The quadrupole interaction of 111Cd in RNi5 (R=rare earth) compounds

RNi5 (R=rare-earth) compounds have hexagonal CaCu5 type structure with one rare-earth atom per unit cell but two inequivalent Ni sites. Carrier-free 111In activity was diffused in these compounds and the quadrupole interaction at 111Cd site was measured by the TDPAC technique to study the site occupancy of the dopant 111In atoms and the valence state of the rare-earth ions. The observed TDPAC patterns can be quite well fitted with a single interaction frequency indicating that the 111In preferentially occupies one of the two Ni sites. The quadrupole interaction frequency is almost constant for the six RNi5 compounds studied being around the value #betta#Q=17.0 x 106 rad/sec. This is suprising in view of the fact that Ce in CeNi5 is expected to be partially in 4+ state on the basis of several measurements like lattice parameters susceptibility etc., while Yb in YbNi5 may have valency 2+. This would indicate that the EFG at the 111Cd site in these compounds may not be very sensitive to the valence of the rare-earth ions. The temperature dependence of the QI from 80 K to 500 K also did not show any anomalous behaviour. (author)