Preparation, Crystal Structure, and Reducibility of K2NiF4Type Oxides Eu2−xSrxNiO4+δ

K2NiF4type compounds Eu2−xSrxNiO4+δ(0.5≤x≤1.2) have been prepared by a citric acid complex decomposition method. Rietveld refinement of the powder X-ray diffraction data showed that there was a crystal system transformation from orthorhombicFmmmto tetragonalI4/mmmat aroundx=0.6–0.7. The Sr substitution caused a drastic shift of the OIIions along thec-axis from Eu(Sr) toward Ni while scarcely affecting the NiO4network in the basal plane. The Jahn–Teller distortion of the NiO6octahedron decreased while the percentage of Ni3+increased with increasingx. The variation of the higher peak temperature on the TPR profiles withxare opposite to the variation of the cell parametersc.

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