Li3Sc2−xFex(PO4)3 thin films and powders prepared by ultrasonic spray pyrolysis

Thin films of Li3Sc2−xFex(PO4)3 (x=0.5, 2) solid electrolytes have been prepared on quartz glass substrates by ultrasonic spray pyrolysis (USP) using aqueous solutions of LiH2PO4, Sc(NO3)3 and Fe(NO3)3 at substrate temperature of 500–700°C. The amorphous as-deposited films were converted into crystalline materials by heat treatment at 800–1000°C. The optimal deposition parameters for formation of uniform precursor films with good adhesion to the substrate were determined. The dense films composed of fine columnar grains were obtained using the three cycles of deposition and annealing. The room temperature ionic conductivity of the film with the composition x=0.5 was 5×10−6 S/cm. The superionic γ-phase of USP ceramics of Li3Sc2−xFex(PO4)3 (0<x≤0.6) was shown to be stabilized at room temperature, which may be caused by slight structural distortions and changes in the interactions between the lithium ions during Sc3+→Fe3+ substitution. The highest ionic conductivity σ(25°C)≈1×10−5 S/cm was observed for ceramics with x=0.4.