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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.

Experimental studies on binary, ternary and quaternary Cu–Fe–Ni–S systems are fundamental for the investigation of magmatic sulfide deposits, the main source of Ni, Co and platinum group elements (PGE). Previous experimental studies successfully formulated our general understanding of the evolution of magmatic sulfide systems but, yet, in many cases could not explain some of the key geological, mineralogical and geochemical features of sulfide ore deposits. The challenges are imposed by not well-defined solidus of the Cu-rich sulfide melts, yet poorly constrained phase stability at subliquidus conditions, and poorly resolved subsolidus evolution of magmatic sulfide phases. In this study we aim at better understanding how base metal sulfides crystallize from the evolving sulfide liquid during cooling from superliquidus to room temperatures. We report on controlled cooling (15 °C/day) experiments from 1100 to 25 °C in evacuated silica tubes of a single composition of the quaternary Cu–Ni–Fe–S system similar to the Merensky Reef sulfide ore. Run products were sampled at various temperatures along the cooling path and examined on the microscopic scale by back scattered electron imaging and on the nanometer scale by transmission electron microscopy. The compositions of coexisting phases were analysed using electron microprobe. We show that the sulfide melt (SM) coexists with monosulfide solid solution (MSS) above 950 °C and persists to 700 ± 25 °C before it crystallizes to intermediate solid solution (ISS). The transition to subsolidus state is clearly traced by abrupt change in the Cu/(Fe + Ni) distribution between MSS and Cu-rich phase (either SM or ISS) and in the composition of SM or ISS. The compositional jump at ca. 700 °C is also accompanied by the inverse change in the proportions of coexisting phases indicating significant subsolidus reactions and evolution with decreasing temperature. Pentlandite commences crystallization around MSS grains between 550 and 450 °C and coarsens to a granular-type pentlandite at 450 °C by diffusion of nano pentlandite exsolutions from MSS. Pentlandite exsolves and grows as “flames” and “brushes” in both MSS and ISS at lower temperatures (< 250 °C). Mass balance calculations suggest that 32% of pyrrhotite and 7% of pentlandite in magmatic deposits like the Merensky Reef exsolve from ISS. Results imply that magmatic sulfide systems evolve to lower temperatures than previously thought, leading to significant ore metal fractionation and redistribution. Base metal sulfide phases re-equilibrate extremely fast during cooling, ensuring that primary phase compositions and textures are inevitably and completely eradicated during cooling histories even as short as a few days. The sulfide mineral assemblage, texture and modal abundance of magmatic sulfide phases could be used as a proxy for the reconstruction of the parent sulfide liquid evolution in the deposit. The newly established mechanism and timing of base metal sulfides crystallization provides possible explanation of PGE distribution in base metal sulfides.

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.

Syngas can be produced from biomethane via Partial Oxidation of Methane (POM), being an attractive route since it is ecofriendly and sustainable. In this work, catalysts of Ni supported on MgO–ZrO 2 solid solutions, prepared by a one-step polymerization method, were characterized by HRTEM/EDX, XRD, XPS, H 2 -TPR, and in situ XRD. All catalysts, including Ni/ZrO 2 and Ni/MgO as reference, were tested for POM (CH 4 :O 2 molar ratio 2, 750 ºC, 1 atm). NiO/MgO/ZrO 2 contained two solid-solutions, MgO–ZrO 2 and NiO-MgO, as revealed by XRD and XPS. Ni (30 wt%) supported on MgO–ZrO 2 solid solution exhibited high methane conversion and hydrogen selectivity. However, depending on the MgO amount (0, 4, 20, 40, 100 molar percent) major differences in NiO reducibility, growth of Ni 0 crystallite size during H 2 reduction and POM, and in carbon deposition rates were observed. Interestingly, catalysts with lower MgO content achieved the highest CH 4 conversion (~ 95%), high selectivity to H 2 (1.7) and CO (0.8), and low carbon deposition rates (0.024 g carbon .g cat −1 h −1 ) with Ni4MgZr (4 mol% MgO) turning out to be the best catalyst. In situ XRD during POM indicated metallic Ni nanoparticles (average crystallite size of 31 nm), supported by MgO–ZrO 2 solid solution, with small amounts of NiO–MgO being present as well. The presence of MgO also influenced the morphology of the carbon deposits, leading to filaments instead of amorphous carbon. A combustion-reforming mechanism is suggested and using a MgO–ZrO 2 solid solution support strongly improves catalytic performance, which is attributed to effective O 2 , CO 2 and H 2 O activation at the Ni/MgO–ZrO 2 interface.

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.

The thermal conductivity of aluminum alloys is mainly influenced by alloying elements, including their species, content, and existing state, but the influence level of each factor is not quantified. In this work, we propose a quantitative relationship between the thermal conductivity of aluminum alloys and alloying elements based on the theory of thermal conductivity of metals. The results demonstrate the weakening order of alloying elements in solid solution on thermal conductivity of aluminum is Cr > V > Mn > Ti > Zr > Si > Mg > Cu > Zn, which relates to the difference of outer electronic structure and atom radii. Besides, the weakening effect of alloying elements in the solid solution is much more significant than in precipitated state. Furthermore, the synergistic effect of Si, Mg, and Cu on thermal conductivity is unequal to the sum of effects of each alloying element in Al–Si–Mg and Al–Si–Cu alloys. Graphical abstract

A thermodynamic analysis of coherent lamellar intergrowth resulting from the exsolution of initially homogeneous alkali feldspar is presented. In contrast to earlier treatments, where the simplifying assumption of zero strain in the lamellar interfaces was used, our treatment is more general. The elastic stresses and strains associated with coherent lamellar intergrowth of Na-rich and K-rich alkali feldspar are calculated by minimising the overall elastic energy of the lamellar microstructure. At given pressure and temperature, the elastic energy depends on the volume proportions of the two lamellar types, and thus on the composition of the homogeneous precursor feldspar. As a consequence, there is no single coherent solvus for alkali feldspar, but coherent solvi are different for different compositions of the homogeneous precursor phase. Experimentally observed lamellar orientations agree with those predicted by minimising the strain energy on a set of all possible lamellar orientations.

Using ZIF-67 as a precursor, a series of Pt/Ce y CoO x composite metal oxide catalysts with different molar ratios were prepared by a co-precipitation method and further used for catalytic oxidation of toluene. The Pt/Ce 0.2 CoO x catalyst showed the highest activity for toluene oxidation (T 90  = 173 °C), which was related to the presence of Co-Ce solid solution, the more abundant surface adsorbed oxygen species and the enhanced redox property. Graphic abstract

The as-cast microstructure of low carbon CoCrMo alloy was studied by means of optical microscope, scanning electron microscope and tensile tester, and the microstructure and properties after heat treatment for 30min, 60min and 120min at 1150 °C, 1200 °C and 1250 °C were studied. The results show that the element segregation and M23C6 content in the alloy are decreased by solution treatment. The tensile strength and plasticity of the alloy increase with the increase of solution time. At 1250 °C, the tensile strength and plasticity of the alloy increase first and then decrease with solution temperature and solution time. The element segregation in the alloy is serious, and with the increase of holding temperature and time, the element segregation of Mo decreases. Solid solution heat treatment at 1150 °C and 1200 °C reduces the segregation and carbides decompose and disperse uniformly into the matrix, which improves the strength and plasticity of the alloy. However, at 1250 °C/120min, the growth of grains makes the strength and plasticity of the alloy decrease.