On the compressibility of ferrite spinels: a high-pressure X-ray diffraction study of MFe₂O₄ (M=Mg, Co, Zn)

Abstract

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/ų. 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.

Keywords:

• high pressure
• ferrite spinels
• diamond anvil cell
• pressure media
• X-ray diffraction
• compressibility

Acknowledgements

This research was supported in part by the Israeli Science Foundation Grant #36/05, the Marie Curie Action for Early Stage Training of Researchers within the 6th Framework Programme (Contract No. MEST-CT-2005-019700) and the DFG. A part of the experiments were performed at the Bayerisches Geoinstitut under the EU ‘Research Infrastructures: Transnational Access’ Program (Contract No. 505320 (RITA) – HP). We acknowledge the European Synchrotron Radiation Facility for the provision of synchrotron radiation facilities and we thank M. Hanfland for assisting with the preparation of the DACs for XRD measurements.

Notes

K ₀ for fixed K′=4 calculated from PV data through personal communication.

K ₀ for fixed K′=4 calculated from PV data in original article.