Influence of Al3+ on glass-forming ability, structural and electrical properties of the Na3.4Sc2Si0·4P2·6O12 superionic conductor

Abstract This work reports the structural, microstructural, and electrical properties of Na3.4AlxSc2-xSi0.4P2·6O12 (0.0 ≤ x ≤ 1.7) NASICON (Na+ Super-Ionic Conductor) compounds obtained from the crystallization of a precursor glass. The addition of aluminum in the Na3.4Sc2Si0·4P2·6O12 NASICON composition improves the glass-forming ability of the precursor glass, which is evaluated by thermal analysis. Moreover, the Al3+/Sc3+ isovalent substitution allows us to change the lattice parameters of the NASICON structure, without varying the number of charge carriers (Na+ ions) per unit formula. X-ray diffractograms reveal the formation of the Na3Sc2(PO4)3 NASICON-type phase after crystallization of the parent glasses. From the structural characterization, it is also noted that the inclusion of Al3+ in the NASICON structure causes a volume contraction, which in turn, increases the activation energy and decreases the ionic conductivity. Thus, we demonstrated that the substitution of Sc3+ ions in the Na3Sc2(PO4)3 NASICON-type structure by an ion of the same valence, but with a smaller atomic radius, decreases the ionic conductivity of the material.