STRUCTURAL DEFECTS IN YBA2CU2COO6+X AND YBACUCOO5

YBa2Cu2CoO6+x and YBaCuCoO5 were prepared at 900-degrees-C. Tetragonal unit cells determined by electron and x-ray diffraction: YBa2Cu2CoO6+x prepared in air, a = 3.88, c = 11.66 angstrom and YBaCuCoO5, a = 3.87, c = 7.56 angstrom. A variation in c of 11.61 to 11.73 angstrom was caused by the oxygen non-stoichiometry in YBa2Cu2CoO6+x. The unit cell size of YBaCuCoO5 was constant, indicating a stoichiometric phase. Imaging and electron diffraction reveal that the triple-layer perovskite YBa2Cu2CoO6+x contains double-layer defects, while the double-layer structure of YBaCuCoO5 exhibits triple-layer defects. X-ray microanalysis indicated defects with a decreased Ba/Y ratio in YBa2Cu2CoO6+x and an increased Ba/Y ratio in YBaCuCoO5. The Co/Y ratios remained fairly constant in both compounds, when defect and well-ordered areas were compared.