Stability Test of HTSC Phases in PdH System

Abstract

In previously published papers, preliminary results on highly hydrogen loaded palladium (PdHx) samples with H/Pd stoichiometric ratio x > 1, have shown probable multiphase HTSC superconducting states. In this letter, the stability of the new phases in the sample has been verified. After long-term sample storage of two years at room temperature and room pressure, ac susceptibility measurements in temperature have been done. The sample, that two years earlier exhibited a high temperature phase at Tc = 261.5K with x∼1.56, presented now a Tc shift down to Tc = 160.5K with a x∼1.46 and Tc = 82K with a x∼1.34. The H/Pd decreases by Δx∼0.1 and ∼0.21 while the Tc diminishes down to ΔTc∼101K and 180K. In very high x ratio phase, slight hydrogen leakage causes significant Tc drop. Moreover, another previously existing low temperature phase Tc = 9K with x∼1, shifts down to 6K with x∼0.85. In this case the decrease of Δx ∼0.15 causes the ΔTc drop by 3K. In both phases, similar calculated Δx decrease percentage with subsequent reduction of the Tc estimated percentage shows a like behavior. This suggests that a single process takes place in the formation of HTSC and low Tc superconducting state in PdHx. The measured PdH sample, before and after long-term storage and trough the thermal cycles, maintains high H loading value with high transition temperatures.