Alloying effects of Y on in superconducting (La1−xY x)NiC2

As revealed in the powder X-ray diffraction and crystallographic data, the partial substitution of La with Y in (La1−xY x)NiC2 could be systematic up to the solubility limit near x=0.35. The variation of room temperature lattice parameters, a, b, c and v of these substitute compounds are consistent with what one would expect from a chemical pressure effect. Magnetic, electrical and heat capacity measurements indicate that the change in T c with x is similar to the change in the lattice parameter. It is found that the T c change rate is d T c / d x = − 7.0 K and d T c / d v = 0.46 K / Å 3 . According to the BCS theory, the stiffening of the lattice under pressure may change both the electron–phonon coupling strength V and the electron density of states at the Fermi level, N(0), which will lead to the change of T c . Analysis of the electron density of states at Fermi level N(0) from the specific heat data indicates that the effect of N(0) on T c dominates in the (La1−xY x)NiC2 system.