Influence of synthesis conditions on microstructure and phase transformations of annealed Sr2FeMoO6−x nanopowders formed by the citrate–gel method

• Main Authors: Marta Yarmolich, Nikolai Kalanda, Sergey Demyanov, Herman Terryn, Jon Ustarroz, Maksim Silibin, Gennadii Gorokh
• Format: Article
• Language: English
• Published: Beilstein-Institut 2016-08-01
• Series: Beilstein Journal of Nanotechnology
• Subjects: magnetic materials; microstructure; nanoparticles; phase transformation; sol–gel preparation
• Online Access: https://doi.org/10.3762/bjnano.7.111

The sequence of phase transformations during Sr2FeMoO6−x crystallization by the citrate–gel method was studied for powders synthesized with initial reagent solutions with pH values of 4, 6 and 9. Scanning electron microscopy revealed that the as-produced and annealed powders had the largest Sr2FeMoO6−x agglomerates with diameters in the range of 0.7–1.2 µm. The average grain size of the powders in the dispersion grows from 250 to 550 nm with increasing pH value. The X-ray diffraction analysis of the powders annealed at different temperatures between 770 and 1270 K showed that the composition of the initially formed Sr2FeMoO6−x changes and the molybdenum content increases with further heating. This leads to a change in the Sr2FeMoO6−x crystal lattice parameters and a contraction of the cell volume. An optimized synthesis procedure based on an initial solution of pH 4 allowed a single-phase Sr2FeMoO6−x compound to be obtained with a grain size in the range of 50–120 nm and a superstructural ordering of iron and molybdenum cations of 88%.