Neutron scattering and stability of certain disordered magneli phases of YBa2Cu3O6+x

Two partially ordered phases A and B of the CuOx planes (those which contain the O vacancies) of YBa2Cu3O6+x are studied. They consist of a random distribution of two types of parallel strips. In phase A, for x > 1/2, one strip is given by a full Cu-O chain and the other is composed of one full and one empty chain. In phase B, for x > 1/2 the first strip is replaced by one consisting of three chains, two of them full and the other empty. For x < 1/2, full and empty chains are interchanged. While diffraction patterns of phase B are known to consist of two peaks for x > 0.556, only one broad peak is obtained in phase A at k→ = (π/α,0,0) exists. Comparing the stability of finite domains of both phases, 0-0 repulsive interactions are shown at distances of at least 2α necessary to explain the diffraction experiments. (Author)