  The temperature and magnetic field dependences of the electronic specific
heat in the superconducting mixed state as well as the upper critical field
have been measured on a (Y,Lu)Ni2B2C series to study the influence of disorder.
The electronic specific heat in the vortex state shows deviations from the
usual gamma(H) proportional to H-law for conventional superconductors for all
samples resulting in a disorder dependent negative curvature of gamma
proportional to H sup(1-beta). For samples with disorder at the R site beta and
the positive curvature exponent alpha of H sub(c2) are reduced but alpha, beta
remain always positive, as distinct from much stronger disorder due to Pt
substions at the Ni site where alpha, beta rapidly tend to 0. Alpha shows a
minimum at equal Y and Lu concentration. H sub(c2)(00, T sub(c), the curvatures
of H sub(c2) and gamma(h), as well as the normal state Sommerfeld constant
gamma sub(N) are reduced similarly.
