Bulk and thick films of the superconducting phase YBa2Cu3O7−y made by controlled precipitation and sol-gel processes

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Abstract
The synthesis of high‐temperature superconducting oxides using solution chemistry has been investigated and physical properties are compared to ceramics obtained by conventional solid‐state reactions. We report on controlled precipitation and sol‐gel processes, both of which produce materials with particle sizes smaller than 5 μm. We find that the superconducting properties of the high Tc ceramics are affected by their manner of preparation, such that the transitions are slightly lower in temperature, but sharper, for samples made by solution rather than solid‐state chemistry. The ability to prepare stable viscous gels provides an opportunity for obtaining large areas of superconducting coatings. For thick films on alumina or silicon substrates, contamination from the substrate is shown to be a problem. Finally, we observe that the sol‐gel process lowers the synthesis temperature by 100 °C.