Next Article in Journal
Technology-Driven Governance: Advancing CSR Practices in LQ45 Companies
Previous Article in Journal
Integrating Internet with Long-Term Care Management Policy with the Internet
 
 
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Proceeding Paper

Investigation of Structural, Morphological, Optical, and Dielectric Properties of Magnesium Chromite (MgCr2O4) Spinel Oxide †

by
Pavithra Gurusamy
,
Anitha Gnanasekar
and
Geetha Deivasigamani
*
MIT Campus, Anna University, Chennai 600044, India
*
Author to whom correspondence should be addressed.
Presented at the 5th International Electronic Conference on Applied Sciences, 4–6 December 2024; https://sciforum.net/event/ASEC2024.
Eng. Proc. 2025, 87(1), 109; https://doi.org/10.3390/engproc2025087109
Published: 17 September 2025
(This article belongs to the Proceedings of The 5th International Electronic Conference on Applied Sciences)

Abstract

The citrate–nitrate method was employed to synthesize the magnesium chromite (MgCr2O4) spinel, followed by calcination at 700 °C for 3 h. The synthesized compound was analyzed using techniques including powder XRD, SEM-EDAX, FTIR, UV-DRS, and LCR Meter. The structural analysis was conducted using an X-ray diffractometer, which revealed the formation of the cubic crystal symmetry of the sample with the corresponding Fd-3 m space group. The average crystallite size of the sample was calculated around 15.38 nm. Using tetrahedral and octahedral positions, the lattice vibrations of the associated chemical bonds were identified using Fourier transform infrared (FTIR) spectroscopy. SEM (scanning electron microscopy) micrographs showed that the spherical nature of the particles and the constituent particles were between 10 and 40 nm in size. The optical bandgap value was evaluated using Tauc’s plot. Pellets of the powdered sample were prepared for determining the dielectric aspects, such as the dielectric constant (ε′) and tangent loss (tanδ), in the frequency range of 10 Hz–8 MHz at room temperature. The charge transport mechanism was explored from the complex impedance spectroscopy study. The obtained results indicate that magnesium chromite may be a potential candidate in the fabrication of sensors, micro-electronic devices, etc.

1. Introduction

Metal oxides with spinel structure have gained popularity in nanomaterials research because of their distinct physicochemical properties and other potential applications, including superconductors [1], humidity sensors and actuators [2], high-temperature ceramics [3], catalysts [4], magnetic materials [5], and semiconductors [6]. Spinel aluminates, cobaltites, ferrites, and manganates have been extensively studied for their prospective applications in data storage, healthcare, and the electronic industry. However, there are limited investigations on spinel chromites. Spinel chromites are given by the general formula ACr2O4, where A is a divalent metal ion such as Mn2+, Fe2+, Zn2+, Co2+, Cu2+, Ni+2, Ag2+, or Cd+2. Spinel’s electrical transport properties are heavily impacted by their structural and synthesis aspects. Ionic spinels have both electro-active and electro-resistive grains, which affect polaronic transport at different temperatures and frequencies. MgCr2O4 is a p-type semiconductor with a spinel structure consisting of Mg+2 ions in tetrahedral and Cr+3 ions in octahedral sites. The unit cell and structural factors significantly impact the overall transport properties [7]. Dielectric analysis is a potent method for analyzing a material’s electrical response to varying voltages over time and at different frequencies. This technique simulates a genuine system’s electrical conduction response to an idealized model circuit with discrete electrical elements, allowing for distinguishing between the contribution of grains and grain borders to charge transport [8]. Previously, MgCr2O4 was synthesized using traditional methods such as solid-state reaction, co-precipitation, co-crystallization, the microwave method, and hydrated thermal solution. However, these methods resulted in low yield, specific surface area, and catalytic activity even at high sintering temperatures [9]. Sol–gel combustion offers several advantages, including cost effectiveness, auto-purification, chemical homogeneity, fine crystalline powders, low energy consumption, and shorter reaction time [10]. Previous research has focused on magneto-crystalline interactions and magneto-dielectric coupling in spinel chromite [11]. Optimizing microstructural and frequency-dependent electrical transport relaxation mechanisms is critical in determining the magneto-electric properties of spinels for spintronic device applications [12]. This work aims to analyze the dielectric response of MgCr2O4 electro-ceramic oxide to limit its electrical properties for prospective applications. This is the first complete report on the frequency-dependent investigation of magnesio-chromite spinels with a high dielectric constant and low dielectric loss.

