Characterization and thermal expansion of Sr2Fe x Mo2−x O6 double perovskites

Double perovskite oxides Sr2 Fe x Mo2−x O6 (x = 0.8, 1.0, 1.2, 1.3 and 1.4) (SFMO) of different compositions were prepared by sol–gel growth followed by annealing under reducing atmosphere conditions of H2/Ar flow. X-ray powder diffraction studies revealed that the crystal structure of the samples changes from tetragonal to cubic at around x = 1.2. Lattice parameters and unit cell volume of these samples found to decrease with the increase in Fe content. The characteristics absorption bands observed in the range 400–1000 cm−1 of Fourier transform infrared spectra indicate the presence of FeO6 and MoO6 octahedra and confirm the formation of double perovskite phase. The value of g ∼ 2.00 obtained from electron spin resonance studies indicates that Fe is in 3+ ionic state in the SFMO samples. Dilatometric studies of these samples reveal that the average value of coefficient of thermal expansion ( $ {\overline {\alpha }}$ ) increases with the increase in temperature or Fe content in SFMO samples. The low value of coefficient of thermal expansion 1.31 × 10−6 ∘C−1 obtained for Sr2Fe0.8Mo1.2O6 in the present study in the temperature range of 40–100∘C makes it useful as anode material in fuel cells. The coefficient of thermal expansion ( $ {\overline {\alpha }}$ ) and the unit cell volume (V) of SFMO samples vary inversely with composition in agreement with Gruneisen relation.