title: Glassy Dynamics versus Thermodynamics: The Case of 2-Adamantanone.
abstract: The heat capacity and thermal conductivity of the monoclinic and the fully ordered orthorhombic phases of 2-adamantanone (C10H14O) have been measured for temperatures between 2 and 150 K. The heat capacities for both phases are shown to be strikingly close regardless of the site disorder present in the monoclinic crystal which arises from the occupancy of three nonequivalent sites for the oxygen atom. The heat capacity curves are also well accounted for by an evaluation carried out within the harmonic approximation in terms of the g(ω) vibrational frequency distributions measured by means of inelastic neutron scattering. Such spectral functions show however a significant excess of low frequency modes for the crystal showing statistical disorder. In contrast, large differences are found for the thermal conductivity which contrary to what could be expected, shows the substitutionally disordered crystal to exhibit better heat transport properties than the fully ordered orthorhombic phase. Such an anomalous behavior is understood from examination of the crystalline structure of the orthorhombic phase which leads to very strong scattering of heat-carrying phonons due to grain boundary effects able to yield a largely reduced value of the conductivity as well as to a plateau-like feature at intermediate temperatures which contrasts with a bell-shaped maximum shown by data pertaining the disordered crystal. The relevance of the present findings within the context of glassy dynamics of the orientational glass state is finally discussed.
authors.affiliation: †Institute for Low Temperature and Structure Research, Polish Academy of Scienceul. Okólna 2, 50-422 Wrocław, Poland.
authors.forename: D
authors.initials: D
authors.lastname: Szewczyk
authors.affiliation: †Institute for Low Temperature and Structure Research, Polish Academy of Scienceul. Okólna 2, 50-422 Wrocław, Poland.
authors.forename: A
authors.initials: A
authors.lastname: Jeżowski
authors.affiliation: ‡B. Verkin Institute for Low Temperature Physics and Engineering of NAS Ukraine, 47 Lenin Avenue, Kharkov 61103, Ukraine.
authors.forename: G A
authors.initials: GA
authors.lastname: Vdovichenko
authors.affiliation: ‡B. Verkin Institute for Low Temperature Physics and Engineering of NAS Ukraine, 47 Lenin Avenue, Kharkov 61103, Ukraine.
authors.forename: A I
authors.initials: AI
authors.lastname: Krivchikov
authors.affiliation: ¶Instituto de Estructura de la Materia, Consejo Superior de Investigaciones Cientficas, CSIC, Serrano 123, 28006 Madrid, Spain.
authors.forename: F J
authors.initials: FJ
authors.lastname: Bermejo
authors.affiliation: §Grup de Caracterització de Materials, Departament de Física i Enginyieria Nuclear, ETSEIB, Universitat Politècnica de Catalunya, Diagonal 647, 08028 Barcelona, Catalonia Spain.
authors.forename: J Ll
authors.initials: JL
authors.lastname: Tamarit
authors.affiliation: §Grup de Caracterització de Materials, Departament de Física i Enginyieria Nuclear, ETSEIB, Universitat Politècnica de Catalunya, Diagonal 647, 08028 Barcelona, Catalonia Spain.
authors.forename: L C
authors.initials: LC
authors.lastname: Pardo
authors.affiliation: ∥Rutherford Appleton Lab, ISIS Facility, Didcot OX11 0QX, Oxon, England.
authors.forename: J W
authors.initials: JW
authors.lastname: Taylor