Giant Anomalous Strain between High-Pressure Phases and the Mesomers of Urea

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• 作者：Kinga Roszak ; Andrzej Katrusiak
• 刊名：Journal of Physical Chemistry C
• 出版年：2017
• 出版时间：January 12, 2017
• 年：2017
• 卷：121
• 期：1
• 页码：778-784
• 全文大小：557K
• ISSN：1932-7455

文摘

At high pressure the urea crystal abruptly collapses in two stages. When transforming from phase I to III at 0.48 GPa, the crystal volume is abruptly compressed by 7.3%. At this transition a huge abrupt linear compression to 65% along a and to 95% along c is partly compensated by an unprecedented abrupt negative linear compression (i.e., expansion) to 148% along b. At another discontinuous transformation, at 2.8 GPa to phase IV, the crystal still displays an abrupt negative linear compression to 106% along c. The intermediate phase III between 0.48 and 2.80 GPa increases the contribution of the zwitterionic mesomeric structure of urea molecules and the formation of weak NH···N bonds has been evidenced in phase III. The formation of phase II, above 373 K and above 0.6 GPa reported by Bridgman, has not been confirmed.