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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]

Due to the enlarged interlayer spacing of anion-inserted hydroxides and their increased surface area, the unique structure of double-layered hydroxides is often beneficial for electrochemical energy storage. This work demonstrates that Ce3+-regulated CoNi-layered double hydroxides (CoNi-LDHs) significantly enhance the kinetics of electron transfer and ion motion with increased layer positive charges and weakened O–H bonds. The Ce3+ addition enabled a high rate capacitance of 1000 F g−1 at an ultrahigh charge rate of 50 A g−1 compared with 1322 F g−1 at 1 A g−1. Served as Lewis acid sites, the substituting trivalent Ce3+ for Co2+ decreases the energy barrier of proton diffusion and promotes the fast charge storage kinetics by increasing the hole carrier concentration (6.74 × 1024 cm−3). The fabricated supercapacitor device achieves a high energy density of 30 W h kg−1 at a power density of 10 kW kg−1 (40 A g−1) based on the total mass of active materials. This work simultaneously enhanced intrinsic electronic conductivity and ion diffusion in an electrode by Ce3+ addition. [ABSTRACT FROM AUTHOR]

Due to yttrium aluminum garnet (YAG) having many excellent properties, investigation of the liquid structure of YAG at high temperatures is significant for numerous fields, including crystal nucleation, glass fabrication, and single-crystal growth. The structure of YAG within a certain temperature range, including the melting point, was studied by molecular dynamic simulations, and a YAG single crystal was rapidly grown. Compared with the YAG crystal, the coordination number of oxygen ions for both Al3+ and Y3+ dropped, and the bond length between the cations and anions shortened after melting. These two phenomena can be understood systematically within the framework of Pauling's third rule, and its universality has been verified in various oxide systems. In the liquid YAG, the coordination number decreased and the bond lengths between cations and anions reduced with the increase in temperature. Furthermore, the motifs in the melt were very different from those in the YAG crystal, and the main structural units in the melt were AlO4 and YO7. Based on the understanding of the structure of the YAG melt, an insight could be gained into the phase selection in the undercooled YAG melt, and a rapid pull-up growth of YAG was realized by using the Czochralski method. [ABSTRACT FROM AUTHOR]

Size and shape uniformity of nanomaterials are extremely important for their applications in batteries, supercapacitors, catalysis, etc. In the crystallization process, finding proper synthesis conditions is necessary to have control over size dispersion, as well as crystal planes. In this work, we synthesized Cu2O rhombic dodecahedra (exposing 12 {110} planes) with size range from 1351 nm to 142 nm at a reaction temperature of 31–60 °C. The main parameters governing the size of Cu2O were the concentration of the precursor species and reduction reaction, which were affected by a given temperature. Results of crystallization experiments indicated that reaction and crystallization kinetics were mainly enhanced by raised temperature. Serving as lithium ion battery anodes, Cu2O rhombic dodecahedra showed higher capacity than cubes and octahedra. This work gives us a way of optimizing the temperature conditions for obtaining size uniformity of nanomaterials. [ABSTRACT FROM AUTHOR]

MnCO3 precursors with different morphologies were crystallized using three kinds of surfactants as soft templates, i.e., cation surfactant cetyl trimethyl ammonium bromide (CTAB), anion surfactant sodium dodecyl sulfate (SDS) and neutral poly(vinyl pyrrolidone) (PVP). When PVP was used, the reaction manner was changed from only stirring at room temperature to a hydrothermal route. Under hydrothermal conditions, different ethanol/water ratios and sources of CO32− (NaHCO3 and urea) were used. Porous cubic, regular spherical and nut-like spherical Mn2O3 samples can be obtained by a simple post-annealing process. The correlation between the morphology of Mn2O3 and its performance as an anode material for Li-ion batteries was evaluated. The nut-like spherical Mn2O3 sample has the best cycling performance, with a specific discharge capacity of 925 mA h g−1 at a current density of 100 mA g−1 after 180 cycles. The sample composed of cubes and spheres has superior rate performance. The specific discharge capacity decreases with increasing current density from ~872 mA h g−1 at 100 mA g−1 to ~361 mA h g−1 at 2000 mA g−1. [ABSTRACT FROM AUTHOR]

