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

Double perovskite oxides Sr-2 Fe (x) Mo2-x O-6 (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 H-2/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 similar to 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 ((alpha) over bar) increases with the increase in temperature or Fe content in SFMO samples. The low value of coefficient of thermal expansion 1.31 x 10(-6) C-a similar to(-1) obtained for Sr2Fe0.8Mo1.2O6 in the present study in the temperature range of 40-100(a similar to)C makes it useful as anode material in fuel cells. The coefficient of thermal expansion ((alpha) over bar) and the unit cell volume (V) of SFMO samples vary inversely with composition in agreement with Gruneisen relation.