Experimental evidence of the ramsdellite-rutile intergrowth model in electrolytic γ-MnO 2

Abstract

Electrolytical synthesis allowed the synthesis of γ-MnO 2 samples with grain size suitable for single-crystal electron diffraction for the first time. The diffraction patterns consist of sets of strong, sharp reflections and additional weak, broad reflections. While the former are compatible with both the γ-MnO 2 (orthorhombic cell) and ε-MnO 2 (hexagonal cell) structures, the observed extinctions and the weak spot patterns are totally consistent with a structural model proposed by P. M. De Wolff [ Acta Crystallogr., 12, 341 (1959)] and consisting of an intergrowth of pyrolusite (rutile-type) and ramsdellite domains. The position of reflections with k odd allows an estimate of the fraction of pyrolusite blocks, which can vary within a given sample.