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

Abstract

SummaryThe 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%.

Functional Multicomponent Metal Oxide Films Based on Sr, Sn, Fe, and Mo in the Anodic Alumina Matrices

“…By adding ethylenediamine (EDA) into two parts of this solution, their pH values were adjusted to 4 and 9, respectively. In previous works, we showed that the synthesis of Sr 2 FeMoO 6−δ powders obtained at the solution with a pH of 4 allowed obtaining films with maximum superstructural ordering, but the raising of pH decreased the degree of order superstructure . Finally, the obtained solutions were continuously stirred at 353 K until the light green gels were formed.…”

“…The compound of Sr 2 FeMoO 6−δ system was prepared by the sol–gel method, using Sr(NO 3 ) 2 , Fe(NO 3 ) 3 ·9H 2 O (NH 4 ) 6 Mo 7 O 24 , and C 6 H 8 O 7 ·H 2 O as starting materials . At first, the aqueous solutions of Sr(NO 3 ) 2 (0.4 mol dm −3 ) and Fe(NO 3 ) 3 (2 mol dm −3 ) were mixed in a molar ratio of 2(Sr):(Fe), and then C 6 H 8 O 7 ·H 2 O was added to the solution in a molar ratio of 6.5(C 6 H 8 O 7 ·H 2 O):(Fe).…”

“…The first stage of gel heating up to 473 K was carried out by the polythermal regime at rate of 0.4° min −1 . Then the samples were held at this temperature for 2 h . In the second stage, the formed composite systems were annealed in air at a partial oxygen pressure of pO 2 = 0.21·10 5 Pa at T = 773 K for 8 h to form the Sr 2 FeMoO 6−δ film distributed over the porous oxide surface.…”

“…The compound of Sr 2 FeMoO 6Àδ system was prepared by the sol-gel method, using Sr(NO 3 [19] At first, the aqueous solutions of Sr(NO 3 ) 2 (0.4 mol dm À3 ) and Fe(NO 3 ) 3 (2 mol dm À3 ) were mixed in a molar ratio of 2(Sr):(Fe), and then C 6 H 8 O 7 ·H 2 O was added to the solution in a molar ratio of 6.5(C 6 H 8 O 7 ·H 2 O):(Fe). After this, (NH 4 ) 6 Mo 7 O 24 solution (0.2 mol dm À3 ) was added to the prepared solution in a molar ratio of (Mo):(Fe).…”

“…Among the technological methods of film deposition, liquid‐phase methods occupy an increasingly significant position as they are less expensive in comparison with gas‐phase high‐temperature or vacuum processes . The most suitable and effective chemical methods for the formation of metal oxide films with a controlled composition and properties on nanoporous matrices are the electrophoretic layer‐by‐layer deposition, the ion layer deposition, the sol–gel method, and drop method using the aqueuos salts solutions . The electrophysical, chemosensitive, and magnetic characteristics of such composite films are related to their structural ordering, which is determined by the presence of the regularity of the arrangement of elementary crystallites .…”