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<p>A Zr-substituted chromite spinel, Mg<sub>0.5</sub>Zr<sub>0.5</sub>Cr<sub>2</sub>O<sub>4</sub>, was investigated to elucidate the interplay between defect chemistry, charge transport, dielectric relaxation, magnetic response, and optical activity. Comprehensive magnetic, ESR, impedance, dielectric, and optical spectroscopies were performed over 80–300&#xa0;K and 10&#xa0;Hz–6&#xa0;MHz. Magnetization and ESR measurements reveal thermally driven exchange-coupled Cr-based magnetic ordering. Electrical and dielectric analyses demonstrate that charge transport is governed by a correlated barrier hopping (CBH) mechanism, with a barrier height of approximately 0.19&#xa0;eV and DC activation energy of 0.17&#xa0;eV, confirming small-polaron-mediated hopping between defect-induced localized states created by aliovalent Zr<sup>4+</sup> substitution and oxygen vacancies. The dielectric response shows strong Maxwell–Wagner polarization and non-Debye relaxation, with grain-boundary resistance decreasing from 4.3 × 10<sup>5</sup> Ω at 80&#xa0;K to 2.4 × 10<sup>4</sup> Ω at 280&#xa0;K, while grain resistance drops from 2.0 × 10<sup>4</sup> to 4.0 × 10<sup>3</sup> Ω, indicating a transition from grain-boundary- to bulk-dominated conduction. Optical spectroscopy reveals wide-band gap semiconducting behavior with an indirect band gap of ~3.51&#xa0;eV and a direct transition at ~3.93&#xa0;eV, accompanied by strong Cr–O charge-transfer absorption and a maximum optical conductivity of ~8 × 10<sup>7</sup>&#xa0;s<sup>−1</sup> in the visible–UV region. Compared with heterostructured and transition-metal-doped MgCr<sub>2</sub>O<sub>4</sub> systems, Mg<sub>0.5</sub>Zr<sub>0.5</sub>Cr<sub>2</sub>O<sub>4</sub> achieves intrinsic multifunctionality through internal defect engineering, providing simultaneous enhancement of electrical, dielectric, and optical responses within a single-phase spinel lattice.</p>

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Zr-induced defect engineering in MgCr2O4 spinel: from correlated barrier hopping to enhanced optical and dielectric responses

  • 期刊论文

  • 发表日期：

    2026年4月8日

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  • Ghada Raddaoui,
  • Karim Souifi,
  • Abdullah Saad Alsubaie,
  • Elyor Berdimurodov,
  • Khasan Berdimuradov

摘要

A Zr-substituted chromite spinel, Mg0.5Zr0.5Cr2O4, was investigated to elucidate the interplay between defect chemistry, charge transport, dielectric relaxation, magnetic response, and optical activity. Comprehensive magnetic, ESR, impedance, dielectric, and optical spectroscopies were performed over 80–300 K and 10 Hz–6 MHz. Magnetization and ESR measurements reveal thermally driven exchange-coupled Cr-based magnetic ordering. Electrical and dielectric analyses demonstrate that charge transport is governed by a correlated barrier hopping (CBH) mechanism, with a barrier height of approximately 0.19 eV and DC activation energy of 0.17 eV, confirming small-polaron-mediated hopping between defect-induced localized states created by aliovalent Zr4+ substitution and oxygen vacancies. The dielectric response shows strong Maxwell–Wagner polarization and non-Debye relaxation, with grain-boundary resistance decreasing from 4.3 × 105 Ω at 80 K to 2.4 × 104 Ω at 280 K, while grain resistance drops from 2.0 × 104 to 4.0 × 103 Ω, indicating a transition from grain-boundary- to bulk-dominated conduction. Optical spectroscopy reveals wide-band gap semiconducting behavior with an indirect band gap of ~3.51 eV and a direct transition at ~3.93 eV, accompanied by strong Cr–O charge-transfer absorption and a maximum optical conductivity of ~8 × 107 s−1 in the visible–UV region. Compared with heterostructured and transition-metal-doped MgCr2O4 systems, Mg0.5Zr0.5Cr2O4 achieves intrinsic multifunctionality through internal defect engineering, providing simultaneous enhancement of electrical, dielectric, and optical responses within a single-phase spinel lattice.