Structure, crystal chemistry and magnetism of rare earth calcium-doped cobaltates: Ln2−xCaxCoO4+δ (Ln = Pr, Nd, Sm, Eu and Gd)

Single-phase samples of Ln2−xCaxCoO4+δ (Ln = Pr3+ − Gd3+) around x∼1 have been prepared. For the first time, the phase field for these compounds has been defined using powder X-ray diffraction and a very narrow solid solution was observed. Under our synthetic conditions, the K2NiF4 structure was not formed for the large La3+ ion, or for compositions containing the smaller rare earths ions (

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► Phase field for Ln2−xCaxCoO4+δ (Ln = Pr3+ − Gd3+) determined.
► Average cobalt oxidation states between ∼3.2+ and ∼3.3+.
► Tetragonal to orthorhombic transition upon cooling and with decreasing ionic radius.
► Paramagnetic with weak antiferromagnetic interactions.
► Co3+ in low-spin state.