THERMAL-BEHAVIOR OF GAMMA MANGANESE-DIOXIDE .1. STRUCTURAL EVOLUTION

The crystallographic structure of gamma-MnO2 is an important factor of its electrochemical reactivity in primary battery cathods. In order t o characterize two industrial samples (EMD and CMD), the structural ev olution induced by static thermal treatment in air up to 450-degrees-C has been studied using FTIR spectroscopy in diffuse reflectance and E XAFS spectroscopy. Diffuse reflectance FTIR spectra, which can not be correlated to transmittance spectra, show that gamma-MnO2 samples are progressively transformed into beta-MnO2 with increasing temperature, but that increasing treatment duration at 450-degrees-C of up to 60 da ys does not allow to complete it. EXAFS spectroscopy allows to describ e quantitatively the short-range order in such poorly crystallized com pounds, and give precise informations on the breadth of the ''tunnels' ' of the structure, which plays a significant part in proton insertion .