Stability of 2{radical} (2) {times}2{radical} (2) oxygen ordered superstructures in YBa{sub 2}Cu{sub 3}O{sub 6+x}
- International Centre for Theoretical Physics, Strada Costiera 11, P.O. Box 586, 34100 Trieste (Italy)
- Facultad de Ciencias Exactas, Ingenieria y Agrimensura e Instituto de Fisica de Rosario, Universidad Nacional de Rosario, Boulevard 27 de febrero 210 bis, 2000 Rosario (Argentina)
We have compared the ground-state energy of several observed or proposed {open_quotes}2{radical} (2) {times}2{radical} (2) oxygen ordered superstructures{close_quotes} [{open_quotes}herringbone{close_quotes} structures (HS{close_quote}s)], with those of {open_quotes}chain superstructures{close_quotes} (CS{close_quote}s) (in which the O atoms of the basal plane are ordered in chains), for different compositions x in YBa{sub 2}Cu{sub 3}O{sub 6+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{close_quote}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. {copyright} {ital 1998} {ital The American Physical Society}
- OSTI ID:
- 565925
- Journal Information:
- Physical Review, B: Condensed Matter, Journal Name: Physical Review, B: Condensed Matter Journal Issue: 2 Vol. 57; ISSN PRBMDO; ISSN 0163-1829
- Country of Publication:
- United States
- Language:
- English
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