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DOI: 10.1039/A905914H (Paper) Reference Section for: J. Mater. Chem., 1999, 9, 3131-3136

Structural investigation of oxygen insertion within the Ce2Sn2O7–Ce2Sn2O8 pyrochlore solid solution by means of in situ neutron diffraction experiments

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Bruno Tolla, Alain Demourgues, Olivier Isnard, Michel Menetrier, Michel Pouchard, Louis Rabardel and Thierry Seguelong

Abstract

The amazing oxygen exchange properties within the Ce2Sn2O7–Ce2Sn2O8 pyrochlore solid solution were investigated by means of in situ neutron diffraction experiments. The structural modification of the Ce2Sn2O7 phase heated under oxygen up to 1000[thin space (1/6-em)]°C was followed on the basis of the neutron diffraction patterns, continuously collected with a 5 min counting rate at 2.529 Å. The structure of the Ce2Sn2O8 pyrochlore phase has been previously determined at room temperature on the basis of the powder neutron diffraction pattern collected at 1.594 Å. Contrary to the oxygen-intercalated zirconate pyrochlores, oxygen atoms preferentially occupy a 32e crystallographic site, which is more distant from the Sn4+ cation than the other interstitial 8a site. Two kinds of local oxygen defects were identified within the Ce2Sn2O8 – ε (0 ≤ ε ≤ 0.05) pyrochlore at 400[thin space (1/6-em)]°C. The most stable is a tetrahedron of oxygen atoms (32e site) around an oxygen vacancy (8b site), comparable to the Willis clusters found in UO2 + x. The other, lying around the 8a site, involves short oxygen–oxygen distances and constitutes a new type of oxygen cluster around tin atoms. In addition to the successive disappearance of these local defects from 400[thin space (1/6-em)]°C to 700[thin space (1/6-em)]°C, cerium deinsertion was detected above 500[thin space (1/6-em)]°C. This leads to new cerium deficient Ce2 – xSn2Oy phases, which exhibit structural changes. The oxygen storage capacity (OSC) of the Ce2Sn2O7 pyrochlore was thus detailed by considering the successive insertion/deinsertion reactions and the Ce–Sn–O phase diagram.

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