Hydrogen and water intercalation into YBa2Cu3O7-delta: structural properties of H2YBa2Cu3O8-delta

Abstract

Structural properties of hydrogen-and water-intercalated superconductors YBa 2 Cu 3 O 7 are discussed on the basis of new high-resolution electron microscopy, electron di raction, X-ray di raction, extended X-ray absorption ® ne structure (EXAFS) and Raman measurements. The multistep intercalation reaction proceeding at temperatures below 200 ë C leads to signi® cant changes in the crystal structure via shear transformation resulting in a highly crystalline end phase. A new structure model was proposed for H 2 YBa 2 Cu 3 O 8 which includes Cu± O single chains as in YBa 2 Cu 3 O 7 . This result di ers in principle from all models proposed before. §1. Introduction Investigations on the chemical reaction of water or reducing agents with superconducting materials like YBa 2 Cu 3 O 7 are of fundamental interest in terms of corrosion processes (for a review see Barkatt et al. (1993)), electronic± protonic conductivity (Baikov and Nikitin 1996) and the understanding of reaction mechanisms of low-temperature solid-state transformations. It has been reported that the intercalation of lower concentrations of hydrogen (less than 0.3 H per formula unit) into YBa 2 Cu 3 O 7 results in the topotactic formation of a solid solution (Reilly et al.