A study of temperature and pressure induced structural and electronic changes in SbCl 5 intercalated graphite: Part I. S
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O. E. Andersson and B. Sundqvist Department of Experimental Physics, Umea University, S-90187 Umea, Sweden (Received 26 March 1992; accepted 6 July 1992)
We have studied the effects of temperature (10 =£ T =£ 295 K) and pressure (0 =£/?=£ 0.8 GPa) on the state of intercalate layer crystallization in SbCl5 graphite intercalation compounds of stages 2, 4, and 8. At room temperature (RT), the intercalate layer may in some second stage compounds be fully crystallized and lowering the temperature creates no further modifications. In all other cases, i.e., those in which the intercalate layer has only partial crystallization at RT, lowering T leads to the formation of new in-plane unit cells, the final state depending on the kinetics. Applying pressure to above 0.3-0.5 GPa results in crystallization in all cases, different from that induced simply by lowering of the temperature. We discuss the unit cells observed and the relationships they bear to each other in the light of other works on similar compounds.
I. INTRODUCTION Graphite intercalation compounds (GIC's) have been a subject of considerable interest over the past decade because of the rich variety of chemical species that can be intercalated into the galleries (interlayer spaces) and because of the novel electronic properties of GIC's, spanning the range from 3D to quasi-2D behavior.1"5 Among the structural parameters used to define a GIC are the stage index, 5 designating the number of graphene sheets between two successive layers of intercalate, the interplanar distance dt indicating the "sandwich thickness", and the c-axis repeat distance Ic separating two layers of intercalate. If dt is stage-independent and the unfilled galleries in the intercalation compound retain the 0.335 nm spacing of graphite, then Ic = dt + (s - 1) X 0.335. In this paper, we shall discuss certain structural aspects of SbCl5 intercalated graphite as functions of temperature (T) and pressure (p). In the following paper (Ref. 6, hereafter referred to as paper II) we treat the electronic properties of the same materials and in Ref. 7, henceforth referred to as paper III, we will discuss at some length the interactions and correlations between structure and order on one hand and transport properties on the other. Diffraction studies8"25 of these GIC's have revealed the existence of a certain number of structures; however, of the several hypotheses proposed, none has resulted in a completely satisfying explanation of the different molecular entities dissimulated behind each of the various structures observed. Most authors agree 2978
J. Mater. Res., Vol. 7, No. 11, Nov 1992
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that the 2D in-plane structure depends on the nature of the intercalated layer, that it is well defined once the compound has been formed, and that the compound itself is relatively stable. Following the initial work by Melin,8'9 Homma and Clarke,16 considering that the redox reaction 3SbCl 5 + 2e~
SbCl 3 + 2SbCl 6
(1)
goes to completion (no SbCl5 in the galle
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