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 recently discovered amorphous layer of YBCO-S between YBCO grains, was studied with mu+ spin rotation/relaxation techniques in zero and applied magnetic fields. It was found that the new phase acts as a magnetic impurity. Sulphur substitution increases the penetration depth in the bulk of the grains (lambda(0) = 290 nm), and a reduced superconductivity percolation effect is obtained. The role and location of sulphur is discussed in view of recent electron microscopy and X-ray emission spectroscopy results on the same samples.