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Crystallization from solution is a materials synthesis process common both in nature and in the laboratory. Unlike conventional high-temperature solid-state synthesis, solution-based syntheses often yield metastable phases, contrary to expectations from equilibrium thermodynamics. Using a recently developed ab initio scheme to calculate the surface energy of a critical nucleus in equilibrium with the aqueous environment, we present a framework to compare relative nucleation rates between competing polymorphs as a function of solution chemistry. We apply this approach to demonstrate how seawater chemistry can preferentially bias nucleation toward the metastable aragonite phase of calcium carbonate, rather than the stable phase calcite––which is of great relevance to biomineralization, carbon sequestration, paleogeochemistry, and the vulnerability of marine life to ocean acidification. Predicting the conditions in which a compound adopts a metastable structure when it crystallizes out of solution is an unsolved and fundamental problem in materials synthesis, and one which, if understood and harnessed, could enable the rational design of synthesis pathways toward or away from metastable structures. Crystallization of metastable phases is particularly accessible via low-temperature solution-based routes, such as chimie douce and hydrothermal synthesis, but although the chemistry of the solution plays a crucial role in governing which polymorph forms, how it does so is poorly understood. Here, we demonstrate an ab initio technique to quantify thermodynamic parameters of surfaces and bulks in equilibrium with an aqueous environment, enabling the calculation of nucleation barriers of competing polymorphs as a function of solution chemistry, thereby predicting the solution conditions governing polymorph selection. We apply this approach to resolve the long-standing “calcite–aragonite problem”––the observation that calcium carbonate precipitates as the metastable aragonite polymorph in marine environments, rather than the stable phase calcite––which is of tremendous relevance to biomineralization, carbon sequestration, paleogeochemistry, and the vulnerability of marine life to ocean acidification. We identify a direct relationship between the calcite surface energy and solution Mg–Ca ion concentrations, showing that the calcite nucleation barrier surpasses that of metastable aragonite in solutions with Mg:Ca ratios consistent with modern seawater, allowing aragonite to dominate the kinetics of nucleation. Our ability to quantify how solution parameters distinguish between polymorphs marks an important step toward the ab initio prediction of materials synthesis pathways in solution.

The excellent dielectric properties and tunable structural design of metal sulfides have attracted considerable interest in realizing electromagnetic wave (EMW) absorption. However, compared with traditional monometallic and bimetallic sulfides that are extensively studied, the unique physical characteristics of solid‐solution‐type sulfides in response to EMW have not been revealed yet. Herein, a unique method for preparing high‐purity solid‐solution‐type sulfides is proposed based on solid‐phase in situ exsolution of different metal ions from hybrid precursors. Utilizing CoAl‐LDH/MIL‐88A composite as a precursor, Fe0.8Co0.2S single‐phase nanoparticles are uniformly in situ formed on an amorphous substrate (denoted as CoAl), forming CoAl/Fe0.8Co0.2S heterostructure. Combing with density functional theory (DFT) calculations and wave absorption simulations, it is revealed that Fe0.8Co0.2S solid solution has stronger intracrystal polarization and electronic conductivity than traditional monometallic and bimetallic sulfides, which lead to higher dielectric properties in EM field. Therefore, CoAl/Fe0.8Co0.2S heterostructure exhibits significantly enhanced EMW absorption ability in the low‐frequency region (2–6 GHz) and can achieve frequency screening by selectively absorbing EMW of specific frequency. This work not only provides a unique method for preparing high‐purity solid‐solution‐type sulfides but also fundamentally reveals the physical essence of their excellent EMW absorption performance. In situ exsolution strategy is developed to construct CoAl/Fe0.8Co0.2S heterostructures, in which solid‐solution‐type sulfides inherit internal crystal polarization and outstanding dielectric loss ability.

Developing metallic materials with a good combination of strength and ductility has been an unending pursuit of materials scientists. The emergence of high/medium-entropy alloys (HEA/MEA) provided a novel strategy to achieve this. Here, we further strengthened a strong-and-ductile MEA using a traditional solid solution strengthening theory. The selection of solute elements was assisted by mechanical property and microstructure predictive models. Extensive microstructural characterizations and mechanical tests were performed to verify the models and to understand the mechanical behavior and deformation mechanisms of the designated CoCrNi–3W alloy. Our results show good experiment-model agreement. The incorporation of 3 at.% W into the ternary CoCrNi matrix increased its intrinsic strength by ∼20%. External strengthening through microstructural refinement led to a yield strength nearly double that of the parent alloy, CoCrNi. The increase in strength is obtained with still good ductility when tested down to 77 K. Nanoscale twin boundaries are observed in the post-fracture microstructure under 77 K. The combination of strength and ductility after W additions deviate from the traditional strength-ductility-trade-off contour.

