Preparation of alpha-MnO2 with an open tunnel

A single-phase alpha-MnO2 without any large stabilizing cations was success fully prepared by starting from hollandite-type (NH4)(x)Mn8O16 and quenchin g 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) An gstrom and c = 2.859(1) Angstrom), the a dimension increased while the c di mension changed little. No presence of ammonium ions in the structure of th is specimen was shown by IR spectroscopy, the Kjeldahl analysis, or tempera ture-programmed-desorption (TPD) measurement. The structural change from th e hollandite phase to Mn2O3 was observed at 540 degrees C. TPD analysis ind icates the presence of nitrogen other than ammonium ions in the hollandite material we prepared, and also suggests that this nitrogen might have a str ong chemical interaction to the hollandite structure, (C) 1999 Academic Pre ss.