Electrical degradation of LSM–YSZ interfaces

The impedance of an interface between La1−xSrxMnO3 (x=0.55−0.6) and yttria-stabilized zirconia has been analyzed as a function of time during high temperature annealings in air, and at medium temperatures. For curing below 1100°C, an improvement of intimate contacts between the electrode and the electrolyte materials is evidenced. Even at 1100°C, the electrode characteristic proper shows a marked degradation which increases with time. It mainly comes from an additional semicircle located on the low frequency side of the electrode impedance diagram. The additional low frequency satellite is ascribed to an alteration of the electrode reaction mechanism itself. The interface properties are shown to degrade only from 1200°C. Up to 1200°C, the degradation of both contributions appears reversible when cooling down the electrode. This is interpreted in terms of a narrowing of the contact area between the insulating phase and yttria-stabilized zirconia. Above 1200°C, the interface aging obeys linear laws. As could be expected, the growth of a reaction product along the LSM–YSZ interface results in an increased blocking effect. A remaining degradation of the reaction rate is also detected. The results suggest that the cathodic degradation mainly proceeds in the vicinity of the triple phase boundary (TPB) line, while the alteration of interface properties acts on a larger electrode area. The formation and the growth of an insulating layer results in ohmic and polarization losses.