Carbon in iron phases under high pressure

Abstract

The influence of carbon impurities on the properties of iron phases (bcc, hcp, dhcp, fcc) has been studied using the first-principles projector augmented-wave (PAW) method for a wide pressure range. It is shown that the presence of ∼6 at. % of interstitial carbon has a little effect on the calculated structural sequence of the iron phases under high pressure. The bee → hcp transition both for pure iron and iron containing carbon takes place around 9 GPa. According to the enthalpies comparison, the solubility of carbon into the iron solid is decreased by high pressure. The coexistence of iron carbide (Fe3C) + pure hcp Fe is most stable phase at high pressure compared with other phases. Based on the analysis of the pressure-density dependences for FC3C and hcp Fe, we suggest that there might be some fraction of iron carbide present in the core. Copyright 2005 by the American Geophysical Union.