Photoemission study of the hydrogenation of the intermetallic compoundsYFe3andYFe2

Intermetallic yttrium-iron compounds do have a strong affinity to hydrogen. Exposure to ${\mathrm{H}}_2$ at 300 K leads to a hydrogen-induced state at 5.3 eV below $E_F$ and a strong reduction of d-like states at $E_F$. For higher ${\mathrm{H}}_2$ exposures at 700 K, these hydrides undergo a metal-to-semiconductor transition with an energy gap $E_0$=0.3±0.1 eV. In addition to the lowering of d-like states at $E_F$, a second ${\mathrm{H}}_2$-induced structure appears at 10 eV.