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Ko, Taegyung,Bang, Gyusuk,Shin, Jungmuk The Korean Ceramic Society 1998 The Korean journal of ceramics Vol.4 No.2
The structure refinements and the electrical and magnetoelectric measurements were performed for BIT.1BF and BIT.2BT. The tetragonal distortion of the ab plane became lessened with the addition of $4BiFeO_3 into Bi_4Ti_3O_{12}$ significantly. However, the tilting of the outer-oxygen octahedra of the perovskite unit and the elongatin of the $(Bi_2O_2)^{2+}$ layers became more pronounced. For the both phases, the bariations of dielectric properties and electrical conductivities at high temperatures showed that the ferroelectic I-rerroelectric II phase transition existed before reaching the Curie temperature. The electrical conductivity became higher with the increase of $Fe^{3+}$ ions, implying that the electron transfer increased correspondingly. The magnetoelectric effect was observed linear up to ~8 kOe, which was stronger in BIT.1BF than BIT.2BF. This behavior indicates that the distortion of the ab plane may affect the induced polarization as well as magnetic moment.
Function through Defects: Thermodynamic and Kinetics of Point Defects in Ionic Solids
Ko, Taegyung,Bang, Gyusuk,Shin, Jungmuk The Korean Ceramic Society 1998 The Korean journal of ceramics Vol.4 No.2
The significance of point defects as relevant centers concerning electrochemical function is highlighted. Starting from the most simple case of dilute equilibrium bulk defect chemistry, influence of defect interaction and in particular the impact of interfaces on point defect redistribution are considered. Then recent progress in the field of kinetics in bulk and at boundaries is discussed. Finally, selected applications with emphasis on battery and sensor technology are presented.
An Approach for Synthesis and Characterization of Zirconia Nanopowder via Microwave Thermal Process
Athar, Taimur,Han, Sanghwan,Ko, Taegyung,Lee, Ik-Mo Taylor Francis 2009 Synthesis and reactivity in inorganic, metal-organ Vol.39 No.5
<P> We applied a simple, versatile and an efficient non-toxic methodology based on microwave irradiation process to prepare a gel from n-zirconium butoxide without using any solvent at ambient temperature to open new possibilities to control particle size distribution, surface chemistry and agglomeration. The alkoxy-derived gel changed to tetragonal zirconia powder on heating at 400°C with crystalline particles size (3 ∼ 5 nm). Zirconia exhibited strong luminescence under a UV laser. The presence of a organic moieties as impurities exhibit a strong luminescence in zirconia powder. From the structural analysis it is concluded that the morphology of the oxide strongly depends on the nature of the precursors and the synthetic methology.</P>
An Integrated Low Temperature Approach for the Synthesis of Titania via Sol-Gel process
Athar, Taimur,Han, Kyusuk,Han, Sanghwan,Ko, Taegyung,Lee, Ik-Mo Taylor Francis 2009 Synthesis and reactivity in inorganic, metal-organ Vol.39 No.5
<P> Colloidal titania particles with nanosize size distribution were prepared via sol-gel process by using oxo-titanium alkoxide as a molecular precursor. The transformation from oxo-titanium alkoxide to metal oxide was studied by IR, UV, thermal analysis, X-ray and TEM. TEM and XRD techniques were used to characterize the microstructure and crystallite morphology. The experimental results show that the titania has a good crystallinity with a particle size (5 nm), shape and with favorable surface morphology. These results support that titania has strong implications for the interaction between the oleic acid used as surfactant and Ti nanoparticle to enhance the stability with controlled functional properties.</P>
Park, Sunghoon,Kheel, Hyejoon,Sun, Gun-Joo,Ko, Taegyung,Lee, Wan In,Lee, Chongmu Hindawi Limited 2015 Journal of nanomaterials Vol.2015 No.-
<P>Fe2O3-decorated CuO nanorods were prepared by Cu thermal oxidation followed by Fe2O3decoration via a solvothermal route. The acetone gas sensing properties of multiple-networked pristine and Fe2O3-decorated CuO nanorod sensors were examined. The optimal operating temperature of the sensors was found to be 240°C. The pristine and Fe2O3-decorated CuO nanorod sensors showed responses of 586 and 1,090%, respectively, to 1,000 ppm of acetone at 240°C. The Fe2O3-decorated CuO nanorod sensor also showed faster response and recovery than the latter sensor. The acetone gas sensing mechanism of the Fe2O3-decorated CuO nanorod sensor is discussed in detail. The origin of the enhanced sensing performance of the multiple-networked Fe2O3-decorated CuO nanorod sensor to acetone gas was explained by modulation of the potential barrier at the Fe2O3-CuO interface, highly catalytic activity of Fe2O3for acetone oxidation, and the creation of active adsorption sites by Fe2O3nanoparticles.</P>
