Papers by Author: Naratip Vittayakorn

Abstract: Nanocrystalline barium zirconium titanate, BaZr_0.4Ti_0.6O₃, was synthesized successfully via the sonochemical process. The effects of reaction time on the precipitation of Ba(Zr,Ti)O₃ particles were investigated briefly. The crystal structure as well as molecular vibrations and morphology were investigated. X-ray diffraction indicated that the powders exhibited a single phase perovskite structure, without the presence of pyrochlore or unwanted phases at the reaction time of 60 min. Nanocrystals were formed before being oriented and aggregated into large particles in aqueous solution under ultrasonic irradiation. A scanning electron microscopy (SEM) photograph showed the BZT powder as spherical in shape with uniform nanosized features.

Abstract: Titanium dioxide nanoparticles (TiO₂) were successfully synthesized via a sonochemical-assisted process using titanium isopropoxide as the titanium sources and calcination process at 300-500 °C. The effect of sonication time and heat treatment temperature on structural and nanostructure properties of the nanoparticles were characterized by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscope (SEM) and transmission electron microscope (TEM). The XRD and Raman results indicated that the crystalline of as-sonochemically synthesized TiO₂ nanoparticles corresponded to anatase phase of TiO₂ after sonication for 30 mim. The high quality crystalline anatase phase and increasing of crystalline size can be obtained after calcinations process.

Abstract: The microwave-assisted solution combustion synthesis was applied to the initial synthesizing of Ca₃Co₂O₆ powder using glycine as a fuel and nitrate as an oxidant. The as-synthesized powders were calcined at 700-1,000^ºC for 4h. Product characterization was performed using Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and Scanning electron microscope (SEM). The fuel-to-oxidizer molar ratio was found to affect the combustion reaction and character of the powder obtained. The phase composition of powder after calcination at various temperatures has shown that the formation of Ca₃Co₂O₆ occurs directly. The calcined powder possesses a rhombohedral crystal structure with an X-ray diffraction pattern that could be matched with the Ca₃Co₂O₆JCPDS: 89-0629. This method is a simple way of synthesizing fine Ca₃Co₂O₆ powder with a low calcination temperature.

Abstract: 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 Co_0.5Ni_0.5Fe₂O₄ 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 Co_0.5Ni_0.5Fe₂O₄ nanopowders were prepared by a conventional mixed oxide method. The multiferroic ceramics were compounded with the formula, (1-x)BaTiO₃-(x)Co_0.5Ni_0.5Fe₂O₄, 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.

Abstract: Manganese zinc pyrophosphate (Mn_(2-x)Zn_xP₂O₇ when x = 0.0, 0.5, 1.0, 1.5 and 2.0) ceramics were fabricated by conventionally mixing oxide using the normal sintering method. The samples were characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR), Raman spectroscopy and scanning electron microscopy (SEM). The XRD results indicated that synthesized Mn_(2-x)Zn_xP₂O₇ systems have a pure monoclinic phase without the presence of phase impurities. The lattice parameters and crystalline sizes analyzed from XRD data were changed depending on the amount of added Zn²⁺ ion concentration in the Mn₂P₂O₇ structure. The FT-IR and Raman results showed the fundamental vibrations of P₂O₇^4-ion and Mn-O or Zn-O, which confirmed the Mn_(2-x)Zn_xP₂O₇ formation. In addition, dielectric stability of temperature and frequency was observed in the composition, x = 1.0, with a dielectric constant value of 11.5 at 1 MHz.

