Wanwilai Vittayakorn

Sonochemical Synthesis of Spherical BaTiO3 Nanoparticles

Monosized spherical barium titanate (BaTiO3) nanoparticles have been synthesized successfully via sonochemical reaction. The as-synthesized BaTiO3 nanoparticles were characterized using X-ray diffraction of powder, Fourier transform infrared spectroscopy, Raman spectroscopy, scanning electron microscopy and transmission electron microscopy. The XRD pattern of BaTiO3 particles, which were synthesized under irradiation of ultrasonic sound for 0.5 h, showed sharp diffraction peaks that corresponded to the cubic BaTiO3 phase. Only a small amount of BaCO3 contamination was present in the sample. The Raman active modes of the samples in this study were similar to the cubic phase of BaTiO3. The average diameter of sonochemical synthesized particles was ∼99.54 ± 18.25 nm. The synthesized BaTiO3 nanoparticles were almost spherical.

Synthesis of Monodispersed Perovskite Barium Zirconate (BaZrO3) by the Sonochemical Method

Barium zirconate (BaZrO3) was synthesized successfully by the sonochemical method. The monophase of BaZrO3 was formed completely in short irradiation time without the calcination process. X-ray diffraction, Fourier transform and Raman spectroscopy were used to characterize formation of the perovskite BaZrO3 phase, which occurs in a 60 minute single phase with a cubic crystal structure at room temperature. Therefore, sonochemical irradiation could accelerate the formation of BaZrO3 particles significantly. Furthermore, scanning electron microscopy investigated the uniform shape and size. The size distribution became narrow with increasing time, as a function of irradiation.

Influence of Mn Doping on the Magnetic Properties of CoFe2O4

A series of CoFe2−x Mn x O4 ceramics were synthesized successfully by conventional solid state reaction. The X-ray diffraction analysis proved that all samples were found to have a cubic spinel structure. Diffractograms were used for Rietveld refinement to determine lattice parameters, of which lattice parameter increased with increasing Mn concentration. The microstructure of the samples was studied using scanning electron microscopy. The vibrating sample magnetometer measurements showed that the highest saturated magnetization of 118.11 emu/g and coercivity of 46.89 Oe were observed in CoFe1.85Mn0.15O4 ceramic. Furthermore, X-ray absorption spectra of the samples were recorded to determine the Co, Fe and Mn valence states and their preferentially sites of the spinel structure.

Effect of Annealing Time on the Cation Distribution in Mn Doped CoFe2O4

In this work, the series of CoFe2-xMnxO4 powders were synthesized using the solid state method. The structure and lattice parameter of the samples were determined by the X-ray diffraction (XRD) and Rietveld refinement method. The morphology was confirmed without annealing and with annealing at 500°C for 4 and 100 h, with the samples examined by scanning electron microscopy (SEM). Then, the distribution of migrating cations was analyzed using X-ray absorption spectroscopy (XAS). Also, magnetic properties were examined by a vibrating sample magnetometer (VSM). It can be confirmed from the morphology that the average particle size before and after annealing remained unchanged, and ranged from 0.66 ± 0.20 μm to 0.79 ± 0.26 μm. Furthermore, the distribution of cations was no different after annealing Mn ions at 500°C for 100 h. However, the distribution of cations migrated to their site of preference after annealing Co and Fe ions in the structure. The result of migrations induced a saturated magnetization increase to 42.24 emu/g.

Fine Grain BaTiO3-Co0.5Ni0.5Fe2O4 Ceramics Prepared by the Two-Stage Sintering Technique

This work investigated the improvement of density and controllable grain size of multiferroic ceramics by using the system of (0.8)BaTiO3-(0.2)Co0.5Ni0.5Fe2O4 nanocomposites via the two-stage sintering technique. The sintering process was divided into two steps. Firstly, samples were fired at the optimized temperature of T1 to activate grain boundary migration in order to obtain an initial high density. Secondly, the samples were cooled immediately to the temperature of T2 and soaked at various times to enable dense ceramics without grain growth. All of the samples were characterized by an X-ray diffractometer, and the results confirmed that all samples were composite ceramics. Scanning electron microscopy showed the grain size of all the samples and proved that the two-stage sintering technique achieved fine grain ceramics when compared with traditional sintering. Electrical properties of all the samples were investigated using an LCR meter at room temperature to 200°C with various frequencies, and magnetic properties were characterized by a vibrating sample magnetometer.

