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The effect of Ca doping on the flux pinning and the weak link structure of the LaBa2Cu3O7-y system have been studied. The magnitude and the magnetic field dependence of the critical current density were improved by Ca doping. A small amount of impurity phases of Ca-related compounds such as Ca2Cu1O3 and Ca1Cu2O3 may work as a desirable flux pinning center. Moreover, it was found that the current-temperature characteristics for Ca-doped samples showed the evidence of two kinds of superconductor phases which have different transition temperatures T c and T c'. The experimental result agreed well with the Ambegaokar-Baratoff theory for asymmetric Josephson junctions (S-I-S') in the temperature range of T<T c' and with the proximity junction theory (S-N-S) in the range of T c'<T<T c.

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