Crystal structure and superconductivity in (La$_{1-x}$Y$_{x})$NiC$_{2}$*

As observed in the powder X-ray diffraction and crystallographic data, the partial substitution of La with Y in (La$_{1-x}$Y$_{x})$NiC$_{2}$ 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 dT$_{c}$/dx = --7.0 K and dT$_{c}$/dv = 0.46 K/{\AA}$^{3}$. 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 (La$_{1-x}$Y$_{x})$NiC$_{2}$ system.