Random-Field Structural Transition in YBa2Cu3

Abstract

Synchrotron x-ray diffraction measurements on a high purity single crystal reveal that the absence of long-range ortho-II order in YBa&Cu306+, is most likely due to random-field effects. The ortho-II superstructure peaks show three qualitative features consistent with random-field behavior: First, instead of the development of a sharp Bragg peak at the transition Tot& = 125(5) 'C (for x = 0.5), the initial diffuse anisotropic Lorentzian (critical scattering) above Tp~, transforms to a Lorentzian-squared form below Tp». Second, the equilibration time increases dramatically at the onset of ordering. And third, the domain growth is logarithmic in time below Tp».

Mean-field and Monte Carlo calculations of the three-dimensional structure factor forYBa2Cu3Fiig1, Andersen2, Lindgård3 et al. 1996Phys. Rev. BSelf Cite8071View full textAdd to dashboardCite

“…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.…”

“…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. 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.…”

“…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.…”

“…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.…”

A survey of the Van Hove scenario for high-tc superconductivity with special emphasis on pseudogaps and striped phases

“…At exactly δ = 0.5, the Ortho II phase transition occurs at 398K, Fig. 62; however, domain growth is logarithmically slow, due to random field effects [701].…”