Preparation, crystal structure, and reducibility of K2NiF4 type oxides Sm2–xSrxNiO4+δ

Abstract

K₂NiF₄ type compounds Sm_2–xSr_xNiO_4+δ(0.4≤x≤1.2) have been synthesized 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 orthorhombic Fmmm to tetragonal I4/mmm at around x=0.6. The Sr substitution caused a drastic shift of the O_II ions along the c axis from Sm(Sr) towards Ni whilst scarcely affecting the NiO₄ network in the basal plane. The distortion of the NiO₆ octahedron decreased, while the average bond valence of Ni increased with increasing x.