investigated Na 3 PS 4 using ab initio MD simulations and discovered that Na + ions primarily migrate through interstitial Na1 (6b) and Na2 (12d) sites, with a preference for the Na1 sites. Aliovalent substitution, such as Na 3+x M x P 1-x S 4 with M = Si, Ge, and Sn, significantly enhances sodium ion conductivity at RT. The excess Na + ions introduced by substitution create a shallow energy landscape, promoting cooperative Na + ion motion and ultimately resulting in high conductivity.