Flux pinning and magnetic relaxation in melt-processed YBa2Cu3O(Sub 7-delta) doped with Li

Melt- processed samples of YBa2Cu3O(Sub 7-delta) (YBCO) doped with Li additions substituting at Cu(2) planes sites are used to study the effects of doping on the superconducting temperature, critical current density, irreversibility field, upper critical field, coherence length, and magnetic relaxation as a function of temperature and magnetic field. The pinning parameters estimated show a considerable enhancement of the critical current density in the optimally doped sample, but only an insignificant change in the effective activation energy, pointing to a weak pinning of pointlike pinning centers, created by Li additions.