Photon Factory Activity Report 2005 #23 Part B (2006)
Crystallography

3A/2005G157, 2005G158
2004G256, 2004G058

Phase Transition of Doped Lanthanum Cobaltite throughsynchrotron powder diffraction
Takayuki Tsuji, Masatomo Yashima*, Kenjiro Oh-uchi, Syuuhei Kobayashi, Wataru Nakamura,
1
2
Yoshiaki Ando, Takeharu Mori , Masahiko Tanaka
Department of Materials Science and Engineering, Interdisciplinary Graduate School of Science andEngineering, Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-ku, Yokohama, 226-8502,
Japan
1
Photon Factory, Institute for Materials Structure Science, High Energy Accelerator ResearchOrganization, 1-1 Ooho, Tsukuba-shi, Ibaraki, 305-0801, Japan
2WEBRAM, National Institute for Materials Science, SPring-8, 1-1-1 Kouto Mikazuki-cho, Sayogun, Hyogo 679-5198, Japan
Introduction
SOFC (Solid Oxide Fuel Cell) is an attractive energygeneration system due to high efficiency and cleaness.
Some ABO3 perovskite-related compounds such as doped
lanthanum cobalt oxides can be utilized as electrodematerials in the SOFCs due to excellent ionic andelectronic conductivity. The development of better
electrode materials requires a better understanding of themechanism of ionic conduction, and crucial to this is acomprehension of the crystal structure and phasetransition at high temperatures where the materials work
efficiently. Here we report the phase transition ofLa0.601Sr0.394Co0.802Fe0.203O3-δ (LSCF6482) at hightemperatures.
Experiment
Synchrotron powder diffraction experiments of theLSCF6482 sample were conducted using thediffractometer installed at the beam line BL-3A of thePhoton Factory, KEK, Japan. Monochromatized 0.908 ÅX-ray and a furnace with the MoSi2 heaters were used forthe high-temperature diffraction experiments (Yashima &Tanaka, J. Appl. Cryst. 37 (2004) 786-790).We installed aSi(111) analyzer crystal between the sample and thescintillation counter to obtain high angular resolution of
δd/d ~0.03% .
Results and discussion
The diffraction profile of the LSCF 6428 at room
temperature was identified to be the trigonal phase with adistorted perovskite-type structure (space group R3 c ).
Figures 1 and 2 show the temperature dependence of thesynchrotron powder diffraction profiles. At room
temperature the peak split into 4 0 4 and 0 0 12reflections was clearly observed (Fig. 1). Similarly thepeak split between the 2 2 0 and 2 0 8 reflections wasalso detected as shown in Fig. 2. The difference between
the peak positions between 4 0 4 and 0 0 12 reflections
became smaller with increasing temperature and merged
between 773 K and 823 K (Fig. 1). The difference
between the 2 2 0 and 2 0 8 peak positions also became
smaller with increasing temperature and merged between
773 K and 823 K, indicating the trigonal ( R3 c ) to cubic( Pm 3 m ) phase transition. These peak splits continuously
decreased and disappeared, suggesting that the phasetransition is continuous.

Fig. 1. Diffraction profiles of LSCF6482 around the 4 0 4
and 0 0 12 reflections measured at different temperatures.

Fig. 2. Diffraction profile of LSCF6482 around the 2 0 2 and 20 8 reflections measured at different temperatures.
* yashima@materia.titech.ac.jp

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