Superconductivity in (La$_{1-x}$Th$_{x})$PtSi and LaPt$_{1-x}$Si systems*

As revealed in the powder x-ray diffraction and crystallographic data, the partial substitution of La with Th in (La$_{1-x}$Th$_{x})$PtSi is able to be systematic up to the solubility limit near x = 0.5 and the parent compound LaPtSi admits considerable vacancies up to 20{\%} on the Pt sublattice while still retaining its tetragonal symmetry. The refined lattice parameters show that both the c-axis and the volume of the unit cell v shrink clearly due to the doping with Th or the existence of vacancies in the compound. These results are consistent with what one would expect from a chemical pressure effect. We will present the static magnetization and specific heat data for these pseudo-ternary compounds investigated in the necessary temperature range. Discussion of the change in the superconducting critical temperature T$_{c}$ will be directed toward the changes of electron number density as well as the lattice parameters with respect to pure LaPtSi.