Our work on “Divalent-doped Na3Zr2Si2PO12 Natrium Superionic Conductor: Improving the ionic conductivity via simultaneously optimizing the phase and chemistry of the primary and secondary phases” has just been published in the Journal of Power Sources. In this work co-first-authored by Mojitaba Samiee (Luo group) and Balachandran Radhakrishnan (Ong group), we show that divalent dopants with low solubility in NASICON lead to the formation of a conducting secondary phase, thereby improving the grain boundary conductivity compared to undoped NASICON. Concurrently, the introduction of divalent dopants is accompanied by a change in the Si/ P ratio in the primary NASICON bulk phase, transforming monoclinic NASICON to rhombohedral NASICON. NASICON chemistries with significantly improved and optimized total ionic conductivity of 2.7 mS/cm have been synthesized. This work suggests a new general direction to improve the ionic conductivity of solid electrolytes via simultaneously optimizing the primary bulk phase and the microstructure (including grain boundary segregation and secondary phases).