Atomistic simulation of the surface structure of electrolytic manganese dioxide

Atomistic simulation methods were used to investigate the surface structures and stability of pyrolusite and ramsdellite polymorphs of electrolytic manganese dioxide (EMD). The interactions between the atoms were described using the Born model of Solids. This model was used to calculate the structures and energies of the low index surfaces {0 0 1}, {0 1 0}, {0 1 1}, {1 0 0}, {1 0 1} and {1 1 0} for both pyrolusite and ramsdellite. Pyrolusite is isostructural with rutile and similar to rutile the {1 1 0} surface is found to be the most stable with the relaxed surface energy 2.07 J m−2. In contrast, for ramsdellite the {1 0 1} surface is the most stable with a surface energy of 1.52 J m−2. Pyrolusite {1 0 0} and ramsdellite {1 0 0}b surfaces have equivalent energies of 2.43 J m−2 and 2.45 J m−2, respectively and similar surface areas and hence are the likely source for the intergrowths. Finally, comparison of the energies of reduction suggests that the more stable surfaces of pyrolusite are more easily reduced.