Pravica Michael, Shen Yongrong, Quine Zachary, Romano Edward, Hartnett David
Department of Physics and High Pressure Science and Engineering Center (HiPSEC), University of Nevada Las Vegas, Las Vegas, Nevada 89154-4002, USA.
J Phys Chem B. 2007 Apr 26;111(16):4103-8. doi: 10.1021/jp070052b. Epub 2007 Apr 4.
We present data from two room temperature synchrotron X-ray powder diffraction studies of cyclohexane up to approximately 40 and approximately 20 GPa. In the first experiment, pressure cycling was employed wherein pressure was varied up to approximately 16 GPa, reduced to 3.5 GPa, and then raised again to 40 GPa. Initially, the sample was found to be in the monoclinic phase (P12(1)/n1) at approximately 8.4 GPa. Beyond this pressure, the sample adopted triclinic unit cell symmetry (P1) which remained so even when the pressure was reduced to 3.5 GPa, indicating significant hysteresis and metastability. In the second experiment, pressure was more slowly varied, and the monoclinic unit cell structure (P12(1)/n1) was observed at lower pressures up to approximately 7 GPa, above which a phase transformation into the P1 triclinic unit cell symmetry occurred. Thus, the pressure onset of the triclinic phase may be dependent upon the pressurizing conditions. High-pressure Raman data that further emphasize a phase transition (probably into phase VI) around 10 GPa are also presented. We also have further evidence for a phase VII, which is probably triclinic.
我们展示了在室温下对环己烷进行的两次同步加速器X射线粉末衍射研究的数据，压力范围高达约40 GPa和约20 GPa。在第一个实验中，采用了压力循环，其中压力变化至约16 GPa，降至3.5 GPa，然后再次升至40 GPa。最初，发现样品在约8.4 GPa时处于单斜相（P12(1)/n1）。超过此压力后，样品采用三斜晶胞对称性（P1），即使压力降至3.5 GPa时仍保持如此，这表明存在明显的滞后现象和亚稳性。在第二个实验中，压力变化更为缓慢，在高达约7 GPa的较低压力下观察到单斜晶胞结构（P12(1)/n1），高于此压力会发生向P1三斜晶胞对称性的相变。因此，三斜相的压力起始点可能取决于加压条件。还展示了高压拉曼数据，这些数据进一步强调了在10 GPa左右可能发生的相变（可能转变为VI相）。我们还有进一步证据表明存在VII相，其可能为三斜晶系。
