Phase transitions in europium at high pressures

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 42GPa.