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Shape and size control of metal nanocrystals has become a powerful tool in tuning their physicochemical properties for applications, however, the growth mechanisms controlling shape and size are not fully elucidated. Gold nanocuboids provide a simple nanoparticle system for investigating nanocrystal growth mechanisms. Here, we study the control over size and shape anisotropy of gold nanocuboids by copper additives. We first optimize the synthesis and yield. We find that, in the presence of copper additives, symmetry is broken and anisotropic growth can occur, leading to nanobars, rather than nanocubes, accompanied by a significant reduction in particle size. We show that symmetry breaking is caused by a combination of rapid deposition on {111} facets coupled with the slow surface diffusion rate introduced by surface copper. This reveals a mechanism by which metal additives can cause symmetry breaking and control shape in nanoparticle growth. [ABSTRACT FROM AUTHOR]

Permanent magnet synchronous motors (PMSMs) with nonconcentric magnetic poles (NCMP) structure are widely used as high-precision servo motors. The current subdomain method mainly equates the NCMP to a rectangular magnet to make each subdomain boundaries of magnet parallel when calculating the magnet eddy current loss (ECL), which results in a lower accuracy of the calculation. This article divides the NCMP into nonconcentric region and concentric region along the radial direction. The nonconcentric region is further divided along the circumferential direction, and each divided region has a single thickness. Based on the subdomain method, a novel analytical method of magnet ECL in PMSMs with NCMPs is proposed. Moreover, the three-dimensional distribution coefficient of ECL in the NCMP is derived by the equivalent impedance method. The effects of eddy current reaction and stator slotting are taken into account to improve the calculation accuracy. Then, through theoretical derivation, the relationship between the minimum magnet loss and the pole parameters is obtained, which provides a reference for the design of NCMPs. Finally, the loss separation experiment is performed on four prototypes with NCMPs. The experimental results, finite element method results and analytical results are compared to verify the correctness of the model. [ABSTRACT FROM AUTHOR]

This paper proposes a novel analytical model which combines subdomain method and magnetic equivalent circuit (MEC) method to predict the no-load performance of V-shape interior permanent magnet (IPM) motors with any slot-pole combination considering the nonlinearity of magnetic bridges (MBs). The V-shape magnets are equivalent to the form of distribution along radial and tangential directions, and the motor is divided into two corresponding structures to facilitate the establishment of subdomains. To consider the saturation of MBs, the MEC method are employed to obtain the permeability of MBs to establish the boundary conditions. The no-load magnetic field of slotless motor can be obtained by solving the equations established by boundary conditions, and the conformal mapping is used to consider the effect of slotting. The proposed model can be used to calculate the no-load magnetic field, back electromotive force, and cogging torque of IPM motor. The results are verified by finite element analysis (FEA) and experiments, which confirms the validity of the model for facilitating the motor design and optimization. Compared with FEA, the proposed method has the advantages of faster modeling, shorter time consuming and meanwhile achieves the approximate accuracy. In addition, U-shape motors with MBs can also be analyzed by this model. [ABSTRACT FROM AUTHOR]

It is recognized that the rotor with shielding cylinder (SC) is one of the effective measures to restrain the rotor eddy current loss (RECL) for high-speed surface-mounted permanent magnet synchronous motors (PMSMs). At present, the RECL of PMSMs with multilayer composite rotor structure is mainly analyzed by the finite element method (FEM), which has obvious shortcomings in time-consumption and the mesh generation of thin SC. In this paper, a multi-layer subdomain analytical model for calculating the RECL of high-speed PMSMs with both non-ferromagnetic retaining sleeve and SC is proposed by taking the effects of eddy current reaction, stator slotting and current harmonics into account. Moreover, the 3-D distribution coefficient of eddy current in the SC is derived by the equivalent impedance method and the effects of temperature on the conductivity of the SC and RECL are obtained through equivalent thermal network (ETN) model. Based on the analytical model, the SC parameters are calculated to obtain the variation ranges when the RECL is minimum. Finally, the C-shape core experiment was built up to verify the correctness of the multilayer analytical model under different shielding layer conductivities and thicknesses. [ABSTRACT FROM AUTHOR]

