A ceramic interconnector of a solid oxide cell (SOC) should require high phase stability and conductivity in a redox environment. Due to these limitations, only a few materials were found to meet the usage requirement as SOC interconnector. Under various synthetic conditions, La_0.6Sr_0.4Fe_1-xSc_xO_3-δ (LSFSc) was synthesized for the purpose of introducing a redox stable and electrically conductive ceramic interconnector. The crystalline phases of LSFSc are stable when the solution pH is low (pH=2), and the calcination temperature is sufficiently high (T=1200ºC). From the XPS analysis, it is accepted that incorporation of Sc in the B site of La_0.6Sr_0.4FeScO_3-δ lattice further stabilizes its structural stability under reducing conditions. When the Sc concentration exceeds 10 mol%, phase stability of La_0.6Sr_0.4Fe_1-xSc_xO_3-δ was obtained. Figure 1 shows the ASR variations of ceramic interconnectors based on LaFeO₃ doped at A-site with Sr and B-site with Sc in various redox environments. The electrical conductivity of La_0.8Sr_0.2FeO_3-δ is remarkably low at both oxidation and reduction atmospheres due to the high area specific resistance. However, the ASR of La_0.6Sr_0.4FeO_3-δ is less than half of La_0.8Sr_0.2FeO_3-δ when exposed to air at one side and is exposed to H₂ on the opposite side. This is one of the main reasons why we selected the composition as the basic crystal structure. However, La_0.6Sr_0.4FeO_3-δ shows big augment due to the decomposition at reduction atmosphere. Moreover, the instability against high relative humidity (RH) is the main downside of La_0.6Sr_0.4FeO_3-δ. For these reasons, it is difficult to employ La_0.6Sr_0.4FeO_3-δ as an interconnector material. Among the proposed materials, La_0.6Sr_0.4Fe_0.9Sc_0.1O_3-δ exhibited the most desirable performances at the various gas conditions for 1000 h. Therefore, La_0.6Sr_0.4Fe_0.9Sc_0.1O_3-δ is considered to be the most stable composition for redox stable and electrically conductive ceramic interconnectors for solid oxide cells.

Figure 1. The ASR variations of the La_0.6Sr_0.4Fe_1-xScxO_3-δ specimen depending on gas atmosphere and operation time.