Interaction between atomic hydrogen and YBa₂Cu₃O₇

Abstract

Atomic hydrogen obtained from dissociative chemisorption of molecular H₂ on Pt particles deposited on the surface of YBa₂Cu₃O₇ reacts with the oxide in producing O vacancies and intercalating H at 82 °C under a H₂ pressure of about 400 Torr. An induction period which extends over 1 h is observed as long as the concentration in O vacancies is below 0.1. Above this approximate limit the reaction proceeds quickly until about 1 mol H₂ has been consumed. It then slows down progressively, but it is not completed even after 27 h of reaction and ∼1.4 H₂ consumed, under these experimental conditions. The enthalpy for the creation of the O vacancy is 143 kcal/g mol O, while the H intercalation enthalpy is −57.5 kcal/g mol H. It appears that the reaction of molecular H₂ over YBa₂Cu₃O₇ not coated with Pt proceeds similarly, but the rate is nearly one order of magnitude slower, under identical conditions. The stoichiometry of the reaction agrees with the earlier suggestion that O₁ is a labile oxygen which can be replaced by intercalated H. This site and the interstitial vacant sites in the copper chains square plane would be the first ones to be occupied by intercalated H.