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MXenes have attracted considerable attention due to their tunable surface chemistry, high electrical conductivity, and ease of solution processing, making them promising candidates for a wide array of applications. The inherent tendency of MXenes to degrade under environmental conditions constrains their compositional diversity and limits certain practical applications. Our computational study shows that degradation of defect-free Ti3C2Tx is kinetically limited, whereas common defects markedly lower the activation barriers for water attack. Using ab initio molecular dynamics simulations (AIMD) combined with thermodynamic analysis, we show that titanium vacancies VTi act as active sites for the protonation of subsurface carbon atoms, weakening the bonds with and accelerating the release of adjacent Ti atoms. Targeted passivation of these sites by adsorbed metal cations (e.g., Li+, Na+, K+, and Mg2+) is predicted to effectively mitigate degradation by suppressing protonation and increasing the barrier for Ti oxidation. This stabilization arises from two synergistic effects: (i) electronic structure modification driven by a strong dipole moment, which markedly shifts the work function, and (ii) steric hindrance that limits water access to reactive defect sites. We also demonstrate that carbon vacancies VC significantly destabilize adjacent Ti atoms, lowering the energy barrier for the water attack reaction. The substitution of VC with electronegative species such as O or N does not significantly improve the stability of Ti3C2Tx, highlighting the detrimental role of any defects in the carbon sublattice. Because VC are typically inherited from the precursor phase and cannot be removed during postsynthesis, controlling their concentration during Mn+1AXn phases synthesis is essential. Our thermodynamic analysis reveals that A-rich (e.g., Al-rich) synthesis conditions substantially increase the formation energy of VC and VN defects in a large spectrum of Mn+1AXn phases, providing a generalizable strategy for defect suppression and improved durability of the resulting MXenes. 

MXenes are versatile 2D materials demonstrating outstanding electrochemical and physical properties, but their practical use is limited, because of fast degradation in an aqueous environment. To prevent the degradation of MXenes, it is essential to understand the atomistic details of the reaction and to identify active sites. In this letter, we provided a computational analysis of the degradation processes at the interface between MXene basal planes and water using enhanced sampling ab initio molecular dynamics simulations and symbolic regression analysis. Our results indicate that the reactivity of Ti sites toward the water attack reaction depends on both local coordination and chemical composition of the MXene surfaces. Decreasing the work function of the Ti3C2Tx surfaces and avoiding Ti sites that are loosely anchored to the subsurface (e.g., O-coordinated) can improve surface stability. The developed computational framework can be further used to investigate other possible culprits of the degradation reaction, including the role of defects and edges. 

Cation lattice flexibility and covalent bond lengths serve as good physical descriptors of proton conduction in solid acids and enable the discovery of promising proton conductors beyond traditional chemistries. 

Abstract Single-phase multiferroic materials that allow the coexistence of ferroelectric and magnetic ordering above room temperature are highly desirable, motivating an ongoing search for mechanisms for unconventional ferroelectricity in magnetic oxides. Here, we report an antisite defect mechanism for room temperature ferroelectricity in epitaxial thin films of yttrium orthoferrite, YFeO 3 , a perovskite-structured canted antiferromagnet. A combination of piezoresponse force microscopy, atomically resolved elemental mapping with aberration corrected scanning transmission electron microscopy and density functional theory calculations reveals that the presence of Y Fe antisite defects facilitates a non-centrosymmetric distortion promoting ferroelectricity. This mechanism is predicted to work analogously for other rare earth orthoferrites, with a dependence of the polarization on the radius of the rare earth cation. Our work uncovers the distinctive role of antisite defects in providing a mechanism for ferroelectricity in a range of magnetic orthoferrites and further augments the functionality of this family of complex oxides for multiferroic applications. 

Abstract This work characterizes the structural, magnetic, and ferroelectric properties of epitaxial LuFeO₃orthoferrite thin films with different Lu/Fe ratios. LuFeO₃thin films are grown by pulsed laser deposition on SrTiO₃substrates with Lu/Fe ratio ranging from 0.6 to 1.5. LuFeO₃is antiferromagnetic with a weak canted moment perpendicular to the film plane. Piezoresponse force microscopy imaging and switching spectroscopy reveal room temperature ferroelectricity in Lu‐rich and Fe‐rich films, whereas the stoichiometric film shows little polarization. Ferroelectricity in Lu‐rich films is present for a range of deposition conditions and crystallographic orientations. Positive‐up‐negative‐down ferroelectric measurements on a Lu‐rich film yield ≈13 µC cm⁻²of switchable polarization, although the film also shows electrical leakage. The ferroelectric response is attributed to antisite defects analogous to that of Y‐rich YFeO₃, yielding multiferroicity via defect engineering in a rare earth orthoferrite.