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

Marta Yarmolich; Nikolai Kalanda; Sergey Demyanov; Herman Terryn; Jon Ustarroz; Maksim Silibin; Gennadii Gorokh

doi:10.3762/bjnano.7.111

Influence of synthesis conditions on microstructure and phase transformations of annealed Sr₂FeMoO_6-x nanopowders formed by the citrate-gel method

Beilstein J Nanotechnol. 2016 Aug 22:7:1202-1207. doi: 10.3762/bjnano.7.111. eCollection 2016.

Authors

Marta Yarmolich¹, Nikolai Kalanda², Sergey Demyanov², Herman Terryn³, Jon Ustarroz³, Maksim Silibin⁴, Gennadii Gorokh⁵

Affiliations

¹ Scientific-Practical Materials Research Centre, NAS of Belarus, Minsk 220072, Belarus; National Research University of Electronic Technology "MIET", Moscow 124498, Russia.
² Scientific-Practical Materials Research Centre, NAS of Belarus, Minsk 220072, Belarus.
³ Research Group Electrochemical and Surface Engineering, Vrije Universiteit Brussel, Brussel 1050, Belgium.
⁴ National Research University of Electronic Technology "MIET", Moscow 124498, Russia.
⁵ Belarusian State University of Informatics and Radioelectronics, Minsk 220013, Belarus,; ITMO University, St. Petersburg 197101, Russia.

Abstract

The sequence of phase transformations during Sr₂FeMoO_6-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 Sr₂FeMoO_6-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 Sr₂FeMoO_6-x changes and the molybdenum content increases with further heating. This leads to a change in the Sr₂FeMoO_6-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 Sr₂FeMoO_6-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%.

Keywords: magnetic materials; microstructure; nanoparticles; phase transformation; sol–gel preparation.