Effect of ZrO2 stoichiometry on the structural and electrical properties of Na3Zr2-xSi2PO12-2x solid electrolyte

Na3Zr2Si2P2O12 (NZSP) has potential use as a solid electrolyte in Na-ion solid-state batteries due to its high ionic conductivity (10- 3-10-4 Scm- 1) at room temperature. It is established that all previous preparations involving the solid-state method for NZSP compositions contain m-ZrO2 as a secondary phase. Here, the solid-state method is used to prepare single-phase NZSP by modifying the mole fractions of the ZrO2 reactant. Reducing ZrO2 concentration may also create Zr and O vacancies and potentially increase the hopping sites for Na-ion conduction. X-ray diffraction, scanning electron microscopy, Raman and Fourier Transform Infrared spectroscopy, dilatometry and impedance spectroscopy were used to characterise the structure, morphology and electrical properties of single-phase NZSP, and the results were compared with samples that have m-ZrO2 secondary phase (Na3Zr2Si2PO12). The role of m-ZrO2 impurities on the conductivity of NZSP is investigated and compared with available literature.