Defect-Mediated Electronic Structure in Ag2CrO4: From Electronic Structure and Bonding Analysis to Optical, Magnetic, and Transport Responses

Abstract

Silver chromate (Ag2CrO4) was synthesized via a microwave-assisted hydrothermal route to elucidate how defect-mediated structural distortions govern its multifunctional properties. X-ray diffraction and Rietveld refinement suggest a phase-pure orthorhombic structure, while selected-area electron diffraction (SAED) and Raman analyses reveal local lattice strain and symmetry breaking associated with defect-induced heterogeneity. Electron microscopy shows platelet-like microcrystals with a hierarchical morphology. Optical measurements indicate strong visible-light absorption with an indirect band gap of 1.91 eV, in excellent agreement with density functional theory (DFT) calculations (1.94 eV). Electronic-structure analysis reveals that O 2p states dominate the band edges, with strong Ag–O hybridization playing a central role in stabilizing the electronic states. Crystal orbital Hamilton population (COHP) results further suggest antibonding contributions near the band edges, explaining the enhanced defect sensitivity. Photoluminescence exhibits a broad emission dominated by deep-level states, evidencing a high density of defect-induced traps. Magnetization measurements reveal a complex magnetic response characterized by the coexistence of weak ferro-/ferrimagnetic and temperature-dependent paramagnetic contributions, consistent with structural distortions of the [CrO4] tetrahedra and the associated defect states. Temperature-dependent electrical measurements show a nearly 4-order-of-magnitude increase in conductivity between 373 and 573 K, following Arrhenius behavior with an activation energy of approximately 0.76 eV. These results indicate thermally activated transport consistent with carrier release from localized states and defect-mediated conduction. Overall, the combined experimental and theoretical results establish a consistent defect-driven structure–property framework, providing mechanistic insight into the coupling between bonding, electronic structure, and multifunctional response in Ag2CrO4.