Structural and Valence Changes of Europium Hydride Induced by Application of High-Pressure H2

Europium hydride EuHx, when exposed to high-pressure H-2, has been found to exhibit the following structural and valence changes: Pnma(x = 2, divalent) -> P6(3)/mmc(x = 2, 7.2-8.7 GPa) -> I4/m(x > 2, 8.7-9.7 GPa) -> I4/mmm(x > 2, 9.7 GPa-, trivalent). With a trivalent character and a distorted cubic fcc structure, the I4/mmm structure is the beta phase commonly observed for other rare-earth metal hydrides. Our study clearly demonstrates that EuHx is no longer an irregular member of the rare-earth metal hydrides.