X-RAY-DIFFRACTION STUDY OF THE INFLUENCE OF HYDROGEN ON THE CRYSTALLOGRAPHIC STRUCTURE OF HXYBA2CU3O7-DELTA

X-ray diffraction was performed on powder samples of HxYBa2Cu3O7-delta where delta almost-equal-to 0.07 and 0 less-than-or-equal-to x less-than-or-equal-to 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 almost-equal-to 0.8.(3) The a parameter in the tetragonal phase is larger when hydrogen is added than when oxygen is removed. (4) While c increases monotonically upon oxygen extraction, it decreases upon hydrogen addition both in the orthorhombic and tetragonal phases such that when the hydrogen concentration reaches x almost-equal-to 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.