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 Ba 2 Cu 3 O 6+ x (RE123, REY, Nd, La, 0 ≤ x ≤ 1) we have determined the relative intensities of the resonance lines belonging to the Cu(1) 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 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 ≥ 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.