GROWTH OF YBA2CU3O7-DELTA ON ALKALINE-EARTH FLUORIDE SUBSTRATES AND THIN-FILMS

The growth and characterization of YBa2Cu3O7-delta (YBCO) thin films grown by laser ablation on MgF2 (100), CaF2 (100), SrF2 (100), and BaF2 (100) substrates, and on CaF2 and BaF2 thin films on LaAlO3 (100) substrates, are described. High quality superconducting YBCO films could be grown directly only on the BaF2 substrates and thin films. YBCO films grown directly on MgF2 or CaF2 substrates were insulating and showed clear signs of interdiffusion and reaction, as measured by X-ray photoelectron spectroscopy. Superconducting YBCO films could be grown on SrF2 and CaF2 substrates and thin films only with an yttria-stabilized zirconia buffer layer and/or with a low YBCO growth temperature, while YBCO grown on MgF2 yielded insulating films for all growth conditions investigated. The highest quality YBCO films were obtained on BaF2 substrates (T(c) = 87.6 K, DELTAT(c) = 0.3 K). These results are discussed in terms of the thermodynamic stability of possible reaction products and the temperature dependence of the ionic mobilities.