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. t 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.