Non-ohmic I - V behavior in YBa₂Cu₃O_7-δ/Ag₂O high T_c superconductors composite

Current-voltage isotherms performed on YBa₂Cu₃O_7-δ/Ag₂O and YBa₂Cu₃O_7-δ high T_c composites below their transition temperatures revealed a power law (V = αI^β) behavior over a wide range of applied voltage. The exponent β decreases linearly with increasing temperature, deviating from linearity at temperature T_nl lower than T_c. Moreover, we evaluate the average thermal activation energy U(T) using the exponent β and Sun's model. We found that U(T) is reduced upon increasing Ag₂O content. We argue that T_nl may reflect changes in the dynamics of the intergranular (or Josephson) vortices just below the superconducting transition temperatures.