Figure 2

Schematic of amorphous FePO₄ synthesis and electron microscopy studies. (a) The preparation procedure consists of the following steps. The Fe(II) precursor is dissolved in water, and the complete hydrolysis of the Fe(III) salt is prevented by the addition of alcohol to facilitate alkoxidation, as observed by the change in the solution color from bright transparent red to dark red. Introducing phosphoric acid at room temperature to the solution under stirring promotes the precipitation of hydrated phosphates. Finally, the sample is vacuum-annealed under mild temperatures (250 °C) to obtain dehydrated amorphous phases of FePO₄. The procedure can be adopted for the general synthesis of metal oxides or phosphates to develop amorphous hosts for energy-storage applications. (b) TEM images of amorphous FePO₄. (c) High-resolution TEM (HRTEM) image shows distinct pore-like features, and the inset shows the corresponding SAED pattern obtained using the electron diffraction technique, which confirms the amorphous nature of the prepared FePO₄.