2. Experimental Methods

Sol–gel auto-combustion was employed to synthesize MgAl2O4 spinel nanoparticles, which has been extensively researched by Vasyl et al. [10]. This is employed using precursors such as magnesium nitrate, chromium nitrate, citric acid, and an ammonia solution to form the magnesium aluminate nanoparticles ranging from 10 to 40 nm. The particles were then thermally treated for 3 h at 700 °C. Further, the calcined materials were ground with an agate mortar and pestle. Habi ben et al. [13] investigated how the calcination temperature affects the morphology of sol–gel samples using propylene oxide as a fuel. The powder samples were blended with 5% PVA binder for the dielectric study, and then a 13 mm pelletizer was used for compressing the mixture into pellets at the optimum pressure. After polishing the pellets to obtain a smooth surface, they were sintered for 3 h at 700 °C. Finally, the powders and pellets were sent for further characterization.

3. Results and Discussion

3.1. XRD Analysis

The structural characteristics of the synthesized MgCr2O4 powder were investigated using X-ray diffraction (XRD) at room temperature after annealing the sample at 700 °C for 3 h. Figure 1 shows the XRD profile of magnesium chromite, revealing distinct peaks that correlate to the material’s stoichiometry.
Apart from MgCr2O4, no reflections from crystalline MgO, Cr2O3, or CrO3 phases were identified. Hence, the diffractograms confirm the pristine MgCr2O4 spinel formation. The observed patterns with planes (111), (220), (311), (222), (400), (331), (422), (511), (440), (531), and (533) are in accordance with JCPDS Card. No. 82-1529 [7].
The crystallite size is found using Debye Scherrer’s equation [14].
D = K λ β c o s θ
Here, “D” represents the crystallite size, “K” denotes the shape factor, which is a constant value (0.9), “λ” indicates the wave-length source of Cu-Kα at 1.5405 Å, and “β” is the Full-Width Half Maxima (FWHM) of the diffracted peaks [14].
Table 1 shows the derived structural parameters calculated from the XRD spectra. The crystallite size was obtained from Debye Scherrer’s equation and was found to be 15.38 nm. The other structural parameters such as Interplanar distance, volume of the unit cell, lattice constant, Polaron radius, dislocation density, micro-strain, X-ray density, specific surface area, packing factor, and stacking fault were calculated using formulas from the given literature [15,16].

3.2. Functional Group Analysis

Fourier transform infrared (FTIR) spectroscopy was used to establish the formation of metal–oxygen bonds and to eliminate organic and nitrogen phases throughout the post-synthesis and annealing process [10]. In the mid-infrared region (400–4000 cm−1), atomic bonds in molecules exhibit distinct vibration modes that correspond to discrete energy levels. Figure 2 illustrates the IR spectra of samples synthesized with MgCr2O4 using the sol–gel auto-combustion process. The vibrational bands measured around 549.38 cm−1 and 415.59 cm−1 indicate Cr3+-O2− lattice vibrations attributed to the vibrations of Mg2+, Cr3+-O2− in tetrahedral and octahedral configurations [10]. The marker at 1628.72 cm−1 corresponds to the symmetric stretching while 1504.78 cm−1 corresponds to the asymmetric stretching of C-H [14].

