AC-Calorimetric Measurement of Low-Temperature Specific Heat of Graphite-Iodine Monochrolide Intercalation Compounds

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By means of the AC-calorimetric technique, the specific heats of well-definedspecimens of highly oriented pyrolytic graphite and its stages-1, -2, and -3 intercala-tion compounds with ICI have been investigated at temperatures down to 2.2 K. Theapparatus was calibrated through a comparison of the data for pristine graphite withthose in past studies. The specific heat in the range 2.2-5 K is represented, in an ap-proximation, as a sum of electronic and lattice terms (yT and a7") for pure graphite,and additionally of an extra term due to the dispersionless optical-mode vibration ofionized ICI species in the compounds. y and (115 both increase steeply with the ICI con-centration, reflecting a monotonous increase of positive holes and softening of the Hat-lice in the c-direction respectively. A phenomenological theory, which correlates thelattice term to the elastic constants C.. and C.., turns out that (15 tends to decrease withincreasing temperature.[specific heat, graphite, intercalation compound, AC calorirnetry, Debye temper- ll ature, elastic stiffness constantl
社団法人日本物理学会の論文
1990-11-15