The structural simulation and study of LaGaO3-based electrolyte in the solid oxide fuel cell

• Main Authors: Cheng-Long Chang, 張承龍
• Other Authors: 吳玉娟
• Format: Others
• Language: zh-TW
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/s7a8z2

碩士 === 國立臺北科技大學 === 材料科學與工程研究所 === 101 === A Solid Oxide Fuel Cell(SOFC) is composed of anode, cathode and electrolyte. The operating temperature of SOFC is between 600 to 1000℃, and it is between 400 to 800℃ for Intermediate Temperature Solid Oxide Fuel Cell(IT-SOFC). Most of the electrolyte materials are Yttrium stabilized Zircomic(8mole％YSZ) CaF2 cubic crystal. The ion conductivity of CaF2 cubic crystal is 0.036 S/cm, and its operating temperature is 1000℃. After doping Sr2+ and Mg2+-substituted La1-xSrxGa1-yMgyO3-δ(LSGM) in the LaGaO3-based electrolyte material, the ion conductivity is increased to 0.1 S/cm and the operating temperature is decreased to 800℃. Most research used synthesis method to analyze the material rather than used simulation software. In this study, simulation software is used and the phase transition is discussed based on the adopt atom projection pattern, stereographic projection pattern, electron diffraction, and polyhedron. According to the reference, phase transition of LaGaO3-based changes with the dopant content and the temperature. The following is the transformation of the crystal structure: orthorhombic Pnma(62) => pseudo-orthorhombic Imma(74)[like monoclinic I2/a(15)] => pseudo-rhombohedral R-3c(167)[ like monoclinic I2/a(15)] =>? rhombohedral R3c(167) => cubic Pm-m(221)。 According to references, GaO6 octahedral crystal structure of LaGaO3 distorted at the room temperature, and that lowered the symmetry. The atom projection pattern created by simulation software showed the degree of distortion of different crystal structures, and Watching overlapped stereographic projection pattern of every structure knows overlapping relation for direction and mirror. The LSGM structure is mostly analyzed by XRD, neutron diffraction, Rietveld refinement method analysis, but XRD could not observe the subtle changes in crystal structure. Hence, neutron diffraction and Rietveld refinement analysis are used more often. The study, which used the simulation software (CaRIne Crystallography 3.1), mainly used electron diffraction to analyze the four different crystal structures and the five space groups. It is concluded that the diffraction direction [210]//[210]//[0-2-1]//[00-1] [000-1]//[1-1-1] and [11-1]//[11-1]//[-1-1-2]//[-2-1-1][-101-1]//[1-10] relation for parallel each other. The diffraction pattern of orthorhombic Pnma(62) is different from other space groups. The diffraction patterns of orthorhombic Imma(74) and monoclinic I2/a(15) and rhombohedral R c(167) are very similar to distinguish. CBED or LACBED may have to be used for further analysis.