Elsevier

Current Applied Physics

Volume 22, February 2021, Pages 20-29
Current Applied Physics

Structural, magnetic and dielectric study of Fe2O3 nanoparticles obtained through exploding wire technique

https://doi.org/10.1016/j.cap.2020.11.009Get rights and content

Highlights

  • α and γ-phase Fe2O3 nanoparticles were synthesized by Exploding Wire Technique (EWT).

  • Structural, thermal, optical, magnetic and dielectric properties studied in detail.

  • Enhanced Eg, TB at 57K, double excitation and ligand field transitions are detected.

  • Dielectric constant and loss decrease with increase in applied high frequency.

  • AC conductivity and dielectric attributes are suitable for high frequency devices.

Abstract

We propose an exploding wire technique based facile approach to prepare Fe2O3 nanoparticles in ambient conditions. TG-DSC analysis of the prepared precursor (Fe(OH)3) nanoparticles were done. The phase, lattice parameter and the average crystallite size were evaluated through X-ray diffraction analysis. The morphology of prepared nanoparticles was studied by scanning electron microscopy and Transmission electron microscope. The functional group formation of Fe2O3 nanoparticles and intrinsic stretching vibration bands of Fe–O were estimated through FTIR analysis. The direct band gap of Fe2O3 nanoparticles occurring in conjunction with indirect band gaps was established via Tauc plot. The magnetic parameters were studied through Mössbauer spectroscopy, ESR, M-H and M-T plot analysis. The attributes of dielectric behaviour like dielectric constant (ε′), loss tangent (tan δ), dielectric loss (ε″) and alternating current (AC) conductivity (σAC) were measured at various temperatures in the frequency range of 10 Hz-106 KHz.

Introduction

In recent years, researchers have shown interest in developing and enhancing magnetic properties using well controlled synthesis conditions [1,2]. Iron oxide nanoparticles attract scientific groups due to their catalytic, optic, magnetic and electric properties [3,4]. Out of three oxides of iron, iron (III) oxide (Fe2O3) is the main oxide, whereas iron (II, III) oxide (Fe3O4) is naturally occurring and iron (II) oxide (FeO) is scarcely found. Hematite (α-Fe2O3) is used as main component for steel production. It also acts as starting material for the synthesis of maghemite (γ-Fe2O3) and magnetite (Fe3O4) [5]. Hematite (α-Fe2O3), an iron oxide, is widely studied because of its technological utilities like catalyst (used in fuel-cell reactions), ferrofluids, information storage disks, pigment, environmental pollutant cleaning agent, sensor, biological material for targeted drug delivery, cancer diagnoses, electrode material and magnetic material [[6], [7], [8]]. Fe2O3 nanoparticles can be easily converted to spinel ferrite MFe2O4 (M is divalent cation) [[9], [10], [11]] like zinc ferrite which could be proposed for active detection of COVID 19 [12]. Hematite (paramagnetic) has superior properties of highly resistive against corrosion, highly chemically stable oxide of iron, biocompatibility, non-toxic, environment friendly and cost effective. The advanced oxidation process (AOP) is the best alternative to precipitation, adsorption and filtration for decomposition of waste organic pollutants. Photocatalytic process used for waste treatment, uses AOP to produce highly reactive hydroxyl radical (OH−1). Fe+3/Fe+2 (catalyst) interacts with H2O2 (oxidising agent) to form hydroxyl radical (OH−1) [13]. Fe2O3 is semiconducting (n type under ambient condition) in nature with rhombohedral crystal structural (space group R-3c) [6]. Band gap of 2.1 eV is reported for Fe2O3 [14]. The values of isomer shift less than 0.5 mm/s of Mössbauer spectra indicates the existence of Fe+3 valence states [15]. Magnetic material exhibits highly exclusive applications in high frequency region (MHz to GHz) [16]. Analogous to curie temperature for ferromagnetic, Néel temperature (TN) is temperature above which antiferromagnetic material becomes paramagnetic. Marin temperature (TM) is magnetic phase transition temperature (a spin-flip transition), below which antiferromagnetic ordering flips from perpendicular to c-axis to parallel to c-axis. A weak ferromagnetic material becomes antiferromagnetic below TM [6]. Néel temperature (TN) and Marin temperature (TM) of bulk hematite (TN ~960 K, TM~263 K) decrease with decrease in particle size [6,17]. Morin temperature is not shown by particles of size 10 nm or lesser [6,18]. Lu et al. described size dependent Néel temperature (TM) and Morin temperature (TM) of hematite through cohesive energy model and thermodynamic analytic models respectively [17]. As hematite shows superparamagnetic, weak-ferromagnetic and antiferromagnetic properties, it is interesting material for researchers to investigate magnetic properties [6,18]. Dielectric constant describes the electrical properties of insulators (dielectric material) [19]. The state of material is defined by dependence of dielectric constant on temperature and frequency of applied alternating fields [20]. The low eddy currents and high resistivity are favorable properties for materials used for electronic and electrical devices [20].

