Structural-electrical-optical properties relationship of sodium superionic conductor sputter-deposited coatings

Thin films of various compositions in the Na2O-SiO2-P2O5-ZrO2 system were deposited in glassy form by reactive magnetron sputtering. An analysis by spectrophotometry showed an increase of the extinction coefficient (k) with the amount of Fe contamination. This contamination, originating from parasitic plasmas, was suppressed when convenient protections were used. Therefore, it was possible to produce optical clear films. A structural study by X-ray diffraction and Raman spectroscopy proved a reorganization in the amorphous state at low temperature and the appearance of a NASICON structure around 750 °C. The ionic conductivity, measured by impedance spectroscopy, and the optical properties were strongly affected by the thermal annealing process. The reorganization in the amorphous state and strong modifications of the ionic conductivity values and the refractive index (n) appeared in the same range of temperatures. This suggested a strong correlation between these different phenomena.