Misfit Layered Compounds: Insights into Chemical, Kinetic, and Thermodynamic Stability of Nanophases.

IF 16.4 1区 化学 Q1 CHEMISTRY, MULTIDISCIPLINARY Accounts of Chemical Research Pub Date : 2024-11-19 Epub Date: 2024-11-04 DOI:10.1021/acs.accounts.4c00412
Azat Khadiev, M B Sreedhara, Simon Hettler, Dmitri Novikov, Raul Arenal, Reshef Tenne
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Abstract

ConspectusCompounds with layered structures (2D-materials), like transition metal-dichalcogenides (e.g., MoS2), attracted a great deal of interest in the scientific community in recent years. This interest can be attributed to their unique lamellar structure, which induces large anisotropy in their physicochemical properties. Furthermore, owing to the weak van der Waals interaction between the layers, they can be cleaved along the a-b plane, which allows fabricating single layers with physical properties entirely different from the bulk material. Moreover, stacking layers of different 2D-materials on top of each other has led to a wealth of new observations, for instance, by twisting two layers with respect to each other and producing Moiré lattice. Another outstanding property of inorganic layer compounds is their tendency to form nanotubes, reported first (for WS2) many years ago and subsequently from many other layered compounds.Among the 2D-materials, misfit layer compounds make a special class with an incommensurate and nonstoichiometric lattice made of an alternating layer with rocksalt structure, like LaS (O) and a layer with hexagonal structure, like TaS2 (T). The lack of lattice commensuration between the two slabs leads to a built-in strain, which can be relaxed via bending. Consequently, nanotubes have been produced from numerous MLC compounds over the past decade and their structure was elucidated.Owing to their large surface area, nanostructures are generally metastable and tend to recrystallize into microscopic crystallites via different mechanisms, like Ostwald ripening, or chemically decompose and then recrystallize. The stability of nanostructures at elevated temperatures has been investigated quite scarcely so far. In this perspective, electron microscopy as well as synchrotron-based X-ray absorption and reflection techniques were used to elucidate the chemical selectivity and decomposition routes of rare-earth based MLC nanotubes prepared at elevated temperatures (800-1200 °C).As for the chemical selectivity, entropic effects are expected to dictate the random distribution of the chalcogen atoms on the anion sites of the MLC nanotubes at elevated temperatures. Nonetheless, the sulfur atoms were found to bind exclusively to the rare-earth atom (Ln = La, Sm) of the rocksalt slab and the selenium to the tantalum of the hexagonal TX2 slab. This uncommon selectivity was not found in other kinds of nanotubes like WSe2xS2(1-x). In other series of experiments, the lack of utter symmetry in the multiwall nanotubes leads to exclusions of certain X-ray (0kl) reflections, which was used to distinguish them from the bulk crystallites. The transformation of Ln-based MLC nanotubes into microscopic flakes was followed as a function of the synthesis temperature (800-1200 °C) and the synthesis time (1-96 h). Furthermore, sequential high-temperature transformations of the (O-T) lattice into (O-T-T) and finally (O-T-T-T) phases via deintercalation of the LnS slab was observed. This autocatalytic process is reminiscent of the deintercalation of alkali atoms from different layered structure materials. Annealing at higher temperatures and for longer periods of time eventually leads to the decomposition of the ternary MLC into binary metal-sulfide phases, as well as partial oxidation of the product. This study sheds light on the complex mechanism of high-temperature chemical stability of the nanostructures.

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错层化合物:纳米相的化学、动力学和热力学稳定性透视。
Conspectus 具有层状结构(二维材料)的化合物,如过渡金属二钙化物(如 MoS2),近年来引起了科学界的极大兴趣。这种兴趣可归因于它们独特的层状结构,这种结构使它们的物理化学特性具有很大的各向异性。此外,由于层间存在微弱的范德华相互作用,它们可以沿 a-b 平面裂开,从而制造出物理性质完全不同于块体材料的单层。此外,将不同的二维材料层层叠加还能产生大量新的观察结果,例如,将两层材料相互扭转就能产生莫伊里格。无机层状化合物的另一个突出特性是容易形成纳米管,许多年前就有相关报道(WS2),随后许多其他层状化合物也出现了这种情况。在二维材料中,错配层状化合物是一个特殊的类别,它的晶格不对称且非共计量,由具有岩盐结构的交替层(如 LaS (O))和具有六边形结构的交替层(如 TaS2 (T))组成。由于两层板之间的晶格不协调,因此会产生内置应变,可通过弯曲来放松应变。因此,在过去的十年中,许多 MLC 化合物被制成了纳米管,其结构也得到了阐明。由于纳米结构的表面积很大,它们通常是易变的,往往会通过不同的机制(如奥斯特瓦尔德熟化)重新结晶成微小的晶体,或者通过化学分解然后重新结晶。迄今为止,有关纳米结构在高温下稳定性的研究还很少。在化学选择性方面,预计熵效应将决定 MLC 纳米管阴离子位点上的查尔根原子在高温下的随机分布。然而,我们发现硫原子只与岩盐板的稀土原子(Ln = La、Sm)结合,而硒则与六方 TX2 板的钽结合。这种罕见的选择性在其他类型的纳米管(如 WSe2xS2(1-x))中没有发现。在其他系列的实验中,由于多壁纳米管缺乏完全对称性,导致某些 X 射线(0kl)反射被排除,从而将它们与块状晶体区分开来。锰基 MLC 纳米管向微观薄片的转化是合成温度(800-1200 °C)和合成时间(1-96 小时)的函数。此外,还观察到(O-T)晶格通过 LnS 板坯的脱插而连续高温转变为(O-T-T)相,最后转变为(O-T-T-T)相。这一自催化过程让人联想到不同层状结构材料中碱原子的脱嵌。在较高温度和较长时间下进行退火,最终会导致三元 MLC 分解为二元金属硫化物相,以及产物的部分氧化。这项研究揭示了纳米结构高温化学稳定性的复杂机理。
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来源期刊
Accounts of Chemical Research
Accounts of Chemical Research 化学-化学综合
CiteScore
31.40
自引率
1.10%
发文量
312
审稿时长
2 months
期刊介绍: Accounts of Chemical Research presents short, concise and critical articles offering easy-to-read overviews of basic research and applications in all areas of chemistry and biochemistry. These short reviews focus on research from the author’s own laboratory and are designed to teach the reader about a research project. In addition, Accounts of Chemical Research publishes commentaries that give an informed opinion on a current research problem. Special Issues online are devoted to a single topic of unusual activity and significance. Accounts of Chemical Research replaces the traditional article abstract with an article "Conspectus." These entries synopsize the research affording the reader a closer look at the content and significance of an article. Through this provision of a more detailed description of the article contents, the Conspectus enhances the article's discoverability by search engines and the exposure for the research.
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