Chemistry of Materials最新文献

Conjugated polyelectrolytes (CPEs) are a distinct class of polymers that feature a π-conjugated backbone and pendant ionic groups, which confers them unique properties. In particular, since the discovery, during their purification in water, that some CPEs have the ability to be self-doped, they have attracted increasing interest from the organic electronics community. More recently, a self-acid doping mechanism was proposed after it was proven that the degree of doping can be modulated by the addition of an acid or a base. However, the explanation of both the self-doping and self-acid doping processes remains ambiguous, and their investigation continues to present significant challenges. In this work, we address the problem through a combination of experimental and computational techniques, including spectroscopy (UV–vis and Raman) and electrochemistry measurements in conjunction with DFT calculations and molecular dynamics simulations. We performed a comprehensive investigation into the self-doping mechanism of CPE-2K, poly [2,6-(4,4-bis-potassium butanylsulfonate-4H-cyclopenta-[2.1-b:3,4-b′] dithiophene)-alt-4,7-(2,1,3-benzothiazole)], and its homologue with only one alkyl ionic chain, CPE-K. Our findings point to a framework that integrates the self- and self-acid doping mechanisms into a unified one, in which backbone aggregation acts as the driving force.

Operando Raman spectroscopy measurements are becoming increasingly common in battery materials research. Yet, from a measurement science perspective, there is little consistency in the literature in terms of experimental design, and methodological validity is often not thoroughly considered. In this paper, we experimentally critique the most commonly used operando Raman approach to examining commercial battery electrodes─the “through-hole” method, in which optical access to the electrode under investigation is gained via a hole in the opposing electrode and separator. We benchmark the electrochemical performance of the operando cell against a conventional 2032 coin cell, identifying critical factors that can negatively impact electrochemical performance. Using the well-established lithiation of graphite as a test system, we demonstrate systematic spatial variations in the localized operando Raman response upon moving from the center to the edge of the optical access hole. These variations highlight the importance of sampling location and statistical analysis in connecting local spectral metrics with the global electrochemical characteristics of the cell. Secondary ion mass spectrometry imaging also indicates spatial variations in surface chemistry resulting from the reduced stack pressure at the position of the optical window, which is an important consideration when interpreting the observed operando Raman response.

Atomic layer etching (ALE) enables atomic-scale removal of thin films through self-limiting reactions, and robust ALE processes for high-κ oxides are essential for semiconductor applications. Here, we report the ALE of HfO₂ and ZrO₂ using a novel NbF₅/TiCl₄ precursor combination. HfO₂ films retained structural quality after ALE, with minimal impurity incorporation and preservation of density, roughness, and refractive index. In contrast, ZrO₂ etched more rapidly but showed surface degradation and higher impurity levels. Density functional theory calculations support these findings by indicating that ZrO₂ more readily undergoes the ligand-exchange step, which is consistent with its faster etching. ALE was further applied to HfO₂ films in 3D nanohole structures, revealing crystallinity- and location-selective etching in complex geometries. These results highlight the importance of developing selective ALE processes for high-κ oxides, underscoring their potential for precise patterning and integration in advanced semiconductor manufacturing.

Ionic liquids (ILs) possess exceptional physicochemical properties, such as negligible vapor pressure, wide electrochemical stability windows, and tunable molecular architectures, making them attractive candidates for advanced electrolyte applications. These properties arise from intricate ionic correlations and variable ionicity between cations and anions, which govern thermal stability, electrical conductivity, and other key behaviors. In this work, we employ the neuroevolution potential (NEP) framework to develop machine learning-based force fields for a series of imidazole ILs with four distinct anions. The NEP models are rigorously validated against density functional theory (DFT) calculations, showing excellent agreement in energies and forces, and outperforming classical force fields in reproducing structural properties. Molecular dynamics simulations based on the NEP accurately predicted physical properties, including density, self-diffusion coefficients, and viscosity, in close agreement with experimental measurements. Importantly, the ML-driven NEP framework enables simulations of much larger system sizes and longer time scales than are feasible with DFT, while achieving significant speedups over classical force fields. Analysis of ionicity revealed values near 1/3, consistent with previous studies, and provided molecular-level insights into the interplay between ionicity and structural features. This study highlights the potential of machine learning-driven force fields for efficient, accurate, and scalable modeling of complex IL systems, providing practical guidance for designing IL-based electrolytes with tailored properties.

Amorphous calcium carbonate phases are common intermediates in multistep crystallization processes. In many cases, it was shown that these dense and liquid-like phases function as transient metastable precursors that transform into mature crystalline phases. However, some biological systems consist of inorganic condensates that serve only as ion carriers and dissolve prior to the formation of the mineral. In this work, we study the chemical conditions that regulate the release of calcium ions from polymer condensates toward the formation of calcium carbonate. It is shown that the presence of bicarbonate ions tunes the stability of biogenic and bioinspired polymer–Ca condensates. In specific conditions of the carbonate system, condensate dissolution is induced, affecting calcium carbonate supersaturation and crystallization kinetics. This behavior recapitulates observations on the roles of such condensates in vivo, suggesting that bicarbonate ions indirectly affect mineralization by turning inorganic condensates from mineral precursors into sacrificial ion pools.