In the flux system of GdAl3(BO3)4, the compromise in competition between thermodynamic and kinetic control on the mass transfer has been studied from the viewpoint of chemical engineering. Different control mechanisms on the mass transfer in the melt growth system result in various mesoscale morphologies of a single crystal. Both the calculated and experimental results demonstrate thermodynamic control of the anisotropic mass transfer during crystal growth, leading to the mesoscale morphology evolution of the GdAl3(BO3)4 single crystal similar to the matryoshka. The present work can deepen our understanding of mesoscale morphology evolution of the GdAl3(BO3)4 single crystal in the flux growth system. [ABSTRACT FROM AUTHOR]

The chemical bonding theory of single crystal growth was applied to a Gd3Ga5O12 (GGG) Czochralski growth system. On the basis of anisotropic chemical bonding characteristics, the mesoscale process controlled by both thermodynamics and kinetics has been studied in GGG single crystal growth. Starting from the unit-scale in the growth system, the mesoscale structures undergo evolution from GdO8, GaO6, and GaO4 to Gd3Ga5O12 clusters and to a GGG single crystal via chemical bonding between Gd, Ga, and O. On the basis of the chemical bonding theory of single crystals, the GGG single crystal thermodynamically prefers to exhibit a hexagonal configuration along the [111] pulling direction. Kinetically, isotropic mass transfer in the Czochralski growth process leads to formation of a GGG single crystal with a circular configuration, as viewed down along the [111] direction. In such a case, the GGG single crystal maintains the lowest energy. In order to satisfy both thermodynamic and kinetic controls, the thermodynamically preferred {−110} microfacets are exposed on the microscale and the single crystal adopts a circular shape on the macroscale. The present work deepens our understanding of the mesoscale process in the GGG Czochralski growth system. [ABSTRACT FROM AUTHOR]

Both the crystallizing molecule without long-range ordered arrangement and the complex interactions between solvent, anti-solvent, and molecule crystal challenge the imaging of molecule configurations during anti-solvent crystallization. Here, the structural evolution of NH4H2PO4 during anti-solvent crystallization was tracked by in situ ATR-IR spectroscopy. The NH4H2PO4 molecule undergoes D2d→C2v→D2d or C2v→D2d during anti-solvent crystallization, depending on both V(H2O)/V(ethanol) ratio and the concentration of NH4H2PO4 aqueous solution. Moreover, IR spectroscopy can also be used to confirm the anti-solvent role of ethanol in the NH4H2PO4–H2O–ethanol crystallization system. The volatilization of ethanol has been demonstrated as an effective approach to control the dissolution process of NH4H2PO4, which can be used to study the crystallization–dissolution–recrystallization process. The present study can shed light on the anti-solvent crystallization physical and chemistry of NH4H2PO4 from a molecule-level viewpoint. [ABSTRACT FROM AUTHOR]

Micro- and nanocrystals with different facets may exhibit different chemical activities that are of great importance in practical applications. The electrochemical performances of Cu2O anodes with different crystal planes are compared. This work comprehensively investigates the effect of the crystal plane on the electrochemical performance of Cu2O. Firstly, Cu2O polyhedra with different morphologies, i.e., cube, octahedron and truncated octahedron, with different degrees of exposed {110} facets, were synthesized. Cu2O cubes show the highest capacity among these Cu2O polyhedra. The present results prove that the {100} facets of Cu2O display high electroactivities toward redox reactions. The electroactivity sequence of the crystal planes is {100} ＞ {111} ＞ {110}. These results confirm that the additional capacity of Cu2O is due to the generation of CuO, which can conduct a two-electron redox reaction. The anode performances of Cu2O polyhedra are dependent on planes, and this can provide a novel route to design high performance electrode materials for lithium-ion batteries. [ABSTRACT FROM AUTHOR]

In this work, we studied the crystallization of FeOOH nanorods via hydrolysis of FeCl3·6H2O solution under a low-temperature hydrothermal route (100 °C). The effect of Fe3+ concentration and solution pH on the crystallized morphology and size of FeOOH nanorods was systematically studied based on the chemical reaction and crystallization process. The electrochemical performance of the as-obtained FeOOH materials as supercapacitors is evaluated and the effect of Fe3+ concentration on the pseudocapacitance of iron-based materials is also discussed. FeOOH electrode materials obtained in 0.2 M FeCl3·6H2O solution display the highest specific capacitance of 714.8 F g−1, which is higher than reported values for FeOOH electrode materials. The present work demonstrates a simple hydrolysis route to synthesize high capacitance electrode materials. [ABSTRACT FROM AUTHOR]

