It was recalled that electrochemically active -MnO2 contained physical and chemical crystal defects which were related to the structural water content and which played an important role in the mechanisms of proton insertion and migration during charge/discharge cycles. The loss of structural water from 2 industrial-grade samples, during static and dynamic thermal treatments in an oxidizing atmosphere, was studied by using several experimental methods. A correlation of FTIR spectra with photoluminescence spectra made it possible to associate hydroxyl groups with point defects such as Mn4+ vacancies. The residual presence of OH groups and Mn4+ vacancies at 400C revealed that the present material was not stoichiometric at this temperature. This was confirmed by chemical measurements of the degree of oxidation of annealed samples, by thermogravimetric analyses and by analyses of the gas which was evolved during heat treatment. Such results partially contradicted the Ruetschi formula, for -MnO2, and its overall water loss process.

F.Petit, M.Lenglet, J.Arsène: Materials Research Bulletin, 1993, 28[5], 1093-100