Thermodynamic and Kinetic Fragility of Freon 113: The Most Fragile Plastic Crystal.
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.
Grup de Caracterització de Materials, Departament de Física, EEBE and Barcelona Research Center in Multiscale Science and Engineering, Eduard Maristany, 10-14, 08019 Barcelona, Catalonia, Spain.
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Vispa
Grup de Caracterització de Materials, Departament de Física, EEBE and Barcelona Research Center in Multiscale Science and Engineering, Eduard Maristany, 10-14, 08019 Barcelona, Catalonia, Spain.
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Romanini
Laboratorio de Bajas Temperaturas, Departamento de Física de la Materia Condensada, Condensed Matter Physics Center (IFIMAC) and Instituto Nicolás Cabrera, Universidad Autónoma de Madrid, Francisco Tomás y Valiente 7, 28049 Madrid, Spain.
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Ramos
Grup de Caracterització de Materials, Departament de Física, EEBE and Barcelona Research Center in Multiscale Science and Engineering, Eduard Maristany, 10-14, 08019 Barcelona, Catalonia, Spain.
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Pardo
Instituto de Estructura de la Materia, CSIC, Serrano 123, 28006 Madrid, Spain.
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Bermejo
Laboratorio de Bajas Temperaturas, Departamento de Física de la Materia Condensada, Condensed Matter Physics Center (IFIMAC) and Instituto Nicolás Cabrera, Universidad Autónoma de Madrid, Francisco Tomás y Valiente 7, 28049 Madrid, Spain.
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Hassaine
B. Verkin Institute for Low Temperature Physics and Engineering of NAS Ukraine, 47 Science Avenue, 61103 Kharkov, Ukraine.
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Krivchikov
Rutherford Appleton Lab, ISIS Facility, Didcot OX11 0QX, Oxon, England and European Spallation Source, Data management and software centre, COBIS, Copenhagen 2200, Denmark.
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Taylor
Grup de Caracterització de Materials, Departament de Física, EEBE and Barcelona Research Center in Multiscale Science and Engineering, Eduard Maristany, 10-14, 08019 Barcelona, Catalonia, Spain.
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Tamarit