High pressure investigation of α-form and CH_4-loaded β-formof hydroquinone compounds

摘要

The high pressure compression behaviors of two hydroquinone compounds have been investigatedusing a combination of in situ synchrotron x-ray powder diffraction and Raman spectroscopy up toca. 7 GPa. The structural integrity of the a-form hydroquinone clathrate is maintained throughout the pressure range, whereas the CH4-loaded /3-form hydroquinone clathrate decomposes andtransforms to a new high pressure phase near 5 GPa. The bulk modulus (K) and its pressure derivative (K') of the a-form and the CH4-loaded /3-form hydroquinones are measured to be 8.2(3) GPa and 8.4(4), and 10(1) GPa and 9(2), respectively, representing one of the mostcompressible classes of crystalline solids reported in the literature. The corresponding axial compression behaviors, however, show greater contrast between the two hydroquinone compounds;the elastic anisotropy of the a-form is only marginal, being K(a):K(c)=1.08: 1, whereas that of theCH4-loaded /3-form is rather drastic, being K(a):K(c)=11.8: 1. This is attributed to the differentdimensionality of the hydrogen bonding networks between the two structures and might in turnexplain the observed structural instability of the /3-form, compared to the a-form.