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.

Thermal conductivity of argon-SiO2 cryocrystal nanocomposite

“…In the temperatures below 6 K the dependence can be approximated by ( ) n T T κ ∝ , where n = 1.55. Here it should be noted that the exponent n < 2 is, in some cases, the manifestation of a complex fractal structure of a substance [21][22][23].…”

Implanted muon spin spectroscopy on 2-O-adamantane: a model system that mimics the liquid$\longrightarrow $ glasslike transitions

“…Both crystals show a rather small difference in volume, which indicates that the transition into the truly ordered ground state involves a volume contraction, amounting a mere two per cent. In stark contrast, dynamical quantities such as the spectral frequency distribution, as well as the thermal conductivity of both phases, unveil significant differences attributable to substitutional disorder [13]. More specifically, the frequency distribution of the metastable phase shows a population of vibrational low energy states larger than that of the ground state, a difference most noticeable somewhat above 1 THz.…”

“…The material here investigated, which has some distinctive features with respect to CN-a, has shown the persistence of motions within its "glassy-crystal state" down to around 150 K, which are found to be fast enough to be explorable by means of dielectric broadband spectroscopy [11]. The thermal and dynamic characterization of such a metastable phase, as well as the comparison of its properties to those of the true crystal ground state, namely an orthorhombic crystal with Cmc2 1 lattice structure, has recently been achieved [9,13]. Both crystals show a rather small difference in volume, which indicates that the transition into the truly ordered ground state involves a volume contraction, amounting a mere two per cent.…”

Elasticity of disordered binary crystals

“…Note the resemblance between the left hand sides of Eqs. (18) and (13). They can be matched (but for the prefactor k B T ) by applying the following Fourier transform to the left hand side of Eq.…”