Chemistry of Materials最新文献

Recently, hexagonal boron nitride (h-BN) films have been considered as an effective alternative material for preventing metal oxidation due to its electrical insulating properties and ultrathin thickness. However, there are some issues when using synthesized h-BN on metal protection, especially because its antioxidation performance will decrease after a period of time. To address this problem, the h-BN films were synthesized at commercial Cu foil by the chemical vapor deposition (CVD) method, and the failure mechanism is proposed by experimental and density functional theory (DFT) calculations. The results indicate that a twin boundary with 558-N/B structures would be formed when two different orientation domains meet, and the h-BN domains can seamlessly stitch together for the same orientations or h-BN domains located in the different adjacent single atomic layer. Next, the failure mechanism of the antioxidant is considered and the synthesized h-BN at the Cu foil was treated by thermal oxidation, and we found the generation of Cu₂O/CuO induced the decoupling phenomenon between h-BN and Cu. Further DFT calculations indicate that the presence of twin boundaries and point defects can also facilitate the diffusion of the O atom, and h-BN edges terminated with H can promote the diffusion of the O atom and the diffusion and decomposition of H₂O molecules more than Cu(111) passivated h-BN, which accelerates the oxidation of Cu foil, leading to the formation of Cu₂O/CuO. This process increases the distance between h-BN and Cu and decreases the amount of Bader transfer and orbital hybridization of B, N, and Cu atoms between h-BN and Cu foil, thereby reducing the coupling between h-BN and Cu foil. This study can provide experimental and theoretical explanations for the failure mechanism of h-BN films in protecting metals from oxidation.

Metal exsolution is a smart strategy that allows modification and enrichment of a material’s surface with highly active catalytic phases, thus offering the possibility to fine-tune the surface chemical composition. We study the exsolution of Ru from a perovskite solid solution LaFe_0.9Ru_0.1O₃ (LFRO) to form Ru nanoparticles and their passivation by a conforming LaO_x layer by applying a variety of in situ techniques, including TEM and XPS, in combination with ex situ infrared and Raman spectroscopy, but most notably by utilizing the catalytic propane combustion to probe the formation of the passivating LaO_x layer. During the Ru exsolution process, Ru³⁺ in LFRO is reduced first to the Ru^β species and subsequently into a Ru⁰ species, evidencing the exsolution of Ru particle. The transformation of Ru³⁺ → Ru^β proceeds already below 300 °C and is correlated with the formation of oxygen vacancies under a reductive atmosphere. The subsequent transformation of Ru^β toward Ru⁰ needs at least a reduction temperature of 400 °C that is likely to be determined by the diffusion of Ru³⁺ from the near-surface region of LFRO toward the surface. Only above 600 °C ruthenium cations from the bulk of LFRO are exsolved, leading to the further growth of Ru particles. Around 600 °C, the exsolution of Ru particles is accompanied by the formation of a covering LaO_x layer. We propose that La segregation and precipitation as surface LaO_x are driven by the overstoichiometry of La in LFRO after Ru exsolution.

Specific structural motifs in inorganic solids are often related to their targeted physical properties. For many classes of solids, such as Zintl phases and polar intermetallics, the crystal structures are diverse and not easy to predict. Various antimonides that are potential thermoelectric materials were proposed to be synthesizable on the basis of their estimated formation energies. Their structures were broadly classified as clathrate, channel, layered, or network through a machine learning model trained on existing ternary phases and features based on elemental properties using the sure independence screening and sparsifying operator algorithm. Through experimental validation, three new ternary antimonides were synthesized and confirmed to form layered structures: tetragonal RbAlSb₂ and CsAlSb₂, which are isopointal but not isotypic to LiBSi₂; and monoclinic Rb₂Al₂Sb₃, which adopts the Na₂Al₂Sb₃-type structure. Reinvestigation of the related compound Cs₂In₂Sb₃ revealed a low thermal conductivity and p-type semiconducting behavior.

