Static and dynamic dilatation of the high-Tc superconductor EuBa2Cu3O7 − δHx

Hydrogen induces an orthorhombic-to-tetragonal transformation in superconducting ceramics of the type RBa2Cu3O7. We have studied this transformation by measuring the thermal expansion coefficients of the system EuBa2Cu3O7Hx between liquid nitrogen and room temperature by X-ray diffractometry. For the hydrogen-free orthorhombic compound, the relative thermal expansion is approximately 50% stronger along b and c than along the a axis. Upon the addition of hydrogen, all thermal expansion coefficients decrease, with a strong drop near x = 0.5 (e.g. by more than a factor of four for a −1 Δa ΔT . The lattice parameters increase with x, with in general 1 a Δa Δx > 1 b Δb Δx > 1 c Δc Δx up to x ≈ 0.5, from whereon one observes coexistence of an orthorhombic and tetragonal phase, the former vanishing for x > 1. The results seem to indicate that the hydrogen atoms occupy the empty oxygen sites in the Cu(1) basal plane, together perhaps with sites in the europium planes.