Abstract
The effect of substitutional disorder on the superconducting properties of YNi2B2C was studied by partially replacing yttrium and nickel by Lu and Pt, respectively. For the two series of (Y, Lu)Ni2B2C and Y(Ni, Pt)2B2C compounds, the upper critical field H c2(T) and the specific heat c p(T, H) in the superconducting mixed state have been investigated. Disorder is found to reduce several relevant quantities such as T c, the upper critical field H c2(0) at T=0 and a characteristic positive curvature of H c2(T) observed for these compounds near T c. The H c2(T) data point to the clean limit for (Y, Lu) substitutions and to a transition to the quasi-dirty limit for (Ni, Pt) substitutions. The electronic specific heat contribution γ(H) exhibits significant deviations from the usual linear γ(H) law. These deviations reduce with growing substitutional disorder but remain even in the quasidirty limit which is reached in the Y(Ni1−x , Pt x )2B2C samples for x=0.1.
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