3.3. SEM-EDAX Analysis

A scanning electron microscope (SEM) was employed to examine the morphology of the MgCr2O4 sample (Figure 3). Surface topography of MgCr2O4 reveals the structure, size, and shape of elementary grains/agglomerates. SEM images of the prepared MgCr2O4 powder shows particles in the range of 10–40 nm in dense, homogenous stacks with a porous nature. SEM analysis also confirms that spinel-type nano-powders are homogeneous and include consistently sized nanoparticles when citric acid is utilized as fuel.
Energy dispersive X-ray analysis, EDAX, is a widely used technique for determining a material’s stoichiometric composition. The EDAX analysis in Figure 4 shows peaks for magnesium (Mg), chromium (Cr), and oxygen (O), indicating the presence of all ions. Thus, no other impurities were found. Elemental composition data obtained on MgCr2O4 is given in Table 2.

3.4. UV-DRS Analysis

To investigate the optical properties of the prepared sample, UV-DRS was performed. The bandgap of the material is determined using Tauc’s plot method [17]:
α h ν = A ( h ν E g ) n
Here, α = the absorbance coefficient; h = Planck’s constant; ν = the frequency of incident light; A = the arbitrary constant; and Eg = the optical energy bandgap. The exponent n represents the kind of optical transition: if n = 1/2 there is a direct transition, and if n = 2 there is an indirect transition. Figure 4 plots (αhν)2 (where n = 1/2) against hν. The energy bandgap values were determined by intersecting the fitted linear component above the sharp absorption at 1.95 eV with the horizontal axis of energy, depicted in Figure 5.

3.5. Dielectric Analysis

Generally, the dielectric characteristics of spinel aluminates depend upon the compound’s stoichiometry, electric field, preparation methods, and temperature [14]. Oxygen excess and deficit can increase and decrease the oxidation degree of 3d metals. The changing of the charge state of 3d metals as a consequence of changing of oxygen content results in variations in electrical parameters such as resistivity and bandgap. An increase in the unit cell parameter may also be due to oxygen deficiency [18,19]. Figure 6 depicts the relative permittivity of the MgCr2O4 sample at room temperature. The values are relatively high, and the slope of the curve is large. These findings align with previous research indicating that charge polarization, or relaxation polarization, in dense materials with high carrier mobility leads to higher relative permittivity at low frequencies [7]. The dielectric characteristics of MgCr2O4 were investigated between the frequency range of 10 Hz–8 MHz. The dielectric constant of MgCr2O4 depends on the applied electric field and the distribution of magnesium and chromium ions in the sample, and it was found to be very high in this case of MgCr2O4. This might be due to the space charge polarization and grain boundary effects of the prepared sample. The Maxwell–Wagner (M-W) model and Koop’s hypothesis suggest that at low frequencies, the ε r is high, whereas at higher frequencies, it is low.
Figure 7 depicts the room temperature measurement of the tangent loss (tanδ) of MgCr2O4 particles. The relaxation maxima appears in the low frequency range, with a decrease in the higher frequency region. The tangent loss (tanδ) decreases according to Koop’s hypothesis, which states that the loss is higher at lower frequencies and decreases as frequency increases. The dielectric loss factor was found to be tanδ = 3.63, which is less in regard to the previous literature on MgCr2O4 [8].
The relaxation peak might be due to the presence of additional defects within the energy gap, which can lead to space charge polarization or increased energy dissipation [20]. The calculated dielectric characteristics indicate a combination of a high dielectric constant and minimal loss; hence, the results indicate that magnesium chromite may be a potential candidate in the fabrication of sensors, micro-electronic devices, and other electronic equipment.

