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<p>Cd<sub>x</sub>Co<sub>1−x</sub>Fe<sub>2</sub>O<sub>4</sub> (x = 0.25, 0.50, 0.75) spinel ferrite nanoparticles were successfully synthesized using the co-precipitation technique. X-ray diffraction (XRD) analysis confirmed the formation of cubic spinel structure with space group Fd̅3m for all compositions. The structural analysis revealed a non-monotonic dependence of the average crystallite size (D) on Cd content, varying from a minimum of 9.58&#xa0;nm at x = 0.50 to a maximum of 16.36&#xa0;nm at x = 0.75. A similar non-linear trend was observed in the defect-related parameters, where the dislocation density (δ), microstrain (ε), and stacking fault probability (SF) reached their highest values at x = 0.50 (δ = 10.90 × 10<sup>−3</sup> lines/nm2, ε = 11.73   ×  10<sup>−3</sup>, SF = 7.04  ×  10<sup>−3</sup>). Scanning electron microscopy (SEM) images confirmed a transition from spherical nanoparticles to well-defined crystalline facets as cadmium substitution increases. Also, SEM analysis demonstrates that Cd<sup>2+</sup> substitution significantly promotes grain growth and alters surface topography, providing a mechanism for tuning the microstructural properties of spinel ferrites. Fourier-transform infrared spectroscopy (FTIR) confirmed the formation of the spinel structure through the characteristic metal–oxygen stretching vibrations at tetrahedral (551–587&#xa0;cm<sup>−1</sup>) and octahedral (416–458&#xa0;cm<sup>−1</sup>) sites. The presence of residual organic species from the washing process was also identified. UV–Vis diffuse reflectance spectroscopy revealed that the optical bandgap (E<sub>g</sub>) decreases monotonically with increasing Cd<sup>2+</sup> concentration, from 4.89&#xa0;eV (x = 0.25) to 4.83&#xa0;eV (x = 0.50), and further to 4.79&#xa0;eV (x = 0.75). This bandgap narrowing is attributed to lattice expansion, cation redistribution, and the possible introduction of mid-gap defect states. These findings demonstrate that controlled cadmium substitution provides an effective strategy for tailoring both the structural characteristics and optical bandgap of cobalt ferrite nanoparticles. The composition with x = 0.75, exhibiting the largest crystallite size, lowest defect density, and smallest bandgap, is identified as the most promising candidate for potential applications in photocatalysis and optoelectronics.</p>

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Structural, optical, and morphological characterization of CdxCo1−xFe2O4 spinel ferrite nanoparticles synthesized via the co-precipitation method

  • 期刊论文

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  • 发表日期：

    2026年7月7日

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  • Yousef A. Alsabah,
  • A. M. Abdulkarem,
  • Ibrahim Alsuqia,
  • Olfat Humaid,
  • Abdelrahman A. Elbadawi,
  • Gobran N. Ali,
  • A. A. Al-Muntaser

摘要

CdxCo1−xFe2O4 (x = 0.25, 0.50, 0.75) spinel ferrite nanoparticles were successfully synthesized using the co-precipitation technique. X-ray diffraction (XRD) analysis confirmed the formation of cubic spinel structure with space group Fd̅3m for all compositions. The structural analysis revealed a non-monotonic dependence of the average crystallite size (D) on Cd content, varying from a minimum of 9.58 nm at x = 0.50 to a maximum of 16.36 nm at x = 0.75. A similar non-linear trend was observed in the defect-related parameters, where the dislocation density (δ), microstrain (ε), and stacking fault probability (SF) reached their highest values at x = 0.50 (δ = 10.90 × 10−3 lines/nm2, ε = 11.73   ×  10−3, SF = 7.04  ×  10−3). Scanning electron microscopy (SEM) images confirmed a transition from spherical nanoparticles to well-defined crystalline facets as cadmium substitution increases. Also, SEM analysis demonstrates that Cd2+ substitution significantly promotes grain growth and alters surface topography, providing a mechanism for tuning the microstructural properties of spinel ferrites. Fourier-transform infrared spectroscopy (FTIR) confirmed the formation of the spinel structure through the characteristic metal–oxygen stretching vibrations at tetrahedral (551–587 cm−1) and octahedral (416–458 cm−1) sites. The presence of residual organic species from the washing process was also identified. UV–Vis diffuse reflectance spectroscopy revealed that the optical bandgap (Eg) decreases monotonically with increasing Cd2+ concentration, from 4.89 eV (x = 0.25) to 4.83 eV (x = 0.50), and further to 4.79 eV (x = 0.75). This bandgap narrowing is attributed to lattice expansion, cation redistribution, and the possible introduction of mid-gap defect states. These findings demonstrate that controlled cadmium substitution provides an effective strategy for tailoring both the structural characteristics and optical bandgap of cobalt ferrite nanoparticles. The composition with x = 0.75, exhibiting the largest crystallite size, lowest defect density, and smallest bandgap, is identified as the most promising candidate for potential applications in photocatalysis and optoelectronics.