PREPARATION AND MAGNETIC-PROPERTIES OF THE 95-K SUPERCONDUCTOR Y2BA4CU7O15

We show that bulk, large-grained Y2Ba4Cu7O15 + delta (247) may be prepared with a T(c) of 95 K exceeding that of its constituent blocks, i.e. Y1Ba2Cu3O7-delta (123) and Y1Ba2Cu4O8 (124). Suitable conditions of synthesis are a high sintering temperature (990-degrees-C), and a high oxygen pressure (20 bar). The normal-state susceptibility exhibits an unusually wide fluctuation domain above T(c), extending at least to 150 K. The field-cooling Meissner effect in a 20 Oe field shows a single sharp transition at 95 K. The fraction of full flux expulsion is 45%. Several properties, such as the normal-state susceptibility, the slope of H(c)2 near T(c), the magnetically determined variation of the specific heat near T(c) and the resistivity show an intermediate behaviour between 123 and 124.