Synthesis and characterization of perovskite-type SrxY1−xFeO3−δ (0.63≤x<1.0) and Sr0.75Y0.25Fe1−yMyO3−δ (M=Cr, Mn, Ni), (y=0.2, 0.33, 0.5)

Abstract Oxygen-deficient ferrates with the cubic perovskite structure Sr x Y 1− x FeO 3− δ were prepared in air (0.71≤ x ≤0.91) as well as in N 2 ( x =0.75 and 0.79) at 1573 K. The oxygen content of the compounds prepared in air increases with increasing strontium content from 3− δ =2.79(2) for x =0.75 to 3− δ =2.83(2) for x =0.91. Refinement of the crystal structure of Sr 0.75 Y 0.25 FeO 2.79 using TOF neutron powder diffraction (NPD) data shows high anisotropic atomic displacement parameter (ADP) for the oxygen atom resulting from a substantial cation and anion disorder. Electron diffraction (ED) and high-resolution electron microscopy (HREM) studies of Sr 0.75 Y 0.25 FeO 2.79 reveal a modulation along 〈1 0 0〉 p with G± ∼0.4〈1 0 0〉 p indicating a local ordering of oxygen vacancies. Magnetic susceptibility measurements at 5–390 K show spin-glass behaviour with dominating antiferromagnetic coupling between the magnetic moments of Fe cations. Among the studied compositions, Sr 0.75 Y 0.25 FeO 2.79 shows the lowest thermal expansion coefficient (TEC) of 10.5 ppm/K in air at 298–673 K. At 773–1173 K TEC increases up to 17.2 ppm/K due to substantial reduction of oxygen content. The latter also results in a dramatic decrease of the electrical conductivity in air above 673 K. Partial substitution of Fe by Cr, Mn and Ni according to the formula Sr 0.75 Y 0.25 Fe 1− y M y O 3− δ ( y =0.2, 0.33, 0.5) leads to cubic perovskites for all substituents with y =0.2. Their TECs are higher in comparison with un-doped Sr 0.75 Y 0.25 FeO 2.79 . Only M =Ni has increased electrical conductivity compared to un-doped Sr 0.75 Y 0.25 FeO 2.79 .