J. Phys. Colloques 47 (1986) C8-937-C8-941
LATTICE DYNAMICS OF THE HEAVY FERMION COMPOUND UBe13J.M. TRANQUADA1, S.M. HEALD1, M.A. PICK1, Z. FISK2 et J.L. SMITH2
1 Brookhaven National Laboratory, Upton, NY 11973, U.S.A.
2 Los Alamos National Laboratory, Los Alamos, NM 87545, U.S.A.
UBe13 has unusual electronic and magnetic properties due to a narrow band of U 5f states near the Fermi energy. We have used EXAFS to compare the interatomic forces in UBe13 with those in ThBe13, which has the same structure but no 5f electrons. From measurements made over the range 10 to 308 K, we have determined the temperature dependences of the mean square relative displacements (MSRD's) for the first actinide-beryllium and actinide-actinide shells in each material. The MSRD's for the corresponding shells in the two compounds were found to be quite similar. The thermal motion of the nearest-neighbor actinide-actinide pairs is shown to be due entirely to a single Einstein mode, the square of whose frequency is proportional to the actinide-Be force constant. We conclude that the presence or absence of 5f electrons on the actinide has very little effect on the actinide-beryllium bonding.