Multiple Crossed Isopolymorphism: Two-Component Systems CCl4 + CBr2Cl2 and CBrCl3 + CBr2Cl2; Inference of a Metastable Rhombohedral Ph

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• 作者：Mar&iacute ; a Barrio ; Philippe Negrier ; Josep Ll. Tamarit ; Luis C. Pardo ; Denise Mondieig
• 刊名：Journal of Physical Chemistry B
• 出版年：2007
• 出版时间：August 2, 2007
• 年：2007
• 卷：111
• 期：30
• 页码：8899 - 8909
• 全文大小：225K
• 年卷期：v.111,no.30(August 2, 2007)
• ISSN：1520-5207

文摘

The phases diagrams of the two-component systems CCl₄ +CBr₂Cl₂ and CBrCl₃ + CBr₂Cl₂ have beendetermined by means of X-ray powder diffraction and thermal analysis techniques from the low-temperatureordered phase to the liquid state. The isomorphism relationship between the stable orientationally disordered(OD) face-centered cubic (FCC) phases of CBrCl₃ and CBr₂Cl₂ and the metastable OD FCC phase (monotropicbehavior with respect to the OD rhombohedral stable phase) of CCl₄ has been put into evidence throughoutthe continuous evolution of the lattice parameters and the existence of the two-phase equilibrium [FCC + L]for the whole range of composition in both two-component systems. This equilibrium interferes, for the CCl₄+CBr₂Cl₂ system, with a rhombohedral (R) plus liquid ([R + L]) equilibrium giving rise to a peritecticinvariant. In addition, whatever the system, [R + FCC] equilibrium also interferes with the low-temperatureequilibria between the low-temperature monoclinic (C2/c) phase and the OD R and FCC phases. In regardsto the low-temperature monoclinic phases, isomorphism is evidenced, and by means of Rietveld profilerefinement, any ordering of the molecules by varying the fractional occupancy of the halogen sites has beendetected. The thermodynamic assessment, conducted by means of the concept of crossed isopolymorphism,coherently reproduces all the involved equilibria and provides a coherent set of data for the thermodynamicproperties of nonexperimentally available phase transitions of pure compound CBr₂Cl₂ which enables us toobtain the topological properties of its pressure-temperature phase diagram and to infer the existence of ahigh-pressure R phase for such a compound.