Multiple melting of orientationally disordered mixed crystals of the two-component system (CH₃)₂CCl₂–(CH₃)CCl₃

Stable and metastable mixed crystals in the orientationally disordered state of the [(CH3)3CCl]+[(CH3)2CCl2] system

“…As far as temperatures are concerned, T R!L is obtained by extrapolating the [R + L] equilibrium temperatures to X ¼ 0. The extrapolated value agrees with that obtained in the same way from the two-component systems ðCH 3 Þ 3 CCl þ CCl 4 and ðCH 3 Þ 3 CCl þ ðCH 3 ÞCCl 3 [5,6]. Owing to the large extension of the [FCC + L] equilibrium, extrapolating T FCC!L for pure ðCH 3 Þ 2 CCl 2 , i.e., X ¼ 1, can easily be performed.…”

“…In addition, extrapolating the melting enthalpy of the R and FCC mixed crystals to X ¼ 0 and X ¼ 1, respectively, leads to the melting enthalpy of a 'virtual' R (metastable) phase of pure ðCH 3 Þ 3 CCl and to the one of a 'virtual' FCC (supermetastable) phase of pure ðCH 3 Þ 2 CCl 2 . Once again, the extrapolated value at X ¼ 0 for the melting enthalpy of the 'virtual' R phase hits the ones previously inferred by applying the same procedure to the ðCH 3 Þ 3 CCl þ CCl 4 and ðCH 3 Þ 3 CCl þ ðCH 3 ÞCCl 3 two-component systems (2:63 kJ mol À1 ) [5,6]. As regards the melting enthalpy of the 'virtual' FCC phase of ðCH 3 Þ 2 CCl 2 the same conclusion can be achieved when compared to the value obtained for the ðCH 3 Þ 2 CCl 2 þ CCl 4 two-component system (0:86 kJ mol À1 ) [4] for which the FCC mixed crystals were also found to behave monotropically within a large composition range.…”

“…To account for, the melting phase diagram is the result of two interfering melting loops: the first one corresponds to the melting of a complete series of R mixed crystals, [R + L], and the other one to a complete series of FCC mixed crystals, [FCC + L]. This corresponds to the well-known case of crossed isodimorphism [5,6,28]. The metastable ends of the loops are the metastable melting points of the isomorphous metastable phases of the pure compounds, i.e., T R!L and T FCC!L for ðCH 3 Þ 3 CCl and ðCH 3 Þ 2 CCl 2 , respectively.…”

Relationship between the two-component system 1-Br-adamantane + 1-Cl-adamantane and the high-pressure properties of the pure components

“…9(a), the entropy factor for both  = M and  = O. Such an inequality should be attributed to the easiness of formation of mixed crystals into an orientationally disordered phase, as it was shown previously in many other two-component systems involving such phases [1][2][3][4][5][6][7]. Fig.…”

“…Even more, the field of phase diagrams involving at least two chemical species, the temperature-composition (T-X) phase diagrams, is generally decoupled from the field of the polymorphic behavior at high pressure. Nevertheless, thermodynamics imposes an univocal relation between the controlled pressure and temperature conditions at which a polymorph should exist and the physical properties derived at normal pressure and, hence, the properties that can be extracted from a temperature-composition phase diagram [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. The other way around also holds, properties derived for stable or metastable phases emerging in the temperature-composition phase diagrams can provide information about the nature of high-pressure phases even when they do not exist as stable phases at normal pressure.…”