Role of oxygen pressure during deposition on the microwave properties of YBCO films

We have studied the effect of oxygen pressure (PO,) during pulsed laser dep osition on the properties of YBCO films, with particular attention to the l ow power microwave surface resistance R-s. Above a threshold oxygen pressur e the properties of the films are nearly independent of PO2 during depositi on and are typical of high quality YBCO films. The films made below this th reshold pressure have increased disorder which produces a reduced T-c and a n expanded c-axis lattice parameter. However, these films also have signifi cantly reduced low temperature R-s, which is likely a direct result of the increased scattering in these films. Preliminary Raman measurements show no increase in the Y-Ba cation disorder in these low PO2 films, so that a dif ferent disorder mechanism must be present.