4. Conclusions

The extensive optical, dielectric, and structural experiments performed here show that the synthesized MgCrO4 is a promising material for sophisticated dielectric applications. XRD investigation verified the formation of a pure spinel structure with the Fd-3 m space group. The average crystallite size was approximately 15.4 nm, which is in accordance with the grain diameters observed in SEM (10–40 nm). Additionally, the FTIR spectra confirmed the existence of distinctive vibrational modes that match the spinel structure. According to UV-DRS, the optical bandgap is 1.95 eV. A high dielectric constant and low dielectric loss were observed in room temperature dielectric experiments, indicating MgCrO4’s potential as an effective choice for sensor technology and for the fabrication of micro-electronic devices.

Author Contributions

Conceptualization, methodology, software, and validation, P.G., A.G., and G.D.; formal analysis and investigation, P.G. and G.D.; writing—original draft preparation, writing—review and editing, P.G. and A.G.; visualization, G.D.; supervision, G.D. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Data will be made available upon request.

Acknowledgments

We thank J. Ramajothi, Department of Applied Sciences and Humanities, MIT Campus, Anna University, Chennai for helping in the dielectric characterization facility.

Conflicts of Interest

The authors declare no conflicts of interest.

References

  1. Kholil, I.; Bhuiyan, M.T.H. Physical properties of spinel-type superconductors CuRh2S4 and CuRh2Se4: A DFT study. Results Phys. 2019, 12, 73–82. [Google Scholar] [CrossRef]
  2. Mansour, A.M.; Morsy, M.; El Nahrawy, A.M.; Abou Hammad, A.B. Humidity sensing using Zn(1.6−x)Na0.4CuxTiO4 spinel nanostructures. Sci. Rep. 2024, 14, 562. [Google Scholar] [CrossRef]
  3. Salomão, R.; Bôas, M.O.C.V.; Pandolfelli, V.C. Porous alumina-spinel ceramics for high temperature applications. Ceram. Int. 2011, 37, 1393–1399. [Google Scholar] [CrossRef]
  4. Gao, F.; Tang, X.; Yi, H.; Zhao, S.; Zhu, W.; Shi, Y. Mn2NiO4 spinel catalyst for high-efficiency selective catalytic reduction of nitrogen oxides with good resistance to H2O and SO2 at low temperature. J. Environ. Sci. 2020, 89, 145–155. [Google Scholar] [CrossRef] [PubMed]
  5. Narayanasamy, A. Magnetic properties of nanostructured spinel ferrites and nanocomposite Nd2Fe14B/α-Fe permanent magnets. Pramana 2005, 65, 893–900. [Google Scholar] [CrossRef]
  6. Chambers, S.A.; Droubay, T.C.; Kaspar, T.C.; Nayyar, I.H.; McBriarty, M.E.; Heald, S.M.; Keavney, D.J.; Bowden, M.E.; Sushko, P.V. Electronic and Optical Properties of a Semiconducting Spinel (Fe2CrO4). Adv. Funct. Mater. 2017, 27, 1605040. [Google Scholar] [CrossRef]
  7. Javed, M.; Khan, A.A.; Ahmed, M.S.; Khisro, S.N.; Kazmi, J.; Bilkees, R.; Khan, M.N.; Mohamed, M.A. Temperature dependent impedance spectroscopy and electrical transport mechanism in sol-gel derived MgCr2O4 spinel oxide. Phys. B Condens. Matter. 2020, 599, 412377. [Google Scholar] [CrossRef]
  8. Goud, T.A.; Charan, G.V. Influence of Ce on structural and electrical properties on Mg nano chromites synthesized by Citrate Gel Auto Combustion method. IOSR J. Appl. Chem. IOSR-JAC 2023, 16, 11–17. [Google Scholar] [CrossRef]
  9. Lenaz, D.; Skogby, H.; Princivalle, F.; Hålenius, U. Structural changes and valence states in the MgCr2O4-FeCr2O4 solid solution series. Phys. Chem. Miner. 2004, 31, 633–642. [Google Scholar] [CrossRef]
  10. Mykhailovych, V.; Kanak, A.; Cojocaru, Ş.; Chitoiu-Arsene, E.-D.; Palamaru, M.N.; Iordan, A.-R.; Korovyanko, O.; Diaconu, A.; Ciobanu, V.G.; Caruntu, G.; et al. Structural, optical, and catalytic properties of MgCr2O4 spinel-type nanostructures synthesized by sol–gel auto-combustion method. Catalysts 2021, 11, 1476. [Google Scholar] [CrossRef]
  11. Lin, G.T.; Tong, W.; Luo, X.; Chen, F.; Yin, L.; Wang, Y.; Hu, L.; Zou, Y.; Yu, L.; Song, W.; et al. Magnetocrystalline interactions in spinel MnCr2O4 single crystal probed by electron spin resonance. J. Alloys Compd. 2017, 711, 250–257. [Google Scholar] [CrossRef]
