1：Experimental Design and Method Selection:

The study used a standard Pechini sol–gel process for synthesis, followed by annealing. Characterization techniques included FESEM, EDX, DRS, FTIR, Hall Effect measurements, and I–V characteristics to analyze morphology, composition, optical properties, and electrical behavior.

2：Sample Selection and Data Sources:

Samples were synthesized with varying Fe concentrations (x = 0, 0.027, 0.055, 0.097, 0.125) using high-purity precursors. Data were collected from laboratory measurements on these synthesized nanopowders.

3：027, 055, 097, 125) using high-purity precursors. Data were collected from laboratory measurements on these synthesized nanopowders. List of Experimental Equipment and Materials:

3. List of Experimental Equipment and Materials: Equipment included Bruker D2 Phaser X-ray diffractometer, FT-IR Tensor 27 (Bruker), FE SEM JSM-7600F, Agilent UV-vis spectrometer (Cary 60), Hall Effect Set-up (DHE-21), and Keithley source meter 2401. Materials included copper(II) oxide (99.7%, Alfa Aesar), iron(III) nitrate nonahydrate (98%, Alfa Aesar), citric acid, glycerol, HNO3, and double distilled water.

4：Materials included copper(II) oxide (7%, Alfa Aesar), iron(III) nitrate nonahydrate (98%, Alfa Aesar), citric acid, glycerol, HNO3, and double distilled water. Experimental Procedures and Operational Workflow:

4. Experimental Procedures and Operational Workflow: Precursors were dissolved, mixed with gelling agents, heated to form a gel, burnt to produce powder, and annealed at 450°C and 600°C. Characterization involved sample preparation and measurement using the specified instruments under standard conditions (e.g., room temperature for optical and Hall measurements).

5：Data Analysis Methods:

Data were analyzed using techniques such as Scherrer equation for crystallite size from XRD, Tauc relation for band gap from DRS, and standard formulas for Hall coefficient and carrier density.