X-ray diffraction study of the influence of hydrogen on the crystallographic structure of H_xYBa₂Cu₃O_7-δ

X-ray diffraction was performed on powder samples of H_xYBa₂Cu₃O_7-δ where δ≈0.07 and 0≤x≤1.52. A comparison is made with the crystallographic behavior upon oxygen extraction. The following features were found: (1) In the orthorhombic phase the a and b lattice parameters were consistent with the assumption that the addition of two hydrogen atoms is equivalent to the removal of one oxygen. (2) The orthorhombic-to-tetragonal transition takes place at x≈0.8 (3) The a parameter in the tetragonal phase is larger when hydrogen is added than when oxygen is removed. (4) While c increase monotonically upon oxygen extraction, it decreases upon hydrogen addition both in the orthorhombic and tetragonal phases such that when the hydrogen concentration reaches x≈1.0, then a=b= c 3. (5) At x=1.0, the Cu(2) and Cu(1) planes are evenly spaced, c 3 apart. These phenomena are discussed in the context of the superconducting properties of the material upon oxygen removal or hydrogen addition. In addition, comparison between a pellet and a powder is made, which indicates that some surface oxygen may be removed upon hydriding.