Papers by Keyword: Ferroelectric Ceramics

Abstract: This paper considers the mechanochemical synthesis of advanced electroceramic material with a perovskite structure as well as this method as an effective way for modifying the properties of BaTiO₃ by substitution of foreign ions. Dielectric properties mainly para-ferroelectric phase transitions in Ba_1-xSr_xTiO₃ solid solutions (0.0 x 0.6) are presented.

Abstract: In the present work the influence of neodymium concentration (0-1at-%) and sintering conditions on 8/65/35 PLZT:Nd³⁺ ceramics were studied. All ceramic powders were synthesized by MOM technique from high purity raw materials (>99,9%), and subsequently sintered by free sintering and hot uniaxial pressing method. To analyze the powders and ceramics more the XRD, EDS SEM, and ferroelectric measurements were performed. Optical spectra were examined for all prepared samples, and their optical properties were analyzed using reflectance, excitation and luminescence measurements. The study gives a detailed account of the relationships between doping and preparing conditions on the basic physical and dielectric and optical properties of obtained ceramic materials.

Abstract: We demonstrated the superior electrocaloric effect (ECE) in BaTiO3 multilayer structure. The sample fabricated by tape-casting process has 120 effective ferroelectric layers with average layer thickness of 1.7 μm. The ferroelectric hysteresis loops were measured in the temperature range from 30 to 180 oC, and then the temperature dependences of ECE adiabatic temperature change and heat absorption were obtained according to Maxwell relation. A peak ECE adiabatic temperature change of 0.027 K/V and heat absorption of 0.36 J/g were observed near the ferroelectric phase transition at 125 oC under Vmax=25 V. The BaTiO3 thick film can sustain an external electric field (>500 kV/cm) several times higher than bulk ferroelectric ceramics (~30 kV/cm). Although the EC coefficient of BaTiO3 is much lower than lead-based ferroelectric ceramics, the ultrahigh working electric field endows it a large ECE, higher than that of most reported lead-based ferroelectric ceramics. In addition, the lead-free composition provides it a promising future in solid-state cooling technology.

Abstract: Modern scanning electron microscopes (SEMs) increase the ability to study a wide range of materials. Especially, an application of low vacuum conditions enables characterization of nonconductive samples without complicated preparation procedure. However, the operator must be aware of several problems he may encounter collecting electron diffractions in the SEM with variable pressure. The charge control and quality of the surface are the challenges when running experiments on insulators. Specimen charging obscures forward scatter electrons images and decreases the EBSD pattern quality making indexing difficult or even impossible. Another crucial question is how to limit the influence of so called "skirt effect" caused by ionization of gas molecules followed by electron beam broading above the sample. The influence of several important parameters (gas pressure, a type of gas, working distance and energy of electron beam) on the EBSD pattern quality must also be considered. When it is properly done, a coupling of crystallographic information with the chemical data obtained from Energy Dispersive Spectroscopy (EDS) in the LV-SEM allows to perform phase identification of insulators. The paper presents some ideas how to deal with the (Pb, La)(Zr, Ti)O₃ ceramics in high resolution Quanta 3D SEM (with thermally assisted Schottky type FEG) equipped with EDAX-TSL system in low vacuum environment. The problems occurring during EBSD analysis of the PLZT ceramics are discussed and some solutions are suggested. Paper summarizes the results obtained from PLZT ferroelectric ceramics in the low vacuum FEGSEM and shows how to optimise experimental parameters in order to achieve the best quality of orientation maps acquired from nonconductive samples.

Abstract: Ferroelectric BiFeO₃ (BFO) is potential candidate for future generation of FeRAM due to its large polarization. However, BFO is very sensitive to secondary phase formation during synthesis because of volatility issues related to Bismuth. Investigation of the microstructure for phase purity is the key as impurities can destroy the desired properties. We have used backscattered electron diffraction to study the microstructure of BFO ceramic. The EBSD results provide a direct evidence of the appearance of secondary phase that XRD could not be detected in XRD.

Abstract: Effects of amount of Ca on crystal structure, microstructure, ferroelectric properties, and dielectric properties of the CaxSr2-xBi4Ti5O18 (CSBTi-x) ferroelectric ceramics were investigated. The results show that single-phase layered perovskite ferroelectrics were obtained and no appreciable secondary phase was found.Ca-doping results in a notable enlargement of remnant polarization 2Pr. The 2Pr of CSBT-0.15 reaches a large value, the remnant polarization 2Pr and coercive field 2Ec were 18.1µC/cm2 and 120.2kV/cm, respectively. Dielectric constant and dielectric loss of CSBT-0.15 was also measured, showing dielectric constant εr=199~194 and dielectric loss tanδ=0.02~0.014 over the range of 100 kHz~1MHz, respectively.

Abstract: The structure and property of Ce-doped Ba0.2Sr0.8TiO3 (BST) were investigated as a function of Ce content. The density experiment results confirmed that increasing the Ce doping ratio caused the decrease in shrinkage factor of BST in the sintering procedure. Additionally, both Scanning Electron Microscope (SEM) and X-ray diffraction (XRD) analysis showed that the grain size of Ce-doped BST was dependent on the Ce content. Further more, the dielectric constant and dielectric loss had a curve relationship with increasing Ce content. The improvement of the electrical properties of Ce doping BST may be related to the decrease in the concentration of oxygen vacancies. According to the research, the diameter of grain, the dielectric constant and loss factor of the 1mol% Ce-doped Ba0.2Sr0.8TiO3 were 500nm, 365.8 and 0.0063, respectively.

Abstract: Bi4Ti3-xNbxO12+x/2 (BNT) ceramics were prepared by a solid-state reaction method. Effects of Nb doping on dielectric and ferroelectric properties of BNT were investigated. XRD patterns show that Nb5+ substitutions do not change the phase structure. With the increase of Nb doping, dielectric constant and Curie temperature decrease gradually. At the same time, dielectric loss peaks become flatter and dielectric losses become smaller due to the decrease of oxygen vacancies derived from the introduction of Nb5+ at Ti4+ site in BNT. Remanent polarization Pr and coercive field EC of BNT ceramics are both larger than those of BIT without Nb doping. With the increase of Nb doping from 0 to 0.045, Pr increases to the largest value of 17 μC/cm2 and EC decreases to the lowest value of 87 kV/cm, but Pr will decrease when Nb doping content is over 0.045.

Abstract: The ferroelectric ceramic BaTiO3 was synthesized at 1000 °C for 5 h. The structure of the system under study was refined on the basis of X-ray powder diffraction data using the Rietveld method. The system crystallizes in the space group P4mm（99）. The refinement of instrumental and structural parameters led to reliable values for the Rp, Rwp and Rexp.We use the TOPAS software of Bruker AXS to refine this ceramic powders and show its conformation

Abstract: In this work, barium zirconate titanate (Ba(Zr0.07Ti0.93)O3) ferroelectric ceramics doped with B2O3 were prepared by the conventional mixed-oxide method. The properties of the ceramics as a function of sintering temperature were investigated. Various technique such as X-ray diffraction (XRD) technique, scanning electron microscopy, dielectric permittivity spectroscopy and ferroelectric property measurement were used to obtain characteristic of the ceramics. The optimum density was observed for 1250 oC sintered sample. An increase in sintering temperature produced a decrease in dielectric constant. However, ferroelectric behavior was improved in 1275 oC sintered sample. The results were discussed in term of microstructure and crystallinity of the ceramics.