Superconductivity in the ternary rare-earth (Y, La, and Lu) compounds R${\mathrm{Pd}}_2$${\mathrm{Si}}_2$ and R${\mathrm{Rh}}_2$${\mathrm{Si}}_2$

We have investigated the superconducting and metallurgical properties of the ternary compounds R${\mathrm{Pd}}_2$ ${\mathrm{Si}}_2$ and R${\mathrm{Rh}}_2$ ${\mathrm{Si}}_2$ with R=Y, La, and Lu. All R${\mathrm{Pd}}_2$ ${\mathrm{Si}}_2$ compounds and ${\mathrm{LaRh}}_2$ ${\mathrm{Si}}_2$ were found to be type-I superconductors below 1 K. A detailed metallurgical analysis shows that segregation of second phases can easily mask the intrinsic (stoichiometric ratio 1:2:2) intermetallic-compound properties. Two sample-preparation techniques, viz., single crystals and off-stoichiometry, were utilized to establish where bulk superconductivity occurs. The type-I behavior of these compounds is explained with an analogous model as is used for the heavy-fermion superconductors ${\mathrm{CeCu}}_2$ ${\mathrm{Si}}_2$ and ${\mathrm{URu}}_2$ ${\mathrm{Si}}_2$.