EXAFS Studies of Synthetic γ-MnO2 and Related Pyrolusite and Ramsdellite Minerals

Various structural aspects of two well-known varieties of MnO2: the pyrolusite (and its synthetic equivalent β-MnO2) and the ramsdellite are re-examined by studying the long-range order from previous X-ray diffraction results and the short-range order using EXAFS. From both, it is concluded that, in EXAFS fitting procedure, local Mn neighbors must include two Mn shells and two oxygen shells. These studies are extended to a third variety, the γ-MnO2, whose structure is supposed to be based on intergrowth domains of the two previous varieties. The two types CMD and EMD of γ-MnO2 used in commercial batteries are investigated. EXAFS is shown to be a powerful technique to define exactly structural aspects on those poorly crystallized materials.