Interfacial Reaction between Nickel Oxide and Lanthanum Gallate during Sintering and its Effect on Conductivity

The results of interdiffusion and reaction between NiO and strontium‐ and magnesium‐doped lanthanum gallate (LSGM) during sintering were investigated. Electron microprobe analysis showed that the NiO content of LSGM sintered 4 h at 1350°C was slightly >2 wt% within 5 µm of the interface, which is equivalent to 7 mol% nickel on B cation sites. This concentration decreased rapidly to <0.25% at a distance of 15 µm. The interfacial reaction between NiO and LSGM, however, led to the formation of a LaSrGa(Ni)O 4‐delta ‐type phase. A separate experiment involving conductivity measurements of nickel‐doped LSGM indicated that the oxygenion conductivity did not decrease significantly if the nickel content was <5%‐8%. At higher nickel contents, the conductivity increased in air because of hole conduction and markedly decreased under conditions of low oxygen pressure because of the formation of the LaSrGa(Ni)O 4‐delta ‐type phase. The nickel ions in the LSGM electrolyte and in the reaction product, LaSrGa(Ni)O 4‐delta , were stable as Ni 2+ at reduced oxygen pressures and, therefore, did not cause electronic shorting.