Na⁺ and Li⁺ NASICON Superionic Conductors Thick Films

Abstract

For microionic applications, superionic conductors have been elaborated in the form of thick films, using silk-screen printable powders. Na 3 Zr 2 Si 2 PO 12 , Na 3.1 Zr 1.55 Si 2.3 P 0.7 O 11 and Li 0.8 Zr 1.8 Ta 0.2 (PO 4 ) 3 compositions are synthesized by a sol-gel process involving hydrolysis-polycondensation reactions of metal-organic alcoholic solutions. A thermal treatment (600°C–800°C) allows to obtain very fine particles (<1 µm) with the pure NASICON phase. Inks are prepared with these powders, an organic binder, volatile fluidifying agents and mineralizers. The layers, about 50 µm in thickness, are achieved by successive deposits and sinterings (950°C–1050°C) onto alumina substrates. Films conductivity is determined by the complex impedance method. Values measured at 300°C (Na + : σ∼10 -2 Ω -1 cm -1 , E A =0.25 eV, Li + : σ∼5 10 -4 Ω -1 cm -1 , E A =0.5 eV) reach those obtained with well-densified ceramics. An anisotropic behaviour related to microstructure is pointed out.