Physics

Layered Na 2 CaV 4 O 12 is a highly promising electrode material and a key intermediate in the hydrometallurgical extraction of vanadium from raw materials; however, the mechanism of its dissolution in water remains unclear. A combined experimental and density functional theory (DFT) study was conducted to elucidate the dissolution process at the atomic scale. Experimental results show that Na 2 CaV 4 O 12 completely dissociates in neutral water, releasing Na + and vanadate species into solution, while Ca 2+ reprecipitates as CaV 2 O 6 upon reaching supersaturation. DFT simulations reveal that the dissolution proceeds spontaneously via a layer-by-layer exfoliation mechanism on the dominant (001) surface. Water adsorption sequentially weakens Na-O bonds (E ads = −0.628 eV), leading to the release of Na + , promotes Ca 2+ detachment through a hydrogen-bonding network (E ads = −0.873 eV), and finally triggers dissociative chemisorption on the exposed cyclic V 4 O 12 clusters (E ads = −2.501 eV), cleaving them into chain-like VO 3 - units. This work provides fundamental insights for the design of stable vanadium-based materials and the optimization of hydrometallurgical processes. • Na 2 CaV 4 O 12 fully decomposes in neutral water; Ca reprecipitates as CaV 2 O 6 . • Leaching shows Na and vanadate species enter solution while pH stays near-neutral. • DFT reveals self-promoting (001) exfoliation: water weakens Na-O then Ca-O bonds. • Dissociative water adsorption on V 4 O 12 rings drives reconstruction to VO 3 chains.

Amorphous calcium phosphate (ACP) and amorphous calcium carbonate (ACC) are the core materials in the biogenic construction of protective shells and functional architectures. Through non-classical crystallization pathways, organisms transform these amorphous phases into inorganic materials with excellent mechanical, optical or adhesive properties, such as bones, nacre, and oyster reefs, which are formed under mild environments but exhibit remarkable resilience in extreme conditions. Consequently, biomimetic mineralization strategies leveraging ACP and ACC hold significant promise for novel material synthesis. At present, ACP and ACC cannot be synthesized under the same mechanism, and the existing methods usually weaken the stability and biomaterial properties of products. In this study, an ethanol-based system was employed to achieve the stable synthesis of ACP and ACC with the assistance of biocompatible γ-aminopropyltriethoxysilane (APTES). The mechanism of APTES with Ca 2+ , PO 4 3- , and CO 3 2- during the synthesis process was elucidated. The resulting ACP and ACC exist as stable nanoclusters that can be stored long-term at room temperature. Upon induced crystallization, they crystallize into hydroxyapatite, calcite, vaterite, and magnesium calcite. The excellent biomaterial properties make them highly suitable as precursors for biomimetic mineralization. • New synthetic route for amorphous calcium phosphate (ACP) and amorphous calcium carbonate (ACC). • The non-toxic, odorless and excellent biocompatibility of amino silane effectively protects the biological properties of amorphous precursors. • The preparation and storage of ACP and ACC were achieved at room temperature, and the products were stable and could be stored for extended periods under ambient conditions. • First-principles calculations were employed to elucidate the interaction mechanism between amino silane and the target ions. • The products ACP and ACC nanoclusters show excellent biomimetic mineralization potential.

The investigation and understanding of the magnetic complexity in magnetic refrigeration candidates is crucial for a better search of new materials. This work investigates the magnetic ordering and magnetocaloric properties of Sc 2 CoSi 2 -type Tb 2 CoGe 2 and Tb 2 CoSi 2 intermetallic compounds. Through detailed magnetic measurements and neutron diffraction analysis, the study clarifies the impact of Si−Ge substitution on microscopic magnetic structures and macroscopic magnetocaloric performance. The substitution of Si by Ge leads to an expansion of the unit cell and strongly alters the magnetic behaviour. Tb 2 CoSi 2 shows a high temperature paramagnetic (PM) to ferromagnetic (FM) transition at T C =198 K, a lower temperature spin reorientation transition at T m = 75 K and an antiferromagnetic (AFM) transition at T N = 13 K. In contrast, Tb 2 CoGe 2 undergoes a PM to AFM transition at a significantly lower temperature, T N =126 K, before evolving into an F M -like state at T M =66 K. Neutron diffraction confirms that Tb 2 CoSi 2 is an ac -plane collinear ferromagnet below T C , while Tb 2 CoGe 2 is an ac -plane collinear antiferromagnet below T N . Tb 2 CoGe 2 exhibits a metamagnetic transition from the antiferromagnetic state to a mixed collinear FM+AFM state upon application of an external magnetic field. Both compounds display a highly desirable table-like magnetocaloric effect over a wide temperature range, suitable for magnetic refrigeration applications in the N 2 and H 2 gas liquefaction regions. These findings emphasize that Si−Ge substitution is an effective mechanism for tuning magnetic properties in this intermetallic family in order to optimize their performance for magnetic refrigeration. • Tb 2 CoSi 2 and Tb 2 CoGe 2 magnetic and magnetocaloric properties studied. • Neutron diffraction reveals magnetic structures and Si-Ge substitution impact. • Tb 2 CoGe 2 shows a metamagnetic transition from AFM to mixed FM+AFM state. • Both compounds display a table-like magnetocaloric effect for gas liquefaction. • Si-Ge substitution effectively tunes magnetic order and refrigeration performance.