ABA2CU4O8 AND ABA2CU5O10 FORMED BY INTERCALATION IN ABA2CU3O7 AT 20-DEGREES-C IN AIR

The decomposition of 123-like compounds in the temperature range 20-60-degrees-C has been studied with High Resolution Electron Microscopy to determine whether ABa2Cu5O9 can be formed locally by the intercalation of Cu and O. Upon exposure to air, many planar defects are formed, a majority of which corresponds to the composition ABa2Cu4O8. Also, planar defects are observed corresponding to structures with c-axes of 1.46 to 1.56 nm; these defects are obtained by insertion of two extra layers with respect to the 123 structure. The contrast in the structure images shows that these extra layers do not contain A or Ba cations, suggesting that two extra Cu containing layers are formed, resulting in an ABa2Cu5Oz composition. The stacking of the three Cu ions is different from that in the 124 structure: the sequence of the Cu positions along the c-axis is 0,0,z; 1/2,1/2,z + partial derivative; 0,0,z + 2 partial derivative. A model is proposed based on the composition ABa2Cu5O10 with a defect layer sequence CuO2-Cu-CuO2, whereby a fraction of the Cu ions might have been replaced by C, thus forming CO3 groups. The rate of formation of the 124 and 125 defects in A1+xBa2-xCu3O7-partial derivative was found to depend on A, x and partial derivative.