Abstract
A partial substitution of Zr4+ in silicophosphate Na3Zr2Si2PO12 by trivalent element has been studied. By the example of Fe3+-substituted NASICON, it has been shown that the resulting complex does not correspond to the generally accepted formula Na3 + y \({\text{M}}_{y}^{{{\text{III}}}}\) Zr2 – ySi2PO12, where electroneutrality of obtained compound is reached due to charge compensation by additional Na+ ions. On the basis of X-ray powder diffraction data, scanning electron microscopy, and the Rietveld refinement of crystal lattice parameters, the formation of complexes Na3 \({\text{M}}_{y}^{{{\text{III}}}}\) Zr2 – ySi2 – yP1 + yO12 has been found. Precursor of composition Na3 + y \({\text{M}}_{y}^{{{\text{III}}}}\) Zr2 – ySi2PO12 is excessive toward Na and Si for Fe-substituted complex. Elements that proved to be super-stoichiometric for the new crystal lattice are partially inserted in the main NASICON phase thus increasing unit cell parameters and are partially involved in the formation of additional phases (amorphous or crystalline). Amorphous phase is formed at the grain boundaries of low doped materials. Admixture crystalline phases appear in high doped samples.
