Microwave properties of large YBCO films on as-prepared and annealed MgO substrates

We have studied the microwave surface impedance of large YBCO films on as-prepared MgO substrates and on annealed MgO substrates with 50 mm in diameter. YBCO films were prepared by pulsed laser deposition. The surface resistance (R/sub S/), homogeneity in the R/sub S/, and structural properties of YBCO on annealed MgO appeared improved compared with those of YBCO on as-prepared MgO. The reduced R/sub S/ of YBCO films on annealed MgO is attributed to improved inplane orientation of the YBCO grains in the films with local variations in the in-plane orientation of YBCO grains correlated well with the R/sub S/ for both YBCO films on as-prepared MgO and those on annealed MgO.