Structure of crystalline and amorphous materials in the NASICON system Na_1+<i>x</i>Al_<i>x</i>Ge_2?<i>x</i>(PO₄)₃

The structure of crystalline and amorphous materials in the sodium (Na) super-ionic conductor system Na1+xAlxGe2?x(PO4)3 with x = 0, 0.4, 0.8 was investigated by combining (i) neutron x-ray powder diffraction pair-distribution function analysis (ii) 27Al 31P magic angle spinning (MAS) 31P/23Na double-resonance nuclear magnetic resonance (NMR) spectroscopy. A Rietveld patterns shows that 0 0.4 compositions crystallize into space group-type R3?, whereas composition crystallizes R3?c. For as-prepared glass, functions MAS NMR spectra show formation sub-octahedral Ge Al centered units, which leads to creation non-bridging oxygen (NBO) atoms. influence these atoms on ion mobility is discussed. When glass relaxed thermal annealing, there an increase coordination numbers a decrease fraction NBO model proposed for super-structural units containing octahedral Ge(6) tetrahedral P(3) motifs are embedded matrix Ge(4) where superscripts denote number bridging can grow size reaction used convert units. resultant P(4) thereby provide nucleation sites crystal growth via homogeneous mechanism.