Papers by Author: Satoko Takase

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Authors: Youichi Shimizu, Satoko Takase, Daisuke Koba
Abstract: A new solid-electrolyte impedance-metric NOx sensor device composed of a lithium ionic solid electrolyte: Li1.5Al0.5Ti1.5(PO4)3 (LATP) as a transducer and ceramic oxides (perovskite-type oxides, TiO2, SnO2, etc) as a receptor, respectively, have been systematically investigated for the detection of NOx (NO and NO2 ) in the range 10 – 200 ppm at 400 - 500°C. Responses of the sensors were able to divide component between resistance and capacitance, and it was found that the device was applicable to the selective detection of NO or NO2 concentration in each ingredient. Especially, those using TiO2, SnO2 (n-type semiconductor) and perovskite-type oxides (LaCoO3, LaNiO3 and LaCrO3) based receptors gave good responses to NO and NO2. It was also found that the responses were different between n-type or p-type semiconductors, in which we tried to elucidate the sensing mechanism
Authors: Youichi Shimizu, Satoko Takase, Mariko Yoshida
Abstract: Novel sol-gel processing techniques of ceramic materials were developed for designing new functional environmental ion sensors. Wet-chemical preparation methods for metal-oxide thin-films, perovskite-type oxide thin-films, and solid-electrolyte discs could be developed by using solution techniques based on polymer precursors, etc. New electrochemical sensing techniques to hydrogen-phosphate ion with high sensitivity and selectivity were developed by the use of ceramic-based sensors. A sol-gel processing technique was developed for the preparation of La-based perovskite-type oxide thin-films using an acetylacetone (AcAc)-modified poly(vinyl alcohol) (PVA)-based polymeric precursor method. The AcAc modified PVA-based sol made it possible to deposit a thin-film as well as to lower the sintering temperatures. The La0.8Sr0.2CoO3 perovskite-type oxide thin-film electrode prepared at 500°C showed good properties of amperometric sensing to hydrogen-phosphate ion. A new solid-electrolyte ion sensor device using a Na+-ion conductor (Na5DySi4O12: NaDyCON) as an impedancemetric transducer and a perovskite-type oxide thin-film as a receptor has been further developed. The AC impedance of the device with a LaCoO3 receptor was found to vary logarithmically with increasing K2HPO4 concentration between 1.0 x 10-5 and 1.0 x 10-2 M at 10 kHz. The 90% response time was ca. 2 min at room temperature. The sensor showed a little sensitivity to NO3- at higher concentration, while no response was observed to the examined anions of Cl- and ClO4-.
Authors: Kengo Oda, Satoko Takase, Youichi Shimizu
Abstract: Lithium ionic conductive solid electrolyte discs based on NASICON-type Li1+xGaxTi2-x(PO4)3 (x = 0.1 - 0.9) were prepared by a wet-chemical route at 1173 - 1273K. Crystalline phase, density, and electrical conductivity of the sintered discs were systematically investigated. Single phase of LiTi2(PO4)3 systems were obtained at the calcination temperatures above 773K. Maximum conductivity 7.3 x 10-4 S/cm at 303K and activation energy of 0.30eV were obtained for the Li1.25Ga0.25Ti1.75(PO4)3 discs sintered at 1223K.
Authors: Youichi Shimizu, Satoko Takase, Kensaku Ida, Masataka Imamura, Ikuhiro Koguma
Abstract: Electrophoretic deposition method was applied to prepare some solid-electrolyte thick-films of Na1+xZr2SixP3-xO12 (x = 2, 3; NASICON) and Na5DySi4O12 (NDSO) on Au-coated alumina substrates. With the ethanol-based medium, the deposition process was investigated under constant voltage mode. The concentration of the suspension and applied voltage were optimized with respect to the rate of deposition and quality of the deposit. The NASICON (Na3Zr2Si2PO12) -based solid-state ionic conductor thick-film as a host ceramic with a guest Cu+ ion has been produced as a noble phosphor thick-film by using an electrochemical ion doping method. The photoluminescence (PL) device of the NASICON:Cu+ film showed good photo-luminescent peaks near 450-500nm depending on the host materials.
Authors: Toru Inagaki, Toshikazu Matsumoto, Satoko Takase, Youichi Shimizu
Abstract: Perovskite-type oxide (LaCoO3) fine powders were prepared by a polymer precursors (PP) methods at 300~500°C. The LaCoO3 fine powder could be prepared at 380°C when the use of EDA and PEG for organic-and polymer-additives, respectively. The surface area of LCO was ca. 39m2/g. LCO thick-film could be prepared from the steady state suspension with the addition of AcAc or PVAby the EPD method at +10V, 3min.The current density of the LaCoO3 film sensor was changed with changing HPO42- concentration at +1.00 V vs. SCE. The device showed relatively good amperometoric response to H2PO4- from 1.0x10-5M to 1.0x10-3M with the 90% response time of ca 2min. The LaCoO3-based sensor also showed a good selectivity among the examined anions of NO3-, Cl- and SCN-.
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