Correlation between microwave surface resistance, AC susceptibility and in-plane ordering in YBa2Cu3O7 thin films epitaxially grown on (100) MgO substrates

Epitaxial c-axis YBa2Cu3O7 thin films presenting a rate of c perpendicular to 45 in-plane orientation (eta) ranging from 0.2 to 49.7% have been grown in situ by laser ablation on (100) MgO in order to study the influence of the high-angle grain boundaries on the microwaves and low-frequencies properties. In spite of the mixed in-plane orientation, the good epitaxial quality is maintained. We found that the microwave surface resistance R(s) (10 GHz and 77 K), ranging from 0.7 to 46 m Omega, and the surface of the chi '' peak obtained in AC susceptiblity (119 Hz) strongly correlate with eta. In contrast a poor or even no correlation was observed with other characteristics such as for example Delta theta, T-c, or Delta T-c. A minimum of R(s) has been measured for eta between 3 and 6% suggesting the necessity of a low quantity of defects such as high-angle grain boundaries in view of microwave applications.