Superconductivity in Palladium Hydride Systems

The superconductivity of palladium–hydride (Pd–H) system was discovered by Skoskiewicz in 1972. Thereafter, many studies have been carried out on Pd–H and palladium deuteride (Pd–D) systems along with their alloyed (Pd–metal–H) systems. In this paper, we present a brief overview of superconducting properties of these systems. First, we describe methods for H loading into Pd, in which three principal techniques, i.e., gas loading, electrochemical loading, and H implantation are introduced. Next, we briefly summarize the superconducting properties of Pd–H(D) systems, e.g., the concentration dependence of the transition temperature T_c, inverse isotope effect, critical field, pressure dependence of T_c, and the impurity effects. Subsequently, we describe our recent in-situ magnetization measurements of superconducting Pd–H and Pd–D powders with 1–2 µm diameters prepared by low-temperature H absorption, in which the absorption was performed below 200 K under hydrogen (H₂) or deuterium (D₂) gas atmosphere. Additionally, we report resistance measurements of a Pd–H film with ∼100 nm thickness prepared by the same H absorption procedure. The superconducting transition temperature of the film is consistent with that of the powders. From these results, we conclude that the low-temperature H absorption method is useful for preparing high quality Pd–H and Pd–D samples.