José Artigas dos Santos Laranjeira

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.

Replacing lead in halide perovskites without sacrificing their optoelectronic versatility remains a central challenge in sustainable materials chemistry. Bismuth(III), isoelectronic with Pb2+, offers a chemically robust route to this goal, but its compounds are typically evaluated for a single function, namely light absorption, photocatalysis, or thermal transport in isolation. In this work, we show that a single, mechanochemically synthesized layered halide platform, Cs3Bi2Br9 and its iodine-substituted analogue Cs3Bi2Br6I3, integrates all three. High-resolution synchrotron diffraction resolves the corner-sharing [Bi(Br,I)6] octahedral layers and reveals a stereochemically active Bi3+ lone pair whose signature, being pronounced, temperature-dependent atomic displacement anisotropy; we quantify with a site-resolved Debye model. This lone-pair-driven lattice softness rationalizes an intrinsically low thermal conductivity (~0.15–0.25 W m−1K−1), further suppressed by iodine substitution. Group-theory-assigned Raman and infrared phonons, validated against DFT lattice dynamics, and direct optical gaps of 2.65 and 2.20 eV place both compounds’ absorption edges in the visible range. We demonstrate that Cs3Bi2Br9 photocatalytically degrades the organic dye Rhodamine B roughly 75-fold faster than direct photolysis and retains full activity over four reuse cycles. These results establish compositional Br/I tuning as a single structural handle for co-engineering optical, thermal and catalytic function in lead-free layered halides.

Phase-dependent optoelectronic, excitonic properties and solar energy conversion efficiency of up to 33% of monolayer Y ₂ TeO ₂ MOenes (1T and 2H Phases).

Two-dimensional carbon nitride materials have emerged as promising candidates for multifunctional applications. Motivated by the growing interest in carbon nitride-based two-dimensional materials, we investigated the hydrogen storage capacity of a Li-decorated P–C3N (Li@P–C3N) monolayer using density functional theory (DFT) calculations. Upon functionalization with Li atoms, the P–C3N monolayer can accommodate up to 12 H2 molecules, achieving a hydrogen storage capacity of 9.59 wt % with adsorption energies ranging from −0.18 to −0.13 eV per H2. The calculated material-level gravimetric capacity exceeds the numerical value of the DOE system-level gravimetric target. The hydrogen adsorption mechanism on Li@P–C3N was analyzed through charge transfer analysis, projected density of states (PDOS), and noncovalent interaction (NCI) analysis. The thermal stability of both pristine P–C3N and Li@P–C3N systems was examined using ab initio molecular dynamics (AIMD). Furthermore, the dynamical stability of Li@P–C3N was confirmed through phonon dispersion calculations. The reversibility of hydrogen adsorption in the Li@P–C3N + 12H2 system was also investigated using AIMD simulations. These results demonstrate that Li-decorated P–C3N is a highly efficient candidate for hydrogen storage. Therefore, experimental investigations of P–C3N are strongly encouraged to validate its potential for reversible hydrogen storage applications.