Microstructural characterisation by X-ray scattering of perovskite-type La_0.8Sr_0.2MnO_3±δ thin films prepared by a dip-coating process

Abstract

The La_0.8Sr_0.2MnO₃ (LSM) cathode materials are widely used in solid oxide fuel cells (SOFCs) as electronic conductors. In such materials, the reduction of oxygen is located at the triple contact boundaries: air/cathode LSM/electrolyte which is generally Yttria Stabilised Zirconia (YSZ). In order to improve the chemical reactions at these air/cathode LSM/electrolyte interfaces, the triple phase boundary length has to be optimised. In this aim, we have first synthesised the La_0.8Sr_0.2MnO₃ phase by a sol–gel route and, second, LSM thin films have been deposited on various polished substrates by using a dip-coating process. The structure and microstructure of the resulting LSM thin layers have been investigated by using well suited complementary techniques such as X-ray reflectometry, grazing incidence small angle X-ray scattering, X-ray diffraction and scanning electronic microscopy. The structural and microstructural parameters of LSM thin films have been managed and studied as a function of synthesis parameters such as initial metallic salt concentration, time and temperature of annealing. The higher the metallic salt concentration, the higher the thickness of the film, the smaller the film density. The as-prepared layers are amorphous and the single crystallised perovskite form is obtained for low temperature heat treatments. Therefore, the annealed coatings are constituted by randomly oriented LSM nanocrystals, which organise in a more or less dense close-packed microstructure according to the initial metallic salt concentration.