Meng Ying S, Hinuma Yoyo, Ceder Gerbrand
Department of Materials Science and Engineering, University of Florida, Gainesville, FL 32611, USA.
J Chem Phys. 2008 Mar 14;128(10):104708. doi: 10.1063/1.2839292.
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.
为了表征层状Na(x)CoO(2)不同组成下稳定的钠空位有序模式，已经开展了大量实验工作。然而，文献中仍存在矛盾和争议，特别是在高钠浓度x>0.5时。要理解该体系中奇异的电子性质，需要深入了解钠空位的结构有序性。使用广义梯度近似（GGA）下的密度泛函理论，并结合团簇展开结构预测算法，我们在Na(x)CoO(2)（0.5≤x≤1）中发现了一组复杂的钠空位有序基态。我们展示了一种新预测的0.67≤x≤0.71之间的有序模式。通过比较GGA和GGA+U（哈伯德U校正）近似下的第一性原理电子结构方法，我们证明在特定钠浓度下，稳定的有序性会通过钠和钴晶格之间的耦合受到钴层上电荷局域化的影响。
