Origin of nonlinear surface impedance and intermodulation distortion in YBa2Cu3O7−x microstrip resonator

We present measurements of the nonlinear surface impedance Zs and the third-order intermodulation distortion (IMD) of a YBa2Cu3O7−x microstrip resonator, which is initially in the as-processed state and subsequently annealed at 450–600 °C. Zs of the as-processed sample in the high-dissipated-power range is explained in terms of the vortices in weak links. In the low-dissipated-power range, outputs of IMD are changed by annealing the resonator, and the minimum IMD generation is obtained with a sample annealed at 500 °C. By comparing the IMD generation of the samples with the crystalline structure measured by x-ray diffraction and transmission electron microscopy, it is shown that IMD of the YBa2Cu3O7−x film is generated at lattice distortions of the a−b plane in grains and grain boundaries.