Synthesis and Characterization of Desified Amorphous Phasee

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According to the present research project, we have pefformed following three studies.1) Glasses of composition GeO_2 and Li_2O-3GeO_2 were compressed up to 30 GPa at temperatures from 27 to 500^oC where sixfold coordination of Ge is stable. Densification of 10 and 15% was achieved for GeO_2 and Li_2O-3GeO_2 glasses, respectively. Ge EXAFS measurements of Li_2O-3GeO_2 glasses retrieved from high pressure indicated that the coordination number of Ge is 4. The second and third neighbor distances (Ge-Gel and Ge-Ge2) determined by EXAFS show that the densification mechanism is explained by more distorted packing of GeO_4 tetrahedra than that in ambient glass. Coordination change by compression in the present Li_2O-3GeO_2 and GeO_2 glasses is reversible. The quenchability of the sixfold coordination of Ge in germanate glass is discussed.2) Using High-Pressure Differential Thermal Analysis (HP-DTA) system with a cubic multi-anvil high pressure apparatus, we measured the melting points of port … More landite, Ca(OH) _<nu> up to 6GPa and 1000ﾟC.We detected endothermic due to meeting peaks at the temperature and pressure conditions of 800ﾟC and 2.5GPa, 769ﾟC and 3.5GPa, 752ﾟC and 4.0GPa, 686ﾟC and 5.0GPa, and 596ﾟC and 6.0GPa. By in-situ x-ray studies under pressure, the melting of portlandite was observed at 730ﾟC and 4.32GPa and at 640ﾟC and 5.81GPa. Results of both HP-DTA and x-ray studies were harmonious within their experimental errors. The melting curve has a negative gradient indicating the higher density of liquid Ca(OH)_2 than that of portlandite in this pressure range.3) EXAFS spectra near the Ge K-edge in diamond and white-tin type Ge under high temperature and pressure were measured using a cubic anvil type high pressure device with synchrotron radiation from thr Photon Factory. Pressure values up to 10.6GPa were estimated on the basis of the isothermal equation of state of the-diamond type Ge within an accuracy of 0.4GPa. Pressures in the sample cell assembly were also determined by X-ray diffraction experiment using the NaCl scale. The diamond type Ge is of great advantage to the pressure calibrant of EXAFS measurements at elevated temperature because a harmonic approximation can be applied up to 700ﾟC. Less