Influence of different substrates on the ionic conduction in LiCoO₂/LiNbO₃ thin‐film bi‐layers

Abstract

LiNbO3 thin films, deposited by e‐gun evaporation, show lithium deficiency, which is cured by “Li doping”. The “Li doping” of the films was achieved by preparing a structure of Li‐Nb‐O/Li/Li‐Nb‐O, which after annealing forms a homogenized LiNbO3 layer because of diffusion of Li in the two Li‐Nb‐O layers. The LiCoO2/LiNbO3 bi‐layers were prepared either on Stainless Steel/TiN or on Al2O3/Co/Pt substrates/ohmic‐contacts by depositing first either the cathode LiCoO2 or the electrolyte LiNbO3. The Nyquist plots of the AC impedance measurements of all structures showed that the interfaces prepared on Stainless‐Steel/TiN consisted of two semicircles. The structures deposited on Al2O3/Co/Pt showed a third semicircle, which is probably due to the roughness of the substrate. It is important that the ionic properties of the bi‐layers with the cathode material deposited first, a usual structure in a microbattery, are improved compared to the other structures. The quality of the LiNbO3 layer depends very much on the substrate. It can be evaluated from Arrhenius plots that the activation energy of this layer is considerably lower when the whole structure is deposited on Stainless Steel/TiN. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)