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Zr-engineered charge transport and magnetic frustration in MgCr2O4 spinel: combined impedance spectroscopy, optical analysis, and first-principles study
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DOI：10.1007/s42247-026-01458-9.png)
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Abstract
En 中文
Mg0.8Zr0.2Cr2O4 spinel oxide was successfully synthesized via a sol–gel route, and Rietveld refinement confirmed the formation of a single-phase cubic spinel structure (space group Fd-3 m) with slight lattice expansion (a ≈ 8.342 Å) induced by Zr substitution. Electrical investigations reveal typical semiconducting behavior governed by thermally activated hopping conduction. The AC conductivity follows Jonscher’s universal power law, while the temperature dependence of the frequency exponent s and Seebeck analysis indicate a non-overlapping small-polaron tunneling (NSPT) mechanism with a low hopping barrier (Wₘ ≈ 0.143 eV). DC conductivity obeys Arrhenius behavior with activation energies in the range of 0.27 to 0.35 eV. Dielectric measurements demonstrate pronounced Maxwell–Wagner interfacial polarization and non-Debye relaxation dynamics. Impedance spectroscopy shows a negative temperature coefficient of resistance (NTCR) and dominant grain-boundary contributions, with relaxation processes exhibiting thermally activated behavior consistent with polaronic transport. Optical absorption and reflectance analyses confirm wide-band-gap semiconducting characteristics with an indirect optical band gap of approximately 3.60–3.95 eV, associated with O²⁻ → Cr³⁺ charge-transfer and Cr³⁺ crystal-field transitions. Complementary DFT calculations identify a mixed ferrimagnetic (FM0) ground state stabilized by Zr-induced magnetic frustration and confirm semiconducting electronic structure dominated by O-2p/Cr-3d hybridization with additional Zr-4d contributions. The calculated optical functions reveal moderate anisotropy and low high-energy dielectric losses. Overall, Mg0.8Zr0.2Cr2O4 emerges as a structurally stable wide-band-gap semiconductor with coupled electrical, dielectric, magnetic, and optical functionalities, making it a promising candidate for oxide-electronic and optoelectronic applications.
Keywords:
Mg0.8Zr0.2Cr2O4
Spinel Oxide
Small-Polaron Hopping
Impedance Spectroscopy
Optical Band Gap
DFT
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