Preparation of α-MnO2 with an open tunnel

A single-phase alpha-MnO2 without any large stabilizing cations was successfully prepared by starting from hollandite-type (NH4)(x)Mn8O16 and quenching from 440 degrees C during heating in flowing Ar. The unit-cell dimension was determined by XRD analysis to be a 10.308(2) Angstrom and c = 2.854(1) Angstrom. In comparison with that of the starting material (a = 9.896(1) Angstrom and c = 2.859(1) Angstrom), the a dimension increased while the c dimension 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 Mn2O3 was observed at 540 degrees 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, (C) 1999 Academic Press.