关键词: 氧化锂, 氧化锰, 晶体结构, 焙烧, X射线衍射分析, X射线光电子谱法, 层状结构

Precursors of the P2 type Na_(2/3) [M_(1-x)M_x] 0_2 (M= Cr, Mg) were prepared by solid state reaction methods and Ly[Mn_(1-x)M_x] O_2 materials were obtained by ion-exchange. XRD patterns indicate that Ly [Mn_(1-x)M_x] O_2 has the layered 02 structure with the hexagonal space group P3 ml. It is shown by XRD that the structure of the Cr- doped precursors is influenced by the dopant content. When 0≤x≤0.05, Na_ (2/3)Ly[Mn_(1-x)M_x] O_2 materials with the P2 structure were obtained. When x > 0.05, the structure was gradually changed from P2 structure to orthorhombic Na4Mn9O18. X-ray photoelectron spectra indicate that surface and bulk compositions of Ly[Mn_(1-x)M_x] O_2 are different. The oxidation states of manganese and chromium in the near-surface region are largely tetravalent and the Cr/Mn ratio in the near-surface region is higher than that in the bulk. The presence of Mn~(4+) and Cr- rich surface layers leads to an improvement in the stability of the material. In the case of the Mg-doped compounds, however, layered 02- type structure Ly[Mn_(1-x)M_x] O_2 materials can be obtained in the range ofO≤x≤0.15. The layered structure becomes more distinct as the content of Mg increases. The Mg/Mn ratio in the near-surface region is consistent with that in the bulk, indicating the formation of stoichiometric Mg-Mn mixed oxides.

Key words: LITHIUM OXIDE, MANGANESE OXIDE, CRYSTAL STRUCTURE, ROASTING, XRD, XPS, LAYER STRUCTURE