Apatite-type lanthanum silicate showed a high ionic conductivity and low activation energy at intermediate temperature (600–800C) compared with yttria stabilized zirconia. In addition, its excellent stability in a wide oxygen partial pressure range meets the requirement for the electrolyte. Thus it was a potential candidate for intermediate temperature solid oxide fuel cell electrolytes. Moreover, atmospheric plasma spraying was expected to be a promising alternative to other costly or low-deposition rate electrolyte processing methods. However, the amorphous phase and pores existing in the plasma sprayed coatings might impair the stability and the higher ionic conductivity of lanthanum silicate. The present work investigated the effect of substrate surface temperature from 545 to 900C on the microstructure and ionic conductivity of the lanthanum silicate coating. The crystallinity of as-deposited coatings increased with the increase of substrate surface temperature, whereas the porosity showed a contrary tendency. Ionic conductivity increased about four times with increasing substrate surface temperature, which was related to the low porosity and high crystallinity of coatings. Increasing the substrate surface temperature during plasma spraying was a feasible method to increase ionic conductivity of the lanthanum silicate coatings by reducing the porosity and enhancing the crystallinity.

Effect of Substrate Surface Temperature on the Microstructure and Ionic Conductivity of Lanthanum Silicate Coatings Deposited by Plasma Spraying. W.Z.Wang, F.Sun, X.P.Guo, H.L.Liao, O.Elkedim, J.C.Liang: Surface and Coatings Technology, 2011, 205[12], 3665-70