Multiple Orientation Relationships Among Nanocrystals of Manganese Oxides

In a series of experiments[1,2] aimed at preparing anisotropic nanoparticles of transition metal oxides, we have produced nanorods of manganite (γ-MnOOH, monoclinic, space group P21/a, with a = 0.5304 nm, b = 0.5277 nm, c = 0.5304 nm, and β = 114 38 ) that nucleate and grow on octahedral hausmannite (Mn3O4, space group I41/amd, and a = 0.5762 nm, c = 0.9470 nm) crystals, as well as octahedral hausmannite crystals that nucleate and grow on manganite nanorods. We show that, even though it is possible to induce the nucleation of one onto the other, there seems to be no consistently observed crystallographic relationship between them. Hausmannite and manganite are both naturally occurring minerals, and they also may occur within the cathode materials of Li ion manganese oxide batteries, where the irreversible formation of these two phases is believed to contribute to the decrease in performance.