In the present work, size-tunable Fe2O3 microspindles were crystallized by a simple feasible ethylenediamine (EN) ligand-controlled hydrothermal approach. The size of Fe2O3 microspindles can be controlled from several hundreds of nanometers to above 1 micrometer. Fe2O3 particles with spindle-like structure can be controlled well via the assistance of EN. A clear growth pathway of the EN-assisted synthesis of Fe2O3 microspindles was illustrated by us. As-obtained Fe2O3 microspindles in different sizes exhibit high specific capacitance values of 558.7, 496.6, 504.7 and 271.0 F g−1, which are much higher than previous reported results. The smaller size of Fe2O3 microspindles can lead to higher specific capacitance. [ABSTRACT FROM AUTHOR]

Currently, one of the biggest challenges in the field of pseudocapacitors is their capacitance value. Current knowledge on improving specific capacitance values is mainly focused on the synthesis of electrode materials with different structures and sizes. However, no studies have addressed using soluble inorganic salts directly as electrode materials. For the first time, we have reported that water-soluble CuCl2 electrodes show a fast and reversible redox reaction of Cu2+↑ Cu+ and deliver a very high specific pseudocapacitance, ~5442 F g−1. We have identified that the cation Cu2+ is responsible for achieving this big number. The chemical and crystallization transformation of the CuCl2 electrode is presented. Commercial inorganic salts can be used directly as electrodes neglecting complex synthesis procedures, which is an easily scalable and highly economical method. This method can be extended to a large variety of commercial inorganic salt electrodes following the guideline of ionic electronegativity. [ABSTRACT FROM AUTHOR]

Uniform hollow octahedra of Cu2O were successfully synthesized by the facile room-temperature chemical reaction of copper acetate and N2H4 without using any surfactant. The growth mechanism of the hollow octahedra and the solution environment in the chemical reaction were investigated. The chemical reactions from Cu2+ to Cu(OH)42− and finally to Cu2O can be done within ＜2 s. In this reaction system, N2H4 served as an alkali and reducing agent. Acetate ions, Ac−, can serve as buffer, act as counterions, and Ac− are coordinated to the Cu2O particle surface. The hollow-octahedron@nanoparticles-aggregate core@shell structures were synthesized by the introduction of NH4+ cations. The core@shell structures show a higher capacity and better cycling stability than the hollow octahedra as lithium-ion battery anodes because the core@shell structures can endure large volume changes during electrochemical reactions and nanoparticles with small sizes can shorten the diffusion path of the Li+ ions and electrons. As supercapacitors, the core@shell structures have a higher specific capacitance than that of the hollow octahedra. [ABSTRACT FROM AUTHOR]

Crystallization of KDP-family crystals depends on the chemical bonding behavior of the crystal constituents in aqueous solution, which are sensitive to solution conditions. We applied in situ ATR-IR spectroscopy combined with a morphology-evolution calibration to declare the structural dynamics of NH4+ and H2PO4− during the NH4H2PO4 crystallization in aqueous solution with different concentrations and pH values. For unsaturated NH4H2PO4 solution, both the H2PO4− stretching vibration mode and NH4+ bending vibration mode are enhanced with increasing concentration. When the NH4H2PO4 solution becomes a saturated and then supersaturated and crystalline state, H2PO4− ions undergo hydrated dimerisation and polymerisation, which can be recorded by the appearance and red shift of the P–O…H–O–P in-plane bending vibration mode from 1250 to 1263 cm−1. During this process, hydrated NH4+ ions bind to the (H2PO4−)n frame, reflected by the splitting of the HN4+ bending vibration mode at 1450 and 1400 cm−1. For the supersaturated NH4H2PO4 solution, HPO42− and H2PO4− coexist in solution with increasing pH value up to 6.64, whereas H3PO4 and H2PO4− coexist with decreasing pH value down to 1.52. Such an in situ recording strategy is of particular value in studying system dynamics, and in general to monitor the solution concentrations and compositions before and during the crystallization process. [ABSTRACT FROM AUTHOR]