3-D vacancy ordered superstructures in “homogeneous” YBa2Cu3O7-δ

Mean-field and Monte Carlo calculations of the three-dimensional structure factor forYBa2Cu3Fiig1, Andersen2, Lindgård3 et al. 1996Phys. Rev. B8071View full textAdd to dashboardCite

“…Thus, good agreement has been obtained for the experimental phase boundary and that found by Monte Carlo simulations and for the anisotropy of the in-plane peak widths of the structure factors. 23 However, it is evident from the experiments [7][8][9]14 that there is a significant correlation between the oxygen ordering in adjacent CuO x planes. Hence there is a need for a three-dimensional model.…”

“…It is of particular interest to investigate the influence of a change in the oxygen stoichiometry around xϭ0.5 on both the short-range order and the line shape of the diffuse scattering. In this region the doublecell ortho-II structure is observed [7][8][9][10][11][12][13][14] and there is evidence for a relation between the superconducting properties and the short-range oxygen order. 4,15 This is the reason why the oxygen ordering phenomena in YBa 2 Cu 3 O 6ϩx have been studied intensively by neutron and x-ray diffraction 7,8,[16][17][18][19][20]9 as well as other techniques.…”

“…Consider first the subsystem consisting of sublattices 1,2,3,4 ͑ortho-I symmetry͒. The average susceptibility for this subsystem, 14 ( ,q), can be calculated using Eq. ͑4͒ where the 4ϫ4 matrix A(q), Eq.…”

“…20,21 Computer simulations 5,[22][23][24][25][26] using the 2D ASYNNNI model have contributed to an understanding of an important part of the behavior in a certain range of temperatures T and oxygen stoichiometry x. However, it has become clear that the ASYNNNI model is an idealized model, capable neither of describing thermodynamic properties like the chemical potential of oxygen faithfully in a large temperature interval 23,26,8 nor of structural properties at low temperatures, 11,12,14 or low oxygen stoichiometry, 11,14,27 where additional long-range interactions including elastic forces seem to be needed to describe the observed partially ordered superstructures. [28][29][30][31] Therefore, it is important to limit the use of the model to the region where it is valid.…”

Critical chain length and superconductivity emergence in oxygen-equalized pairs ofYBa2Cu3O<

“…Its structural order drives the whole crystal structure in a variety of superstructures which have been observed [1][2][3][4][5][6][7][8] and modeled theoretically [9][10][11][12][13] in the whole compositional x-range. Beside the tetragonal (T, empty chain) and orthorhombic-I (OI, full chain) structures that characterize the end members of the compositional x-range (x=0 and 1 respectively), at least two orthorhombic modifications, ortho-II (OII) and ortho-III (OIII), occurring around the ideal x=0.5 and x=0.67 compositions and characterized by a ...-full-empty-.. and a ...-full-full-empty-... chain sequence along the a direction, are considered thermodynamically stable 8,9 .…”