Pressure-Induced Structure Transitions in Eu Metal to 92 GPa

TL;DR

This study investigates the structural phase transitions of europium metal under high pressure up to 92 GPa using synchrotron x-ray diffraction, revealing complex phase behavior and valence state changes.

Contribution

It provides the first detailed experimental characterization of Eu metal's structural transitions up to 92 GPa and compares findings with theoretical predictions.

Findings

Eu transitions from bcc to hcp at 12 GPa

A mixed phase region exists from 18 to 66 GPa

Eu remains in an intermediate valence state above 15 GPa

Abstract

Synchrotron x-ray diffraction experiments have been carried out on Eu metal at ambient temperature to pressures as high as 92 GPa (0.92 Mbar). Following the well-known bcc-to-hcp transition at 12 GPa, a mixed phase region is observed from 18 to 66 GPa until finally a single orthorhombic (Pnma) phase persists from 66 to 92 GPa. These results are compared to predictions from density functional theory calculations. Under pressure the relatively large molar volume Vmol of divalent Eu is rapidly diminished, equaling or falling below Vmol(P) for neighboring trivalent lanthanides above 15 GPa. The present results suggest that above 15 GPa Eu is neither divalent nor fully trivalent to pressures as high as 92 GPa.