Bulk moduli of magnesiowüstites from static compression measurements

Abstract

The static compression of two magnesiowüstites with 60 and 80 mol % FeO has been measured up to 500 kbar under quasi‐hydrostatic conditions. Within the framework of a Birch‐Murnaghan equation of state, these and other data for magnesiowüstites are consistent with linear variations of the 1‐bar isothermal bulk modulus and of its 1‐bar pressure derivative, from pure wüstite ( K o = 1.545 ± 0.01 Mbar, K o ′ = 2.75 ± 0.3) to periclase ( K o = 1.600 ± 0.005 Mbar, K o ′ = 4.85 ± 0.2). The composition with 80% FeO, but not that with 60% FeO, exhibits a second‐order like phase change analogous to the magnetic transition already described for wüstite at around 150 kbar. The lack of a significant dependence of the bulk moduli on nonstoichiometry suggests that the effect of pressure on the defect structure is not as simple as assumed previously.