The effects of plasma reactants on the plasma-assisted atomic layer deposition (ALD) of lithium phosphate are investigated in relation to the fabrication of high-quality lithium phosphorus oxynitride (LiPON) thin films for potential use as a solid-state electrolyte (SSE) in both microbatteries and neuromorphic devices. Our ALD processes enable the incorporation of nitrogen into a lithium phosphate matrix, using lithium tert-butoxide and tris(dimethylamino)phosphine as the lithium and phosphorus precursors, respectively, in a deposition temperature window of 220–300 °C. With O₂ plasma, polycrystalline lithium phosphate films, with a relatively well-arranged pyrophosphate, are deposited. Amorphous LiPON films, with a mixture of pyrophosphates and orthophosphates, are obtained when Ar or NH₃ plasma is used. When the NH₃ flow rate increases, the nitrogen composition increases up to ∼13%, while residual carbon is kept below a few percent. For a Li_2.5PO_1.9N_0.8 film deposited at 300 °C with NH₃ plasma, the ionic conductivity is measured as 1.65 ± 0.42 × 10^–6 S/cm at 25 °C, with an activation energy of 0.66 eV. This conductivity is the highest value of any ALD LiPON film reported to date. Our ALD processes exhibit a high level of controllability of the molecular structures of the phosphorus oxynitride matrix with high ionic conductivity, which makes them suitable for realizing high-performance Li SSE thin films.

A-site layer-ordered double perovskites LnBaFe₂O₆ (Ln = Pr, Sm) were synthesized by topotactic ozone oxidation, and their successive phase transition behaviors were investigated. The results of differential scanning calorimetry, X-ray powder diffraction, Mössbauer spectroscopy, and magnetization measurements suggested that both compounds exhibited successive charge transitions accompanied by complicated changes in physical properties, involving the charge, lattice, and spin degrees of freedom. For SmBaFe₂O₆, the first-order structural and magnetic transition related to the first charge disproportionation transition (2Fe^3.5+ → Fe³⁺ + Fe⁴⁺) occurred at a higher temperature than that of PrBaFe₂O₆, while the second-order magnetic transition, which was induced by the second charge disproportionation (Fe⁴⁺ → 0.5Fe³⁺ + 0.5Fe⁵⁺) was observed at a lower temperature. The obtained results suggest that the metastable charge-disproportionated state (Fe³⁺ + Fe⁴⁺) of LnBaFe₂O₆ is more stabilized when the lanthanoid ion at the A-site is smaller.

Indium phosphide (InP) quantum dots (QDs) represent the main alternative to restricted Cd-based QDs in lighting and display applications. Typically, the photoluminescence (PL) of InP QDs is increased by overgrowth of a zinc chalcogenide shell, consisting of ZnSe and/or ZnS. Here, we show that the outer surface of InP/ZnSe QDs synthesized using aminophosphine-based chemistry is passivated by oleylamine and zinc chloride, while zinc oleate, used as a precursor for shell growth, is absent from the surface. The resulting low surface concentration of zinc salts leads to an incomplete passivation of undercoordinated surface chalcogenides, a known source of trap states. We demonstrate that a subsequent exposure of the QDs to zinc acetate, a mild Lewis acid, drastically enhances the PL quantum yield (PLQY) from approximately 40% before to 90% after exposure. This outcome is highly reproducible and can be realized either through an in situ exposure by adding zinc acetate to the reaction mixture or an ex situ exposure on purified InP-based QDs. Given that zinc chalcogenides are frequently used as an outer shell for QDs, this method of passivating undercoordinated chalcogenides holds significant promise for enhancing the PLQY across a wide array of core/shell QD systems.

Hybrid organic–inorganic perovskites are a rapidly developing class of materials due to their desirable properties for optoelectronic applications such as their ease of synthesis, solution-processable film formation, tunable band gap, strong photoluminescence, good charge carrier mobilities, and high defect tolerance. We present a novel 2D perovskite motif that seamlessly integrates the structural elements from both Ruddlesden–Popper and Dion–Jacobson halide perovskites. We demonstrate the incorporation of two different organic spacer cations in an ordered manner in 5 novel 2D perovskite iodide materials. Both a cyclic diammonium cation 3-(aminomethyl)piperidinium (3AMP) and a linear alkyl monoammonium cation (Cn = C_nH_2n+4N, n = 4–8) are present in distinct alternating layers, making the new series (Cn)₂(3AMP)[PbI₄]₂. The crystallization of these materials was optimized through careful temperature control to obtain precise crystal structures via single-crystal X-ray diffraction (XRD) which confirmed the presence of the two cations in distinct layers. The influence of the two spacers on optical properties including the band gaps and photoluminescence spectra are found to more closely resemble (3AMP)PbI₄ than (Cn)₂PbI₄, which can be attributed to the amount of distortion imposed by the 3AMP spacer on the lead iodide layers. The findings are supported by density functional theory calculations. The strong photoelectric response of solution-processed thin films shows the potential of these materials in photodetectors or photovoltaics. This unprecedented amalgamation of RP–DJ in (Cn)₂(3AMP)[PbI₄]₂ in a structurally ordered fashion suggests a potential vastly underexplored phase space of 2D perovskites in which there are chemically different spacers in distinct layers of the structure, providing an additional parameter to tune perovskite properties.

