The specific heat of high-purity Acheson graphite prepared by the National Carbon Company has been measured from 13° to 300 0 K. In the region 13° to 54°K the Cp data follows a]'2 dependence quite accurately in agreement with previous experimental work and recent theoretical investigations of specific heat in strongly anisotropic solids.On the basis of some recent studies for other highly anisotropic solids, it is suggested that the specific heat of graphite will eventually follow a ]'2 dependence at still lower temperatures.The derived thermodynamic functions, entropy, enthalpy, and free energy, have been determined by graphical integration and tabulated at integral values of temperature up to 300 o K. The entropy of graphite at 298.16°K is 1.372±0.OO5 cal/g-atom deg, of which 0.004 is extrapolated from 13° to OOK assuming the third law and the 1'2 dependence. INTRODUCTIONM EASUREMENTS on the specific heat of graphite commenced with those of Weber l in 1875, and Zakrzewiski 2 in 1891. The room temperature values deviated considerably from the predictions of the classical Dulong and Petit law. Nernst's3 investigation represents the first real attempt to measure the specific heat of graphite below ordinary temperatures (25.8° to 92.6°K). These measurements were followed by those of Magnus,4 who measured the specific heat of graphite over a large temperature range (44.1° to llOOOK), and the work of Jacobs and Parks,6 whose measurements 2.2 2.0
stated at this stage that existence of a hysteresis effect, as discovered by Bommel, 2 has been confirmed and that in the normal metal, the absorption does depend strongly on magnetic field (so far applied only along the specimen). This effect was also originally found by Bommel"; in the specimen described here, at the shorter length and at 3.9'K, about 200 oersted will double the amplitude of the transmitted pulse.in the making of the transducer-specimen bond and "H. E. Bommel (verbal communication). also to Dr. H. E. Bommel for early information about his work. (This investigation was started independently without the knowledge that other work was being done, but the discovery of the effect is due to Dr. Bommel. )He also acknowledges with thanks assistance given during the measurements by graduate students and others at Brown University.He would also like especially to thank Dean R. B.Lindsay for his encouragement throughout this work and for making possible his visit to Brown University. He is also grateful to the Headmaster and Governing Body of Charterhouse School for an extended leave of absence.The temperature dependence of the electrical resistivity and Hall coefficient in pand n-type manganesedoped germanium crystals indicates that manganese introduces two acceptor levels in germanium at 0.16&0. 01 ev from the valence band and 0.37&0.02 ev from the conduction band. The distribution coeflicient for manganese in germanium is (1.0+0.2)X10 . Comparison is made with other fourth-row metals (V, Fe, Co, and Ni) as impurities in germanium.
Pha thermal conductivity, electrical resistivity and thermoelectric power have been measured in the temperature range from 20°K to 300°K for samples of artificial extruded granhite, natural molded graphite and la/npblack graphite. ^Experimental results are prasonted and discussed briefly in relation to theory. Due to the vary largo Wiedemann-Franz ratio and its dependence on temperatura and type of graphite, thermal conductivity in graphite is attributed primarily to lattice waves. Scattering of lattice waves from crystallite boundaries lirrtios the conductivity through most of the tonperature range investigated, Inbarnretation of the data in terms of the sinnle Debye equation for lattice conductivity permits rough estKaates of effective crystallite size. At low temperatures, the dependence of conductivity on temperature is more rapid than the dependence of heat capacity, in disagreement with the Debye equation,, The temperature dependence of elecurical resistivity is inturpreted using a modified .('all^ce zone theory vrfiich perniite the Fermi level bo differ in position from the zone boundary, due to an excess or deficit of electrons. Scattering of electrons in the temperature range of interest is attributed to crystallite boundaries or impurities and assumed temperature indepandentc The temperature dependence of the Fermi level wtiich gives the bast fit to experijaental data, is not in ai-rcement with theoretical predictionso
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