We investigated through noncommercial calorimetry and elastoacoustic Brillouin experiments the phase diagram of n-butanol and measured the specific heat and the thermal conductivity in a wide low-temperature range for its three different states, namely, glass, crystal, and the so-called "glacial" states. The main aim of the work was to shed light on the controversial issue of these allegedly polyamorphic transitions found in some molecular glass-forming liquids, first reported to occur in triphenyl phosphite and later in n-butanol. Our experimental results show that the obtained glacial state in n-butanol is not a homogenous, amorphous state, but rather a mixture of two different coexisting phases, very likely the (frustrated) crystal phase embedded in a disordered, glassy phase.

We have conducted x-ray diffraction, calorimetric and Brillouin-scattering experiments on n-butanol between 77 and 300 K, aiming to explore the physical nature of the so-called 'glacial state' previously found in n-butanol as well as in triphenyl phosphite. In addition to our structural and thermodynamic studies of the liquid-glass transition and of the stable crystal state in n-butanol, we have found that the metastable 'glacial state' that can be obtained in the temperature range 125-160 K is not a second amorphous state, but rather the result of a frustrated or aborted crystallization process that produces plenty of nanocrystallites embedded in a disordered matrix. The crystalline order of these nanocrystallites of the 'glacial phase' is exactly the same as that well observed in the fully ordered stable crystal into which it transforms by heating above 160 K.

We present a dynamic and thermodynamic study of the orientational glass former Freon 113 (1,1,2-trichloro-1,2,2-trifluoroethane, CCl 2 F-CClF 2 ) in order to analyze its kinetic and thermodynamic fragilities. Freon 113 displays internal molecular degrees of freedom that promote a complex energy landscape. Experimental specific heat and its microscopic origin, the vibrational density of states from inelastic neutron scattering, together with the orientational dynamics obtained by means of dielectric spectroscopy have revealed the highest fragility value, both thermodynamic and kinetic, found for this orientational glass former. The excess in both Debye-reduced specific heat and density of states (boson peak) evidences the existence of glassy low-energy excitations. We demonstrate that early proposed correlations between the boson peak and the Debye specific heat value are elusive as revealed by the clear counterexample of the studied case. DOI: 10.1103/PhysRevLett.118.105701 When a structurally disordered system is rapidly cooled to avoid crystallization, some properties, such as viscosity, show a dramatic increase down to the glass transition where the material reaches viscosity values comparable to those of a solid (10 12 Pa s), i.e., relaxation times of ≈100 s. Such behavior contrasts with that typical for most liquids at high temperatures, which usually exhibit a simple Arrhenius behavior of the relaxation time, τ ¼ τ 0 expðE a =k B TÞ, where the activation energy is temperature independent.Decreasing temperature relaxation time shows a stronger increase, faster than that of the Arrhenius law and accompanied with an increase of some characteristic cooperativity relaxation length. The viscosity (or τ) increase is generally characterized by recourse to the concept of the kinetic fragility [1,2], m ¼ fð∂ log τÞ=½∂ðT g =TÞg T¼T g , which accounts for the deviation of the Arrhenius temperature dependence.In terms of fragility index m, materials for which τ follow an Arrhenius law are known as "strong" glass formers, whereas "fragile" glass formers are those exhibiting super-Arrhenius behavior. For such cases, the temperature dependence of τ is given through the Vogel-FulcherTammann (VFT) expression,where the temperature T 0 is associated with an ideal glass transition and even with the so-called Kauzmann temperature [3], and the fragility strength parameter D is linked to the fragility parameter by. Typical strong glass formers (m ≈ 16, or D ≥ 100) are tetrahedral network liquids as SiO 2 or GeO 2 . The highest values of fragility for organic materials (exception made of polymers) have been found in cis-or trans-decahydronaphthalene (m ¼ 147 [4]). Another group of materials exhibiting glasslike properties is that of crystals with positional order and orientational disorder [5]. Such plastic phases are formed from the liquid and can be supercooled, giving rise to the so-called orientational glasses (OG) or "glassy crystals" [6][7][8][9]. They show typically low fragility, as cyclooctanol (m ¼ 33) [10,11]

The thermal conductivity, specific heat, and specific volume of the orientational glass former 1,1,2-trichloro-1,2,2-trifluoroethane (CCl 2 F-CClF 2 , F-113) have been measured under equilibrium pressure within the low-temperature range, showing thermodynamic anomalies at ca. 120, 72, and 20 K. The results are discussed together with those pertaining to the structurally related 1,1,2,2-tetrachloro-1,2-difluoroethane (CCl 2 F-CCl 2 F, F-112), which also shows anomalies at 130, 90, and 60 K. The rich phase behavior of these compounds can be accounted for by the interplay between several of their degrees of freedom. The arrest of the degrees of freedom corresponding to the internal molecular rotation, responsible for the existence of two energetically distinct isomers, and the overall molecular orientation, source of the characteristic orientational disorder of plastic phases, can explain the anomalies at higher and intermediate temperatures, respectively. The soft-potential model has been used as the framework to describe the thermal properties at low temperatures. We show that the low-temperature anomaly of the compounds corresponds to a secondary relaxation, which can be associated with the appearance of Umklapp processes, i.e., anharmonic phononphonon scattering, that dominate thermal transport in that temperature range. C 2015 AIP Publishing LLC. [http://dx

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