Homogeneous nucleation in phosphate-based glassy precursors to fast-ion conducting glass-ceramic electrolytes

The structure of the phosphate materials Na_{1+x}Ge_{2-x}Al_x(PO_4)_3 with x = 0, 0.4 and 0.8 will be investigated using high real-space resolution neutron diffraction. In the crystalline phases with x = 0.4 and 0.8, fast-sodium ion conductivity occurs. These solid electrolyte materials are best prepared via the glass-ceramic route, which indicates a homogeneous nucleation mechanism. The objectives are (1) to understand the structural relationship between an ion-conducting glass ceramic and its precursor glass, and (2) to monitor the structural rearrangements that may occur during the early stages of crystallization. The latter is of general scientific interest for any glass undergoing homogeneous nucleation, and has never been explored in non-siliceous systems. The experiments will reveal the Ge coordination environment, which is inaccessible from spectroscopic methods.