A trial for distinguish of Mn³⁺ and Mn⁴⁺ ions in LiMn₂O₄ by anomalous powder x-ray diffraction with focused beam flat sample method

X-ray diffraction with anomalous scattering (anomalous diffraction) is an effective method to distinguish the positions of atoms which have similar number of electrons in crystal structure. We have been developing a method for anomalous powder X-ray diffraction with synchrotron X-ray by the combination of focused beam, flat sample and area detector and succeeded in the determination of the distribution of cations with neighboring atomic numbers. This method can be applied to analysis of the position of ions with different valence of an atom in crystal structure, therefore we have tried anomalous powder X-ray diffraction experiments of materials that include different valence ions of an atom. LiMn₂O₄ was an example of such material. In the crystal structure, a normal spinel, the Mn atoms in octahedral site takes mixed valence state of Mn³⁺ and Mn⁴⁺. This material has a phase transition near room temperature and below the phase transition temperature a structure with partial ordering of Mn³⁺ and Mn⁴⁺ has been proposed. In order to examine anomalous scattering effect of Mn³⁺ and Mn⁴⁺, diffraction experiments using X-rays near Mn K edge were conducted. The result of diffraction experiments shows that the diffraction peak intensity change depend on the incident X-ray energy in different manner peak by peak. Powder diffraction data that include anomalous scattering effect can be successfully obtained from material with mixed valence state of Mn³⁺ and Mn⁴⁺.