The activation energy U0 has been measured for melt-textured YBa2Cu3O7 samples at low magnetic induction Bc. The data indicate that U0 has a nearly linear temperature dependence in a certain temperature regime (1060 K) and is insensitive to magnetic induction. In terms of the collective-pinning ideas and taking into account the modification due to the thermal fluctuation of the flux-line lattice, we propose a possible theoretical explanation. Meanwhile, the critical current Jc, which depends upon the magnetic induction B as Jc1/ B, was obtained.
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