Phase Transformation Related Conductivity Degradation of NiO Doped YSZ: An In-situ Micro-Raman Analysis
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Phase Transformation Related Conductivity Degradation of NiO Doped YSZ: An In-situ Micro-Raman Analysis Haruo Kishimoto1, Keiji Yashiro2, Taro Shimonosono1, Manuel E. Brito1, Katsuhiko Yamaji1, Teruhisa Horita1, Harumi Yokokawa1 and Junichiro Mizusaki2 1 National Institute of Advanced Industrial Science and Technology (AIST) AIST Central No. 5, Higashi 1-1-1, Tsukuba, Ibaraki, 305-8565 Japan 2 Tohoku University, LAMR2 bldg., 2-1-1 Katahira, Aoba-ku, Sendai, 980-8577 Japan
ABSTRACT In-situ micro Raman spectroscopy has been adopted as one of the most powerful analytical techniques with high spacial resolution under controlled atmospheres. In the present study, phase transformation of NiO doped yttria stabilized zirconia (YSZ) was monitored by insitu micro-Raman spectroscopy. Raman spectra change caused by the phase transformation from the cubic phase to the tetragonal phase was observed for the NiO doped YSZ during annealing at a high temperature of 1173 K under reducing atmosphere. INTRODUCTION Solid oxide fuel cells (SOFCs) are one of the most promising systems for distributed power generation. SOFCs have some important features, such as high electric efficiency and high fuel flexibility. SOFCs are operated at a high temperature with continuous feeding of air and fuels and continuous progress of chemical and electrochemical reactions. It is very important for improving the durability, reliability and performances to understand in detail what occurs in SOFCs and how the materials and fuels change under SOFC operations. Needless to say that, it is quite difficult to carry out such an “in-situ” measurement on real SOFC stacks; therefore, model cells are used. Recently, several in-situ optical analysis have been adopted to study SOFC materials; for example, in-situ optical microscopy, in-situ thermal image using an IR camera and in-situ Raman spectroscopy [1-10]. In particular, in-situ Raman spectroscopy has been adopted for carbon deposition behavior on nickel base anodes [1,2,4], gas distribution in the anode channel [10] and temperature and stress distributions in cells [5,9]. It is also demonstrated that Raman spectroscopy is quite sensitive in detecting phase transformation behavior of stabilized zirconia materials [11-14]. It is well known that conductivity of 8 mol% yttria stabilized zirconia (8YSZ) decreases by annealing at high temperatures, around 1273 K, within the time span of several thousand hours [12,13,15,16]. It has been also suggested that phase transformation of 8YSZ from the cubic to the tetragonal phase occurs after such a long annealing time at high temperatures [12,13]. Moreover, for NiO doped 8YSZ, a similar behavior occurs but in a shorter period of time (several hundred hours) under a reducing condition [17-20]. Even when phase transformation has been confirmed by ex-situ analysis at room temperature (R.T.) after annealing treatment, it is still unclear when phase transformation occurs for those cubic stabilized zirconia.
In the present study, the surface of NiO doped 8YSZ was analyzed by in
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