Sodium Trimer Ordering on NaxCoO2 Surface
Woei Wu Pai, S. H. Huang, Ying S. Meng, Y. C. Chao, C. H. Lin, H. L., Liu, F. C. Chou
TL;DR
This study reveals that sodium trimers are fundamental building blocks in the long-range ordering on NaxCoO2 surfaces, with their stability supported by both experimental STM imaging and ab initio calculations.
Contribution
It is the first to identify sodium trimers as key structural units in surface ordering on NaxCoO2, combining experimental and theoretical approaches.
Findings
Na trimers act as basic building blocks for surface order
Three main surface phases with distinct Na concentrations identified
Na trimer stability linked to increased Na-O coordination
Abstract
Sodium ion ordering on in situ cleaved NaxCoO2 (x=0.84) surface has been studied by ultra high vacuum scanning tunneling microscopy (UHV-STM) at room temperature. Three main phases, with p(3x3), (root 7 x root 7), and (2 root 3 x 2 root 3) hexagonal unit cells and surface Na concentration of 1/3, 3/7, 1/2, respectively, were identified. One surprising finding is that Na trimers act as the basic building blocks that order in long range. The stability of Na trimers is attributed to the increased Na coordination with oxygen as indicated by ab initio calculations, and possibly at finite temperature by configuration entropy.
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