Order-disorder phase transitions in YBa₂Cu₃O_6+2c: The asymmetric next-nearest-neighbour interaction model revised from a first-principles point of view

Abstract

First-principles renormalized effective pair interactions up to the fifth shell in the oxygen sublattice of the Cu-O basal plane of the YBa₂Cu₃O_6+2c (0.15≤c≤0.5) system have been calculated using the embedded-cluster method in terms of the real-space scattering cluster coherent-potential approximation. The calculated weakly concentration-dependent pair interactions with distance rapidly decreasing support fairly well the asymmetric next-nearest-neighbour interaction model and are in excellent agreement with the numerical estimate by Hilton et al. In order to illustrate these pair interactions, the Monte Carlo method was used within the lattice-gas model to obtain the order-disorder (c, T) and (μ, T) phase diagrams.