Superconducting hydrides ofPdAlxandPdInxalloys

Ion-implantation studies of Pd-based alloys are presented with emphasis on the superconducting properties of certain metal hydrides. Addition of aluminum to PdH yields an initial small increase in $T_c$ and subsequently lowers $T_c$ rapidly for aluminum content exceeding 10%. Similarly $\mathrm{Pd}{\mathrm{In}}_x{\mathrm{H}}_y$ alloys exhibit a decreasing $T_c$ with increasing indium content, in contrast to expectations of existing theories. The role of spin fluctuations, phonon spectra, and hydrogen content are discussed in view of the strong enhancement of $T_c$ in Pd-noble-metal alloy hydrides.