5(h)), which has a smaller size compared to Zr, resulting in a smaller BN for the smaller cation (Li + ). Further studies have been conducted to understand the correlation between the framework skeleton and cationic conductivity in this series. In general, ionic diffusion increases with a larger BN formed by the NASICON framework skeleton. Martínez-Juárez et al. reported similar behaviors in the LiM 2 (PO 4 ) 3 system, where M = Ge, Ti, Sn, Hf, and Zr, with respective ionic radii σ Ge < σ T i < σ Sn < σ Hf < σ Zr . Consequently, the BN radius formed by the skeleton framework systematically increases with larger cationic substitutions, resulting in higher diffusivity of mobile Li + ions.