Electric quadrupole interaction at 181Ta in RNi5 compounds

The time differential perturbed angular correlation measurements in PrNi5, NdNi5, GdNi5, DyNi5 and ErNi5 rare-earth intermetallics with 181Ta as probe nuclei have revealed that these impurity nuclei experience a non-axial electric quadrupole interaction. In all the cases, except in GdNi5, the interaction frequency has a single value in the range 15-20 MHz with asymmetry parameter eta approx. 0.98. In GdNi5, however there are two interaction frequencies (13.61 MHz and 26.89 MHz), the former being the dominant one (90%) with eta approx. 0.35 and the latter (10%) with eta approx. 0.98. It is concluded that in all cases the probe nuclei experiencing the highly asymmetric electric field gradient (efg) occupy the unique Ni(3g) site. Annealing studies have shown that in the case of GdNi5 the interaction gets highly damped, while there is negligible effect in the other cases. The temperature variation of the efg in all cases seems to follow the empirical Tsup(3/2) relation. (Auth.)