  12. Hirohata, A.; Yamada, K.; Nakatani, Y.; Prejbeanu, I.-L.; Diény, B.; Pirro, P.; Hillebrands, B. Review on spintronics: Principles and device applications. J. Magn. Magn. Mater. 2020, 509, 166711. [Google Scholar] [CrossRef]
  13. Habi Ben Hariz, S.; Lahmar, H.; Rekhila, G.; Bouhala, A.; Trari, M.; Benamira, M. A novel MgCr2O4/WO3 hetero-junction photocatalyst for solar photo reduction of hexavalent chromium Cr(VI). J. Photochem. Photobiol. A Chem. 2020, 430, 113986. [Google Scholar] [CrossRef]
  14. Jamil, Y.; Jeyakumar, G.P.; Deivasigamani, G. Investigation of Transition Metal Ions Cu2+ and Mg2+ Doped Zinc Aluminate (ZnAl2O4) and Their Structural, Spectral, Optical, and Dielectric Study for High-Frequency Applications. Mater. Proc. 2023, 14, 2. [Google Scholar] [CrossRef]
  15. Yasmin, P.; Gracie, J.; Geetha, D. Effect of cerium substitution on structural, optical, electrical transport and magnetic properties of spinel cobaltite synthesized through citrate-nitrate method. J. Mater. Sci. Mater. Electron. 2024, 35, 293. [Google Scholar] [CrossRef]
  16. Arunkumar, M.; Nesaraj, A.S. Photocatalytic degradation of malachite green dye using NiAl2O4 and Co doped NiAl2O4 nanophotocatalysts prepared by simple one pot wet chemical synthetic route. Iran. J. Catal. 2020, 10, 235–245. [Google Scholar]
  17. Elakkiya, V.; Agarwal, Y.; Sumathi, S. Photocatalytic activity of divalent ion (copper, zinc and magnesium) doped NiAl2O4. Solid State Sci. 2018, 82, 92–98. [Google Scholar] [CrossRef]
  18. Trukhanov, S.V.; Trukhanov, A.V.; Vasiliev, A.N.; Balagurov, A.M.; Szymczak, H. Magnetic state of the structural separated anion-deficient La0.70Sr0.30MnO2.85 manganite. J. Exp. Theor. Phys. 2011, 113, 819–825. [Google Scholar] [CrossRef]
  19. Trukhanov, S.V.; Trukhanov, A.V.; Vasiliev, A.N.; Szymczak, H. Frustrated exchange interactions formation at low temperatures and high hydrostatic pressures in La0.70Sr0.30MnO2.85. J. Exp. Theor. Phys. 2010, 111, 209–214. [Google Scholar] [CrossRef]
  20. Rahman, M.M.; Hasan, N.; Hoque, M.A.; Hossen, M.B.; Arifuzzaman, M. Structural, dielectric, and electrical transport properties of Al3+ substituted nanocrystalline Ni-Cu spinel ferrites prepared through the sol–gel route. Results Phys. 2022, 38, 105610. [Google Scholar] [CrossRef]
Figure 1. XRD Diffractogram of MgCr2O4 nanoparticles synthesized by sol–gel method.
Figure 1. XRD Diffractogram of MgCr2O4 nanoparticles synthesized by sol–gel method.
Engproc 87 00109 g001
Figure 2. FTIR spectrum of MgCr2O4 sample prepared by sol–gel combustion method.
Figure 2. FTIR spectrum of MgCr2O4 sample prepared by sol–gel combustion method.
Engproc 87 00109 g002
Figure 3. SEM image of MgCr2O4 sample at 50 μm magnification.
Figure 3. SEM image of MgCr2O4 sample at 50 μm magnification.
Engproc 87 00109 g003
Figure 4. EDAX spectrum of MgCr2O4 sample after calcining at 700 °C for 3 h.
Figure 4. EDAX spectrum of MgCr2O4 sample after calcining at 700 °C for 3 h.
Engproc 87 00109 g004
Figure 5. Bandgap of MgCr2O4 sample obtained through Tauc’s plot method.
Figure 5. Bandgap of MgCr2O4 sample obtained through Tauc’s plot method.
Engproc 87 00109 g005
Figure 6. Frequency-dependent dielectric constant (εr) of MgCr2O4 sample.
Figure 6. Frequency-dependent dielectric constant (εr) of MgCr2O4 sample.
Engproc 87 00109 g006
Figure 7. Frequency-dependent dielectric loss (tanδ) of MgCr2O4 sample.
Figure 7. Frequency-dependent dielectric loss (tanδ) of MgCr2O4 sample.
Engproc 87 00109 g007
Table 1. Structural parameters of MgCr2O4 obtained through XRD.
Table 1. Structural parameters of MgCr2O4 obtained through XRD.
ParameterValuesParameterValues
Crystallite size (D)
(nm)
15.38Dislocation density (δ)
(10−3/m2)
0.004
Interplanar distance (d) Å2.08Micro-strain (ε)1.15
Crystal structureCubic FCX-ray density
Dx (g/cm3)
1.93
Volume of the unit cell (a3) Å631.48Specific surface area S (cm2/g)2.02
Lattice constant Å8.54Packing factor P7.36
Polaron radius γ (Å)1.50Stacking fault SF0.39
Table 2. Percentages of elements obtained from the energy dispersive X-ray spectra of MgCr2O4.
Table 2. Percentages of elements obtained from the energy dispersive X-ray spectra of MgCr2O4.
ElementWeight %Atomic %
O41.0063.82
Mg14.5114.86
Cr44.5021.31
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Share and Cite

