Preparation ofALPHA-MnO2with an Open Tunnel

A single-phaseALPHA-MnO2without any large stabilizing cations was successfully prepared by starting from hollandite-type (NH4)xMn8O16and quenching from 440°C during heating in flowing Ar. The unit-cell dimension was determined by XRD analysis to bea=10.308(2) ? andc=2.854(1) ?. In comparison with that of the starting material (a=9.896(1) ? andc= 2.859 (1) ?), theadimension increased while thecdimension changed little. No presence of ammonium ions in the structure of this specimen was shown by IR spectroscopy, the Kjeldahl analysis, or temperature-programmed-desorption (TPD) measurement. The structural change from the hollandite phase to Mn2O3was observed at 540°C. TPD analysis indicates the presence of nitrogen other than ammonium ions in the hollandite material we prepared, and also suggests that this nitrogen might have a strong chemical interaction to the hollandite structure.