Effect of the ruthenium incorporation on iron oxide phases synthesis, Fe2O3 and Fe3O4, at low annealing temperature

doi:10.1016/j.matchemphys.2019.122272

Materials Chemistry and Physics

Volume 242, 15 February 2020, 122272

https://doi.org/10.1016/j.matchemphys.2019.122272 Get rights and content

Highlights

•
Ru-alloyed iron oxide thin films were obtained with a non-toxic and easy to manipulate technique that is the spray pyrolysis.
•
Two methods are followed to fabricate Ru-alloyed iron oxide with different molar ratios as RuCl₃·3H₂O: FeCl₃·6H₂O = x:1-x.
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Dark layers having granular structure, were obtained.
•
The obtained Ru-alloyed films properties were improved (morphology, structure, optical, and electrical properties).
•
Fe₂O₃, the magnetite, is obtained at a lower annealing temperature of 350 °C.

Abstract

The aim of this work is to make easier the elaboration of two iron oxide phases, Hematite (Fe₂O₃) and magnetite (Fe₃O₄) at the same annealing temperature, by alloying with ruthenium and to widen the scope of sprayed-iron oxide thin films. Two procedures were followed for Ru-alloyed iron oxide thin films elaboration: the first one consists of spraying FeCl₃·6H₂O(0.03 M)-based aqueous solution onto glass substrates heated at 350 °C, on which was sprayed, immediately, an aqueous RuCl₃·3H₂O solution, during shorter time, at the same spray conditions with different molar ratios as RuCl₃·3H₂O: FeCl₃·6H₂O = x:1-x, wherein 0 ≤ x < 0.50. The second procedure consists of preparing an aqueous solution of ferric chloride (FeCl₃·6H₂O) and ruthenium (III) chloride hydrate (RuCl₃·3H₂O)) with other different molar ratios as RuCl₃·3H₂O: FeCl₃·6H₂O = x’:1-x’, wherein 0 ≤ x’ < 0.50. This solution is sprayed onto glass substrates heated at 350 °C. Afterward, the as obtained films are annealed under vacuum at the fixed conditions: Pressure ≅ 10⁻⁴ Pa, duration = 5h, temperature = 350 °C. XRD, and SEM analyses as well as optical, and electrical measurements, showed the effect of ruthenium incorporation into iron oxide films. Fe₃O₄ was obtained as well as Fe₂O₃ at this low annealing temperature depending on the ruthenium amount. Optical properties of the Ru-alloyed iron oxide films had really improved. Furthermore the electrical behavior showed a variation versus the ruthenium concentrations.

Graphical abstract

Introduction

Currently, it is of paramount importance to focus more on iron oxide since it was one of the transition metal being investigated because of its wide applications [[1], [2], [3], [4], [5], [6], [7]]. Iron oxide has been found with several types of crystal structures and compositions such as: wustite (FeO), hematite (α-Fe₂O₃), maghemite (γ-Fe₂O₃), and magnetite (Fe₃O₄). The three latter are the normal stochiometric forms of iron oxide at room temperature [8]. Hematite is the most stable phase of iron oxide with optical band gap about 2.1 eV [[9], [10], [11], [12], [13]]. Wustite (FeO) has a rock salt phase, magnetite (Fe₃O₄) and maghemite (γ-Fe₂O₃), having cubic spinel structure [14].

Nano crystalline Iron oxide thin films have many technical applications in different fields. Some of their applications include catalysis [15], sensing (gas, alcohol and humidity) [[16], [17], [18]], their use as an optical coating [19] or an electrochromic material [20], and in spintronic and data storage devices [21]. Fe₂O₃ is also a major component of airborne dust in the atmosphere, and its optical properties (refractive index and extinction coefficient) are required for calculations of single scattering albedo [22]. Iron oxide films have been produced by different techniques including electrodepositon [23], filtered arcdeposition [24], spray pyrolysis [9,25,26], successive ionic layer adsorption and reaction (SILAR) [27], atomic layer deposition [28], and chemical bath deposition (CBD) [29].

