Structural and electronic insights into Cr-doped CuS nanoparticles through XRD, EPR, and synchrotron radiation-based...

Copper sulfide (CuS) is a multifunctional semiconductor with broad potential in catalysis, energy storage, and spintronics. In this work, Cr-doped CuS nanoparticles (Cu_1-xCr_xS, 0 ≤ x ≤ 0.4) were synthesized and investigated using scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM/EDX), X-ray diffraction (XRD), electron paramagnetic resonance (EPR), and synchrotron-based X-ray absorption fine-structure spectroscopy (XAFS). SEM/EDX analyses reveal the nanostructured morphology of the samples and the homogeneous distribution of Cr within the Cu_1-xCr_xS matrix. XRD suggests the retention of the hexagonal covellite CuS phase across the entire doping series, while increasing Cr content, particularly beyond x ≈ 0.2, induces asymmetric peak broadening, selective intensity variations, and suppression of specific reflections, indicating increased lattice strain and solubility-limit-related structural perturbations. EPR reveals the presence of Cr³⁺ ions and magnetic defect states, accompanied by non-monotonic variations in linewidth and signal asymmetry at higher doping levels. XANES and EXAFS analyses support the substitution of Cu by Cr³⁺ within the covellite lattice, with the Cu-S first coordination shell remaining largely preserved, whereas higher-shell disorder progressively increases with Cr incorporation. Combined XRD, EPR, and XAFS results identify a composition range of x ≈ 0.05-0.1 associated with minimal structural perturbation, a transition regime at x = 0.1-0.2, and increasing local disorder at x ≥ 0.2. These findings correlate local Cr coordination with defect formation, lattice distortion, and local electronic-structure evolution. The results provide a spectroscopic and structural framework for understanding Cr-induced modifications in CuS-based materials.