ON THE CHEMICAL-VAPOR TRANSPORT OF COBALT MONOPHOSPHIDE USING IODINE - EXPERIMENTS AND THERMOCHEMICAL MODEL-CALCULATIONS

CoP can be crystallized by chemical vapour transport using iodine as t ransport agent. Over a wide temperature range (650 degrees C less than or equal to ($) over bar T less than or equal to 1000 degrees C; ($) over bar T = (T-1 + T-2)/2; Delta T = 100 K) the migration from the hi gher to the lower temperature is based on the heterogeneous equilibriu m CoPs + 5/2I(2g) = CoI2g + PI3g. CoI2,1 is observed as second condens ed equilibrium phase besides CoP, in experiments carried out at lower mean temperatures (($) over bar T less than or equal to 800 degrees C) and with sufficiently high amounts of iodine. Thermochemical model ca lculations, based on modified data for CoI2,1, CoI2,g and Co2I4,g, rep roduce the observed deposition rates as well as the compositions of th e condensed equilibrium phases. These calculations allow a detailed de scription of the equilibrium gas phase in the system Co/P/I under vari able experimental conditions. The influence of traces of moisture on t he transport behavior will be discussed.