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 m agnesium-doped lanthanum gallate (LSGM) during sintering were investigated. Electron microprobe analysis showed that the NiO content of LSGM sintered 4 h at 1350 degrees C was slightly >2 wt% within 5 mu m of the interface, w hich is equivalent to 7 mol% nickel on B cation sites. This concentration d ecreased rapidly to <0.25% at a distance of 15 mu m. The interfacial reacti on between NiO and LSGM, however, led to the formation of a LaSrGa(Ni)O4-de lta-type phase. A separate experiment involving conductivity measurements o f nickel-doped LSGM indicated that the oxygen-ion conductivity did not decr ease significantly if the nickel content was <5%-8%, At higher nickel conte nts, the conductivity increased in air because of hole conduction and marke dly decreased under conditions of low oxygen pressure because of the format ion of the LaSrGa(Ni)O4-delta-type phase. The nickel ions in the LSGM elect rolyte and in the reaction product, LaSrGa(Ni)O4-delta, were stable as Ni2 at reduced oxygen pressures and, therefore, did not cause electronic short ing.