Paper TF-ThP22
The Importance of the Valence State of Cu in the Formation of Re-BCO using Low Pressure dc-Magnetron Sputtering

Thursday, October 18, 2007, 5:30 pm, Room 4C

In this work we propose a novel way of explaining the XRD-spectra of our rotatable dc-magnetron low pressure sputtered YBa₂Cu₃O_7-δ and NdBa₂Cu₃O_7-δ thin films. As is frequently the case at low pressure sputtering our films exhibit an expanded c-axis. This expansion is usually attributed to oxygen deficiency and/or cation-disorder in the Re-Ba₂Cu₃O_7-δ structure. However under certain conditions (low pressure, Cu co-sputtering, lowering deposition temperature,...) the spectra of our films not only reveal an expanded c-axis but the (00n) peaks also tend to split up, whereby one peak has the theoretical c-axis value while the other shows an enlargement. This behaviour suggests the presence of two phases in our thin films. A closer look at XRD-spectra of some of our thin films suggest that a large c-axis expansion in Cu-poor conditions might be attributed to the presence of Y₂Ba₂O₅. The conditions triggering the split as well as the possible presence of Y₂Ba₂O₅, point to the importance of the energy and/or valence state of the Cu atoms during the deposition process. Therefore in this paper we explore a possible explanation for the peak splitting in the XRD-spectra of our thin films based not only on the abundance of the Cu atoms at the substrate but also on their energy or valence state.