Preparation of highly oriented poly-diacetylene films with ion beam irradiation

Abstract

Substituting metallic or rare-earth atoms or removing O in the superconductor YBa₂Cu₃O₇ usually has a strong effect on the superconducting properties. We have made extensive XAFS studies on Co, Fe, Ni, Zn, Gd, and Pr substituted materials including some thin film samples. In nearly all cases, significant distortions are found. Although the lattice constant change is small (< 0.05 Å) the local distortions can be significant larger (～ 0.1 to 0.3 Å). The observed large local distortions of the lattice together with a change in the charge distribution at a site indicate that the interior of the unit cell is easily distorted. The correlation of a strong Tc suppression with large local distortions suggests that distortions of the nearby layers must play a significant role in models for superconductivity in high Tc materials.