A different type of oxygen order in RE Ba2Cu3O(6+x)HTc superconductors with different RE ionic radii

Using the copper Nuclear Quadrupole Resonance (NQR) spectra of RE Ba2Cu3O6+x (RE123, RE = Y, Nd, La, 0 less than or equal to x less than or equal to 1) we have determined the relative intensities of the resonance lines belonging to the Cull) sites in the Y123 structure type with two, three and four nearest neighbor oxygens as a function of the oxygen concentration x. The different intensity distribution for different RE shows that, unlike the case in Y123, where the oxygen ions in the basal plane order preferentially into long chain fragments leading to the formation of the ortho-II structure at 0.5 < x < 0.6, the ordering in Nd123 can be described by the model where the chain fragments are formed by random occupation of the oxygen sites along the fragment direction. In La123 oxygen ions below x = 0.5 and oxygen vacancies above this value tend to be single, forming near x = 0.5, most probably, the ''herringbone'' structure, Due to different oxygen order, the Nd123 and La123 become superconducting only at high oxygen contents, x greater than or equal to 0.6, whereas at lower x the systems show the antiferromagnetic order in the Cu(2) planes, detected by the zero field nuclear magnetic resonance spectra of the Cu(2) sites and by muon spin rotation experiments.