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The crystal structures and electron density distributions of the layered oxide Li1−yNi0. 5Mn0. 5O2 (y = 0. 5) were studied using a combination of Rietveld analysis of high-resolution synchrotron powder X-ray diffraction data and the maximum entropy method (MEM). Structural analysis revealed that Li1−yNi0. 5Mn0. 5O2 (y = 0. 5) has the lattice parameters a = 4. 934 Å, b = 2. 852 Å, c = 5. 090 Å, β = 108. 8° and adopts the space group C2/m. The chemical formula can be expressed as Ni0. 08152aLi0. 5Ni0. 01154iMn0. 5Ni0. 407□0. 0932dO2. The electron density map obtained using MEM clearly shows that most of the Li ions migrate from the octahedral 2a site to the tetrahedral 4i site during Li de-intercalation.
Kobayashi et al. (2003) studied this question.