SYNTHESIS AND STRUCTURAL CHARACTERIZATION OF A NEW PEROVSKITE PHASE, BA4CACU3O8.61

A phase of composition Ba4CaCu3O8.61 has been synthesised and its structure determined using time-of-flight powder neutron diffraction. Its structure (cubic, space group Im3m, Z=2, a=8.124 Å) is been on that of an oxygen deficient perovskite, but ordering of Ca and Cu ions in the octahedral sites results in a doubling of the unit cell edge length. Oxygen vacancies are restricted to sites linking Cu ions, and the Ca coordination therefore remains strictly octahedral. The structure is closely related to the recently reported compound, Ba4YCu3O8.5+x, but subtle differences in oxygen order exist. A.C. susceptibility measurements show that Ba4CaCu3O8.61 is not superconducting above 4K. © 1990.