Structural and Magnetic Properties of Zn Doped CoFe2O4

Zinc doped cobalt ferrite powders were prepared by the solid state reaction method. The effect of zinc substitution on structure, morphology and magnetic properties was investigated. The X-ray analysis confirmed existence of the single phase cubic spinel structure, while Rietveld refinement data showed increasing of lattice parameters with zinc content. In addition, saturated magnetization increased with increasing zinc concentration and it was contained at maximum in CoFe1.9Zn0.1O4 powders. However, the value of coercivity was decreased with zinc doped content. Furthermore, the oxidative states were characterized by X-ray absorption spectroscopy. The results confirm that the structure contained Co2+, Fe3+ and Zn2+ ions.

Fabrication and Properties of BaTiO3-CoFe2O4 Nanocomposites

In this work, BaTiO3-xCoFe2O4, where x = 0, 0.1, 0.2, 0.3, 0.4 and 0.5, nanocomposites were prepared by conventional mixing method and followed by normal sintering in air. The effect of processing condition on phase formation, microstructure, magnetic and electrical properties of the BaTiO3-CoFe2O4 nanocomposites was investigated. The phase development and microstructural evolution of this system have been determined via X-ray diffractometer and scanning electron microscope. From the results, it concludes that phase formation, microstructure, electrical and magnetic properties of the BaTiO3-xCoFe2O4 nanocomposites strongly depend on chemical composition.

The Influence of BMN Addition on the Phase Formation, Microstructure and Dielectric Property of BaTiO3 Ceramic

Solid solutions of the (1−x)BT-xBMN system were prepared successfully by the solid state reaction method followed by normal sintering in air. The phase formation, microstructure and dielectric property of BT-BMN ceramics were investigated as a function of compositions. XRD results showed a single perovskite phase for all compositions. Cubic-tetragonal transformation was found after adding BMN into the system. SEM micrographs revealed two very different grain sizes in the ceramics, with compositions of x = 0.02, 0.03, 0.04 and 0.05. Fine grains indicated a cubic structure, whereas large ones indicated a tetragonal structure. Regarding the dielectric property, Curie temperature decreased with increasing BMN content, whereas the ϵr value increased until the BMN content reached 3 mol% before dropping to a lower value.

Effect of Pb(Ni1/2W1/2)O3 on the Phase Transition Behavior of PbZrO3 Ceramic

Solid solution of (1−x)PbZrO3−xPb(Ni1/2W1/2)O3;(1−x)PZ-xPNW ceramics, where x = 0.02-0.10, were prepared by solid state reaction. Dense (1−x)PZ – xPNW ceramics were obtained by sintering at 1,100°C for 4 h. Effect of PNW on crystal structure, phase transitions and thermal and electrical properties was investigated using X-ray diffraction, dielectric spectroscopy, hysteresis measurement and differential scanning calorimetry. The results indicated that the solubility limit of the (1−x)PZ–xPNW system was found at x = 0.04. It was proved that the intermediate phase is an antiferroelectric in the PZ-PNW system. Stability of the AFE intermediate phase was seen to improve with increasing PNW content.

Magnetoelectric Properties of BaTiO3 – Co0.5Ni0.5Fe2O4 Composites Prepared by the Conventional Mixed Oxide Method

Multiferroics, which display simultaneous ferrimagnetic and ferroelectric properties, have been interesting recently because of their potentially significant applications in multifunctional devices such as magnetic resonance, drug delivery, high-density data storage, ferrofluid technology, etc. Composites combining BaTiO3 with Co0.5Ni0.5Fe2O4 have influenced the interest of many researchers, due to their outstanding and distinguished character called magnetoelectric (ME). In this work, ferrimagnetic-ferroelectric composites of BaTiO3 nanopowder and Co0.5Ni0.5Fe2O4 nanopowders were prepared by a conventional mixed oxide method. The multiferroic ceramics were compounded with the formula, (1-x)BaTiO3-(x)Co0.5Ni0.5Fe2O4, in which x = 0, 0.05, 0.10, 0.20 and 0.35. All of the compositions were analyzed by an X-ray diffractometer (XRD) in order to reveal the phase of perovskite and spinal structure. Scanning electron microscopy (SEM) was used to examine the variation of morphology and grain size of the composited ceramics. The magnetism of all the ceramics was measured using a vibrating sample magnetometer (VSM). The results showed that microstructure and the amount of ferrite are related strongly with magnetization.