NMR AND TRANSPORT STUDIES OF Y2BA4CU7O15-DELTA HAVING DIFFERENT T-C VALUES FROM DIFFERENT SYNTHESIS CONDITIONS

Y2Ba4Cu7O15-delta superconductors with similar oxygen contents but dif ferent T-c values have been produced by varying the reaction condition s. Resistivity, Y-89 NMR and thermopower measurements were used to asc ertain the origin of the different T-c's. We find that the sample with the lowest T-c has a lower hole concentration on the CuO2 planes and the normal-state energy gaps are similar to those found in oxygen-depl eted YBa2Cu3O7-delta superconductors. Thus the electronic behaviour of Y2Ba4Cu7O15-delta is similar to that of YBa2Cu3O7-delta and the diffe rent T-c values can be attributed to different hole concentrations on the CuO2 planes and not to different pairing potentials or pair-breaki ng. The difference in the temperature dependence of the thermopower be tween these samples can be understood in terms of the different relati ve CuO chain and CuO2 plane contributions.