In our laboratory we had fabricated in a previous work [9] iron oxide thin films by spray pyrolysis. The obtained films were annealed in a vacuum (~10⁻⁴ Pa)-sealed tube during 5 h at 350 °C. Two iron oxide phases were obtained: the dominant one corresponds to (α-Fe₂O₃) and the minor one corresponds to traces of Fe(OOH); which were transformed after further thermal treatment to Fe₂O₃ [9]. In another work [30], we showed that at a higher temperature of 600 °C we had obtained the Fe₃O₄ oxide phase, which needs more energy to appear. All our obtained iron oxide thin films were homogeneous and well adherent to the substrate.

In the aim to make the as obtained iron oxide films more efficient and with wider scope, we thought about the synthesis of the Fe₃O₄ phase at lower temperature (<600 °C) as well as the Fe₂O₃ one. Thus, we put emphasis in this work on the alloy of the iron oxide films with Ruthenium. Indeed, Stanley E. Livingstone [31] showed that members of group VIII, in the periodic table, such as the triad (Fe, Ru, and Os) resemble each other. Furthermore, these elements have the smallest atomic volumes. Consequently, they display a pronounced tendency to form covalent bonds. Furthermore, the stability of the higher oxidation states increases down this triad: Fe < Ru < Os. The maximum oxidation state is 8 for the ruthenium and the lowest oxidation states yet reported for ruthenium is (−2). Aqua ions of Ru(III) are known to exist in solution but only in the absence of anions which are capable of forming complex ions.

Knowing that in aqueous solutions of FeCl₃·6H₂O and RuCl₃·3H₂O, we have:

Thus, during the iron oxide synthesis, some Ru(III) atoms will be incorporated in the Iron oxide structure taking places of some Fe(III) ones.

Section snippets

Experimental details

Ru-alloyed iron oxide thin films were obtained with a non-toxic and easy to manipulate technique, the spray pyrolysis. Two different experimental procedures were followed. The first one consists of spraying FeCl₃·6H₂O (0.03 M)-based aqueous solution during 10 min onto glass substrates heated at 350 °C with a spray flow of 5 ml/min; on which we sprayed immediately an aqueous RuCl₃·3H₂O solution, during shorter time, with molar ratios as RuCl3·3H2O:FeCl3·6H2O = x:1−x, wherein x = 0.00, 0.0156,

X-ray diffraction

The iron oxide phases detected after alloying with different amount of ruthenium were studied using X-ray diffraction (XRD) with a Siemens D500 powder diffractometer (CuKα radiation) in the usual θ–2θ geometry.

Fig. 1 shows the obtained XRD patterns of the samples fabricated according to the first procedure after annealing under vacuum during 5 h at 350 °C. Consequently we have concluded that all the alloyed samples with the different percentages of ruthenium of 0, 0.0156, 0.0317, and 0.1586

Conclusion

In the present work, we had prepared alloyed-iron oxide thin films with different percentages of ruthenium. We followed two procedures of elaboration to show which one will be more efficient to improve their optical and electrical properties. After annealing under vacuum in sealed-tubes during 5 h at 350 °C, the films properties were studied, first by XRD and SEM then optical and electrical characterizations. While the obtained results were so different concerning the morphology, two phases

Acknowledgments

We would like to thank the Management Company of Borj Cedria Technopark, and Mr. Zied Ounissi, the Director of administrative and financial affairs, for the support. We would like to take this opportunity to express our deep gratitude and regard to Mr. Daniel Lincot, « Directeur de Recherche au CNRS Institut de Recherche et Développement sur l'Energie Photovoltaïque (IRDEP), Unité mixte de recherche CNRS-EDF-Chimie Paris Tech Institut Photovoltaïque Ile de France (IPVF) », who gave us an

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View full text

Effect of the ruthenium incorporation on iron oxide phases synthesis, Fe2O3 and Fe3O4, at low annealing temperature

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Experimental details

X-ray diffraction

Conclusion

Acknowledgments

Thin Solid Films

Ceram. Int.

Adv. Colloid Interface Sci.

J. Catal.

Acta Astronautica

Appl. Catal. B Environ.

Thin Solid Films

Surf. Sci.

Chem. Geol.

Mater. Today: Proceedings

Sens. Actuators B Chem.

Sens. Actuators B Chem.

Sol. Energy Mater. Sol. Cells

Thin Solid Films

Mater. Chem. Phys.

Thin Solid Films

Effect of the ruthenium incorporation on iron oxide phases synthesis, Fe₂O₃ and Fe₃O₄, at low annealing temperature