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To explore the underlying mechanism of chemical disorder in high-entropy pyrochlores, ten rare earth zirconates (nRE1/n)2Zr2O7 (n = 1, 2, and 4, RE = La, Nb, Sm, Eu, and Gd) are studied by using first-principles calculations. The mechanical and thermal properties are carefully analyzed with a special focus on local structural evolution and interatomic interaction. It is found that all three kinds of bond lengths increase linearly with lattice parameters whether the pyrochlore involves chemical disorder or not. Compared with the single-component counterparts, the multi-component pyrochlores are recognized to exhibit higher elastic constants and moduli but lower elastic anisotropy. Meanwhile, (LaSmEuGd)2Zr2O7 shows the lowest thermal conductivity, which can be attributed to the larger La atoms and the weaker La–O bonding. Furthermore, the abnormal strengthening of phonon anharmonicity in (SmEu)2Zr2O7 emphasizes the significance of fluctuation in local distortion rather than enhancement in chemical disorder on decreasing thermal conductivity for high-entropy ceramics. This work uncovers the physical origins of the chemical disorder effect on mechanical and thermal properties for pyrochlores and further shed some lights on the design of high-performance high-entropy ceramics with great potential applications including thermal barrier coatings. [ABSTRACT FROM AUTHOR]

Exploration and exploitation of efficient and nonprecious catalysts for hydrogen evolution reaction (HER) is one of the key solutions to energy problems. Two‐dimensional (2D) MXenes have attracted extensive attention as potential catalysts and supports due to their unique structure and customizable properties. In this work, we have systematically investigated the structural stability and electronic properties of chalcogen‐functionalized MXenes Ti2CT2 (T = O, S, Se, and Te) and Pt‐anchored Ti2CT2 MXenes (Pt‐Ti2CT2). Density functional theory calculations have discovered that all Ti2CT2 exhibit metallic electronic structures except Ti2CO2 with an indirect bandgap. Additionally, the electronic densities of states at Fermi level for Pt‐Ti2CT2 are greatly enhanced after anchoring Pt atoms. The reduction of chalcogen electronegativity is recognized to mainly contribute to weaker bond strength but greater electronic activity. Moreover, Pt‐Ti2CTe2 is predicted to exhibit near‐zero Gibbs free energy of hydrogen adsorption especially at high hydrogen coverage, indicating its significant potential as HER catalysts. It is also revealed that Ti2CT2 and Pt‐Ti2CT2 MXenes are not only ideal candidates of catalyst materials but also could serve as good catalyst substrates. This work provides insights into the structural and chemical complexity of MXenes for catalyst applications but also demonstrates a new strategy to modulate high‐efficiency and low‐cost catalyst and support materials. [ABSTRACT FROM AUTHOR]

Corrosion of silica surfaces by solutions of sodium chloride (NaCl) occurs often; the aggregation of ions and water molecules on the silica surface represents the first step. In this work, the structure and dynamics of ions and water molecules at the silica–solution interface were studied by molecular dynamics simulations. The influence of different NaCl concentrations was explored. With an increase in the NaCl concentration, the hydrogen bonds among water molecules are broken gradually. Meanwhile, more and more water molecules were involved in ionic hydration. Furthermore, the aggregation of ions observed at the silica–liquid interface layer was due to ion hydration. At high NaCl concentrations, self-diffusion of Na+ and Cl− slowed due to the enhanced Coulombic effect and fewer water molecules surrounding an ion during ionic hydration. This work provides a fundamental understanding of the salt solution behavior on a silica surface. [ABSTRACT FROM AUTHOR]

The surface structures, bond variations, and segregation of oxygen vacancies play crucial roles in the structural stability and functionality of nanocrystalline rare‐earth zirconate pyrochlores. In this work, the stabilities of (1 0 0), (1 1 0), and (1 1 1) surfaces of pyrochlore A2Zr2O7 (A = La, Ce, Pr, Nd, Pm, Sm, Eu, or Gd) are investigated by first‐principles calculations. Surface reconstruction occurs on (1 1 0) surface with a transition of ZrO6 octahedron to ZrO4 tetrahedron, leading to their large relaxation energies. In combination with the small amount of broken bonds during the surface formation process, the (1 1 0) surfaces are identified having the lowest surface formation energies than the (1 0 0) and (1 1 1) surfaces. Moreover, the reconstructed (1 1 0) surface has characteristics of the segregation of oxygen vacancies. The surface oxygen vacancies have the low migration barriers (<1.2 eV), which are comparable with those in bulk and ensure the long‐distance diffusion of oxygen vacancies in A2Zr2O7. These discoveries provide fundamental insight to the surface structure and related oxygen vacancy behavior, which are expected to guide the optimization of the surface related properties for nanocrystalline rare‐earth zirconates. [ABSTRACT FROM AUTHOR]

Understanding the mechanism of point defects and the oxygen vacancy diffusion in rare earth (RE) silicates is important to evaluate their performance as environmental barrier coatings. In this work, the defect formation energies are calculated and the similar predominant native point defect type, that is, O Frenkel defect, in RE2SiO5 and RE2Si2O7 (RE = Yb and Lu) is uncovered. Furthermore, the nonstoichiometry related defects and phase composition in RE2SiO5 and RE2Si2O7 is also studied. For RE2SiO5, SiRE·+Oi″ or SiRE·+VRE″′ is the predominate defect complex accompanied with the RE2Si2O7 separation under SiO2‐rich condition, while RESi′+VO·· or RESi′+REi··· is favorable under RE2O3‐rich condition. In the case of RE2Si2O7, SiRE·+VRE″′ or SiRE·+Oi″ is the favorable defect complex under SiO2‐rich condition while RESi′+VO·· or RESi′+REi··· dominates the defects, accompanied with the formation of RE2SiO5, under RE2O3‐rich case. Finally, the high oxygen migration barriers are revealed for both RE2SiO5 and RE2Si2O7, indicating the low oxygen permeability in these silicates. These results will not only guide the future performance optimization of RE2SiO5 and RE2Si2O7 through tailoring their composition, but also suggest their potential application as oxidation protective coatings. [ABSTRACT FROM AUTHOR]

To explore the underlying mechanism of chemical disorder in high-entropy pyrochlores, ten rare earth zirconates (nRE1/n)2Zr2O7 (n = 1, 2, and 4, RE = La, Nb, Sm, Eu, and Gd) are studied by using first-principles calculations. The mechanical and thermal properties are carefully analyzed with a special focus on local structural evolution and interatomic interaction. It is found that all three kinds of bond lengths increase linearly with lattice parameters whether the pyrochlore involves chemical disorder or not. Compared with the single-component counterparts, the multi-component pyrochlores are recognized to exhibit higher elastic constants and moduli but lower elastic anisotropy. Meanwhile, (LaSmEuGd)2Zr2O7 shows the lowest thermal conductivity, which can be attributed to the larger La atoms and the weaker La–O bonding. Furthermore, the abnormal strengthening of phonon anharmonicity in (SmEu)2Zr2O7 emphasizes the significance of fluctuation in local distortion rather than enhancement in chemical disorder on decreasing thermal conductivity for high-entropy ceramics. This work uncovers the physical origins of the chemical disorder effect on mechanical and thermal properties for pyrochlores and further shed some lights on the design of high-performance high-entropy ceramics with great potential applications including thermal barrier coatings. [ABSTRACT FROM AUTHOR]