Thermal behaviour of gamma manganese dioxide: I. Structural evolution

Surface characterization of heat-treated electrolytic manganese dioxide

“…6 contains a comparison of their XRD patterns. The data in the latter figure are consistent with previous studies in this area by, for example, Petit et al [11], Tedjar et al [12], and Chabre and Pannetier [9]. Essentially, as the heat treatment temperature increases from ambient to 450 • C, there is a progressive transformation of the γ -MnO 2 structure to β-MnO 2 [13], while at 500 • C there is a conversion of β-MnO 2 to Mn 2 O 3 [14].…”

“…This is reflected in the increase in x in MnO x from 1.96 for the starting EMD to 2.00 for the sample heat-treated at 450 • C. The smaller and more highly charged Mn 4+ ion would tend to draw electron density from the O-H bond in the hydroxyl group, effectively making the Mn-O bond stronger. A number of previous reports [9,11,12] dealing with the heat treatment of EMD have also shown that other defects such as cation vacancies are annealed out of the structure as the heat-treatment temperature increases. Overall, the removal of these cation vacancies would again lead to a strengthening of the Mn-O bond simply because there is a higher proportion of Mn-O bonds in the structure.…”

XANES study of electronic and structural nature of Mn-sites in manganese oxides with catalytic properties

“…[10], the higher intensity for the second Mn-Mn shell (at $3.4 Å , see vertical line in Fig. 6) in pyrolusite sample evidence the higher mean coordination number of Mn at the second cationic coordination shell.…”

“…The nsutite (gMnO 2 ) is formed by the intergrowth of domains of pyrolusite and ramsdellite. Furthermore, this oxide is present in a nonstoichiometric way with Mn 4+ vacancies, Mn 3+ replacing Mn 4+ cations and OH À species replacing O 2À anions [10]. These characteristics make this oxide interesting from the catalytic and electrochemical point of view, due to their elevated electrical conductivity.…”

Propiedades asociadas a la estructura local en sistemas nanométricos: estudio mediante el empleo de técnicas basadas en el uso de luz de sincrotrón

“…Habitualmente se simboliza como T(1,1)-T(1,2), aunque estudios de microscopia electrónica de transmisión (TEM) revelan que además existen algunos túneles mayores que 1x1 (pirolusita) y 1x2 (ramsdellita), por ejemplo, 1x3 y 3x3, como así también numerosos defectos y bordes de grano (Post, 1999). Este óxido se presenta en general en forma no estequiométrica y formado por vacancias de Mn 4+ , iones Mn 3+ , y especies OHsustituyendo aniones O 2- (Petit et al, 1993). Estas propiedades hacen que este óxido sea interesante desde el punto de vista catalítico y electroquímico por su elevada conductividad eléctrica.…”