GD-155 MOSSBAUER MEASUREMENTS ON GADOLINIUM METAL UP TO 17-GPA

Gd-155 Mossbauer measurements on gadolinium metal have been performed at pressures up to 17 GPa and at T = 4.2 K for the first time. The thr ee different crystallographic phases that Gd exhibits below 24 GPa can be distinguished. The Isomer Shift (IS) changes can be fitted to part ial derivativeIS/partial derivativeln (V/V(p = 0)) = (0.73 +/- 0.08) m m/s. The large increase of the hyperfine fields with increasing pressu re is correlated with the change in IS. Relatively large changes of th e Quadrupole Splitting of the hexagonal sites occur with increasing pr essure. Up to a volume reduction of 30%, the 4f shell proves to be sta ble. Since Gd3+ has the same electronic 4f7 configuration as Eu2+, com paring Gd-155 and Eu-151 Mossbauer measurements may give a clue about the stability of Eu2+ under pressure.