skip to main content

SciTech ConnectSciTech Connect

Title: Calorimetric measurements on Li{sub 4}C{sub 60} and Na{sub 4}C{sub 60}

We show specific heat data for Na{sub 4}C{sub 60} and Li{sub 4}C{sub 60} in the range 0.4-350 K for samples characterized by Raman spectroscopy and X-ray diffraction. At high temperatures, the two different polymer structures have very similar specific heats both in absolute values and in general trend. The specific heat data are compared with data for undoped polymeric and pristine C{sub 60}. At high temperatures, a difference in specific heat between the intercalated and undoped C{sub 60} polymers of 100 J K{sup −1} mol{sup −1} is observed, in agreement with the Dulong-Petit law. At low temperatures, the specific heat data for Li{sub 4}C{sub 60} and Na{sub 4}C{sub 60} are modified by the stiffening of vibrational and librational molecular motion induced by the polymer bonds. The covalent twin bonds in Li{sub 4}C{sub 60} affect these motions to a somewhat higher degree than the single intermolecular bonds in Na{sub 4}C{sub 60}. Below 1 K, the specific heats of both materials become linear in temperature, as expected from the effective dimensionality of the structure. The contribution to the total specific heat from the inserted metal ions can be well described by Einstein functions with T{sub E} = 386 K for Li{sub 4}C{submore » 60} and T{sub E} = 120 K for Na{sub 4}C{sub 60}, but for both materials we also observe a Schottky-type contribution corresponding to a first approximation to a two-level system with ΔE = 9.3 meV for Li{sub 4}C{sub 60} and 3.1 meV for Na{sub 4}C{sub 60}, probably associated with jumps between closely spaced energy levels inside “octahedral-type” ionic sites. Static magnetic fields up to 9 T had very small effects on the specific heat below 10 K.« less
Authors:
;  [1] ; ; ;  [2] ;  [2] ;  [3]
  1. Research Center for Structural Thermodynamics, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043 (Japan)
  2. Department of Physics, Umeå University, S-90187 Umeå (Sweden)
  3. (China)
Publication Date:
OSTI Identifier:
22415723
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Chemical Physics; Journal Volume: 142; Journal Issue: 16; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; CALORIMETRY; CHEMICAL BONDS; CLATHRATES; COMPARATIVE EVALUATIONS; COVALENCE; ENERGY LEVELS; FULLERENES; IONS; LITHIUM COMPOUNDS; MAGNETIC FIELDS; POLYMERS; RAMAN SPECTROSCOPY; SODIUM COMPOUNDS; SPECIFIC HEAT; TEMPERATURE DEPENDENCE; X-RAY DIFFRACTION