Iron-wüstite revisited: A revised calibration accounting for variable stoichiometry and the effects of pressure

We present thermodynamic and empirical calculations for the iron-wüstite (IW) buffer applicable from 100 kPa to GPa 1000 3000 K. The calculation self-consistently accounts changing stoichiometry of iron-saturated wüstite as a function temperature pressure. In contrast some previous models calculating IW at high pressure, model incorporates thermodynamically valid representation free energy stoichiometric FeO kPa. Earlier pressure that relied on JANAF thermochemical tables (Chase, 1998) were compromised because has erroneous values properties FeO. This resulted in predicted oxygen fugacities buffered by are between 0.2 1.1 log units too reducing K, respectively. revised indicate becomes more nearly with increasing but this shift depends temperature. Near-stoichiometric (y < 0.01, Fe1-yO) is reached close 8 K 17 2000 An presented accurately reproduces facilitates easy quantification fO2 over full range temperatures pressures covered model. Some caution warranted pressures, after undergoes transition an insulator conductor where low spin Fe2+ stabilized, does not incorporate effects these transitions buffer.