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

Abstract
From magnetization measurements of Y1-x Ca x Ba2Cu4O8 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 1.5×103 A/cm3 at 2 kOe for the sample of x=0.1. Compared with YBa2Cu3O7, the J c(H) values in Y1-x Ca x Ba2Cu4O8 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.