Magnetic, optical and electrical properties of hematite are sensitive to crystallinity, morphology and inter-particle interactions [6,18]. Magnetic properties like coercivity, saturation magnetization and superparamagnetism are found sensitive to the size of grains, clusters and interactions [21]. Different synthesis methods, such as precipitation, sol-gel, hydrothermal, solvothermal, thermal decomposition, chemical vapour deposition, mechanochemical have been adopted to prepare nanosized hematite [6,7,22]. Bhushan et al. prepared nanosized hematite (7–25 nm) coated with octyl ether and Oleic acid using chemical route [23]. Y. Al-Douri et al. have used pulsed laser ablation method to prepare nanoparticles [24]. Above mentioned methods have demerits like impurity, inferior quality, toxic and hazardous by-products [25]. Drastic variation in magnetic behaviour, like presence or absence of morin temperature, was shown by varying particle size [23]. Yan et al. prepared α-Fe2O3 nanoparticles (size of d~30 nm and L~150 nm) through calcination of spindle shaped β-FeOOH at 600 °C for 2 h [26].

It is well known that microwave sources are controlled by electrical circuits but the control on microwaves in free space is still a challenge. The main goal would be to tune the matter and microwaves interaction through electrical means. The dielectric response of material governs mass interactions. Nanomaterial with tuneable permittivity (or permeability) and conductivity can act as adaptive surfaces in microwave frequencies [27]. Ferromagnetic material like nickel ferrite, cobalt oxides and ferro ferric oxide can achieve high microwave attenuation [28,29]. There is no report available on high temperature microwave absorption capability [29]. Our attempt is motivated by such challenges. In this paper, we report the synthesis of hematite through EWT and perform thermal, structural, optical, morphological, magnetic, electrical and dielectric analysis.

Section snippets

Process and mechanism of synthesis

In present work, we adopted Exploding Wire Technique (EWT) to obtain iron oxide nanoparticles [20,30]. The details of procedure and mechanism of obtaining nanoparticles through EWT are already explained in previous paper. To obtain iron oxide nanoparticles via EWT, Fe wire (purity 99%) was struck against Fe plate (purity 99%) in an aqueous solution of Fecl3.6H2O. The governing chemical reactions that synthesized the nanoparticles are as follows:

When Fecl3.6H2O (solid) is dissolved in deionized

TG-DSC analysis

Thermogravimetry (TG) and Differential Scanning Calorimeter (DSC) analysis of the prepared precursor (Fe(OH)3) nanoparticles are depicted in Fig. 1. The TG curve shows that Fe(OH)3 decomposes in two steps within the measured temperature range of 30 °C–600 °C.

There is mass loss of 7.7% in the temperature range of 30 °C–194 °C. In this interval of temperature, the precursor Fe(OH)3 undergoes dehydration and recrystallization to produce Fe2O3.2H2O. The mass loss is in the form of water molecules.

Conclusions

Mixed phases of rhombohedral hematite (α-Fe2O3) and cubic maghemite (γ-Fe2O3) were successfully synthesized by EWT. It is confirmed through Mössbauer analysis that antiferromagnetic axis is perpendicular and parallel to c-axis at 300 K and 100 K, respectively. It is confirmed here that the direction of antiferromagnetic axis turns continuously as temperature decreases. The absorption intensity of Mössbauer hyperfine lines is higher at lower temperature (100 K) as compared to that at 300 K. The

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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