Sol–Gel Synthesis and Multi-Technique Characterization of Graphene-Modified Ca2.95Eu0.05Co4Ox Nanomaterials

This study employs a multi-technique approach to elucidate how graphene incorporation affects phase formation, microstructure, and thermal behavior in PVA-assisted sol-gel synthesized Ca_2.95Eu_0.05Co₄O_x nanomaterials. XRD confirms the preservation of the primary phases (hexagonal CaCO₃ and cubic CoO) alongside a distinct graphene (002) reflection; a systematic low-angle shift of the calcite (104) peak evidences partial relaxation of residual lattice strain with increasing graphene content, while Scherrer analysis indicates tunable crystallite size. Raman spectroscopy corroborates graphene incorporation through pronounced D (~1300 cm^-1) and G (~1580 cm^-1) bands and supports the XRD-identified phase coexistence via cobalt-oxide and calcite vibrations in the 200-700 cm^-1 region, also indicating increased defect/disorder with graphene loading. SEM shows grain refinement, denser/bridged lamellar textures, and reduced porosity at low-moderate graphene contents (1-3 wt.%), contrasted by agglomeration-driven heterogeneity at higher loadings (5-7 wt.%). EDX reveals increasing carbon with Ca/Co redistribution at accessible surfaces, and TG-DSC corroborates the removal of oxygen-containing groups and oxidative combustion of graphene at mid temperatures. Collectively, Raman-XRD-consistent evidence demonstrates that graphene provides a tunable handle over lattice strain, crystallite size, and grain-boundary architecture, establishing a processing-composition basis for optimizing functional (e.g., electrical/thermoelectric) performance.