Soodkhet Pojprapai

Determination of domain orientation in lead zirconate titanate ceramics by Raman spectroscopy

Raman spectroscopy was employed to investigate the domain orientations of poled and unpoled tetragonal lead zirconate titanate ceramics. Using backscattering geometry, the ceramics were rotated 360° relative to the polarization direction of the incident beam. The ratio of the crossed to parallel polarization intensities in the poled sample demonstrates periodicity with respect to the rotation angle, while that of the unpoled sample does not. The angular periodicity of the intensity ratio is related to the domain orientations through the Raman tensor. Raman spectroscopy is thereby demonstrated as a quantitative technique that can measure domain switching distributions in ferroelastic ceramics.

Electric field-induced phase transitions in Li-modified Na0.5K0.5NbO3 at the polymorphic phase boundary

The electric field-induced phase transitions in Li-modified Na0.5K0.5NbO3 at the polymorphic phase boundary (PPB) were observed using in situ X-ray diffraction. The ratio of monoclinic to tetragonal phase fraction was used as an indicator of the extent and reversibility of the phase transitions. The reversibility of the phase transition was greater in compositions further from the PPB. These results demonstrate that the field-induced phase transition is one of the origins of high piezoelectric properties in lead-free ferroelectric materials.

Analysis methods for characterizing ferroelectric/ferroelastic domain reorientation in orthorhombic perovskite materials and application to Li-doped Na0.5K0.5NbO3

Ferroelectric and ferroelastic domains can be reoriented during the application of electric field through domain wall motion. This study develops a method to quantify the domain reorientation in perovskite ferroelectrics with orthorhombic crystal lattices. In situ, high-energy X-ray diffraction was utilized to obtain intensity ratios that are necessary for the calculation. Domain reorientation in orthorhombic Li-doped Na0.5K0.5NbO3 is then quantified using this method. The preference of domain orientations is explained by considering the angle between spontaneous polarization of the respective domains and the applied electric field direction. The extent of domain reorientation increases as the Li substitution increases which additionally correlates to increased piezoelectric coefficient d33 and field-induced strain. Increased domain wall motion is further proposed to originate due to the increased compositional proximity to the morphotropic phase boundary, a proposed universal behavior in ferroelectric compositions-containing phase boundaries.

Investigation of the Unit Cell Distortion in PZT Ceramic via in-situ XAS Technique

Lead zirconate titanate ceramics, PZT, is a perovskite material that shows a great piezoelectric/ferroelectic effect. This phenomenon is caused by the shift of Ti4+ or Zr4+ ion relative to neighboring atoms. Such movement results in the change of the spontaneous polarization direction known as domain switching. Microscopically, the switching behavior due to the movement of the ions can be analyzed by using X-ray absorption near-edge structure (XANES). The aim of this project is to elicit the relationship between switching behavior and local/unit cell distortion in PZT ceramic under the application of electric field employing X-ray absorption technique. In this experiment, PZT sample was subjected to 0.7 kV/mm and 1.4 kV/mm respectively. The Ti K-edge X-ray absorption spectra reflect the change of the local structure of the unit cell of PZT specimens before and after electrical static loading. The result shows that the XANES spectra intensity changes when the electrical load was applied. This can be caused by the shift of Ti atoms in the unit cells. The experiment result is in agreement with the simulation result obtained from ATOMS (version 2.50) and FEFF (version 8.20) software.

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.

Effect of Sintering Temperature of Lead-free (K0.50Na0.46Li0.04)(Nb(0.96-x)Sb0.04Tax)O3 Ceramics on Piezoelectric Properties

Currently, lead-free piezoelectric ceramics are being investigated to replace lead-contained piezoelectric ceramics such as PZT. In this work, the effect of sintering temperature on piezoelectric properties of (K0.50Na0.46Li0.04)(Nb(0.96-x)Sb0.04Tax)O3 ceramics, where x = 0, and 0.12, (KNN-LST) was studied. KNN-LST ceramics were synthesized by the solid state method and sintered at different sintering temperatures (1000–1200°C) for 4 h in a normal atmospheric pressure. It was found that there was different optimum sintering temperatures for each composition. The samples sintered at the optimum sintering temperatures exhibited relatively high density and piezoelectric constant (d33 ).

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.

Enhancement of fatigue endurance in ferroelectric PZT ceramic by the addition of bismuth layered SBT

Electrical fatigue properties of (1-x)PZT-xSBT ceramics (x = 0–1.0 weight fraction) were characterized. It was found that pure PZT ceramic had severe polarization fatigue. This was mainly attributed to an occurrence of the macroscopic cracks at near-electrode regions. On the contrary, pure SBT ceramic exhibited excellent fatigue resistance, which was attributed primarily to weak domain wall pinning. As small amount of SBT (0.1 ≤ x ≤ 0.3) was added into PZT, a small reduction of remanent polarization after fatigue process was observed. This demonstrated that these ceramics had high stability during the repeated domain switching due to their low oxygen vacancy concentration. Therefore, these results suggested that this new ceramic PZT-SBT system seemed to be an alternative material for replacing pure PZT in ferroelectric memory applications.

THE EFFECT OF TEMPERATURE ON BIPOLAR ELECTRICAL FATIGUE BEHAVIOR OF LEAD ZIRCONATE TITANATE CERAMICS

The ferroelectric fatigue behavior of lead zirconate titanate was investigated under different temperatures (room temperature and 125°C). A bipolar electric field of ±1.5 kV/mm at a frequency of 50 Hz was applied to the samples up to 2 × 105 cycles. A markedly different fatigue rate was observed dependent on temperature. The fatigue degradation represented by the loss of polarization and strain increases with the number of cycles and is more pronounced in the case of the lower temperature. Brennans model based on a logarithmic fatigue rate is applied to explain the temperature effect on fatigue behavior due to the pinning effect.

Polarization Switching of PZT under Electrical Field via in-situ Synchrotron X-ray Absorption Spectroscopy

Lead zirconate titanate (PZT) ceramics have been extensively used for electronic applications due to their ability to couple mechanical and electrical energy, a so-called piezoelectric effect. This effect is caused by the shift of Ti4+ or Zr4+ ion relative to neighbouring atoms. The movement of the ions due to an external load causes reorientation of the ferroelectric polarization. Microscopically, the detail of the shift of Ti ion, reflecting polarization switching behaviour, can be analyzed by X-ray absorption near-edge structure (XANES) technique. The aim of this project is to investigate the shift of Ti4+ ion in PZT under the application of electric field by in-situ X-ray absorption technique. For this project, the special custom-built high voltage sample chamber installed at synchrotron XANES beam line at Synchrotron Light Research Institute, Thailand, was employed to conduct the experiment. XANES spectrum of bulk PZT was collected under the different amplitudes of an applied electric field. Ti K-edge X-ray absorption spectra were analyzed by IFEFFIT software package. The results showed that the pattern of XANES changed with the alternation of the applied field amplitude. The change of XANES spectrum was caused by the movement of Ti4+ ion reflecting the change of ferroelectric polarization. From the analysis, it was found that this technique could be used to investigate the Ti4+ ion shifting of PZT bulk ceramics.