The potential of hybrid improper ferroelectrics (HIFs) in electronic and spintronic devices hinges on their ability to switch polarization. Although the coupling between octahedral rotation and tilt is well established, the factors that govern switching barriers remain elusive. In this study, we explore this area to demonstrate the critical role of causal reasoning in uncovering the mechanisms to control the ferroelectric switching barrier in HIFs. By combining causal discovery, causal interventions, and first-principles simulations, we identify tolerance factor, A-site cation radii mismatch, epitaxial strain, and octahedral rotation/tilt as key parameters and quantify how their interplay directly influences switching barrier. Three key insights emerge from our work: (a) the analysis identifies the structural descriptors controlling polarization reversal across a broad family of A-site-layered double perovskites and superlattices, (b) it uncovers nontrivial, material-specific rotation-tilt mechanisms, including a counterintuitive cooperative pathway where both rotation and tilt change while lowering the barrier, an effect mostly inaccessible to conventional Landau or first-principles-based approaches and (c) it maps these material-specific mechanisms to experimentally realizable parameters, showing that epitaxial strain from orthorhombic substrates (e.g., NdScO₃, NdGaO₃) selectively tunes octahedral distortions to achieve barrier reduction across varied compositions. These results establish actionable, materials-by-design principles linking composition, structure, and strain to polarization switching, while highlighting the potential of causal reasoning to guide intelligent, mechanism-driven strategies for engineering complex functional oxides.

Ytterbium doped cesium lead halide materials exhibit a property known as quantum cutting which allows for greater than 100% photoluminescent quantum yields (PLQYs). The local atomic structure of the defects responsible for these properties and the effectiveness of the doping for producing the desired PLQYs is not readily discerned using techniques requiring long-range order. In this work we prepared 2.5, 5, 10, and 20% Yb³⁺ doped CsPbCl₃ powders using mechanosynthesis under distinct stoichiometric ratio conditions and characterized the defect incorporation and its effects on local atomic disorder using solid-state nuclear magnetic resonance (SSNMR) spectroscopy. We then correlate our observations to the observed PLQYs for each of the prepared samples. All samples prepared were found to be in an orthorhombic phase and no lattice shrinking was observed upon increased Yb³⁺ doping. An increase in doping concentrations was accompanied by a decrease in ¹³³Cs NMR spin–lattice relaxation times T₁ consistent with a paramagnetic relaxation enhancement effect induced by Yb³⁺ incorporation into the perovskite lattice. Through a comparison of synthesis methods, PLQY and NMR T₁ parameters we found that incorporated defects favorable for PLQY in mechanosynthesized samples are more likely to form in the presence of excess lead and excess chloride ions. The maximum PLQY values obtained for each set of samples correlated with T₁ parameters in the range of 13 to 35 s. In addition, we found that the observed PLQY in 5% doped samples was optimized after 1 to 2 h of interval grinding in stainless steel jars. Further grinding beyond 2 h led to a reduction in particle size below 1 μm as well as a reduction in PLQY and spin relaxation times.

The Lewis acidic etching route is an efficient method for preparing MXenes with tunable properties through redox reaction between Lewis acidic salts (such as CuCl₂ and CoCl₂) and the A-layer elements (such as Al, Ga, Sn, and Si) in the MAX phase. However, the etching pathways and phase transition are still lacking in-depth exploration. This work employs in situ time-resolved synchrotron radiation X-ray diffraction (SRXRD) to unveil the contrasted etching processes of Nb₂AlC in different molten salts. It is demonstrated that CuCl₂ etching leads to a transformation from Nb₂AlC to Nb₂CuC and ultimately yields Nb₂CT_x MXene; no intercalation of molten salts into the MXene interlayers is found in the process, while CoCl₂ drives Lewis acidic corrosion, resulting from Nb₂AlC to Nb₂CoC, subsequently decomposing into NbC. Similar NbC layers form during etching with FeCl₂/NiCl₂, indicating that the redox potential of molten salts alone cannot predict the final Lewis acidic etching outcomes. Therefore, two distinct Lewis acidic reactions, including MXene formation etching and carbide decomposition, are identified. This study provides fundamental insights into the selectivity of Lewis acidic reaction routes via in situ X-ray techniques, which is of great significance for the controllable synthesis and specific applications of MXenes.

The design of multimetallic catalysts is a promising strategy for advancing the catalytic synthesis of carbon nanotubes (CNTs). Various element combinations have been explored, and among them, molybdenum (Mo) has been widely studied as a cocatalyst. However, conventional catalyst preparation methods often lead to nonuniform metal distribution, making it difficult to determine the role of Mo. Layered double hydroxides (LDHs), which provide a uniform distribution of metal cations, offer a promising alternative for controlled catalyst design. In this study, cobalt–magnesium–aluminum (CoMgAl) LDHs with varying molecular Mo content were synthesized to investigate the role of Mo in CNT growth. Phase analysis of Mo revealed that Mo₂C forms beyond a specific Mo threshold, significantly enhancing CNT yield. Mo₂C acts as a carbon reservoir, stabilizing Co particles and preventing deactivation. CNT synthesis was further examined using iron (Fe) and Fe–Co LDH systems, confirming that the role of Mo₂C is independent of the active metal. The results demonstrate that Mo₂C formation is essential for optimizing CNT growth, providing a deeper mechanistic understanding of Mo’s catalytic function. This study highlights the advantages of Mo species-intercalated LDH catalysts for achieving high-yield CNT synthesis and offers insights into multimetallic catalyst design.