Structure Peculiarities of Micro- and Nanocrystalline Perovskite Ferrites La Sm FeO.

Micro- and nanocrystalline lanthanum-samarium ferrites La Sm FeO with orthorhombic perovskite structure were obtained by using both solid state reactions (x = 0.2, 0.4, 0.6 and 0.8) and sol-gel synthesis (x = 0.5) techniques. Obtained structural parameters of both series of La Sm FeO are in excellent agreement with the "pure" LaFeO and SmFeO compounds, thus proving formation of continuous solid solution in the LaFeO-SmFeO system. Peculiarity of La Sm FeO solid solution is divergence behaviour of unit cell dimensions with increasing x: systematic decrease of the a and c lattice parameters is accompanied with increasing b parameter. Such behaviour of the unit cell dimensions in La Sm FeO series led to crossover of the a and c perovskite lattice parameters and formation of dimensionally tetragonal structure near x = 0.04. Linear decrease of the unit cell volume of La Sm FeO with decreasing x according with the Vegard's rule indicate absence of short-range ordering of R-cations in the LaFeO-SmFeO system.