INFLUENCE OF THE SUBSTRATE ON THE STRUCTURAL AND TRANSPORT-PROPERTIESOF THE THIN-LAYER MERCURY FAMILY SUPERCONDUCTORS MADE BY HIGH-PRESSURE GAS METHOD

We have found a very promising way for obtaining thin and thick layers of the Hg-12(n-1)n homologous family (n=2,3,4) on various substrates, i.e., SrTiO3, LaAlO3, SrLaAlO4, and SrLaGaO4. Crystal growth of a thi n layer from the melt is rapid (up to 15 microns/hour) and strongly de pends on the p-T-x conditions. The substrate and the crucible material s exert strong influences on the purity of the layers. Pure supercondu cting phases can be grown on SrTiO3 and LaAlO3 substrates, while growi ng on the SrLaAlO4, and SrLaGaO4 lead to chemical reactions and substr ate decomposition. These effects are not observed for low temperature laser ablation. The orientation of the growing layer depends strongly on the initial substrate orientation. To obtain thin layers of mercury compounds, we have developed a special method which enables us to kee p very high pressure vapour of mercury over the substrate during all p rocesses. This is crucial to avoid mercury losses from pre-reacted thi n layers made by laser ablation and subsequent growth under high gas p ressure. Transport parameters, XRD patterns, and morphology by SEM and EDX analysis presented. (C) 1997 Academic Press Limited.