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Kyono, Atsushi*; Kato, Masato*; Sano, Asami; Machida, Shinichi*; Hattori, Takanori
Physics and Chemistry of Minerals, 46(5), p.459 - 469, 2019/05
Times Cited Count:4 Percentile:16.12(Materials Science, Multidisciplinary)To reveal the decomposition mechanism with temperature under high-pressure, crystal structure of a hydrogrossular, katoite CaAl
(O
D
)
has been studied by in-situ neutron diffraction at 8 GPa. Although unusual expansion behavior was discerned at 200-400
C, the unit cell was continuously expanded up to 850
C. At 900
C, katoite was decomposed, indicating that pressure strongly increases dehydration temperature from 300
C to 900
C. On release of pressure, the katoite reappear together with corundum and portlandite. At 8 GPa, CaO
and AlO
polyhedra expand with temperature up to 850
C by about 8% and 13%, respectively. On the other hand, tetrahedral interstices are isotopically squeezed by about 10%: due to the expansion of above polyhedra. The neighboring D-D distance remains almost unchanged in this temperature range, while the O-D bond distance shrinks drastically just before decomposition. This finding suggests that the shortening of O-D distance caused by the D-D repulsion destabilizes the O-D bond, which induces the thermal decomposition of katoite.