Pair weakening in mixed rare-earth nickel borocarbides (R,R')Ni2B2C
  In this study pseudoquaternary rare-earth nickel borocarbide superconductors RxR'1-xNi2B2C have been investigated predominantly in the diluted limit x << 1 or (1 x) << 1. In all of these materials structural disorder results in a reduction of the superconducting transition temperature Tc . Depending on the selection of the rare earth elements R and R' this disorder induced deterioration of superconductivity is combined with magnetic pair breaking of Abrikosov-Gorkov type or pair breaking of non-magnetic impurities in antiferromagnetic superconductors (Morozov-type of pair breaking). 
J. Freudenberger, K.-H. Mueller, G. Fuchs, M. Wolf, K. Nenkov, L.   Schultz