Electrical quadrupole interaction at the Ni site in RNiBC compounds

Fe-57 Mossbauer spectra of RNiBC (R = Gd, To, Dy, Ho, and Er) compounds dop ed with Fe-57 (0.5 at.%) taken above their magnetic ordering temperatures r eveal a quadrupole doublet with a splitting \Delta E-Q\ which decreases on going from Gd to Er. The values of \Delta E-Q\ depend linearly on the param eter c'/a, with c' being the distance apart of the R-C layers between which the Ni-2-B-2 layer is sandwiched and a being the lattice parameter in the basal plane. The \Delta E-Q\ versus c'/a relation is identical with that pr eviously found for RNi2B2C compounds.