Sol-Gel Synthesis of the Double Perovskite Sr2FeMoO6 by Microwave Technique

Abstract

The effect of microwave radiation on the hydrothermal synthesis of the double perovskite Sr2FeMoO6 has been studied based on a comparison of the particle size and structural characteristics of products from both methods. A temperature, pressure, and pH condition screening was performed, and the most representative results of these are herein presented and discussed. Radiation of microwaves in the hydrothermal synthesis method led to a decrease in crystallite size, which is an effect from the reaction temperature. The particle size ranged from 378 to 318 nm when pH was 4.5 and pressure was kept under 40 bars. According to X-ray diffraction (XRD) results coupled with the size-strain plot method, the product obtained by both synthesis methods (with and without microwave radiation) have similar crystal purity. The Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS) techniques showed that the morphology and the distribution of metal ions are uniform. The Curie temperature obtained by thermogravimetric analysis indicates that, in the presence of microwaves, the value was higher with respect to traditional synthesis from 335 K to 342.5 K. Consequently, microwave radiation enhances the diffusion and nucleation process of ionic precursors during the synthesis, which promotes a uniform heating in the reaction mixture leading to a reduction in the particle size, but keeping good crystallinity of the double perovskite. Precursor phases and the final purity of the Sr2FeMoO6 powder can be controlled via hydrothermal microwave heating on the first stages of the Sol-Gel method.

Half-metallic double perovskite oxides: recent developments and future perspectives

“…In order to obtain better crystalline SFMO nanopowders with high cation ordering degrees at B-sites, recently, a microwave-assisted sol–gel process has been developed, in which the reaction mixtures of the metal precursors were placed in a microwave and operated under specific reaction temperature, time, and pH conditions. 135 For example, the particle sizes of the SFMO powders were distributed in the range of 318 to 378 nm when the pH was 4.5 and the pressure was kept under 40 bar. Their T C value was increased from 335 K to 343 K with respect to the normal sol–gel synthesis.…”

“…Reproduced with permission. 135 Copyright 2021, Licensee MDPI, Basel, Switzerland. [110] projection plane.…”

“…As an example, the (Sr, Fe, and Mo) element maps of the SFMO powders synthesized by the sol-gel method are shown in Fig. 22(e), 135 where uniform distributions of Sr, Fe, and Mo elements are clearly observed. However, during the analysis of the EDS data there arises an issue of peak overlapping of characteristic X-rays for many elements such as Ti K b and V K a , Mn K b and Fe K a .…”

“…(e) EDS mapping for a section of the SFMO powders synthesized by the sol-gel method after the reduction process, where a uniform distribution of Sr, Fe and Mo atoms can be observed. Reproduced with permission 135. Copyright 2021, Licensee MDPI, Basel, Switzerland.…”

A Unique Mechanochemical Redox Reaction Yielding Nanostructured Double Perovskite Sr2FeMoO6 With an Extraordinarily High Degree of Anti-Site Disorder

“…Although in the last few years a surge of investigations in the field of mechanochemistry has resulted in the mechanosynthesis of a variety of complex oxides by forcing a system to acquire metastable and non-equilibrium configurations ( Zhang and Saito, 2012 ; Šepelák et al, 2013 ; Wilkening et al, 2017 ; Porodko et al, 2021 ; Szczȩśniak et al, 2021 ; Tsuzuki, 2021 ; Šepelák et al, 2021 ), there is no report in the literature on the nonconventional mechanochemical route to synthesize Sr 2 FeMoO 6 . Commonly, this material is prepared via a conventional multi-step ceramic route ( Valenzuela et al, 2014 ; Kalanda et al, 2019 ; Alvarado-Flores et al, 2021 ) or various wet chemistry-based routes ( Li et al, 2019 ; Farzin et al, 2020 ; Valdés et al, 2021 ); some of them involve a prolonged heat treatment at considerably high temperatures under reducing atmosphere ( Iranmanesh et al, 2016 ). The present work demonstrates that Sr 2 FeMoO 6 can be mechanosynthesized at ambient temperature in air directly from its precursors in the form of nanostructured powders, without the need for solvents and/or calcination under controlled oxygen fugacity, thus making the process very facile and efficient.…”