Zn- and Mn-doped Cerium-oxide based catalyst textured as a solid solutional as well as interfacial form was compared in CO 2 hydrogenation reaction to understand the role of texture as well as dopant type. Ce 0.9 M 0.1 O 2 (M = Zn, Mn) solid solution was prepared by hydrothermal method and CeO 2 supported 10 mol% metal oxide (Metal = Zn, Mn) were prepared by wet impregnation method, where the catalysts were characterized by XRD, N 2 adsorption/desorption isotherm, TEM, Raman spectra, HAADF-STEM and H 2 -TPR. During the CO 2 activation reaction, CO was the major product with minor amounts of methane, ethane, methanol and ethanol. In the case of the Zn-doped CeO 2 catalyst, the presence of Zn improved catalytic activity in both solid solutional and interfacial form due to the synergetic effect of Zn-Ce-based oxide. However, for MnOx/CeO 2 catalysts, the CO 2 consumption rate significantly decreased for 10 mol% MnOx/CeO 2 , Ce 0.9 Mn 0.1 O 2 and Mn 3 O 4 , where the MnO x addition inhibits the reduction of CeO 2 . In the case of the pure CeO 2 , DRIFTS spectra show that formate intermediate formed by reaction between activated CO 2 and OH transformed into methoxy species through formaldehyde intermediates, which leads to the formation of small amount of methanol and ethanol. Graphic Abstract

Magnetite (Fe3O4) is an essential material for enhancing microwave absorption performance and is widespread and abundant as a solid solution in natural minerals and metallurgical slags. In this work, the effect of Mg2+ on the structure, stabilization, and microwave absorption performance of magnesium-containing magnetite (MgxFe3−xO4) was investigated. On the basis of experiments on the reactions of Fe2O3 and MgO under different levels of pCO/(pCO + pCO2), MgxFe3−xO4 (x=0.0,0.2,0.4,0.6,1.0) was synthesized, and Mg2+ was found to inhibit the re-oxidation of magnetite. On this basis, the microwave absorption performance of various synthesized MgxFe3−xO4 samples was measured and analyzed, where Mg2+ was found to enhance the microwave absorption performance of Fe3O4, and the RLmin value of Mg0.2Fe2.8O4 increased to −50.43 dB compared to that of −19.20 dB for Fe3O4. Furthermore, the enhancement mechanism of Mg2+ was revealed through impedance matching, dielectric and magnetic loss tangents, and magnetization curves, where the Mg2+ ions were found to accelerate the hopping of electrons and change the impedance matching of MgxFe3−xO4 to a more ideal state.

Over 150 refractory high-entropy alloys (RHEAs) have been proposed in the last decade. Early alloys such as MoNbTaW and MoNbTaVW still show an unparalleled yield strength of approximately 400 MPa at 1600°C. However, RHEAs with even elevated high-temperature strength are necessary in aerospace vehicles and nuclear reactors to cope with advanced technology in the future. Here, solid-solution strengthening calculation and melting point prediction are combined to design single-phase RHEA for attaining ultrahigh strength at 1600°C. The results show that Hf 0.5 MoNbTaW and HfMoNbTaW alloys after fully homogeneous treatment at 2100°C for 2 h reveal a homogenous body-centered cubic phase. HfMoNbTaW alloy exhibits a yield strength of 571 MPa at 1600°C, much higher than that of MoNbTaVW (477 MPa). It is found that a plateau of strength occurs from 800°C to 1200°C, which is important for raising the strength level of RHEAs at high temperatures. This strengthening mechanism is explained with the change of deformation mode from screw to edge dislocations, which contributes an edge-dislocation-induced strength. A similar alloy design strategy could be applied to develop more RHEAs with an ultrahigh strength level.

