First-principles study of valence and structural transitions in EuO under pressure

The electronic structure of EuO under pressure is studied using the self-interaction corrected local spin density approximation. EuO, which at ambient conditions crystallizes in the NaCl (B1) structure, is predicted to undergo an isostructural insulator to metal transition at 48 GPa. This transition is associated with a change of valence from a divalent to an intermediate valent state, with the resulting effective valency of 2.35. The pressure range between 48 and 70 GPa is characterized by the competition between an intermediate valent B1 structured phase and a CsCl (B2) structured phase where both the divalent and intermediate valence configurations are in play. Eventually, at pressures above 70 GPa, the intermediate valent B2 phase prevails. The effective Eu valence in the B2 intermediate valence phase is around 2.28, i.e., a decrease in effective valence occurs. This scenario is in line with the reentrant valence behavior observed in recent pressure experiments.