Structural and valence changes of europium hydride induced by application of high-pressure H

Matsuoka, Takehiro*; Shimizu, Katsuya*; Fujihisa, Hiroshi*; Hirao, Naohisa*; Oishi, Yasuo*; Yoda, Yoshitaka*; Mitsui, Takaya; Masuda, Ryo; Machida, Akihiko; Aoki, Katsutoshi; Seto, Makoto*

Europium-hydride EuH exposed to high-pressure H conditions has been studied by X-ray diffraction and Mssbauer spectroscopy measurements up to 50 GPa using synchrotron radiation. We report new structural and valence transitions, Pnma(x=2, divalent) P63/mmc(x=2, 7.2-8.7GPa) I4/m(x2, 8.7-9.7 GPa) I4/mmm(x2, 9.7 GPa, trivalent). The phase of I4/mmm having trivalent character is a small distortion from cubic fcc structure which has been commonly observed for -phase of all other trivalent rare-earth metal hydrides. Our study clearly demonstrates the first observation of -phase of EuH and suggest that the material is no longer an irregular member of the rare earth metal hydrides RH systems.