S. Chandarak

Dielectric Properties of BaTiO3-Modified BiFeO3 Ceramics

Multiferroic BiFeO3 has attracted extensive interest due to its potential in several applications. However, pure-phase BiFeO3 is very difficult to obtain. Hence, mixing BiFeO3 with other ferroelectrics, such as BaTiO3, is another approach to obtain materials with possible multiferroic properties. In this study, the BiFeO3 was modified with addition of BaTiO3 via a simple solid state reaction method. Dielectric properties of the BaTiO3-modified BiFeO3 ceramics were investigated over wide range of temperature and frequency. The results show that the (1-x)BiFeO3-xBaTiO3 ceramics with x = 0.1 and 0.2 exhibited large dielectric properties with giant-dielectric-like behavior. The dielectric properties were seen to improve with increasing BaTiO3 content, with the highest dielectric constant (ϵr = 19000) observed in 0.8BiFeO3-0.2BaTiO3 ceramic. The results were explained in terms of the pre-dominantly intrinsic BiFeO3 giant-dielectric behavior as a result of Fe multivalent states, as well as a better grain packing density with increasing BaTiO3 content.

Lattice positions of Sn in Cu2ZnSnS4 nanoparticles and thin films studied by synchrotron X-ray absorption near edge structure analysis

Lattice positions of Sn in kesterite Cu2ZnSnS4 and Cu2SnS3 nanoparticles and thin films were investigated by XANES (x-ray absorption near edge structure) analysis at the S K-edge. XANES spectra were analyzed by comparison with simulations taking into account anti-site defects and vacancies. Annealing of Cu2ZnSnS4 nanoparticle thin films led to a decrease of Sn at its native and defect sites. The results show that XANES analysis at the S K-edge is a sensitive tool for the investigation of defect sites, being critical in kesterite thin film solar cells.

Magnetoelectric Properties of Cu- and Mn-Doped 0.75BiFeO3–0.25BaTiO3 Multiferroic Ceramics

In this study, 0.75BiFeO3–0.25BaTiO3 ceramics doped with Mn and Cu (1, 2, 3, 4 and 5 mol%) have been fabricated with an effective solid-state reaction method developed for high purity ceramics. Attention has been focused on relationships between sintering conditions, phase formation, density, and magnetoelectric properties of the sintered ceramics. It was found that Cu and Mn doping affected significantly the dielectric, ferroelectric, ferromagnetic and magnetoelectric properties of these ceramics. At certain level of addition, both Mn and Cu doping were found to enhance the ferroelectric and ferromagnetic characteristics of the BiFeO3-BaTiO3 multiferroic ceramics. Finally, magnetoelectric properties of the ceramics were also determined. The addition of the Cu and Mn ions was found to noticeably improve the magnetoelectric properties of the ceramics.

Effects of Mn and Cu Doping on Electrical Properties of 0.75BiFeO3-0.25BaTiO3 Ceramics

In this study, 0.75BiFeO3-0.25BaTiO3 ceramics doped with Mn and Cu (0, 1, 2, 3, 4 and 5 mol%) have been fabricated with an effective solid-state reaction method developed for high purity ceramics. Attention has been focused on relationships between phase formation, density, dielectric and ferroelectric properties of the sintered ceramics. It was found that Mn and Cu doping affected the dielectric and ferroelectric properties of these ceramics. In addition, Cu and Mn doping was also found to improve the sintering ability and change the structural symmetry of this system from rhombohedral to tetragonal.

Structural Investigation of PZT-PNN and PZT-PZN Probed by Synchrotron X-ray Absorption Spectroscopy

Relaxor ferroelectric materials PZT-PZN and PZT-PNN were prepared by columbite method. The structural change was investigated by Synchrotron X-ray Absorption Spectroscopy (SXAS) at Zr L3-edge. The results show structural change of both systems affects to white line (WL) intensity significantly as revealed by simulated spectra. At the MPB composition 0.7PZT-0.3PZN shows the enhance magnitude change as structure change from tetragonal to only rhombohedral phase. While the MPB composition 0.8PZT-0.2PNN shows the slight change of magnitude of WL intensity which mixed phases of rhombohedral and tetragonal. Therefore, the MPB composition of PZT-PNN system clearly conclude that is 0.7PZT-0.3PZN but the MPB of PZT-PNN system could not be conclude like that because the structure slightly change.

Synchrotron x-ray absorption spectroscopy study of self-assembled nanoparticles synthesized from Fe(acac) 3 and Pt(acac) 2

The synchrotron X-ray absorption technique was used to complement electron microscopy in the investigation of nanoparticles synthesized from the coreduction of iron acetylacetonate, Fe(acac)3 and platinum acetylacetonate, Pt(acac)2. A much higher Pt composition than Fe leads to an extended X-ray absorption fine structure (EXAFS) spectrum for the sample that differs from that of fcc FePt nanoparticles. Most importantly, X-ray absorption near-edge structure (XANES) spectra clearly indicate the existence of α-Fe2O3 and Pt metal. Since these monodisperse nanoparticles have a diameter of around 4nm and tend to self-assemble into hexagonal arrangements, they can be modeled as Pt-rich cores with an α-Fe2O3 shell stabilized by organic surfactants.

Synchrotron X-Ray Absorption Study of Cu and Mn Doped BiFeO3-BaTiO3 Multiferroic Ceramics

In this work, an experimental X-ray Absorption Spectroscopy (XAS) measurement was employed to determine the local structure and valency of Cu and Mn in BiFeO3-BaTiO3. Synchrotron x-ray absorption near-edge structure (XANES) and extended x-ray absorption fine structure (EXAFS) experiments were performed on Cu-doped and Mn-doped BiFeO3-BaTiO3 samples. The Cu- and Mn-doped BiFeO3-BaTiO3 ceramic samples were used for the XAS experiment. XAS spectra at the Cu and Mn K-edge were recorded in flurorescent mode with 13-element Ge detector. The spectra were collected at ambient temperature with a Ge(111) double crystal monochromator and recorded after performing an energy calibration. The features of the measured Cu and Mn K-edge XANES was consistent with Cu and Mn on the Fe/Ti site and inconsistent with Cu and Mn on other sites. The clear agreement was the strongest evidence of Cu and Mn substituting for B-site in BiFeO3-BaTiO3 materials. In addition, the valency of both Cu and Mn ions in BiFeO3-BaTiO3 materials was also confirmed.

Effect of Temperature on Ferroelectric Properties of Bismuth Ferrite-Barium Titanate

The effect of temperature on ferroelectric properties of the 1 mol% Mn-doped 0.75BF-0.25BT ceramic was investigated under an electric field at various temperatures (−20 to 200°C). An electric field (sine wave) of 52 kV/cm at 50 Hz was applied to the sample. The effect of temperature was represented as the changed of polarization hysteresis loop and dielectric properties with various temperatures. The results show that the polarization hysteresis loops increase with increasing temperature because of greater domain switchability at higher temperature. Dielectric loss and dielectric constant increase with increase temperature and tend to decrease with increasing frequency. The samples break down at higher temperature due to the strong leakage current density, which may be caused by an increase in the activity of the free carries.