Properties and microstructural analysis of La_1−xSr_xCoO_3−δ (x=0-0.6) cathode materials

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• 作者：Yu-Chuan Wu^a ; ^b ; ^c ; ^{wuyc@ntut.edu.tw} ; ^{wuyc@mail.ntut.edu.tw} ; Peng-Yu Huang^b ; Guiying Xu^d
• 关键词：Solid oxide fuel cell ; Sintering ; Microstructure ; Electrochemical impedance spectroscopy ; Transmission electron microscopy
• 刊名：Ceramics International
• 出版年：2017
• 出版时间：1 February 2017
• 年：2017
• 卷：43
• 期：2
• 页码：2460-2470
• 全文大小：2476 K
• 卷排序：43

文摘

La1−xSrxCoO3−δ (LSC; x=0–0.6) materials were synthesized and sintered at 1200 °C for 6 h by solid-state reaction for use as a cathode material in intermediate-temperature solid oxide fuel cells (IT-SOFCs). Physical property and microstructural analyses of the LSC materials were performed via X-ray diffractometry, scanning electron microscopy, transmission electron microscopy, dilatometer testing, dc four-wire measurement, and ac impedance spectroscopy. The sintered LSC samples with x=0–0.5 and x=0.6 showed rhombohedral and cubic perovskite structures, respectively. LSC with x=0.3–0.6 had a dense structure and no secondary phase was observed. The average grain size was approximately 3.1 µm for x=0.3 and increased to 10.8 µm at x=0.6. Grain growth could thus be promoted by Sr ions doping. The LSC samples with x=0 and x=0.3–0.6 respectively exhibited semiconductor-like and metallic-like conduction behavior below 800 °C. The LSC (x=0.3–0.5) materials underwent R- to C-phase transformation at 700–750 °C. At 550–700 °C, the activation energies were in the range of 0.028–0.040 eV for the samples with x=0.3–0.5, while at 700 °C, the conductivities were in the range of 2149–2234 S cm−1. This study found that the La0.6Sr0.4CoO3−δ sample, showing a higher conductivity, is the best material to be used as a cathode for IT-SOFCs (500–700 °C). Two super-lattice diffraction spots: 1/2{110}R (or 1/2{010}C) and 1/2{01̅1̅}R (or 1/2{001̅}C) were evident in the La0.6Sr0.4CoO3−δ material. This super-lattice structure was induced by clustering and short-range ordering of the dopant Sr ions or oxygen vacancies, and the unit cell was defined as a tetragonal cell with aC×aC×2aC. R- and C-phase transformation matrices for the plane indices were also obtained.