A MU+SR STUDY OF THE EFFECT OF SULFUR SUBSTITUTION IN GRANULAR YBA2CU3O6.6

The effect of sulphur substitution in YBCO, which results in the recen tly discovered amorphous layer of YBCO-S between YBCO grains, was stud ied with mu+ spin rotation/relaxation techniques in zero and applied m agnetic fields. It was found that the new phase acts as a magnetic imp urity. Sulphur substitution increases the penetration depth in the bul k of the grains (lambda(0) = 290 nm), and a reduced superconductivity percolation effect is obtained. The role and location of sulphur is di scussed in view of recent electron microscopy and X-ray emission spect roscopy results on the same samples.