We present thermodynamic and empirical calculations for the iron-wüstite (IW) buffer applicable from 100 kPa to 100 GPa and from 1000 to 3000 K. The thermodynamic calculation self-consistently accounts for changing stoichiometry of iron-saturated wüstite as a function of temperature and pressure. In contrast to some previous models for calculating IW at high pressure, the model incorporates a thermodynamically valid representation of the free energy of stoichiometric FeO at 100 kPa. Earlier high pressure models that relied on the JANAF thermochemical tables (Chase, 1998) were compromised because JANAF has erroneous values for the properties of FeO. This resulted in predicted oxygen fugacities buffered by IW that are between 0.2 and 1.1 log units too reducing at 3000 and 1000 K, respectively. The revised thermodynamic calculations indicate that iron-saturated wüstite becomes more nearly stoichiometric with increasing pressure, but that this shift depends on temperature. Near-stoichiometric FeO (y < 0.01, for Fe_1-yO) is reached close to 8 GPa at 1000 K and 17 GPa at 2000 K. An empirical function is presented that accurately reproduces the thermodynamic calculation and facilitates easy quantification of the f_O2 of IW over the full range of temperatures and pressures covered by the model. Some caution is warranted in calculation of IW at high pressures, after FeO undergoes a transition from an insulator to a conductor and where low spin Fe²⁺ is stabilized, as the present model does not incorporate the effects of these transitions on the IW buffer.

我们提供了适用于 100 kPa 至 100 GPa 和 1000 至 3000 K 的铁-方铁矿 (IW) 缓冲液的热力学和经验计算。压力。与之前在高压下计算 IW 的一些模型相比，该模型结合了化学计量 FeO 在 100 kPa 下的自由能的热力学有效表示。早期依赖 JANAF 热化学表 (Chase, 1998) 的高压模型受到了损害，因为 JANAF 对 FeO 的性质具有错误的值。这导致由 IW 缓冲的预测氧逸度在 0.2 和 1.1 log 单位之间也分别在 3000 和 1000 K 时降低。修订后的热力学计算表明，铁饱和的方铁矿随着压力的增加变得更接近化学计量，但这种转变取决于温度。接近化学计量的 FeO (y  < 0.01，对于 Fe _1-y O) 在 1000 K 时达到接近 8 GPa，在 2000 K 时达到 17 GPa。提供了一个经验函数，可以准确地再现热力学计算并有助于轻松量化IW的f _O2模型涵盖的所有温度和压力范围。在高压下计算 IW 时需要谨慎，在 FeO 经历从绝缘体到导体的转变并且低自旋 Fe ²⁺稳定后，因为本模型没有包含这些转变对 IW 缓冲区的影响。