Preparation and characterization of sodium binary system (NaI-Na3PO4) inorganic solid electrolyte

New binary inorganic salt such as sodium iodide (NaI)-sodium phosphate (Na3PO4) has a great potential to be used as a solid electrolyte, and this solid electrolyte system exhibits high ionic conductivity up to 10(-4) S cm(-1). The solid electrolyte compounds were prepared by mechanical milling followed by pelletizing and sintering at low temperature. The electrical conductivity study was carried out as a function of NaI concentration by impedance spectroscopy technique and the maximum conductivity of (1.02 +/- 0.19) x 10(-4) S cm(-1) at room temperature was obtained for the composition 0.50 NaI:0.50 Na3PO4. The increase in conductivity is probably due to the increase in number of mobile charge carriers through the conducting pathway provided by tetrahedral structures of Na3PO4. The presence of P-O and PO4 (3-) bands was detected by the infrared technique Fourier transform infrared spectroscopy had been shifted indicating changes in polyhedral structure which in turn led to the formation of conducting channel by corner sharing or through edges. The mobility of the charge carriers in the various compositions of the binary system was investigated by using Na-23 magic angle spinning solid-state nuclear magnetic resonance. The narrowing of the line width Na-23 spectra in the optimum composition of the binary NaI-Na3PO4 system can be assigned to Na population with higher ion mobility. X-ray diffraction technique revealed that the addition of NaI resulted in reducing the crystallinity of the samples. Field emission scanning electron microscopy micrographs revealed finer microstructure of the milling samples with grains growth formation and densification upon sintering.