Crystal Fields in UO2 - revisited

We performed inelastic neutron scattering (INS) in order to re-investigate the crystal-field ground state and the level splitting in UO2. Previous INS studies on UO2 by Amoretti et al. [Physical Review B 15, 1989, 1856] uncovered four excitations at low temperatures in the 150-180 meV range. Considering the dipole-allowed transitions, only three of these transitions could be explained by the published crystal-field model. Our INS results on a different UO2 sample revealed that the unaccounted peak at about 180 meV is a spurious one, and thus not intrinsic to UO2. In good agreement with Amoretti¿s results, we corroborated that the ground-state of UO2 is the ¿5 triplet, and we computed that the fourthand six-order crystal field parameters are V4 = -116 meV and V6 = 26 meV, respectively. We also studied the INS response of the non-magnetic U0.4Th0.6O2. The splitting for this thoriumdoped compound is similar to the one of UO2, which orders antiferromagnetically at low temperatures. Therefore, we can conclude that magnetic interactions only weakly perturb the energy level plitting, which is dominated by strong crystal fields.

NAKOTTE H.;  RAJARAM R.;  KERN S.;  MCQUEENEY R. J.;  LANDER G.H.;  ROBINSON R. A.; 

2010-12-20

IOP PUBLISHING LTD

JRC53499

0953-8984,   

http://iopscience.iop.org/1742-6596/251/1/012002/pdf/1742-6596_251_1_012002.pdf,    https://publications.jrc.ec.europa.eu/repository/handle/JRC53499,   

10.1088/1742-6596/251/1/012002,