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Zur Struktur des γ‐MnO 2
Author(s) -
Giovanoli R.,
Maurer R.,
Feitknecht W.
Publication year - 1967
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19670500413
Subject(s) - pyrolusite , chemistry , crystallite , crystallography , diffraction , lattice (music) , electron diffraction , condensed matter physics , mineralogy , manganese , optics , physics , organic chemistry , acoustics
By treating Mn 3 O 4 of a specific surface of about 30 m 2 /g with hot diluted nitric acid, a relatively well crystallised γ‐MnO 2 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 B YSTRÖM 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‐MnO 2 (G LEMSER [2]); the whole group of varieties, hitherto distinguished by Glemser as «η‐ and γ‐MnO 2 », have the same lattice and differ only by crystallite size and concentration of microdomains.