VARIATION OF THE SUPERCONDUCTING AND STRUCTURAL-PROPERTIES OF Y2BA4CU7OZ WITH OXYGEN-CONTENT (14.1 LESS-THAN Z LESS-THAN 15.3, 30 K LESS-THAN-OR-EQUAL-TO TC LESS-THAN-OR-EQUAL-TO 95 K)

A great number of pure and homogeneous Y2Ba4Cu7Oz samples were investigated by AC susceptibility, field cooling magnetization measurements, X-ray diffraction, microprobe analysis and microstructural examinations in a light microscope and a scanning electron microscope. The oxygen content z between 14.1 and 15.3 was determined by the reduction of the samples in a hydrogen flow. To reach the (z-T-p) equilibrium, well-crystallized samples were annealed in pure oxygen (10(-6) less-than-or-equal-to p(O2) less-than-or-equal-to 10(2) bar) between 300 and 900-degrees-C and subsequently quenched. The specimens produced in this way show sharp chi(AC) transitions in the entire range of critical temperatures (30 K less-than-or-equal-to T(c) less-than-or-equal-to 95 K). The correlation T(c) versus the orthorhombicity 2(b - a)/(b + a) is almost linear, similar to that observed in YBa2Cu3Ox. This is in contrast to the distinct behaviour of the functions T(c) versus z and T(c) versus x in these two compounds. We present a stability-decomposition map for Y2Ba4Cu7Oz over a wide range of (T,p) coordinates.