Magnetron sputtering of NASICON (Na3Zr2Si2PO12) thin films Part I: Limitations of the classical methods

Despite the discovery of sodium superionic conductivity in Na1+xZr2SixP3−xO12 (0.4 < x < 0.8) compounds in 1976, up to now their synthesis in homogeneous thin films has not been achieved on wide surfaces.In order to study the efficiency of classical sputtering methods for the synthesis of such compounds, thin films have been prepared by sputter deposition from two types of targets with the Na3Zr2Si2PO12 stoichiometry. The first one, associated with a NASICON (Sodium (Na) SuperIonic CONductor) structure, presented strong mechanical and chemical instabilities during sputtering that prevented a good experimental reproducibility. On the other hand the second one, a composite mixture of Na3PO4 and ZrSiO4, was stable. Nevertheless, strong macroscopic and microscopic chemical heterogeneities were observed for the corresponding deposited films. These features are interpreted in terms of sodium mobility in the coating and re-sputtering of light elements during the deposition process.