Splitting Process of Na-Birnessite Nanosheet via Transmission Electron Microscopy

The intermediate phase of hydrothermal synthesis of the Na_0.44MnO₂ (NMO) nanowires is systematically investigated by means of transmission electron microscopy (TEM). The coexistence of Na-birnessite and NMO is commonly observed in the nanosheets. The NMO nanobelts in general have the width of ～15 nm embedded in the (001) oriented Na-birnessite nanosheet. It is also found that the nanosheets of this intermediate phase often split along the NMO and Na-birnessite interface. Our structural study also shows that the NMO nanobelts prefer to grow along the 001 direction and gives rise to the 001 elongated NMO nanowires. Based on our TEM observations, the visible lattice mismatch and the resultant strain at the NMO/Na-birnessite interface play a critical role for formation of notable splitting structures in this kind of nanomaterial. The mechanism for the formation of the 001 NMO nanobelt is briefly discussed.