MDPI and ACS Style

Gurusamy, P.; Gnanasekar, A.; Deivasigamani, G. Investigation of Structural, Morphological, Optical, and Dielectric Properties of Magnesium Chromite (MgCr2O4) Spinel Oxide. Eng. Proc. 2025, 87, 109. https://doi.org/10.3390/engproc2025087109

AMA Style

Gurusamy P, Gnanasekar A, Deivasigamani G. Investigation of Structural, Morphological, Optical, and Dielectric Properties of Magnesium Chromite (MgCr2O4) Spinel Oxide. Engineering Proceedings. 2025; 87(1):109. https://doi.org/10.3390/engproc2025087109

Chicago/Turabian Style

Gurusamy, Pavithra, Anitha Gnanasekar, and Geetha Deivasigamani. 2025. "Investigation of Structural, Morphological, Optical, and Dielectric Properties of Magnesium Chromite (MgCr2O4) Spinel Oxide" Engineering Proceedings 87, no. 1: 109. https://doi.org/10.3390/engproc2025087109

APA Style

Gurusamy, P., Gnanasekar, A., & Deivasigamani, G. (2025). Investigation of Structural, Morphological, Optical, and Dielectric Properties of Magnesium Chromite (MgCr2O4) Spinel Oxide. Engineering Proceedings, 87(1), 109. https://doi.org/10.3390/engproc2025087109

Article Metrics

Back to TopTop