Mean-field and Monte Carlo calculations of the three-dimensional structure factor forYBa2Cu3

Anomalously Large Oxygen-Ordering Contribution to the Thermal Expansion of UntwinnedYBa2Cu3O6.95Nagel1, Pasler2, Meingast3 et al. 2000Phys. Rev. Lett.474430View full textAdd to dashboardCite

“…) [21][22][23]. We note that we do not observe the thermodynamic phase-separation line (ortho-I l ortho-I + ortho-II) predicted by this model [22] in our experimental temperature window (280 K < T < 500 K).…”

“…[14], as well as with the formation of O-clusters [16]. Theoretically, O-ordering has been modeled using the asymmetric-next-nearest-neighborinteraction (ASYNNNI) model, in which several phenomenological parameters (V1 > V2 > V3 > ...) are introduced to describe the O-interactions in the basal plane ) [21][22][23]. We note that we do not observe the thermodynamic phase-separation line (ortho-I l ortho-I + ortho-II) predicted by this model [22] in our experimental temperature window (280 K < T < 500 K).…”

Simple solution to problems concerning oxygen ordering inYBa2Cu3OMønster1, Lindgård2, Andersen3 1999Phys. Rev. B9170View full textAdd to dashboardCite

“…Then the structure factor S(q), the specific heat, correlation length 1/, the concentration c l , of the l fold oxygen coordinated Cu (l ) atoms, and the order parameter were determined by averaging typically a set of ten states, each separated by ten MCS. This scheme was found optimal for studying ordered phases, and is different from previously used strategies, 22,23 where a single ensemble was averaged over a long time series. In particular, the present method allows a study of the average domain structure that the system assumes.…”

“…For a proper comparison we must include the 3D coupling, the effect of which on the phase diagram can be accounted for by reducing ͉V 1 ͉ by 17%, judged from the simulated 2D and 3D T I-II * at xϭ0.5. 23 On the other hand, the effect on the ordering, and hence on c l , in adjacent planes should be negligible. Accordingly, when including V 4 the arrows on The success of the present simple fixed parameter model indicates that the inherent disorder in the oxygen structure, which is always observed in YBa 2 Cu 3 O 6ϩx , may not be driven by the electron transfer between the CuO x and CuO 2 planes.…”

“…Computer modeling is needed in order to give the corresponding real-space picture. Previous model studies [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] are unable to account for a number of pertinent details recently observed in scattering experiments. Here we demonstrate that this can be achieved by Monte Carlo simulations using a simple extension of the ASYNNNI model, 14 with a fixed and limited set of interaction parameters V n .…”