AMBIENT PRESSURE SYNTHESIS AND NEUTRON STRUCTURE-ANALYSIS OF YBA2CU4O8

The high-T(c) superconductor YBa2Cu4O8 has been synthesized by the solid state reaction of Y2O3 with a precursor matrix under ambient oxygen pressure. The final product is single phase 124 which shows zero resistance at 78.5 K (DELTA-T(c) = 2.0 K). DC magnetic susceptibility studies confirm the presence of a single bulk superconducting phase (T(c) congruent-to 82.5 K) and absence of 123 or 247 phases as impurities. Neutron profile refinement studies of the structure of the sample indicate vacancies at 9% of the linear chain oxygen sites, O(1); increased puckering of Cu(1)-O(1) layers, and a much reduced short-contact distance between neighbouring O(1)-anions. Other notable features of the structure are vacancies (14%) at Ba-sites and unusually short bridging bond-length Cu(1)-O(4) and Cu(2)-O(4).