Samples of NASICON ceramics have been synthesized by pyrolysis of organic solutions in rosin melt from Zr-deficient precursors. The phase composition, morphology, and material characteristics have been studied using X-ray powder diffraction analysis, scanning electron microscopy, and electrochemical impedance spectroscopy. It has been demonstrated that, as the zirconium concentration in the initial mixture decreases, some of the superstoichiometric elements (Na, Si, and P) are incorporated into the crystal lattice of the main NASICON phase, while others create an amorphous phase at the grain boundaries. It is shown that the key factors for optimizing the functional characteristics of NASICON ceramics are the absence of impurity crystalline phases, the formation of a crystal structure that best matches the composition of Na3Zr2Si2PO12, and the presence of an amorphous phase, which facilitates dense sintering of the material. Compositions with a zirconium concentration reduced to 20 mol % were studied. It was found that the sample with a zirconium deficiency of 5 mol % exhibited the highest conductivity values.
Grishchenko et al. (Mon,) studied this question.