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Phase transition of enstatite under high pressure and high temperature
| Title: | Phase transition of enstatite under high pressure and high temperature |
| Other Titles: | 高温高圧下におけるエンスタタイトの相転移について |
| Authors: | Shinmei, Toru1 Browse this author |
| Authors(alt): | 新名, 亨1 |
| Issue Date: | 25-Mar-1998 |
| Publisher: | Hokkaido University |
| Abstract: | Crystal structures and phase transitions of enstatite (MgSiO3) at high pressures and high temperatures were studied by several methods, including in situ X-ray diffraction experiments using synchrotron radiation and a multi-anvil high pressure apparatus up to 12 GPa and 1200℃, high temperature X-ray diffraction experiments up to 1100℃, X-ray diffraction analyses and transmission electron microscope observations of the quenched samples from high pressure and/or high temperature experiments. High pressure and high temperature in situ X-ray experiments showed that low clinoenstatite with space group P21/c transforms to clinoenstatite with space group C2/c at the wide range of high pressures, accompanied by a volume reduction of about 2.5%. The β angles of this high pressure C2/c phase range from 101.51° to 101.8°at high pressures and high temperatures, being about 8° smaller than those of the high temperatureC2/c phase previously reported. This suggests that a significant structural gap still exists between both C2/c phase. The equations of state for the high-P C2/c and the P21/c phases determined from the P-V data at room temperature using a third-order Birch-Murnaghan equation of state with the fixed K' of 4 give Ka = 84.3(8.3) GPa and Va = 411.1(2.7) A3 GPa for high-P C2/c and Ka = 104.9(3.5) GPa and Va = 415.9 (8) A3 for P21/c, where K'a, Ka, and Va are the pressure derivative of bulk modulus, the isothermal bulk modulus, and the unit-cell volume, respectively at ambient conditions. High temperature powder X-ray diffraction experiments up to 1100℃ suggest that the high temperature C2/c phase exists at temperatures 1060-1100℃, although the different starting materials give different results. The β angles of this high temperature C2/c phase are around 110° at 1100℃, and consistent with the previously reported value and about 80° larger than those of the high pressure C2/c phase. Transmission electron microscopy (TEM) observations of the quenched samples which were synthesized at 8 GPa and 1000℃ and at 1050℃ showed the offsets of the (100) fringes of the P21/c phase by a half of (100) spacing between the neighboring domains across the (100) stacking faults, suggesting that the antiphase domains were formed by the phase transition from the C2/c phase to P21/c phase during the quenching or upon decompression. Piston cylinder apparatus experiments revealed the different phase relations of orthoenstatite depending on the experiments with or without a MgCL2・6H2O fiux. In the experiments with a MgCL2・6H2O flux at 15 kbar, low clinoenstatite inverts to orthoenstatite at temperature as low as 550℃, suggesting that the orthoenstatite and low clinoenstatite equilibrium boundary may shift toward the lower temperature region than previously reported. |
| Conffering University: | 北海道大学 |
| Degree Report Number: | 甲第4285号 |
| Degree Level: | 博士 |
| Degree Discipline: | 理学 |
| Type: | theses (doctoral) |
| URI: | http://hdl.handle.net/2115/51468 |
| Appears in Collections: | 学位論文 (Theses) > 博士 （理学）
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Submitter: 新名 亨
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