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Sapphire has increasing demand toward optoelectrical devices like LED; its big challenge is to find reasonable growth mechanisms for high quality large size single crystals. In this paper, we proposed both theoretical and experimental studies to clarify multiscale behaviors within the Al2O3 growth system. Molecular dynamics simulation for sapphire crystal growth along c-, a-, and m-axes, and solid–liquid interface structure, and grown 2″ sapphire via the Czochralski method along the c-axis, were reported herein. Our studies show that α-Al2O3 growth behaviors along different crystal directions are different, which is different from the amorphous Al2O3 phase transition at the various α-Al2O3 planes. α-Al2O3 crystal growth in the c-axis system may be a complex process involving solid–liquid and solid–solid transformations, rather than a single solid–liquid transformation that happened in the systems growing along the a- and m-axes. Within the time scale of simulation, the crystals cannot be grown by the lattice period of the seed crystal along the c-axis and transform into γ-Al2O3 rather than α-Al2O3, while it is opposite along the a- and m-axes. This may be the microscopic reason why it is difficult to grow sapphire along the c-axis in the experiment. An abrupt change in the interfacial structure is the key reason to inhibit the transformation of liquid Al2O3 into α-Al2O3 along the c-axis. [ABSTRACT FROM AUTHOR]

Recently, Ni-rich LiNixCoyMn1−x−yO2 (x ≥ 0.8) draw significant research attention as cathode materials in lithium-ion batteries due to their superiority in energy density. However, the oxygen release and the transition metals (TMs) dissolution during the (dis)charging process lead to serious safety issues and capacity loss, which highly prevent its application. In this work, we systematically explored the stability of lattice oxygen and TM sites in LiNi0.8Co0.1Mn0.1O2(NCM811) cathode via investigating various vacancy formations during lithiation/delithiation, and properties such as the number of unpaired spins (NUS), net charges, and d band center were comprehensively studied. In the process of delithiation (x = 1 → 0.75 → 0), the vacancy formation energy of lattice oxygen [Evac(O)] has been identified to follow the order of Evac(O–Mn) > Evac(O–Co) > Evac(O–Ni), and Evac(TMs) shows a consistent trend with the sequence of Evac(Mn) > Evac(Co) > Evac(Ni), demonstrating the importance of Mn to stabilize the structural skeleton. Furthermore, the |NUS| and net charge are proved to be good descriptors for measuring Evac(O/TMs), which show linear correlations with Evac(O) and Evac(TMs), respectively. Li vacancy plays a pivotal role on Evac(O/TMs). Evac(O/TMs) at x = 0.75 vary extremely between the NiCoMnO layer (NCM layer) and the NiO layer (Ni layer), which correlates well with |NUS| and net charge in the NCM layer but aggregates in a small region in the Ni layer due to the effect of Li vacancies. In general, this work provides an in-depth understanding of the instability of lattice oxygen and transition metal sites on the (104) surface of Ni-rich NCM811, which might give new insights into oxygen release and transition metal dissolution in this system. [ABSTRACT FROM AUTHOR]

Rechargeable Na‐CO2 batteries are considered to be an effective way to address the energy crisis and greenhouse effect due to their dual functions of CO2 fixation/utilization and energy storage. However, the insolubility and irreversibility of solid discharge products lead to poor discharge capacity and poor cycle performance. Herein, a novel strategy is proposed to enhance the electrochemical performance of hybrid Na‐CO2 batteries, using water‐in‐salt electrolyte (WiSE) to establish an optimal reaction environment, regulate the CO2 reduction pathway, and ultimately convert the discharge product of the battery from Na2CO3 to formic acid (HCOOH). This strategy effectively resolves the issue of poor reversibility, allowing the battery to exhibit excellent cycle performance (over 1200 cycles at 30 °C), especially under low‐temperature conditions (2534 cycles at −20 °C). Furthermore, density functional theory (DFT) calculations and experiments indicate that by adjusting the relative concentration of H/O atoms at the electrolyte/catalyst interface, the CO2 reduction pathway in the battery can be regulated, thus effectively enhancing CO2 capture capability and consequently achieving an ultra‐high discharge specific capacity of 148.1 mAh cm−2. This work effectively promotes the practical application of hybrid Na‐CO2 batteries and shall provide a guidance for converting CO2 into products with high‐value‐added chemicals. [ABSTRACT FROM AUTHOR]

Large-sized crystals are fundamental materials in many fields such as semiconductors, communication, military, and radiation detection. However, preparing large-sized and high-quality single crystals for high technology demands is still very difficult. Theory is an important part of crystal growth research. In this review, we briefly summarize the crystal growth models and propose the research directions for the future to break through the preparation of large crystals. In terms of application, chemical bonding theory is currently an effective model for the growth of large-sized crystals. In the future, three aspects, such as utilizing artificial intelligence technology to obtain parameters that accurately describe system properties, establishing cross-scale simulation methods, and calculating interface positions accurately, may be the keys to promote the development of large-sized crystal preparation. [ABSTRACT FROM AUTHOR]

Coordination geometry variations of cations in yttrium aluminium garnet (YAG) melt system doped with various Er3+ concentrations were quantitatively simulated at the classical molecular dynamic level. Our calculated radial distribution functions were discussed upon different ionic pairs, mean square displacement, and diffusion coefficient of ions, on which we clarified two important aspects, namely structure and dynamic properties in YAG melts with intermediate-range order (IRO). Our results show that Er3+ doping affects microscopic dynamic melt structures only in a confined scale localizing in the first nearest neighbour of Er3+ and O2−. Furthermore, such a localization effect is not varied with Er3+ concentration and system temperature. In the present melt system, Y3+, Al3+, and Er3+ cations with intrinsic differences (such as mass and electronegativity scales) were found to follow the same diffusion process in this system, which is mainly caused by the wholly collective rearrangement of the network-forming structure. In this Er3+:YAG melt system, there is an equivalence within both structure and dynamics for Er3+ and Y3+, which cannot be affected by the system temperature and Er3+ concentration, ascribing to the origin of the segregation coefficient of Er3+ in YAG to be equal to 1. [ABSTRACT FROM AUTHOR]

In metal–air batteries, the integrated solid‐state cathode is considered a promising design because it can solve the problem of high interfacial resistance of conventional solid‐state cathodes. However, solid discharge products cannot be efficiently decomposed in an integrated solid‐state cathode, resulting in batteries that are unable to operate for long periods of time. Herein, an integrated solid‐state cathode (Gel‐Tempo cathode) of sodium–air batteries (SABs) capable of promoting efficient decomposition of discharge product Na2O2 is designed. The Gel‐Tempo cathode is synthesized by cationic–π interaction of redox mediator 2,2,6,6‐tetramethyl‐1‐piperidinyloxy (Tempo) and ionic liquid with carbon nanotubes. The Gel‐Tempo cathode serves multiple functions as a redox mediator, flame retardancy, and high stability to air. In quasi‐solid‐state SABs, the Gel‐Tempo cathode reduces overpotential to 1.15 V and improves coulomb efficiency to 84.5% (at a limited discharge capacity of 3000 mAh g−1) compared to gel cathodes. Experiments and density functional theory calculations indicate that Tempo significantly reduces the Gibbs free energy in the decomposition reaction of Na2O2, and high Tempo content is more conducive to enhancing the decomposition kinetics of Na2O2 and hence resulting in an ultra‐long cycle life (1746 h). This work is crucial to promote practical applications of SABs, providing guidelines for functionalization design of integrated solid‐state cathodes for metal–air batteries. [ABSTRACT FROM AUTHOR]