Correlation between the microwave surface resistance and the crystal structures of YBa_2Cu_3O_(7-delta) films on CeO_2-buffered sapphire

摘要

Dependence of the microwave surface resistance (R)_S) of YBa_2Cu_3O_(7-delta) (YBCO) films on their crystal structures was studied for YBCO films grown on as-prepared CeO_2-buffered sapphire (CbS) and CbS post-annealed at 950-1100 deg C. At temperatures below 70 K, the R_S appeared to be strongly dependent on the degree of the in-plane alignment of the YBCO films as determined by x-ray PHI-scan analysis. Optimum in-plane alignment could be observed for YBCO films on CbS post-annealed at 1000-1050 deg C, with the R5 appearing significantly smaller than for YBCO films prepared on as-grown CbS or CbS post-annealed at the other temperatures. Conversely, we observed a small correlation between the R_S and the degree of the c-axis alignment as determined using x-ray omega-scan analysis. Similarly, surface roughness of the YBCO films did not strongly influence R_S at temperatures below 70 K.