A luminescent ruthenium complex bearing two 2,6‐di(quinolin‐8‐yl)‐pyridine carboxylic acid (dqpCOOH) ligands has been successfully synthesised and fully characterised. The new metalloligand has been coordinated to zinc ions through the terminal carboxylate groups using a one‐step solvothermal method, to give a multimetallic photoactive 1D coordination polymer, Ru−(dqpCOO)−Zn−(OOCH)2. Through use of X‐ray crystallography, advanced microscopy techniques as well as photophysical studies, we have extensively characterised the coordination polymer. The optical properties of the ruthenium complex and corresponding coordination polymer show that the material experiences a dramatic increase in photostability compared to the free parent metalloligand, in solution. Electrochemical measurements of the coordination polymer also confirm the RuII/RuIII redox couple is maintained in the polymeric network. The development of this material gives a new strategy in the design of novel photoactive materials as multimetallic building blocks for their use in light‐based applications. [ABSTRACT FROM AUTHOR]

Metal–organic frameworks (MOFs) are promising multifunctional porous materials for biomedical and environmental applications. Here, we report synthesis and characterization of a new MOF based on the tetrahedral secondary building unit [Zn4O(CBAB)3]n (NUIG4), where CBABH2 = 4-((4-carboxybenzylidene)amino)benzoic acid. NUIG4 belongs to the family of MOFs with primitive cubic pcu topology, being a rare example with 4-fold interpenetration. The pore architecture enables unprecedentedly high doxorubicin (DOX) loading capacity (1955 mg DOX/g NUIG4) with pH-controlled release. Solid-state NMR and ab initio modeling confirmed formation of aromatic π–π stacking interactions between DOX and the framework. Preliminary cell-line experiments suggested a protective effect of NUIG4 on healthy HDF cells against DOX toxicity. NUIG4 also displays potential for adsorptive small-molecule gas separation, with a BET surface area of 1358 m2 g−1 and high selectivity of 2.75 for C2H2 over CO2. [ABSTRACT FROM AUTHOR]

To research the impact of temperature-dependent characteristics of windings and magnets on the electromagnetic power loss and thermal properties of high-speed (HS) interior permanent magnet synchronous machines (PMSMs), an electromagnetic-thermal bi-directional coupling method (BDCM) is proposed for water-cooled HS PMSMs considering the assembling gaps between the motor components in this paper. The electromagnetic power loss is calculated by 3-D transient finite-element method and loaded into the 3-D temperature field according to the actual loss distribution, and the materials’ properties are in turn updated according to the temperature distributions. The loss and temperature calculation results of a 15kW HS amorphous metal PMSM are calculated by two different coupling methods in the conditions of the rated-load sinusoidal supply and converter supply, and compared with the measured results in the case of converter supply. The results obtained by the BDCM are more consistent with the experiment results, verifying the superiority of the proposed analyzing method in improving the calculation accuracy of motor loss and temperature rise. In addition, the applicable conditions of the proposed method are also summarized in the paper. [ABSTRACT FROM AUTHOR]

The development of synthetic approaches towards new coordination polymers has attracted significant interest due to their fascinating physical properties, as well as their use in a wide range of technological, environmental and biomedical applications. Herein, the initial combination of 2-pyridinemethanol (Hhmp) with 1,4-benzenedicarboxylic acid (H2bdc) or 1,3,5-benzenetricarboxylic acid (H3btc) has been proven a fruitful source of such new species providing access to five new coordination compounds, namely [M2(Hbtc)2(Hhmp)4]·DMF (M = CoII, 1·DMF;NiII, 2·DMF), [Ni(bdc)(Hhmp)2]n·4H2O (3·4H2O), [Zn2(bdc)(hmp)2]n·DMF (4·DMF) and [Fe3(bdc)3(Hhmp)2]n (5). 4·DMF and 5 are the first metal–organic frameworks (MOFs) based on Hhmp with 4 exhibiting an unprecedented 4,4,4-c net with the point symbol {32·103·11}{32·104}2. The framework of 5 is based on a linear FeII3 SBU and possesses a 3,4,6T2 topology with the point symbol {42·83·10}3{43}2{46·86·103}. DC magnetic susceptibility measurements were carried out in 5 and revealed the existence of antiferromagnetic coupling between the FeII cations with a superexchange value of J = −8.46 cm−1. [ABSTRACT FROM AUTHOR]