Prominent Ethanol Sensing with Cr2O3 Nanoparticle-Decorated ZnS Nanorods Sensors
Gun-Joo Sun,Hyejoon Kheel,Taegyung Ko,Chongmu Lee,Hyoun Woo Kim 한국물리학회 2016 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.69 No.3
ZnS nanorods and Cr2O3 nanoparticle-decorated ZnS nanorods were synthesized by using facile hydrothermal techniques, and their ethanol sensing properties were examined. X-ray diffraction and scanning electron microscopy revealed good crystallinity and size uniformity for the ZnS nanorods. The Cr2O3 nanoparticle-decorated ZnS nanorod sensor showed a stronger response to ethanol than the pristine ZnS nanorod sensor. The responses of the pristine and the decorated nanorod sensors to 200 ppm of ethanol at 300 C were 2.9 and 13.8, respectively. Furthermore, under these conditions, the decorated nanorod sensor showed a longer response time (23 s) and a shorter recovery time (20 s) than the pristine one did (19 and 35 s, respectively). Consequently, the total sensing time of the decorated nanorod sensor (42 s) was shorter than that of the pristine one (55 s). The decorated nanorod sensor showed excellent selectivity to ethanol over other volatile organic compound gases including acetone, methanol, benzene, and toluene whereas the pristine one failed to show selectivity to ethanol over acetone. The improved sensing performance of the decorated nanorod sensor is attributed to a modulation of the width of the conduction channel and the height of the potential barrier at the ZnS-Cr2O3 interface accompanying the adsorption and the desorption of ethanol gas, and the greater surface-to-volume ratio of the decorated nanorods which was greater than that of the pristine one due to the existence of the ZnS-Cr2O3 interface.
Fabrication of a regenerable Ni supported NiO-MgO catalyst for methane steam reforming by exsolution
Park, Yong Sun,Kang, Misook,Byeon, Pilgyu,Chung, Sung-Yoon,Nakayama, Tadachika,Ko, Taegyung,Hwang, Haejin Elsevier 2018 Journal of Power Sources Vol.397 No.-
<P><B>Abstract</B></P> <P>Nickel nanoparticles supported on a NiO-MgO solid solution are fabricated using the exsolution process. Upon reduction, the nickel nanoparticles are exsoluted from a Ni<SUB>0·4</SUB>Mg<SUB>0·6</SUB>O solid solution powder. From the results obtained from transition electron microscopy (TEM) and temperature programmed reduction (TPR) measurements, it is concluded that the size and dispersion state of the nickel nanoparticles strongly depend on the homogeneity of the parent solid solution. Sintering the parent solid solution powder at a high temperature results in a homogeneous solid solution, which leads to a decreased reducibility of the nickel ions and, consequently, well-distributed Ni nanoparticles are successfully obtained. The metallic nickel moves reversibly to and out of the parent solid solution in response to a specific atmospheric condition. The methane steam reforming over the as-synthesized nickel nanoparticles are evaluated and appreciable degradation (1000 h) of the catalytic activity is not found for the catalyst sample that is sintered at 1000 °C followed by subsequent reduction to 800 °C.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Ni nanoparticles supported on NiO-MgO solid solution were synthesized by exsolution. </LI> <LI> The growth of Ni nanoparticles depended on the homogeneity of the solid solution. </LI> <LI> The catalytic activity was not to be degraded appreciably for 1000 h of operation. </LI> <LI> The metallic nickel moved reversibly to and out of the parent solid solution. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Sunghoon Park,Hyejoon Kheel,Gun-Joo Sun,Hyoun Woo Kim,Taegyung Ko,Chongmu Lee 대한금속·재료학회 2016 METALS AND MATERIALS International Vol.22 No.4
Cr2O3-functionalized Nb2O5 nanoparticles were synthesized via a facile hydrothermal route. The multiple-networked Cr2O3-functionalized Nb2O5 nanostructured sensor showed enhanced H2 gas sensing performance compared to its pristine Nb2O5 nanostructure counterpart. The Cr2O3-functionalized Nb2O5 nanostructure sensor showed responses of 5.24 to 2 ppm of H2 at room temperature, whereas the pristine Nb2O5 nanoparticle sensors showed responses of 2.29. The former also exhibited a faster response to H2. The multiple-networked pristine and Cr2O3-functionalized Nb2O5 nanostructured sensors were stronger and much shorter, respectively, than other nanomaterial-based Schottky diode-type sensors and Nb2O5-based Schottky diode-type sensors. The underlying mechanism for the enhanced sensing performance of the Cr2O3-functionalized Nb2O5 nanostructured sensor towards H2 gas is discussed in detail. Particular emphasis is placed on the role of the Cr2O3-Nb2O5 p-n junction in the Cr2O3-functionalized Nb2O5 nanostructure sensor.