The stability and compressibility of MgAl2O4 high-pressure polymorphs |
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Authors: | S. Ono T. Kikegawa Y. Ohishi |
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Affiliation: | (1) Institute for Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology, 2-15 Natsushima-cho, Yokosuka-shi, 237-0061 Kanagawa, Japan;(2) High Energy Acceleration Research Organization, 1-1 Oho, 305-0801 Tsukuba, Japan;(3) Japan Synchrotron Radiation Research Institute, Mikazuki-cho, Sayo-gun, 679-5198 Hyogo, Japan |
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Abstract: | High-pressure and high-temperature experiments using a laser-heated diamond anvil cell (LHDAC) and synchrotron X-ray diffraction have revealed a phase transition in MgAl2O4. CaTi2O4-type MgAl2O4 was found to be stable at pressures between 45 and at least 117 GPa. The transition pressure of CaTi2O4-type phase in MgAl2O4 is much lower than that in the natural N-type mid-oceanic ridge basalt composition. The Birch–Murnaghan equation of state for CaTi2O4-type MgAl2O4 was determined from the experimental unit cell parameters with K 0=219(±6) GPa, K 0′=4(constrained value), and V 0=238.9(±9) Å3. The observed compressibility was in agreement with the theoretical compressibility calculated in a previous study. ε-MgAl2O4 was observed at pressures between 40 and 45 GPa, which has not been reported in natural rock compositions. The gradient (dP/dT slope) of the transition from the ε-type to CaTi2O4-type MgAl2O4 had a positive value. These results should resolve the dispute regarding the stable high-pressure phase of MgAl2O4, which has been reported in earlier studies using both the multi-anvil press and the diamond anvil cell. |
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Keywords: | MgAl2O4 polymorphs Phase transition Compressibility High pressure Diamond anvil cell |
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