title: High-pressure-induced phase transitions in pentaerythritol: X-ray and Raman studies.
abstract: The high-pressure response of pentaerythritol crystals has been examined to 10 GPa in diamond-anvil cells using angle-dispersive synchrotron X-ray diffraction and Raman spectroscopy. The results reveal two first-order phase transitions: one at 4.8 GPa from phase I, tetragonal I(), to phase II, orthorhombic Pnn2C2v10, with a small approximately 0.5% volume change, and the other at 7.2 GPa to phase III with an unknown crystal structure. We found that phase I exhibits a large crystallographic anisotropy which rapidly decreases with increasing pressure: the ratio of linear compressibilities between two primary crystal axes decreases from betao= 8.1 at 1 atm to betaP = 2.6 at 4 GPa. We suggest that this apparent decrease in crystal anisotropy is due to the disruption of hydrogen bonding in the (001) plane of phase I and eventually leads to an orthorhombic distortion from a quadrilateral network structure in phase I to a quasi one-dimensional structure in phase II. The crystal structure of phase III exhibits a disordered character, and it is likely a conformational variant of phase II.
authors.affiliation: Institute for Shock Physics and Department of Physics, Washington State University, Pullman, Washington 99164-2816, USA. dreger@wsu.edu
authors.forename: Zbigniew A
authors.initials: ZA
authors.lastname: Dreger
authors.forename: Yogendra M
authors.initials: YM
authors.lastname: Gupta
authors.forename: Choong-Shik
authors.initials: CS
authors.lastname: Yoo
authors.forename: Hyunchae
authors.initials: H
authors.lastname: Cynn