A study of temperature and pressure induced structural and electronic changes in SbCl 5 intercalated graphite: Part IV.
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E. McRae, M. Lelaurain, and J. F. Mareche Universite de Nancy I, Laboratoire de Chimie du Solide Mineral, U.R.A. C.N.R.S. 158, Service de Chimie Minerale Appliquee, B.P. 239, 54506 Vandoeuvre-les-Nancy Cedex, France (Received 19 April 1994; accepted 14 October 1994)
Using an inductive technique, we have measured the in-plane resistivity pa of stages 2, 4, 5, and 8 SbCl 5 -GIC's versus temperature T and pressure p in the ranges 130-300 K and 0-0.85 GPa. The room temperature values of pa range from 4.0 ^tficm for the stages 5 sample to 7.7 yttflcm for the stage 8 sample. At all pressures, pa shows a metallic temperature dependence pa ~ Ta, with 1 «£ a =£ 2, but in contrast to the c-axis resistivity pc, it depends only very weakly on pressure and/or intercalate structural order. We show that the behavior observed is consistent with a band conduction model.
I. INTRODUCTION In a series of recent papers1^3 we have presented data for the in-plane structure1 and for the c-axis resistivity 23 of SbCls intercalated graphite. Our studies were carried out as functions of temperature, T, and pressure, p, over the range 20-300 K and 0-0.8 GPa, and for stage numbers s of 2 - 5 and 8. Regarding structure, our studies showed that the initially disordered intercalate layers could be crystallized either by slow cooling to below 200 K at atmospheric pressure or by slow compression to above 0.4 GPa near room temperature (RT). In what follows, we will refer to these as low temperature crystallization and high pressure crystallization, respectively. The two methods result in different in-plane structures.1 In addition, our studies also revealed that (i) some stage 2 samples were fully crystallized already at RT, with no further evolution with Tor/7, and (ii) several in-plane crystalline structures were possible in the low-7" range, and many samples evolved through a repeatable sequence of structural changes over a narrow range in T near 200 K. The c-axis resistivity pc was found to show a very large decrease upon crystallization, whether by cooling or pressurization, and also large changes on transforming between different crystalline phases.2 Also, near RT pc generally increased with decreasing stage number and, for stage 2 samples, decreased with increasing degree of RT crystallization. Finally, pc had a positive temperature coefficient for low stage samples, changing into a negative temperature coefficient for stage 8 below 200 K, and a negative pressure coefficient in all stable phases. An analysis3 showed that, in spite of the large J. Mater. Res., Vol. 10, No. 7, Jul 1995 http://journals.cambridge.org
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magnitudes of pc, the band conduction model gave the best explanation for these observations. In order to complement our previous studies, we present here the results of a corresponding study of the in-plane pa for some of the samples discussed above, and over approximately the same ranges in T and p. The measurements have been carried out using a contactless method in order to avoid possible errors due to
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