155Gd Moessbauer measurements on gadolinium metal up to 17 GPa

155Gd Moessbauer measurements on gadolinium metal have been performed at pressures up to 17 GPa and at T = 4.2 K for the first time. The three different crystallographic phases that Gd exhibits below 24 GPa can be distinguished. The Isomer Shift (IS) changes can be fitted to ∂IS/∂ln(V/V(p = 0)) = (0.73 ± 0.08) mm/s. The large increase of the hyperfine fields with increasing pressure is correlated with the change in IS. Relatively large changes of the Quadrupole Splitting of the hexagonal sites occur with increasing pressure. Up to a volume reduction of 30%, the 4f shell proves to be stable. Since Gd3+ has the same electronic 4f7 configuration as Eu2+, comparing 155Gd and 151Eu Moessbauer measurements may give a clue about the stability of Eu2+ under pressure. (orig.)