Abstract: The objective of this work is to provide the process for making BaTiO3-based ceramics by adding bismuth oxide (Bi2O3) into the system. The attention is also focused on synthesis conditions, where sintering temperature exhibits a pronounced effect on phase formation, density, microstructure and dielectric properties of BaTiO3 ceramics doped with different contents of Bi2O3 nanoparticles. The phases of BaTiO3-based ceramics have been prepared by solid state reaction using different Bi2O3 amount and characterized by X-ray diffractometry, Archimedes’s method, scanning electron microscopy and dielectric spectroscopy. The results show that single phase of BaTiO3 with no evidence of secondary phase forms in all samples. Abnormal grain growth was found in pure BaTiO3 ceramic with 37.30 µm of average grain size. After added Bi2O3 nanoparticles into system, the grain size significantly decreases and the sintering temperature of BaTiO3-based ceramics efficiently reduces without degrading the dielectric characteristics.

Abstract: Al-doped ZnO nanoparticles were synthesized by sonochemical method from zinc acetate dehydrate and aluminum acetate as starting precursors. The deionized (DI) water was selected as the solvent. Sonication of the precursor was performed by a Sonics Model VCX 750 for 30 minutes until precipitated product was finally obtained. The as-precipitated powders were calcined at different temperature range of 550-1100 °C for 2 hr. For all samples, their crystal structures were investigated by X-ray diffraction (XRD) and surface morphologies were observed by scanning electron microscope (SEM). The XRD results revealed that, the purity of as-synthesized powders increases when the calcination temperature increases. Moreover, it is noticed that the AlZnO partial peaks will appear when the as-synthesized powders were calcined at 800 – 1000 °C. In addition, SEM micrographs show the increase of agglomeration and the particles when the calcination temperature increases.

Abstract: SnO₂ nanoparticles were synthesized by ultrasonic-assisted precipitation process using stannic chloride pentahydrate (SnCl₄·5H₂O) as a precursor. The stannic chloride aqueous solution was precipitated by ammonia under sonication. The as-synthesized precipitates were dried at 80 oC and then calcined at 400 oC for 2 h. The physical properties of nanoparticles with/without sonication were characterized by thermogravimetic and differential thermal analysis, X-ray diffraction, and transmission electron microscope. The results reveal that ultrasonic radiation has significant influence on phase transformation mechanism from Sn (OH)₄ to SnO₂, grain size and uniformity of SnO₂ nanoparticles.

Abstract: Barium hydrogenphosphate, BaHPO₄ was synthesized for the first time through simple and rapid method using BaCO₃-H₃PO₄-NaOH, pH =9.0 at room temperature for 30 min. The studied BaHPO₄ decomposed in a single well-defined stage via deprotonated hydrogenphosphate reactions, revealed by TG/DTG and DSC techniques. The calculated wavenumbers based on DSC peak were comparable with FTIR results, which support the breaking bonds of P-OH (HPO₄^2-) in the deprotonated hydrogenphosphate reactions. The thermodynamic functions (ΔH*, ΔG*, and ΔS*) for the deprotonated hydrogenphosphate reactions calculated from DSC data indicate that the deprotonated HPO₄^2- reaction occur a lower-energy pathway and spontaneous process. The FTIR, XRD and SEM data of the studied BaHPO₄ and its decomposed product Ba₂P₂O₇ are also reported.

Abstract: The Cu_0.95Pt_0.05Fe_0.97Sn_0.03O₂ sample has been synthesized by a solid-state reaction to investigate optical properties of materials of transparent conducting oxide. Crystal structure was characterized by XRD. The Seebeck coefficient and electrical conductivity were measured in the high temperature (300 to 860 K), while the XPS and UV-VIS-NIR spectra were analyzed at room temperature. The XRD peaks confirm the samples forming the delafossite structure phase. The Seebeck coefficient reveals the samples displays the p-type conducting. The XPS spectra show the Sn²⁺ state stabling in this compound. The optical direct gap is 3.45 eV as a visible-transparent material. These results support that the Cu_0.95Pt_0.05Fe_0.97Sn_0.03O₂ oxide compounds, of which the Cu¹⁺ and Fe³⁺ sites are substituted by the Pt¹⁺ and Sn²⁺ ions respectively, are p-type transparent conducting oxide materials.