This paper presents the modified core loss calculation of the high-speed (HS) permanent magnet synchronous machines (PMSMs) with amorphous metal (AM) stator cores. In the initial stage of the HS PMSM design, the calculation of stator core loss is obtained according to the data of AM ribbon provided by the manufacturer, which causes a large error of AM core loss. So how to make the accurate calculation of the AM core loss with only the AM ribbon data from the manufacturer is impending in the initial and advanced design stages of HS PMSM development. In this paper, the characteristics of AM ribbon and AM stator core is measured and compared. According to the experimental results, the modification factor for the accurate calculation of AM core loss is obtained based on the loss characteristics of AM ribbon. Then, the no-load loss of a HS PMSM prototype with an AM stator core is analyzed by numerical methods and verified by experiments. The proposed modification factor of the AM core loss calculation can provide a reference for the design and analysis of HS AM PMSMs in the industry. [ABSTRACT FROM AUTHOR]

A novel hybrid multi‐objective optimization method which combines the Taguchi method with multi‐level Kriging model is developed for optimization of interior permanent magnet synchronous machines (IPMSMs). This method is capable to sharply reduce the finite element analysis calculations for the given multi‐objective optimization problem compared with the conventional optimization method. The method is applied to maximize the power density and the efficiency of an IPMSM under constraints. After adopting the method in the optimization process, the power density of the IPMSM is significantly improved and the volume of the IPMSM is sharply reduced. And the contrast scheme shows that this method can improve the efficiency while increasing the power density. Besides, a prototype is manufactured to verify the feasibility of this method. [ABSTRACT FROM AUTHOR]

This paper proposes an analytical model for analyzing the electromagnetic performance of axial flux permanent magnet machines (AFPMMs) with the coexistence of static rotor radial deviation and angular eccentricity. Firstly, a quasi-3-D analytical model for the healthy AFPMMs is established using the scalar potential. Then, the analytical model of AFPMMs with the mixed eccentricity is derived by the coordinate transformation and air gap length function. The end effect under the mixed eccentricity is considered by an end coefficient, which improves the accuracy of back EMF by 1.3%. Based on the analytical model, the air gap flux density distribution, back EMF and cogging torque of AFPMMs with different rotor radial distances and angular eccentricities are calculated and compared with the corresponding results obtained by finite element analysis (FEA). The proposed model has higher analysis speed and less computer performance requirement than FEA with the similar accuracy. According to the results, the back EMF reduces obviously as the rotor radial deviation distance increases, and the back EMF almost unchanged as the angular eccentricity becomes serious. [ABSTRACT FROM AUTHOR]

This article proposes a novel analytical model which combines subdomain method and magnet equivalent circuit (MEC) method to predict the cogging torque of surface-mounted permanent magnet (SPM) motors with rotor eccentricity and magnet defects in any slot-pole combination cases. Firstly, the general solution of open-circuit magnetic field distribution in a slotless SPM motor with magnet defects is derived. Then, the motor is divided into several subdomains along the air-gap circumferential direction to consider the non-uniform air-gap caused by rotor eccentricity, where the air-gap lengths of each subdomain are considered to be uniform. Finally, the methods of conformal mapping and MEC combined with equivalent current is used to consider the effect of slotting and saturation, which is beneficial to improve the calculation precision. The magnetic field distributions and cogging torque calculated by the proposed model are consistent with the results of finite element analysis (FEA). Compared with the FEA, the proposed model can perform fast calculations of air-gap flux density and cogging torque under rotor eccentricity and magnet defects for SPM motors, which can be utilized for optimizing the motor towards fault tolerance. [ABSTRACT FROM AUTHOR]

This article investigates the electromagnetic vibration characteristics of high-speed (HS) permanent magnet synchronous machines (PMSMs) with amorphous metal stator cores (AMSCs) considering current harmonics. First, an analytical model of radial forces in PMSMs considering current harmonics due to both nonsinusoidal back electromotive force and pulsewidth modulation effects is developed. The cross influences of the two types of current harmonics on vibrations of HS PMSMs in different frequency bands are discussed. Second, the equivalent elasticity modulus parameters of laminated AMSCs are identified by utilizing modal experiment. Third, the influences of slot and pole number combinations on magnetic field harmonic contents and radial force orders for HS PMSMs are investigated by the analytical model. Then, the radial forces of a 15-kW HS PMSM fed by ideal sinusoidal current and experimental current are calculated under different rotational speeds by finite-element method. Finally, the vibrations of the prototype under rated torque and different rotational speeds are tested to verify the theoretical analysis. [ABSTRACT FROM AUTHOR]

