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Kim, Yusung,Noh, Seungtak,Cho, Gu Young,Park, Taehyun,Lee, Yoon Ho,Yu, Wonjong,Lee, Yeageun,Tanveer, Waqas Hassan,Cha, Suk Won Korean Society for Precision Engineering 2016 International Journal of Precision Engineering and Vol.17 No.8
Thin film solid oxide fuel cells with nickel oxide - gadolinia doped ceria anodes deposited by sputtering were operated at <TEX>$500^{\circ}C$</TEX>. The fuel cells each have 750 nm - yttria-stabilized zirconia electrolytes and 200 nm - platinum cathodes. The thicknesses of the anodes are 240 nm, 320 nm, and 400 nm. The cell with the 320-nm-thick anode showed the highest maximum power density among all cells. Through electrochemical impedance spectroscopy, the anodic activation resistance and the ohmic resistance were calculated. The anodic activation loss decreased with an increase in the anode thickness. Therefore, the cell with the 400-nm-thick anode showed the lowest activation polarization resistance. Additionally, the ohmic resistance, the sum of various electronic/ionic resistances, was lowest when using the 320-nm-thick anode. The electronic resistance and the ionic resistance of the anode were found to exist in a trade-off relationship owing to the current-collecting method of the anode.
Thermal oxidation mechanism and stress evolution in Ta thin films
Jin, Yusung,Song, Jae Yong,Jeong, Soo-Hwan,Kim, Jeong Won,Lee, Tae Geol,Kim, Ju Hwang,Hahn, Junhee Cambridge University Press (Materials Research Soc 2010 Journal of materials research Vol.25 No.6
<P>Oxidation-induced stress evolutions in Ta thin films were investigated using ex situ microstructure analyses and in situ wafer curvature measurements. It was revealed that Ta thin films are oxidized to a crystalline TaO2 layer, which is subsequently oxidized to an amorphous tantalum pentoxide (<I>a</I>-Ta2O5) layer. Initial layered oxidation from Ta to TaO2 phases abruptly induces high compressive stress up to about 3.5 GPa with fast diffusion of oxygen through the Ta layer. Subsequently, it is followed by stress relaxation with the oxidation time, which is related to the slow oxidation from TaO2 to Ta2O5 phases. The initial compressive stress originates from the molar volume expansion during the layered formation of TaO2 from the Ta layer, while the relaxation of the compressive stresses is ascribed to the amorphous character of the <I>a</I>-Ta2O5 layer. According to Kissinger's analysis of the stress evolution during an isochronic heating process, the oxygen diffusion process through the <I>a</I>-Ta2O5 layer is the rate-controlling stage in the layered oxidation process of forming a <I>a</I>-Ta2O5/TaO2/Ta multilayer and has an activation energy of about 190.8 kJ/mol.</P>