Institute of General and Inorganic Chemistry, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria.
Inorg Chem. 2010 Feb 15;49(4):1932-41. doi: 10.1021/ic902351u.
High-frequency electron paramagnetic resonance (HF-EPR) spectroscopy was employed to examine the oxidation state and local structure of Ni and Mn ions in Ni,Mn-codoped LiCoO(2). The assignment of EPR signals was based on Mg,Mn-codoped LiCoO(2) and Ni-doped LiCoO(2) used as Mn(4+) and low-spin Ni(3+) EPR references. Complementary information on the oxidation state of transition-metal ions was obtained by solid-state (6,7)Li NMR spectroscopy. For slightly doped oxides (LiCo(1-x)Ni(x)Mn(x)O(2) with x < 0.05), nickel and manganese substitute for cobalt in the CoO(2) layers and are stabilized as Ni(3+) and Mn(4+) ions. The local structure of Mn(4+) ions was determined by modeling of the axial zero-field-splitting parameter in the framework of the Newman superposition model. It has been found that the local trigonal distortion around Mn(4+) is smaller in comparison with that of the host site. To achieve a local compensation of Mn(4+) charge, several defect models are discussed. With an increase in the total dopant content (LiCo(1-x)Ni(x)Mn(x)O(2) and 0.05 <or= x <or= 0.10), a saturation in the Ni(3+) amount (up to x < 0.05) is attained, while the Mn(4+) content increases gradually. Ni(3+) ions are surrounded by Co(3+) ions only in the whole concentration range (0 < x <or= 0.10). The first metal coordination sphere of Mn(4+) ions undergoes a transformation with an increase in the total Ni and Mn contents due to a progressive replacement of Co(3+) by Mn(4+) and Ni(2+) ions. For highly doped oxides (LiCo(1-x)Ni(x)Mn(x)O(2) with x = 0.10), nickel and manganese achieve, with respect to the local charge compensation, their usual oxidation states of 2+ and 4+.
采用高频电子顺磁共振（HF-EPR）光谱研究了 Ni，Mn 共掺杂 LiCoO（2）中 Ni 和 Mn 离子的氧化态和局域结构。EPR 信号的归属基于 Mg，Mn 共掺杂 LiCoO（2）和 Ni 掺杂 LiCoO（2）作为 Mn（4+）和低自旋 Ni（3+）EPR 参比。通过固态（6，7）Li NMR 光谱获得了有关过渡金属离子氧化态的补充信息。对于轻度掺杂的氧化物（LiCo（1-x）Ni（x）Mn（x）O（2），其中 x <0.05），镍和锰替代 CoO（2）层中的钴，并稳定为 Ni（3+）和 Mn（4+）离子。Mn（4+）离子的局域结构通过纽曼叠加模型框架下轴向零场分裂参数的建模来确定。发现与主体位相比，Mn（4+）周围的局部三角畸变较小。为了实现 Mn（4+）电荷的局部补偿，讨论了几种缺陷模型。随着总掺杂量的增加（LiCo（1-x）Ni（x）Mn（x）O（2）和 0.05 <or= x <or= 0.10），Ni（3+）量达到饱和（x <0.05），而 Mn（4+）含量逐渐增加。在整个浓度范围内（0 < x <or= 0.10），Ni（3+）离子仅被 Co（3+）离子包围。由于 Co（3+）被 Mn（4+）和 Ni（2+）离子逐渐取代，Mn（4+）离子的第一金属配位球随着总 Ni 和 Mn 含量的增加而发生转变。对于高掺杂的氧化物（LiCo（1-x）Ni（x）Mn（x）O（2），其中 x = 0.10），镍和锰在局部电荷补偿方面达到其通常的氧化态 2+和 4+。
