RACAL STRUCTURES AND THERMODYNAMIC PROPERTIES OF HIGH DENSITY AMOR PHOUS

1. 利用大体积高压装置，将石英型晶体GeO_2和li22o - 4geo_2玻璃在室温下压缩至14gpa，并用原位XAFS方法研究了它们的局部结构变化。石英型结晶GeO_2中，配位数从4到6的变化从8 GPa以上开始，到12 GPa以下结束。减压时，在8gpa以下开始反转转变，存在较大的迟滞。释放压力后几乎不保留六重配位。玻璃体Li_2O-4GeO_2配位数的变化从6 GPa以上开始，在10 GPa以下结束。在10 GPa以下开始反转转变，其迟滞小于石英型GeO_2。在玻璃体Li_2O-4GeO_2中配位数的变化也是相反的。利用高压差热分析（HP-DTA）系统在立方多砧仪中测量了波特兰石Ca(OH)2的熔点，最高达到6 GPa和1273 K。分别在1027 K和2.5 GPa、1042 K和3.5 GPa、1025 K和4.0 GPa、959 K和5.0 GPa、869 K和6.0 GPa的温度和压力条件下检测了其吸热行为。由于波特兰石的融化。通过原位x射线加压研究，分别在1003 K和4.32 GPa、913 K和5.81 GPa温度下观察到波特兰岩的熔融。HP-DTA和x射线研究结果在实验误差范围内是一致的。在此压力范围内，液态Ca(OH)2的密度高于结晶型波特兰岩。

1. Using a large volume high pressure apparatus, quartz-type crystalline GeO_2 and Li_2O-4GeO_2 glass have been compressed up to 14 GPa at room temperature and their local structural changes have been investigated by an in-situ XAFS method. In quartz-type crystalline GeO_2, the change of the coordination number from 4 to 6 begins above 8 GPa and finishes below 12 GPa. On decompression, reversal transition begins below 8 GPa and there is a large hysteresis. Almost no sixfold coordination of Ge is preserved after releasing pressure. Change of coordination number in vitreous Li_2O-4GeO_2 begins above 6 GPa and is completed below 10 GPa. Reversal transition begins below 10 GPa and the hysteresis is smaller than that of quartz-type GeO_2. Change of coordination number in vitreous Li_2O-4GeO_2 is also reversal.2. Utilizing the high pressure differential thermal analysis (HP-DTA) system in a cubic multianvil apparatus, we measured the melting points of portlandite, Ca(OH)2, up to 6 GPa and 1273 K.We detected endothermic behavior at the temperature and pressure conditions of 1027 K and 2.5 GPa, 1042 K and 3.5 GPa, 1025 K and 4.0 GPa, 959 K and 5.0 GPa, and 869 K and 6.0 GPa, respectively., due to melting of portlandite. By in-situ X-ray studies under pressure, the melting of portlandite was observed at 1003 K and 4.32 GPa and at 913 K and 5.81 GPa, respectively. Results of both HP-DTA and X-ray studieswere consistent within experimental error. The melting is congruent and has a negative Clapeyron slope, indicating that liquid Ca(OH)2 has higher densities than crystalline portlandite in this pressure range.