On the compressibility of ferrite spinels: a high-pressure X-ray diffraction study ofMFe₂O₄(M=Mg, Co, Zn)

High-pressure synchrotron X-ray diffraction studies were carried out on a series of ferrite spinels MFe2O4 (M=Mg, Co, Zn) up to ∼ 70 GPa using diamond anvil cells. He and Ne, used as pressure media, provided quasi-hydrostatic conditions, resulting in a high-quality fit to both second- and third-order equations of state (EOSs). A quality fit to the second-order EOS allows a comparison between the compressibility of these spinels and that of other spinels found in the literature. Fitting to the second-order Birch–Murnaghan EOS results in the values of K 0=170.5(8), 176.1(6) and 174(2) GPa for M=Mg, Co and Zn, respectively. A linear dependence of K 0 is obtained as a function of the normalized average cationic-sphere volume S N of each spinel with a slope of 490(15) GPa/Å3. A number of previous studies of the same and similar spinels exhibit a strong deviation from K 0(S N), which can be attributed to a lack of hydrostatic conditions.