased indicating the change of spontaneous polarization inside the ferroelectric materials.