Mechanism of pressure-induced amorphization, superconductivity and molecular dissociation in tetrahedral-molecular crystals

The objective of the present work is to study structural properties of tetrahedral-molecular crystals SnI D24 D2 and SnBr D24 D2 at low temperature and at ultrahigh pressure。主要目标是（1）在房间温度60 GPa处确定SnI-D24-D2非分子相位晶体的晶体结构，（2）将P-T相位图表降低到10 K，提高到100 GPa。在第一财政年，我们为这些实验设计和建造了两件重要的设备。一种是用金刚石铁砧细胞（DAC）装置组装的低温仪，用于高压产生。另一种是一种光谱仪能力，可以从Ruby微型芯片封装在DAC中的样品室中。后来在SPring-8同步加速器辐射实验设施安装了这些文件。在第二财政年度，我们在SPring-8发射同步加速器X射线干扰实验中安装了该同步加速器X射线干扰实验，并使用了该设备。 ... More ^上面描述的。一个18 K的低温条件和一个89 GPa的高压条件完全达到了。以下结果得到了：（1）SnI-D24-D2的非分子阶段具有相同的晶体结构，作为一种替代性的、无序的阵列，带有fcc晶格。格子网站被Sn占领了，我原子在随机。（2）在18 K时，非典型相位持续到80 GPa的极高压力，建议热激活过程在非分子相位过渡中发挥重要作用。在这个研究中没有新的水晶结构被观察到。在低温度和高压力下，Mossbauer研究的结果需要在目前的研究中重新评估基于相位关系的基础。（3）SnBry D24和D2之间的新晶体结构被确定为立方体。在SnBry D24 y D2和SnI D24 y D2上的压力更敏感，这一研究的结果在IUCr大会和大会（格拉斯哥）、日本物理学会失败会议（Morioka）和日本高压科学和技术学会年度会议（福冈）上介绍。Less（低）

The objective of the present work is to study structural properties of tetrahedral-molecular crystals SnIィイD24ィエD2 and SnBrィイD24ィエD2 at low temperature and at ultrahigh pressure. Major goals are (1) to determine crystal structure of the nonmolecular phase of SnIィイD24ィエD2 crystallizing from the amorphous phase at 60 Gpa at room temperature and (2) to establish a P-T phase diagram down to 10K and up to 100 Gpa. In the first fiscal year, we designed and constructed two pieces of apparatus crucial for those experiments. One is a low-temperature cryostat equipped with a diamond anvil cell (DAC) device for high-pressure generation. Another is a spectrometer capable of measuring fluorescence from ruby micro-chips encapsulated in a sample chamber in a DAC. Duplicates of them were later installed at the BL10XU station at the SPring-8 synchrotron radiation experimental facility.In the second fiscal year, we carried out synchrotron x-ray diffraction experiments at the SPring-8, using the apparatu … More s described above. A low temperature condition of 18K and a high pressure condition of 89 GPa were reached simultaneously. The following results were obtained:(1) The nonmolecular phase of SnIィイD24ィエD2 has the same crystal structure as a substitutional, disordered alloy with the fcc lattice. The lattice sites are occupied by the Sn and I atoms at random.(2)At 18K, the amorphous phase persists to a very high pressure of 80 Gpa, suggesting that a thermal activation process plays an important role in the amorphous-nonmolecular phase transition. No new crystal structures were observed in this study. Results of previous Mossbauer studies at low temperature and high pressure need to be reexamined on the basis of the phase relationship determined in the present study.(3) A new crystal structure of SnBrィイD24ィエD2 stable between 3 Gpa and 9 Gpa was determined to be cubic. Effect of pressure on disordering of crystal structure is much more insensitive in SnBrィイD24ィエD2 than in SnIィイD24ィエD2.The results of this study were presented at the IUCr Congress and General Assembly (Glasgow), the fall meeting of the Physical Society of Japan (Morioka), and the annual meeting of the Japan Society of High Pressure Science and Technology (Fukuoka) in 1999. Less