Magnetron sputtering of NASICON (Na3Zr2Si2PO12) thin films: Part II: A novel approach

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 Part I, we have shown the limitations of the classical radiofrequency sputtering methods for depositing this kind of films with high microscopic and macroscopic chemical homogeneities. The present paper (Part II) proposes a new sputtering method based on the reactive co-sputtering of ZrSi alloy and Na3PO4 targets. The last one is powered by a high frequency pulsed direct current (DC) generator. It is possible to tune the discharge voltage as the current is regulated thanks to the modifications of the discharge frequency and/or the pulse off-time. The deposition rate of the Na3PO4 target is strongly influenced by the discharge voltage. Thin films were deposited in the Na2O–ZrO2–SiO2–P2O5 system with a high physical quality. The experimental configuration allows to adjust the Na/Si atomic ratio by varying the intensity dissipated by the ZrSi target and the target–substrate distance. Hence it is possible to reach on a large area the ratio 1.5 characteristic for Na3Zr2Si2PO12 compound. The structural analysis of a selected film showed an amorphous film in the as deposited condition. After annealing at 700 °C the monoclinic structure, which corresponds to the superionic conducting phase Na3Zr2Si2PO12 was obtained.