Zur Struktur des γ‐MnO2

Abstract

AbstractBy treating Mn3O4 of a specific surface of about 30 m2/g with hot diluted nitric acid, a relatively well crystallised γ‐MnO2 has been obtained. It consists of flat needles of approximately 40,000 × 2000 × 500 Å. Selected area electron diffraction patterns from such single crystals give the (b c) zone of Ramsdellite with c as needle axis. The reflections are broadened in the b‐direction, which is consistent with the shift and broadening of the X‐ray reflections of similar type. The X‐ray Guinier pattern is consistent with the postulated intergrowth structure, proposed by BYSTRÖM and later by de Wolff. Hence the present product consists of a Ramsdellite matrix with statistically distributed Pyrolusite microdomains. The domains are supposed to have the size of one cell only in the b‐direction and of a few cells in the a‐direction, and to be present in relatively small concentrations. From the absence of satellites in the electron diffraction pattern it follows that the domains are disordered and do not form a super‐lattice with giant periods as might be supposed. There is no need to distinguish between η‐ and γ‐MnO2 (GLEMSER [2]); the whole group of varieties, hitherto distinguished by Glemser as «η‐ and γ‐MnO2», have the same lattice and differ only by crystallite size and concentration of microdomains.