Synthesis,Crystal Structure and Reducibility of K2NiF4 Type Oxides Sm2—xSrxCuO4

K2NiF4 type compounds Sm2-xSrxCuO4(0≤x≤1.2)were prepared.Rietveld refinement of powder diffraction data shows that the crystal system of these compounds belongs to T′ type tetragonal structure of space group I4/mmm,and the addition of Sr causes a dramatic shift of the O(I) ions along the c axis from Sm(Sr) toward Cu while scarcely affecting the Cu-O(Ⅱ）bond in basal CuO4 phane.From XRD data,it can be seen that when 0.0≤x≤0.6,Sm2-xSrxCuO4 belongs to a singlephase K2NiF4 type structure,while at x≥0.7,both the free SrO phase and the CuO phase exist in these compounds.From the results of XPS and rietveld refinement,it can be seen that after replacing Sm^3 with Sr^2 of lower valence,the valence of Cu and Sm does not change apparently,and thus some defect must be formed at the oxygen ion positions and/or position A on A2BO4 to keep charge balance and to stabilize the structure.

Synthesis, Crystal Structure and Reducibility of K_2NiF_4 Type Oxides Sm_(2-x)Sr_xCuO_4

K₂NiF₄ type compounds Sm_2‐xSr_xCuO₄(0 ≤ x ≤ 1.2) were prepared. Rietveld refinement of powder diffraction data snows that the crystal system of these compounds belongs to T type tetragonal structure of space group I4/mmm, and the addition of Sr causes a dramatic shift of the O(I) ions along the c axis from Sm (Sr) toward Cu while scarcely affecting the Cu—O (II) bond in basal CuO₄ plane. From XRD data, it can be seen that when 0.0 ≤ x ≤ 0.6, Sm_2‐xSr_xCuO₄ belongs to a single‐phase K₂NiF₄ type structure, while at x ? 0.7, both the free SrO phase and the CuO phase exist in these compounds. From the results of XPS and Rietveld refinement, it can be seen that after replacing Sm³⁺ with Sr²⁺ of lower valence, the valence of Cu and Sm does not change apparently, and thus some defect must be formed at the oxygen ion positions and/or position A on A₂BO₄ to keep charge balance and to stabilize the structure.