YBCO superconducting thin films prepared by vacuum coevaporation without post treatment in oxygen

Results on low-temperature preparation of superconducting thin films of YBa/sub 2/Cu/sub 3/O/sub x/ are presented. YBCO thin films of 0.5-1.0- mu m thickness were prepared by vacuum codeposition of Y, BaO, and Cu onto both polycrystalline and single-crystal Al/sub 2/O/sub 3/, MgO, and SrTiO/sub 3/ and on Si+SrTiO/sub 3/ and Si+SiO/sub 2/ substrates. The temperature of the substrates was 550-580 degrees C and the partial oxygen pressure in the vacuum chamber was 10/sup -2/ Pa. The preparation of in situ superconducting thin films was successful with all substrates. Maximum critical temperature at zero resistance was T/sub ce/=85 K, the onset critical temperature T/sub con/ being from 90 to 95 K. The authors believe that T/sub con/ represents the maximal critical temperature of grains. Thus, the synthesis of superconducting granules with high T/sub c/ is possible even at a relatively low temperature during the deposition. On the other hand, the zero-resistance critical temperature T/sub ce/ characterizes the intercrystalline boundaries with electrical properties sensitive to diffusion processes from substrate or surrounding atmosphere. Additional oxidation of films (thermal or plasmatic) does not much affect T/sub ce/ near 85 K.