The valence state of M-ions in the chemically stabilized YSr(2)Cu(3-x)M(x)O(7+delta) (M=Mo, W and Re) superconductors

Abstract

Single phase Ba- free Sr-based YSr(2)Cu(3-x)M(x)O(7+delta) (M = Mo, W and Re) compounds have been stabilized by chemical doping. Superconductivity is observed for these phases in the range 30-45K. X-ray diffraction studies suggest a relatively small orthorhombicity compared to Ba-analogue. X-ray photoelectron spectroscopic investigations reveal that the stabilizing cations are in the hexavalent state. The observation of the higher oxidation state of M-ions accounts for the excess oxygen content in these phases which is in accordence with the diffraction results.