ARSENIDES OF TRANSITION METALS: THE ARSENIDES OF IRON AND COBALT

Alloys of cobalt and arsenic containing up to 60% As by weight have been studied by means of room temperature and high temperature Debye-Scherrer diagrams. Two compounds exist at room temperature, Co 2 As and CoAs, both of which undergo crystallographic transformations at higher temperatures, the former between 400 °C. and 500 °C., the latter at about 950 °C. A third compound, probably Co 3 AS 2 , is formed by the reaction of Co 2 As with CoAs above 940 °C. The structures of these compounds are compared with the structures of the corresponding compounds in the iron/arsenic system. These results indicate the necessity of slight revisions to the Co/As diagram, and raise serious questions in respect of the validity of decomposition pressure data reported recently for cobalt arsenides.