Thermal stabilization of tin- and cobalt-doped manganese dioxide

We study the thermal stability, local structure, and electrical properties of the alpha-MnO2 phase doped with Sn and Co. It is found that doping prevents the transformation from alpha-MnO2 to alpha-Mn2O3 that occurred in the temperature range of 500-600 degrees C. Samples have been synthesized in an acidic medium using the reduction of potassium permanganate by fumaric acid. X-ray diffraction patterns (XRD) of pure and doped alpha-MnO2 prepared at 450 degrees C do not show new peaks related to dopant species. Thermogravimetric analysis (TGA) of the Sn and Co doped MnO2 reveals that transformation from MnO2 to alpha-Mn2O3 starts above 700 degrees C. The increase in the thermal stability is attributed to the presence of Sn or Co ions incorporated inside the large 2 x 2 tunnels as revealed by Fourier transform infrared (FTIR) spectra measurements. An increase in the electrical conductivity with the presence of Sn or Co ions is observed. Electrochemical features of the doped MnO2 samples in alkaline cells are reported and compared with that of the pristine alpha-MnO2 phase.