Mouahid et al. ( ) conducted a comprehensive analysis of the structure and electrical properties of Na 1+x Ti 2-x Al x (PO 4 ) 3 materials within the range of 0.6< x <0.9, which belong to the NASICON type. This investigation employed a combination of X-ray diffraction, Rietveld analysis, and impedance spectroscopy techniques. The results of their research unveiled that the ion exchange processes were not fully completed. Specifically, they observed that sodium ions predominantly occupied the Na1 site within the NASICON structure, while Li + ions preferentially resided at the Na2 site. This behavior is schematically illustrated in Fig.