Improved high-Tcsuperconductors

Abstract

We report an experimental observation of an increased ${\mathrm{T}}_{\mathrm{c}}$ up to 159 K with temperature cycling in YBaCuO and YBaCuO:F samples. This increase in ${\mathrm{T}}_{\mathrm{c}}$ is tentatively associated with a structural phase transition or ordering occurring at a well defined temperature close to 239 K. We have used the presence of this phase ordering to achieve improved-${\mathrm{T}}_{\mathrm{c}}$ material and tentatively attribute it to a two-dimensional to one-dimensional structural change.