Phase transitions in europium at high pressures

Abstract

For several decades, x-ray diffraction studies on europium (Eu) metal at high pressure were complicated by the presence of a rhombo-hedral contaminant phase, hR6, which has been recognised as such only recently. Using x-ray powder diffraction, we have determined the hR6 contaminant to undergo a phase transition to a cubic phase, cI12, at 34.8(12) GPa. Consideration of the volume per Eu atom of the two contaminant phases at the same pressure suggests that they have different stoichiometries or chemical compositions. We also report a phase transition in pure Eu from the incommensurately-modulated Eu-IV phase to Eu-V between 38 and 42 GPa.

Keywords:

• europium
• diamond-anvil cell
• x-ray diffraction
• structural transition
• contaminant

Acknowledgements

This work was supported by grants and a fellowship (I. L.) from the UK Engineering and Physical Sciences Research Council, and facilities were made available by the ESRF, DLS, SRS and the Research Complex at Harwell. We thank N. Casati, A. Lennie and M. Hanfland for their support on the beam lines, U. Schwarz of the MPI für Chemische Physik fester Stoffe for providing the Eu samples and L.F. Lundegaard and O. Degtyareva for their help with the experiments in the early stages of this study.

Notes

^†This paper was presented at the Lth European High Pressure Research Group (EHPRG 50) Meeting at Thessaloniki (Greece), 16–21 September 2012.