Simple solution to problems concerning oxygen ordering in YBa2Cu3O6+x

Analysis of a simple extension of the ASYNNNI model rationalizes several hi therto unexplained structural observations of the oxygen ordering in YBa2Cu 3O6+x: the existence of ortho-m, ortho-V, and ortho-Vm phase correlations; suppression of the ortho-I-ortho-II transition temperature relative to that of the tetragonal-ortho-I transition; no ortho-II Bragg peaks, but a cross over from Lorentzian towards Lorentzian squared line shapes; the average ch ain length. It yields a realistic picture of the oxygen order of importance for the understanding of the hole doping. [S0163-1829 (99)02326-7].