PREPARATION OF alpha-MnO2 WITH AN OPEN TUNNEL

摘要

A single-phase alpha-MnO2 without any large stabilizing cations was successfully prepared by starting from hollandite-type (NH4)xMn8O16 and quenching from 440 C during heating in flowing Ar. The unit-cell dimension was determined by XRD analysis to be a=10.308(2) angstroms and c=2.854(1) angstroms. In comparison with that of the starting material (a=9.896(1) angstroms and c=2.859(1) angstroms), 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 C. TPD analysis indicates the presence of N other than ammonium ions in the hollandite material we prepared, and also suggests that this N might have a strong chemical interaction to the hollandite structure. 16 refs.