Thermal annealing is the most common postdeposition technique used to crystallize antimony selenide (Sb₂Se₃) thin films. However, due to slow processing speeds and a high energy cost, it is incompatible with the upscaling and commercialization of Sb₂Se₃ for future photovoltaics. Herein, for the first time, a fast-annealing technique that uses millisecond light pulses to deliver energy to the sample is adapted to cure thermally evaporated Sb₂Se₃ films. This study demonstrates how photonic curing (PC) conditions affect the outcome of Sb₂Se₃ phase conversion from amorphous to crystalline by evaluating the films’ crystalline, morphological, and optical properties. We show that Sb₂Se₃ is readily converted under a variety of different conditions, but the zone where suitable films for optoelectronic applications are obtained is a small region of the parameter space. Sb₂Se₃ annealing with short pulses (<3 ms) shows significant damage to the sample, while using longer pulses (>5 ms) and a 4–5 J cm^–2 radiant energy produces (211)- and (221)-oriented crystalline Sb₂Se₃ with minimal to no damage to the sample. A proof-of-concept photonically cured Sb₂Se₃ photovoltaic device is demonstrated. PC is a promising annealing method for large-area, high-throughput annealing of Sb₂Se₃ with various potential applications in Sb₂Se₃ photovoltaics.

Organic–inorganic metal halides (OIMHs) have gained significant attention as promising materials for various applications, including lighting, imaging, and energy conversion. The development of Pb-free alternatives to traditional Pb-based materials has become increasingly important for environmental and health reasons. In this study, we report on the thermally induced fluorochromism of a two-dimensional OIMH based on Cu(I), namely, (Bz)₂Cu₂I₄·H₂O (abbreviated as BzCuI). Density functional theory calculations revealed that BzCuI has a direct bandgap of 2.11 eV. Sequential fluorescence spectral shifts were observed in the temperature range of 80 to 300 K, indicating a reduction in the bandgap due to increased electron–phonon interactions at higher temperatures. The Huang–Rhys factor further confirmed the strong coupling between electrons and phonons in BzCuI. Additionally, BzCuI exhibited a unique fluorescence-switching behavior, transitioning from blue to red, which was triggered by a structural phase change involving the trapping and release of water molecules. This finding was supported by the temperature-dependent X-ray diffraction (XRD) pattern, which showed evidence of crystal lattice contraction upon heating. Furthermore, when mixed with silicon oil, BzCuI demonstrated the potential for applications such as anticounterfeiting ink and moisture-sensitivity assays. Compared to other OIMHs, BzCuI exhibited the most significant fluorescence shift within the visual spectrum, making it highly promising for various optical sensing applications.

Recent advancements in high-throughput screening and data mining have significantly expedited the discovery of new multicomponent materials, replacing the traditionally time-consuming trial-and-error methodologies. However, accurately predicting their synthesizability remains a formidable challenge, primarily due to discrepancies between theoretical predictions and experimental processes. Theoretical predictions are focused on the stability of the final crystal structure, like energy above hull and structural factors. Experimental evolution process has complex conditions: temperature, pressure, and reaction mechanics like interface reaction. This study demonstrates that incorporating reaction pathways markedly enhances the synthesizability prediction accuracy for double perovskite halides. We predict intermediates and synthetic pathways through a detailed analysis of interface reaction mechanisms and chemical reaction networks. Specifically, the formation of the A₃B′₂⁽³⁺⁾X₉ intermediate is predicted with a high driving force during the precursor’s interface reaction. Subsequently, the residual Gibbs free energy of formation necessary for the transition from the A₃B′₂⁽³⁺⁾X₉ intermediate to double perovskite halides is shown to be crucial in determining the synthesizability. This approach surpassed existing structural factor-based approaches in accuracy, enabling us to predict synthesizable double perovskite halides such as Cs₂AgYCl₆ and Cs₂KInCl₆ more effectively. These findings show the critical role of incorporating reaction mechanisms into synthesizability predictions, thereby facilitating the discovery of new multicomponent materials.