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<p>The present study systematically explores defect engineering through co-doping with fixed 2% nickel (Ni) and varying aluminum (Al) concentrations (2%, 4%, 6%, 8%) using a cost-effective co-precipitation method followed by calcination at 1000°C. Pristine Cr<sub>2</sub>O<sub>3</sub>, 2% Ni-doped, and Ni-Al co-doped samples were comprehensively characterized via powder x-ray diffraction (XRD) with Rietveld refinement, x-ray photoelectron spectroscopy (XPS), Raman spectroscopy, Fourier-transform infrared (FTIR) spectroscopy, UV–visible (UV–Vis) spectrophotometry, and vibrating-sample magnetometry (VSM). Rietveld analysis confirms retention of single-phase rhombohedral corundum structure across all compositions, with no secondary phases. However, lattice parameters (a, c) and unit cell volume systematically contract due to the ionic radii mismatch of the host (Cr<sup>3+</sup>) and dopant cation (Al<sup>3+</sup><sub>,</sub> Ni<sup>2+</sup>). XPS reveals successful Ni<sup>2+</sup> and Al<sup>3+</sup>incorporation at Cr<sup>3+</sup> sites, increasing Cr<sup>4+</sup> fraction (up to 4% Al content) and oxygen vacancy for charge balance. Raman and FTIR spectra show redshifted Cr-O octahedral modes, reflecting bond-length shortening and strain without impurity peaks. UV–Vis spectra exhibit bandgap narrowing from 3.0&#xa0;eV (pristine) to 2.89&#xa0;eV (8% Al) due to defects induced by dopant cations. VSM hysteresis loops demonstrate weak room-temperature ferromagnetism (RTFM) peaking at 6% Al, attributed to Cr<sup>4+</sup>/oxygen vacancy synergies, transitioning to paramagnetism beyond 6% Al due to nonmagnetic dilution. These findings demonstrate the synergistic effect of Ni-Al co-doping into Cr<sub>2</sub>O<sub>3</sub> nanoparticles, rendering tunable optical/magnetic properties for <i>p</i>-type transparent conducting oxides and spintronic device-based applications.</p>

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Defect Engineering via Al, Ni Co-Doping: Structural, Optical, and Magnetic Properties of Cr2O3 Nanoparticles

  • 期刊论文

  • 发表日期：

    2026年3月24日

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  • Sandeep Kumar,
  • Jarnail Singh,
  • Kaushal Kumar,
  • Pankaj Bhardwaj,
  • Manvinder Kaur,
  • Sachin Kalsi

摘要

The present study systematically explores defect engineering through co-doping with fixed 2% nickel (Ni) and varying aluminum (Al) concentrations (2%, 4%, 6%, 8%) using a cost-effective co-precipitation method followed by calcination at 1000°C. Pristine Cr2O3, 2% Ni-doped, and Ni-Al co-doped samples were comprehensively characterized via powder x-ray diffraction (XRD) with Rietveld refinement, x-ray photoelectron spectroscopy (XPS), Raman spectroscopy, Fourier-transform infrared (FTIR) spectroscopy, UV–visible (UV–Vis) spectrophotometry, and vibrating-sample magnetometry (VSM). Rietveld analysis confirms retention of single-phase rhombohedral corundum structure across all compositions, with no secondary phases. However, lattice parameters (a, c) and unit cell volume systematically contract due to the ionic radii mismatch of the host (Cr3+) and dopant cation (Al3+, Ni2+). XPS reveals successful Ni2+ and Al3+incorporation at Cr3+ sites, increasing Cr4+ fraction (up to 4% Al content) and oxygen vacancy for charge balance. Raman and FTIR spectra show redshifted Cr-O octahedral modes, reflecting bond-length shortening and strain without impurity peaks. UV–Vis spectra exhibit bandgap narrowing from 3.0 eV (pristine) to 2.89 eV (8% Al) due to defects induced by dopant cations. VSM hysteresis loops demonstrate weak room-temperature ferromagnetism (RTFM) peaking at 6% Al, attributed to Cr4+/oxygen vacancy synergies, transitioning to paramagnetism beyond 6% Al due to nonmagnetic dilution. These findings demonstrate the synergistic effect of Ni-Al co-doping into Cr2O3 nanoparticles, rendering tunable optical/magnetic properties for p-type transparent conducting oxides and spintronic device-based applications.