Metal chalcogenide solid solution, especially ZnCdS, has been intensively investigated in photocatalytic H 2 generation due to their cost-effective synthetic procedure and adjustable band structures. In this work, we report on the defect engineering of ZnCdS with surface disorder layer by simple room temperature Li-ethylenediamine (Li-EDA) treatment. Experimental results confirm the formation of unusual Zn and S dual vacancies, where rich S vacancies (V S ) served as electron trapping sites, meanwhile Zn vacancies (V Zn ) served as hole trapping sites. The refined structure significantly facilitates the photo charge carrier transfer and improves photocatalytic properties of ZnCdS. The disordered ZnCdS shows a highest photocatalytic H 2 production rate of 33.6 mmol·g −1 ·h −1 under visible light with superior photocatalytic stabilities, which is 7.3 times higher than pristine ZnCdS and 7 times of Pt (1 wt.%) loaded ZnCdS.

Nowadays refractory high-entropy alloys (RHEAs) are regarded as great candidates for the replacement of superalloys at high temperature. To design a RHEA, one must understand the pros and cons of every refractory element. However, the elemental effect on mechanical properties remains unclear. In this study, the subtraction method was applied on equiatomic HfMoNbTaTiZr alloys to discover the role of each element, and, thus, HfMoNbTaTiZr, HfNbTaTiZr, HfMoTaTiZr, HfMoNbTiZr, HfMoNbTaZr, and HfMoNbTaTi were fabricated and analyzed. The microstructure and mechanical properties of each alloy at the as-cast state were examined. The solid solution phase formation rule and the solution strengthening effect are also discussed. Finally, the mechanism of how Mo, Nb, Ta, Ti, and Zr affect the HfMoNbTaTiZr alloys was established after comparing the properties of these alloys.

A full complement of standard state thermodynamic properties (ΔfG298.1°, ΔaGT,io, S298.1o, and CPo) has been determined for a magnesian chamosite [Fe-Chl(W)] and a ferroan clinochlore [Mg-Chl] investigated by calorimetry and low-temperature hydrothermal experiments; this makes these two samples the only natural chlorites whose complete set of thermochemical properties have been reported. ΔfG298.1o for Mg-Chl and Fe-Chl (W) have been determined to be -8161.76 ± 32.50 and -7278.97 ± 21.50 kJ/mol, respectively. Ternary molecular chlorite solid solution modeling approaches have been developed for Al-rich and Si-rich chlorites; unlike available atomic site-mixing chlorite solid-solution models, a molecular model obviates the need for the adoption of a putative structural chemistry. The calculated excess entropy of mixing in the ternary system exhibits a curvilinear dependence on composition and at 25 °C, Gssex vary from about -72 to 413 kJ/mol implying a significant deviation from ideality. The effect of di-trioctahedral substitutions was evaluated by modeling the solid solutions in the quaternary amesite-chamosite-clinochlore-sudoite system for aluminous chlorites; excess functions (Sex, Gex) calculated for these quaternary and ternary solid solutions are marginally different, inherently validating the ternary model. The molecular solid solution model further unmasks significant deficiencies in the available database of standard state thermodynamic properties of chlorites. Finally, pursuant to the recent recognition that green rusts probably play significant roles in the cycling of iron through sedimentary sequences, the neoformation of authigenic iron chlorites from green rusts has been examined; green rusts will readily transform to berthierine and Fe-chlorites except under oxidizing conditions atypical of aquatic environments and ferrugineous sediments.

Metal oxides possessing a large surface area, pore volume and desirable pore size provide more varieties and active industrial potentials. Nevertheless, it is very challenging to produce crystal metal oxides while keeping satisfactory porosity features, especially for ternary compositions. High temperature is usually needed to produce crystal metal oxides, which readily leads to the collapse of the pore structure. Herein, by employing a ‘soft’ dispersant agent and a hard silica template, ZrO2, TiO2 and Zr-Ti solid solutions having a tetragonal crystal structure are produced and the silica-leached materials are characterized from macroscopic to atomistic scales. The micron-sized particulate powders are composed of nanoscale ‘building blocks’, with crystallite sizes between ~8 and 21 nm. These polycrystalline ceramic powders exhibit a high specific surface area (up to ~200 m2·g−1) and pore volume (up to 0.5 cm3·g−1), with a pore size range of ~5–20 nm. Importantly, the Zr/Ti–O–Si–OH chemical bonds exist on the particle surface, with about two-thirds of the surface covered by silica. The hydroxyl groups can further post-graft organic ligands or directly associate with species. Synthesized mesoporous metal oxides are highly homogenous and could potentially be used in various applications because of their tetragonal structure and porosity features.