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The crystal structure of ramsdellite, MnO 2 , was refined using time-of-flight powder neutron diffraction data and the Rietveld method in order to assess the effects of reduction in cathodic battery materials. For the first time, we present a refined structure for “groutellite,” a heretofore poorly characterized phase with ideal formula (Mn 4+  0.5 Mn 3+  0.5 )O 1.5 (OH) 0.5 . “Groutellite” is generated synthetically as an intermediate compound during the reduction of ramsdellite to groutite (MnOOH), and it also occurs as an intergrowth in certain natural specimens of ramsdellite. The Jahn-Teller distortions in “groutellite” are confined to the a-c plane, and they result in a 6.8% unit-cell volume increase relative to ramsdellite. The Mn-O bond lengths refined for “groutellite” are consistent with the replacement of half of the Mn 4+  and O 2-  in ramsdellite by Mn 3+  and (OH) - , respectively. In addition, the hightemperature behaviors of ramsdellite and “groutellite” were investigated by temperature-resolved synchrotron powder X-ray diffraction from 298 to 720 K. Rietveld refinements revealed a gradual thermal expansion of the groutellite structure to ∼450 K. At higher temperatures, the unit-cell volume gradually decreased, primarily as a result of a decrease in c.

Neutron and synchrotron X-ray diffraction study of the structures and dehydration behaviors of ramsdellite and “groutellite”