Effect of structural and morphological imperfections on the microwave surface resistance of YBCO thin films

Abstract

The average grain size, non-uniform lattice distortion and the orthorhombic lattice parameters have been measured by means of X-ray diffraction analysis for a series of YBCO thin films. These films exhibited a microwave surface resistance ranging from less than 0.05 to 0.8 Ω (measured at 60 GHz and 77 K) but similarly high dc critical parameters ( T c = 89–90 K, J c(77 K,0 T) > 2×10 6A/cm 2). It has been found for the examined films that the decrease of the orthorhombic splitting, which results from the lattice distortion in the a- b plane, correlates with the increase of the surface resistance. On the other hand, the perfection of the YBCO lattice along the c axis, i.e. the average grain size and the lattice distortion, does not affect the microwave losses in these films. The microwave losses in the YBCO films were also correlated to the film surface morphology.