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Liquid binary alloys Cs-Sb and Cs-As are able to intercalate into graphite, provided that their compositions are neither too rich nor too poor in cesium. Several phases, whose stage varies between 1 and 4 in the case of antimony, and between 1 and 3 in the case of arsenic, have been observed. These new ternary compounds have been characterized by x-ray measurements.

Antimony and arsenic have numerous analogies with bismuth, that follow them in column V A of the periodic classification: these likenesses appear in their chemical properties, their crystal structure, and their electronic properties. Their electron donor character is, of course, too weak for these three elements to intercalate into graphite. However, a detailed study of the intercalation of K-Bi, Rb-Bi, and Cs-Bi alloys has been carried out, and has allowed synthesis of numerous new lamellar phases, that have been mostly isolated1'2; their structural and physical properties have been studied by several authors.3"8 It was therefore natural to try to intercalate the alkali metal-antimony and alkali metal-arsenic alloys into graphite, noting that antimony and arsenic are miscible with the three heavy alkali metals in the liquid phase for all compositions. With potassium and rubidium, the results are very poor; indeed, some intercalation compounds appear during the reaction, but a great part of graphite remains unaltered. Moreover, these intercalated phases are often very badly defined and possess a low intercalated alloy content. On the other hand, the cesium-antimony arid cesium-arsenic alloys easily yield well-defined stages of the indicated ternary intercalation compounds. The reaction is carried out as follows: the pristine graphite (HOPG sample) and the alloy are put together in a glass tube and sealed under vacuum. The tube is subsequently heated until the alloy melts, and the reaction occurs between the graphite and liquid alloy. It is necessary to use a large excess of alloy in order to avoid any variation of its composition during the intercalation. When the end of the reaction is reached, the sample is carefully cleaned to remove any excess alloy that adheres to its surface. It is then subjected to x-ray examination for (001) reflections. When the cesium concentration of the reactive alloy is high, the reaction product is the first stage binary compound CsC8. On the other hand, if the antimony or arsenic concentration of the reactive alloy is too high, no reaction occurs at all. As usual, only the middle concentrations are thus able to lead to new ternary phases. In the case of antimony, the range of composition of the binary alloys leading to ternary compounds extends between 25 and 59 at. % 244

http://journals.cambridge.org

J. Mater. Res., Vol. 4, No. 2, Mar/Apr 1989

Downloaded: 16 Mar 2015

Sb, and with arsenic, it extends from 20 to 62 at. % As. For comparison, this range was between 30 and 54 at. % Bi, in the case of bismuth2 (Fig. 1). Thus a clear shift toward higher cesium concentrations is found: when Bi is replaced by Sb, and Sb by A