Feasibility Synthesis and Characterization of Gadolinia Doped Ceria Coatings Obtained by Cathodic Arc Evaporation.

Pascal Briois,Michel Cassir,Alain Billard,Armelle Ringuedé,Eric Aubry

doi:10.3390/nano11051211

Abstract

Gadolinia doped ceria coatings were elaborated by cathodic arc evaporation from a metallic Ce–Gd (90–10 at.%) target inserted into a conventional multiarc Ti evaporation target in the presence of a reactive argon–oxygen gas mixture. The structural and chemical features of these films were determined by x-ray diffraction and scanning electron microscopy. Their electrical properties were characterized using impedance spectroscopy measurements. It was shown that the as-deposited coatings crystallize in the fluorite type fcc structure of ceria and that their composition is the same as that of the target. The morphology of the coatings is influenced by the evaporation parameter (stress and droplet). The electrical measurements showed two contributions in Nyquist representation and the activation energy was slightly higher than that given in the literature data for the bulk material.

Highlights

According to the Arrhenius law, the ionic conductivity of solid electrolytes is thermally activated and the conventional material used for oxygen transport in numerous applications such as solid oxide fuel cells (SOFC) is yttria stabilized zirconia (YSZ) [1,2].The ionic conductivity increases with the operating temperature, but high temperatures are the origin of several problems: high reactivity between each component of the cell core yielding to the formation of insulating phases, high cost of the ceramic components, and brittleness of the stack due to both the high temperature and the discrepancy of the thermal expansion coefficients (TEC) of those constituting parts [1,2,3,4,5]
It is necessary to decrease the operating temperature of SOFC without a deterioration in their performances, which requires several adaptations to limit the loss of ionic transport properties of the electrolyte: the first is the use of new ionic conductors more efficient than YSZ, and the second is the elaboration of the stack in thin film to decrease the electrical resistance of each element
Ce–Gd–O films were deposited on stainless steel (AISI430) substrates by cathodic arc evaporation under reactive argon–oxygen gas mixtures of a composite target constituted of a 50 mm diameter Ce–Gd (90–10 at.%) metallic disc inserted into a conventional multiarc

Summary

Introduction

According to the Arrhenius law, the ionic conductivity of solid electrolytes is thermally activated and the conventional material used for oxygen transport in numerous applications such as solid oxide fuel cells (SOFC) is yttria stabilized zirconia (YSZ) [1,2]. LaGaO3 [8,9], Ba2 In2 O5 [10], Bi4 V2 O11 (BIMEVOX) [8,11], La2 MoO9 (LAMOX) [12] derivatives, or apatite structure lanthanum silicate [13,14] In these materials, oxygen conduction takes place via a vacancy mechanism and, as a consequence, the conductivity strongly depends on vacancy concentration and oxygen mobility, which is promoted by high temperatures. Cathodic arc evaporation is a powerful technique for high-rate deposition of numerous metallic alloys and more or less complex ceramic coatings, mainly carbides and nitrides [29], but very few works have dealt with the deposition of oxides [30,31]. The electrical properties of thin films are investigated by impedance spectroscopy as a function of the temperature

Experimental Details

Altthough

Grazing incidence x-ray diffractogram

Nyquist

Equivalent

Conclusions