Structural determination of Li_(1-y)Ni_(0.5)Mn_(0.5)O_2 (y=05) using a combination of rietveld analysis and the maximum entropy method

摘要

The crystal structures and electron density distributions of the layered oxide Li_(1-y)Ni_(0.5)Mn_(0.5)O_2 (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 Li_(1-y)Ni_(0.5)Mn_(0.5)O_2 (y=0.5) has the lattice parameters a=4.934A,b=2.852A,c=5.090A,beta=108.8deg and adopts the space group C2/m.The chemical formula can be expressed as [Ni_(0.0815)]_(2a){Li_(0.5)Ni_(0.0115)}_(4i)[Mn_(0.5)Ni_(0.407)square_(0.093)]_(2d)O_2.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.