Improved ionic conductivity of Na sub(3+x) Sc sub(x) Zr sub(2-x) Si sub(2) PO sub(12) (x = 0.2, 0.3, 0.4, 0.5) NASICON via optimized sintering conditions: Investigation of crystal structure, local atomic structure, and microstructure

Abstract

We report enhanced Na0ion conductivity of Na sub(3+x) Sc sub(x) Zr sub(2-x) Si sub(2) PO sub(12) (x = 0.2-0.5), prepared through solid-state reaction method with optimized sintering temperature of 1220 degrees C for 15 h. Among four compositions, Na sub(3.4) Sc sub(0.4) Zr sub(1.6) Si sub(2) PO sub(12) offers highest total ionic conductivity of 2.6 mS/cm at 25 degrees C which is much higher than that of parent material. The Rietveld analysis of XRD data reveals a phase mixture of monoclinic and rhombohedral NASICON phases. NMR results indicate local disordering and a fast exchange of Na-ions between the different Na-sites. SEM observation reveals microcrack-free grain boundaries. An understanding of the underlying causes of higher conductivity has been achieved.