Influence of nickel doping on oxygen-ionic conductivity of the n = 1 Ruddlesden-Popper Phases La1.85Ca0.15(Cu1−xNix)O4−δ (δ = 0.0905)

• We report the synthesis and structure of the La1.85Ca0.15(Cu1−xNix)O4−δ (0≤x≤0.3; δ=0.0905) compounds.
• La1.85Ca0.15(Cu1−xNix)O4−δ (x=0.0, 0.2, 0.3) doped with Ni2+ have a higher conductivity than undoped La1.85Ca0.15CuO4−δ.
• At T=270 °C, sample x=0.3 has the highest conductivity (0.2915 sm−1).

The results of the synthesis and characterization of the optimally doped La1.85Ca0.15(Cu1−xNix)O4-δ solid solution with x = 0, 0.1, 0.2 and 0.3 are reported. The versatility of these La1.85Ca0.15(Cu1−xNix)O4−δ materials is explained on the basis of structural features and the ability to accommodate oxygen nonstoichiometry. According to powder X-ray and neutron diffraction data, La1.85Ca0.15(Cu1−xNix)O4−δ adopts the tetragonal structure with oxygen vacancies occurring preferentially at the Oap sites within the {(La/Ca)O} layers of the perovskite blocks and the oxygen deviation from stoichiometry δ was found to be δ=0.0905(6). The bulk conductivity indicated an Arrhenius-type thermally activated process and oxygen vacancies are the possible ionic charge carriers at T=270 °C. An increase of the conductivity was detected when Ni was introduced. With nickel ratio variation, a strong correlation was observed between the Cu(Ni)-Oap apical bond length variation and the conductivity variation through controlling the O2− ion migration.

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