Acoustic and thermal transport properties of hard carbon formed from C60 fullere

2019-12-01 14:31:28

structure thermal properties phonon fracton

责任者: Lasjaunias, J.C.;Saint-Paul, M.;Bilusic, A.;Smontara, A.;Gradecak, S.;Tonejc, A.M.;Tonejc, A.;Kitamura, N. 单位: Centre de Recherches sur les Tres Basses Temperatures, Grenoble, France 来源出处: Physical Review B (Condensed Matter and Materials Physics)(Phys. Rev, B, Condens, Matter Mater. Phys. (USA)),2002/07/01,66(1):014302-1 摘要: We report on extended investigation of the thermal transport and acoustical properties on hard carbon samples obtained by pressurization of C60 fullerene. Structural investigations performed by different techniques on the same samples indicate a very inhomogeneous structure at different scales, based on fractal-like amorphous clusters on the micrometer to submillimeter scale, which act as strong acoustic scatterers, and scarce microcrystallites on the nanometer scale. Ultrasonic experiments show a rapid increase in the attenuation with frequency, corresponding to a decrease in the localization length for vibrations. The data give evidence for a crossover from extended phonon excitations to localized fracton excitations. The thermal conductivity is characterized by a monotonous increase versus temperature, power law T1.4, for T ranging from 0.1 to 10 K, without any well-defined plateau, and a strictly linear-in-T variation between 20 and 300 K. The latter has to be related to the linear-in-T decrease of the sound velocity between 4 and 100 K, both linear regimes being characteristic of disordered or generally aperiodic structures, which can be analyzed by the “phonon-fracton hopping” model developed for fractal and amorphous structures 关键词: acoustic wave velocity;carbon;crystallites;fractals;fullerenes;high-pressure effects;localised modes;nanostructured materials;noncrystalline structure;thermal conductivity;ultrasonic absorption;acoustic properties;thermal transport properties;hard C;C60 fullerene;pressurization;inhomogeneous structure;fractal-like amorphous clusters;microcrystallites;US attenuation;frequency dependence;vibration localization length;extended phonon excitation/localized fracton excitation crossover;thermal conductivity;temperature dependence;sound velocity;disordered structure;aperiodic structure;phonon-fracton hopping model;0.1 to 10 K;20 to 300 K;4 to 100 K;C60;C