Browsing by Author "Choi Jae-Young"

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Correlation between the green-like coloration and the structural and electronic properties of celadon glazes
(Cer�mica, 2012) Hidaka, M.; Takeuchi, K.; Wijesundera, R.P.; Kumara, L.S.R.; Watanabe, M.; Choi Jae-Young; Sung, N.E.
Correlation between the Izumiyama porcelain ceramics and the red-overglaze enamels of the Kakiemon-style porcelains
(Ceramics International, 2008) Kajihara, S.; Hidaka, M.; Wijesundera, R.P.; Kumara, L.S.R.; Kobayashi, H.; Koga, M.; Tsuru, T.; Koga, K.; Shimomura, K.; Choi Jae-Young; Sung, N.E.; Park, Y.J.
The Kakiemon-style porcelains made from 17th century at Arita are famous Japanese porcelains, characterized mainly by their colored underglaze and overglaze and by their original design of coloring spatial patterns in the porcelain surface. Raw materials of the red-overglaze enamels have been investigated by means of X-ray diffraction and X-ray absorption spectra using synchrotron radiations. It is found that Izumiyama porcelain ceramics of yellow color can produce the Kakiemon red-overglaze enamels by thermal treatment and water-washing, where Izumiyama is a collecting place of the raw porcelain ceramic at Arita. The brightness of the red-overglaze enamels is related on the local structure around Fe ions and the electronic band states of Fe ions near a Fermi level in ?-Fe2O3, in addition to the spatial density of the ?-Fe2O3 fine particles. The structural and electronic properties are slightly affected by an electron-hybridization between Fe ions of ?-Fe2O3 and oxygen ions of the (SiO2?Al2O3) complexes in the red overglaze.
Effects of annealing on the properties and structure of electrodeposited semiconducting Cu?O thin films
(Physica Status Solidi (basic solid state physics), 2007) Wijesundera, R.P.; Hidaka, M.; Koga, K.; Sakai, M.; Siripala, W.; Choi Jae-Young; Sung, N.E.
The structures and the electronic states in electrodeposited semiconductor Cu?O thin films have been investigated for each annealing temperature (TA) by X-ray diffraction (XD) and X-ray absorption spectroscopy (XAS) near the Cu K edge using synchrotron radiation. The thin films prepared as grown and annealed at TA ? 175 �C, 200 �C ? TA ? 300 �C, TA = 400 �C are characterized mainly by the pure Cu2O-type structure, the pseudo-Cu2O-type having a superlattice structure, and two phases of Cu2O-type and CuO-type structures, respectively, while the film annealed at TA = 500 �C is single-phase CuO-type. The XAS spectra suggest that there is a structural phase transition occurring at about 400 �C, which induces a modulation of the local structure around Cu ions observed in the extended X-ray absorption fine structure (EXAFS) and the occupational electronic band states of Cu-4p localized just above the Fermi level, taken from X-ray absorption near edge structure (XANES). The open-circuit voltage suggests that the photosensitivity of the Cu?O thin films strongly depends on the annealing treatment and shows a crossover from an n-type to a p-type semiconductor. (? 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Structural and Electronic Properties of Electrodeposited Heterojunction of CuO/Cu2O
(Ceramics-Silik�ty, 2010) Wijesundera, R.P.; Hidaka, M.; Koga, K.; Choi Jae-Young; Sung, N.E.
The structures and the electronic band states of the electrodeposited thin film CuO/Cu2O heterojunction have been studied by means of the X-ray diffractions (XRD) and the X-ray absorption spectra (XAS) with different grazing angles of the incident X-ray beam using the synchrotron radiation. The heterojunction of about 2 ?m consists of n-type Cu2O (~1 ?m) and p-type CuO (~1 ?m) thin films bi-layer. Scanning electron micrographs (SEMs) show the existence of two different polycrystalline grain layers and the XRD reveals that the different grain layers are high quality CuO-type and Cu2O-type structures respectively. Photoactive performances of the Ti/CuO/Cu2O/Au heterojunction are Voc of ~210 mV and Jsc of ~310 mA/cm2. It reveals that the Cu2O grains are grown from the surfaces of the CuO polycrystalline grains and make very good contact with the CuO grains. It is found that the XAS of CuO/Cu2O heterojunction are convoluted independently by X-ray absorption fine structure (EXAFS) and X-ray absorption near edge structures (XANES) spectra of the Cu2O and CuO grains, depending on the grazing angles. Present study reveals that bottom of the conduction band (Cu-4pp) of the Cu2O in the CuO/Cu2O heterojunction reduces by 0.57 eV relative to the Ti/Cu2O ohmic contact.
Structural properties of the red-color overglaze for the HIZEN porcelains produced in the early Edo period of Japan
(Ceramics International, 2009) Hidaka, M.; Ohashi, K.; Kajihara, S.; Wijesundera, R.P.; Kumara, L.S.R.; Choi Jae-Young; Sung, N.E.
HIZEN porcelains made in 1650s to 1750s (early Edo period) in Arita areas sited in south Japan (SAGA) are famous Japanese porcelains, which are characterized by elegant and bright colors in the overglaze and the underglaze. Red-overglazes and transparent glazes of the HIZEN porcelains have been investigated by means of X-ray diffraction (XRD) and X-ray absorption spectra (XAS) using synchrotron radiation. The results suggest that the red-color brightness of the Hizen porcelains is mainly induced by micro-structural correlation between ?-Fe2O3 fine particles of red-color emission element and the oxide complexes of SiO2?Al2O3?CaO?KNaO or SiO2 in the fritted overglazes. The stability of the red-color overglaze on the porcelain body of white-color results from interfacial fusion between both glass-states in the fritted overglaze and the transparent glaze coating the porcelain body. The refined local structures around Fe ions of the ?-Fe2O3 structure taken EXAFS spectra give the technical and historical relation among four kinds of the HIZEN porcelains for fritted materials of the overglazes and thermal treatment at high-temperature in the porcelain kilns.
Structural properties of the red-color overglazes on the Kakiemon-style porcelains produced in the later 17th century by means of X-ray diffraction (I)
(Cer�mica, 2009) Hidaka, M.; Horiuchi, H.; Ohashi, K.; Wijesundera, R.P.; Kumara, L.S.R.; Choi Jae-Young; Park, Y.J.
Kakiemon-style porcelains produced at Arita areas (SAGA) in Kyushu Island are famous Japanese porcelains. The porcelain-techniques creating its elegant and bright red-color underglaze and overglaze were found and developed in 1650's (early Edo period) first by Kakiemon kiln. Red-color overglaze and transparent glaze of the Kakiemon-style porcelains have been investigated by means of X-ray diffraction using synchrotron radiation. The results suggest that the red-color brightness is mainly induced by micro-structural correlation between ?-Fe2O3 fine particles, as red-color emission elements, and other oxides of SiO2, Al2O3, CaO, KNaO, PbO. The stability of the red-overglaze on the porcelain surface is related to interfacial fusion of the glasses existing in the fritted red-overglaze and the transparent glaze on the porcelain body. The ancient porcelain-techniques of the Kakiemon-style porcelains are clearly based on the micro-structural and material properties of the overglazes, the underglazes, and the transparent glazes, though the techniques were experimentally and accidentally found and developed in the Edo period.