Effect of cobalt substitution on Li(3-2x)Co(x)N local structure: a XAS investigation.
Effect of cobalt substitution on Li(3-2x)Co(x)N local structure: a XAS investigation.
复制标题
钴取代对 Li(3-2x)Co(x)N 局部结构的影响：XAS 研究。
作者：
D. Muller;J. Pereira‐Ramos;S. Bach;P. Willmann;A. Michalowicz
使用 Co K 边 X 射线吸收光谱（EXAFS 和 XANES）研究了钴取代对层状氮化钴酸锂 Li(3-2x)Co(x)N（0.05 ≤ x ≤ 0.44）中 Co 原子周围局部结构变化的影响。 Li(3-2x)Co(x)N 化合物中的 Co-N 键长是通过 EXAFS 拟合得到的，与 x 相比，发现比 x = 0 (Li3N) 时短 (1.80 Å)，并且其值不随 x 变化。讨论了 EXAFS 数据与 XRD 结果的比较。我们表明，根据 XRD 数据描述，层间距离随 Co 含量 (x) 的不断减小，解释了 Co-N 和 Li-N 距离的平均值，并按这些键长的数量加权。此外，目前的工作支持这样的观点：Li1b-N键与x收缩是由于Li(+)/Co(2+)的逐渐取代导致局部库仑吸引力显着增加。 XRD 研究表明，二价 Co 离子与 Li(3-2x)Co(x)N 中的两个氮键合。尽管仍需要进行额外的工作来证明其化合价，但目前的 XAFS 研究结果补充了 XRD 发现的局部结构，与之前报道的电化学性质非常一致。
The influence of cobalt substitution on the local structural changes around Co atoms in the layered lithium nitridocobaltates Li(3-2x)Co(x)N for 0.05 ≤ x ≤ 0.44 is investigated using Co K-edge X-ray absorption spectroscopy (EXAFS and XANES). The Co-N bond length in Li(3-2x)Co(x)N compounds is obtained vs x by performing EXAFS fitting and found to be shorter (1.80 Å) than for x = 0 (Li3N), and its value does not change with x. A comparison of EXAFS data with XRD results is discussed. We show that the continuous decrease of interlayer distance versus Co content (x), described from XRD data, accounts for an average of the Co-N and Li-N distances, weighted by the number of these bond lengths. In addition, the present work supports the proposal that the Li1b-N bonds contract with x due to a significant increase of Coulombic attractive forces locally induced by the progressive Li(+)/Co(2+) substitution. XRD studies suggested that divalent Co ions bond to two nitrogen in Li(3-2x)Co(x)N. Although additional works are still needed to prove its valence, the present XAFS findings complements the local structure found by XRD, in good accord with the electrochemical properties previously reported.