Critical Current Densities of Y1-xCaxBa₂Cu₄O₈ (x=0 and 0.1) Superconducting Ceramics

From magnetization measurements of Y 1- x Ca x Ba 2 Cu 4 O 8 superconducting ceramics with critical temperatures T c of 83 K for x =0.0 and 91 K for x =0.1, the critical current densities, J c ( H ), at 5 K and 77 K are obtained by employing the Bean critical-state model. The J c at 77 K is evaluated to be 1.5×10 3 A/cm 3 at 2 kOe for the sample of x =0.1. Compared with YBa 2 Cu 3 O 7 , the J c ( H ) values in Y 1- x Ca x Ba 2 Cu 4 O 8 are lower and more sensitive to the magnetic field. These J c ( H ) properties are discussed on the basis of the superconducting properties, i.e., critical fields and Ginzburg-Landau parameters.