Alloying effects of Y on TcTc 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 TcTc with xx is similar to the change in the lattice parameter. It is found that the TcTc change rate is dTc/dx=−7.0K and dTc/dv=0.46K/Å3. 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 TcTc. 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 TcTc dominates in the (La1−xY x)NiC2 system.