T-C REDUCTION AND RELATED PHASES AT EARLY STAGES OF YBACUO7-DELTA FILM GROWTH ON LASRALO4

The temperature-dependence of the resistivity of YBa2Cu3O7-delta (YBCO ) films grown on LaSrAlO4 (LSAO) substrate with thicknesses from 12 to 240 nm were studied systematically. It was found that a drastic reduc tion of T-c occurs at a thickness of about 60 nm, which is much larger than the value (10 nm) for YBCO films on SrTiO3. These ultra-thin fil ms were also characterised by Raman, STM, TEM and grazing-incidence X- ray diffraction (GIXRD). With a film thickness below 60 nm Raman spect ra revealed an abnormal enhancement of the intensity of Cu-Cu vibratio n mode, which indicates the formation of oxygen deficient phases. Addi tional evidences were provided by GIXRD and TEM. The formation of oxyg en deficient microdomain phases near the interface explains the observ ed early suppression of T-c in YBCO on LSAO as compared to YBCO on STO .