Glass-to-Crystal Transition in Li1+xAlxGe2–x(PO4)3: Structural Aspects Studied by Solid State NMR

Abstract

The structural aspects of the glass-to-crystal transition in the technologically important ion conducting glass ceramic system Li1+xAlxGe2–x(PO4)3 (0 ≤ x ≤ 0.75) have been examined by complementary multinuclear solid state nuclear magnetic single and double-resonance experiments. In the crystalline state, the materials form solid solutions in the NASICON structure, with additional nanocrystalline AlPO4 present at x values ≥0.5. Substitution of Al in the octahedral Ge sites results in a binomial distribution of multiple phosphate species, which differ in the number P–O–Al and P–O–Ge linkages and can be differentiated by 31P chemical shift and 31P{27Al} rotational echo adiabatic passage double resonance (REAPDOR) spectroscopies. The detailed quantitative analysis of these data, of complementary 27Al{31P} rotational echo double resonance (REDOR) and of homonuclear 31P–31P double quantum NMR studies suggest that the AlO6 coordination polyhedra are noticeably expanded compared to the GeO6 sites in the NASICON-...