Stability of 2 root 2x2 root 2 oxygen ordered superstructures in YBa2Cu3O6+x

Article

关键词: ELECTRONIC-STRUCTURE;    COULOMB REPULSION;    ATOMIC-STRUCTURE;    MADELUNG ENERGY;    PERSISTENT PHOTOCONDUCTIVITY;    OXIDE SUPERCONDUCTORS;    CRITICAL-TEMPERATURE;    HOLE CONCENTRATION;    PHASE-SEPARATION;    DEVILS STAIRCASE;   

DOI  :  10.1103/PhysRevB.57.1241

来源: SCIE

【 摘 要 】

We have compared the ground-state energy of several observed or proposed 2 root 2 x 2 root 2 oxygen ordered superstructures [herringbone structures (HS's)], with those of chain superstructures (CS's) (in which the O atoms of the basal plane are ordered in chains), for different compositions x in YBa2Cu3O6 divided by x. The model Hamiltonian contains (i) the Madelung energy, (ii) a term linear in the difference between Cu and O hole occupancies which controls charge transfer, and (iii) covalency effects based on known results for t-J models in one and two dimensions. The optimum distribution of charge is determined, minimizing the total energy, and depends on two parameters which are determined from known results for x=1 and x=0.5. We obtain that on the O lean side, only CS's are stable, while for x=7/8, a HS with regularly spaced O vacancies added to the x=1 structure is more stable than the corresponding CS for the same x. We find that the detailed positions of the atoms in the structure and long-range Coulomb interactions are crucial for the electronic structure, the mechanism of charge transfer, the stability of the different phases, and the possibility of phase separation.

【 授权许可】

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