Ni-doped lanthanum gallate perovskites: Synthesis and structural, microstructural, and electrical characterisation

This work reports on the synthesis and the characterisation of La0.9Sr0.1Ga1 − xNixO3 − δ (LSGN) with x = 0, 0.1 and 0.2 (nominal compositions). For La0.9Sr0.1GaO3 − δ the XRD spectrum matched with that of orthorhombic LaGaO3. However, when Ni is introduced into the lattice a change in the symmetry from orthorhombic to rhombohedral is produced. The lattice volume decreases when Ni is introduced. EPR measurements confirm the presence of Ni3+ for the Ni-doped LSGN materials. Furthermore, two different environments are detected in samples with x = 0.2, i.e., the highest content in Ni. One of them corresponds to the Ni3+ located in NiO6 octahedra, B sites of the lattice of the perovskite, which is also observed in samples with x = 0.1, and the other one could correspond to the magnetic interaction of Ni3+ cations located in NiO6 octahedra adjacent to each other. An increase of Ga concentration from the surface to the inner part (bulk) of the samples is observed by laser ablation system coupled to an inductively coupled plasma mass spectrometer (LA–ICP-MS). This fact together with the “pinholes” observed by SEM suggests a superficial Ga volatilisation process during the sintering step. Chemical modification of the Sr-doped lanthanum gallate via replacement of nickel cations on the B site increased the conductivity and decreased the activation energy. For the composition with x = 0.2 the activation energy of 0.23 eV is in excellent agreement with expectations of an electronic transport model involving electron hopping within the Ni impurity band.

Research Highlights► La0.9Sr0.1Ga1 − xNixO3 − δ with x = 0, 0.1 and 0.2 as cathodes for IT-SOFCs. ► A change in the symmetry from orthorhombic to rhombohedral is produced with doping. ► EPR measurements confirm the presence of Ni3+ located in NiO6 octahedra. ► A superficial Ga volatilisation process during the sintering step is observed. ► The conductivity when x = 0.2 becomes metallic-like at temperatures above 800 °C.