title: An investigation of the sodium patterning in Na(x)CoO(2) (0.5 < or = x < or = 1) by density functional theory methods.
abstract: Extensive experimental work has been carried out to characterize the stable Na-vacancy ordering patterns at various compositions of layered Na(x)CoO(2). However, contradictions and debates prevail in the literature, particularly at high Na concentrations x>0.5. Understanding of the exotic electronic properties in this system requires a thorough understanding of the Na-vacancy structural orderings. Using density functional theory in the generalized gradient approximation (GGA), combined with a cluster expansion structure prediction algorithm we have found an intricate set of Na-vacancy ordered ground states in Na(x)CoO(2) (0.5< or =x< or =1). We demonstrate a newly predicted ordering pattern between 0.67< or =x< or =0.71. By comparing the first principles electronic structure methods within the GGA and GGA+U (Hubbard U correction) approximations, we demonstrate that at certain Na concentration the stable ordering is affected by charge localization on the Co layer through coupling between the Na and Co lattices.
authors.affiliation: Department of Materials Science and Engineering, University of Florida, Gainesville, FL 32611, USA. ysmeng@mit.edu
authors.forename: Ying S
authors.initials: YS
authors.lastname: Meng
authors.forename: Yoyo
authors.initials: Y
authors.lastname: Hinuma
authors.forename: Gerbrand
authors.initials: G
authors.lastname: Ceder