Two types of surface-mounted permanent magnet synchronous machines (PMSMs) with the same physical dimensions but different stator core materials are comparatively analyzed, prototyped, and tested in this paper. In order to quantify the magnetization and loss characteristics of the stacked amorphous metal (AM) stator core, an experiment is conducted under different supply frequencies. Based on the data, the no-load iron losses, harmonic losses generated by the inverter-induced non-sinusoidal current harmonics, and the $d$ -axis and $q$ -axis inductances of two types of motors are comparatively analyzed by the finite-element method under different conditions and verified by experiments carried out on the two types of PMSM prototypes. The results illustrate that the AM PMSM has a characteristic of extremely low no-load iron losses, relative to the conventional silicon steel PMSM. [ABSTRACT FROM AUTHOR]

This paper investigates the no-load iron loss, on-load loss, and thermal performance of a high-speed surface-mounted permanent-magnet synchronous machine with an amorphous metal stator core (AMSC) and a titanium alloy retaining sleeve by numerical methods. The electromagnetic properties of the AMSC are tested by an experimental platform. The distributions of no-load iron loss, rated-load loss, and the thermal behavior of the motor are investigated under converter supply conditions. Finally, the loss and thermal performances of the prototype are tested and compared with the corresponding simulation results to verify the accuracy of the calculation results and the superiority of the prototype. [ABSTRACT FROM AUTHOR]

This paper presents a quasi-three-dimensional (3-D) nonlinear magnetic equivalent circuit (MEC) model for double-sided axial flux permanent magnet machines (AFPMMs) with fractional slot concentrated windings. The proposed model can take into account not only the local magnetic saturation effect but also the 3-D flux distribution. A coupled variable permeance element is proposed in airgap modeling that captures both axial and circumferential airgap flux densities. With the help of the coupled variable permeance element, the transient magnetic field is considered by the time varying connection of the airgap and the rotor. The proposed model can be used to predict the performance of AFPMMs, including the 3-D distribution of no-load and armature airgap flux densities, no-load back electromotive force, and electromagnetic torque. In order to verify the reliability of the MEC model, two AFPMM prototypes are taken as examples, and the accuracy is verified by comparing the calculated parameters of the MEC model with the finite element analysis and experimental results. Finally, the effect of local saturation on the performances of AFPMMs is investigated. [ABSTRACT FROM AUTHOR]

This paper presents a totally enclosed self-circulation (TESC) axial ventilation system (AVS) for large direct-drive permanent magnet synchronous machines (PMSMs). The configuration and the cooling air circulation process of the cooling system are described in detail. Then, the lumped parameter (LP) based airflow analysis and thermal analysis applicable to large PMSMs with the presented TESC AVS are proposed. The airflow network model and thermal network model are set up, respectively, and both of them are programmed. In order to verify the feasibility of the ventilation system and the accuracy of the LP models, a 1.65-MW PMSM prototype with the proposed ventilation system is developed and manufactured, and the temperature rise of the prototype is tested under generator operation mode. The accuracies of the developed airflow network model and thermal network model are verified by comparing the calculation results of the temperature rise with the test results. The LP models can be used to investigate the effects of different geometrical and operational conditions on the distributions of the airflow rate and the temperature of PMSMs with the TESC AVS. [ABSTRACT FROM AUTHOR]

This paper presents a new numerical and experimental method of the electromagnetic vibration analysis of amorphous alloy (AA) permanent magnet synchronous machines (PMSMs) whose stator cores are made from AA materials. A numerical model which is used to calculate the electromagnetic vibration of AA PMSMs is developed on an experimental basis. Concerning the magnetic performance of AA cores greatly affected by stresses and the elasticity modulus parameters affected by the loose structure of AA cores, data for magnetostriction (MS) curve of AA materials and magnetization curve of AA-stacked core are obtained experimentally, and the elasticity modulus parameters are updated based on the modal testing of the AA-stacked core. The electromagnetic vibration of a 2.1 kW radial flux AA PMSM is analyzed using the proposed calculation method. The electromagnetic vibration of the AAPMSM under two different conditions, which are 1) only radial forces (RFs) and 2) both RFs and MS, is calculated, respectively; then, the effect of MS on the electromagnetic vibration of the AA PMSM is obtained. The accuracy of the calculation method is verified by comparing the calculated results with the experimental results. [ABSTRACT FROM AUTHOR]

