By pinning the magnetic field that can penetrate superconducting material in the regions of weaken superconductivity it is possible to enhance critical parameters of HTSC. Theoretical considerations indicate that best regions should have elongated shape with diameter somewhat larger than the superconducting coherence length (~ 10 ? for the ab-plane of HTSC). Usually, extrinsic methods have been applied to produce effective pinning, where the size (100 - 1000 ?) and spacing (overlapping) of pinning regions is far from optimal. We have investigated the substituted bulk and single-crystals of Y123 materials and show that enhanced critical currents jc can be achieved by formation of intrinsic extended defects with the improved size and distribution for Mo- and Sr- substituted Y123. We describe optimization of the superconducting Tc and jc by determining the best compositions, synthesis and annealing conditions. The structural and superconducting properties of the optimized material with Tc ~ 92 K are studied by neutron powder diffraction and M(B) isotherms measured over wide temperature and field ranges to derive the jc(B) and jc(T) that reveal the pronounced peak effect. The extended defects in the CuO chains, the Mo₂O_7/2 dimers, are identified as effective pinning centers that locally perturb superconductivity in the CuO₂ planes by providing additional weakly interacting pinning centers that increase the pinning force.

Supported by the NSF-DMR-0302617

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