Superconductivity and the structural phase transitions in palladium hydride and palladium deuteride

Abstract

The results of two experimental studies of the superconducting transition temperature, Tc, of palladium hydride, PdHx, and palladium deuteride, PdDx, are presented. In the first study, the superconducting transition temperature of PdHx(Dx) is studied as a function of H(D) concentration, x, in the temperature range from 0.2 K to 4K. The data join smoothly with those reported previously by Miller and Satterthwaite at higher temperatures, and the composite data are described by the empirical relation Tc = 150.8 (x-xo) 2.244, where xo = 0.715 for hydride samples and 0.668 for deuteride samples. The results, when compared with the theoretical predictions of Klein and Papaconstantopoulos, et al., raise questions about the validity of their explanation of the reverse isotope effect, which is based solely on a difference in force constants. In the second study, the effect of the order-disorder structural transition associated with the 50 K anomaly on the superconductivity of PdHx(Dx) is investigated. Samples were quenched to low temperatures in the disordered state, and their transition temperatures measured. The samples were then annealed just below the anomaly temperature, and the ordering process followed by monitoring the change in sample resistance. The transition temperatures in the ordered state were then measured.