In this paper, each component of the no-load loss of interior permanent magnet motors under the conditions of both sinusoidal supply and converter supply is investigated by the finite-element method and experimental method. The no-load loss is calculated at different rotation speeds, two different slot and pole combinations and different converter parameters. The wireless temperature sensor embedded in the interior rotor is used to test the temperature of the permanent magnet under no-load condition, and the permanent magnet loss is calculated according to the slope of the initial temperature–time curve. Then, the mechanical loss of the prototype is measured by dragging a nonmagnetic rotor. The total tested losses are subtracted from the copper loss, the mechanical loss, and the permanent magnet loss to obtain the test results of core loss, and the experimental results of each loss and permanent magnet temperature rise are compared with the corresponding calculated results to verify the correctness of the simulation results. [ABSTRACT FROM AUTHOR]

In recent years, ternary transition metal oxides (TTMOs), especially spinel type TTMOs have attracted widespread attention as promising candidates for electrode materials. Among all of the popular TTMOs, MgCo2O4 is an outstanding one, owing to its superior theoretical capacitance. In this work, MgCo2O4 nanosheet arrays (NSAs) grown directly on nickel foams were fabricated through a facile hydrothermal process at 120 °C for 4 h. With a series of structural and morphological characterization techniques, it was found that the ethanol played a key role in controlling the composition and morphology during the synthesis process. The MgCo2O4 NSAs exhibited a superior specific capacitance of 853.06 C g−1 (at 1 mA cm−2) and enhanced cycling performance, with 94.65 % of initial capacitance retained after 3000 cycles when used as a binder‐free integrated electrode for electrochemical supercapacitors; much higher than other reported data for MgCo2O4 as well. The excellent electrochemical properties mainly came from the unique morphology of the MgCo2O4 NSAs. This study will demonstrate the applications of MgCo2O4 NSAs based large‐scale supercapacitors grown on low‐cost nickel foams. Foam party: MgCo2O4 nanosheet arrays have been prepared on a Ni foam substrate through a facile one‐step hydrothermal method and used as a binder‐free electrode material for supercapacitors. The MgCo2O4 NSAs electrode exhibits an electrochemical capacitance up to 853.06 C g−1 (at 1 mA cm−2) and about 94.65 % of the capacitance was retained after 3000 cycles (at 10 mA cm−2). [ABSTRACT FROM AUTHOR]

We investigate the transformation of single crystal gold nanorod surface morphology over extended growth times. After initial rapid anisotropic growth and disappearance of {111} bridging facets, the aspect ratios converge across AgNO3 concentrations. The surface morphology transitions from faceted to curved. These observations imply the final aspect ratio has little dependence on the AgNO3 concentration, consistent with primary control of the AgNO3 over aspect ratio occurring at the symmetry breaking point. [ABSTRACT FROM AUTHOR]

This paper presents a modified thermal model-based double-loop circulatory technique for the thermal analyses of permanent magnet synchronous machines. The inner loop of the circulation procedure is employed to guarantee the energy conservation of the air enclosed in the endcaps and modify the temperature-dependent heat convection coefficients, while the outer loop is used to correct the heat conductivity coefficients and the electromagnetic losses that change with temperatures. The thermal model based on finite formulation method is modified to simplify the modification process of the outer loop. The temperature estimation techniques are then applied to analyze the temperature distribution of a permanent magnet motor with a spirally mounted water-cooling system. A novel ventilation structure is established to maintain the temperature rise of the rotor parts. The analyses based on the proposed methodologies are validated by experiments. [ABSTRACT FROM AUTHOR]

In recent years, ternary metal oxides with their multiple oxidation states and unique morphologies have attracted widespread attention as a result of their potential applications in the electrochemical energy storage field. However, there are few reports about the energy storage capacity of metal vanadate, and no efficient and environmentally friendly synthesis methods have been reported so far. In our work, Zn3(OH)2V2O7·2H2O nanowires were successfully synthesized through a facile, rapid, and green microwave-assisted hydrothermal method at 100 °C for 50 min, and tightly connected Zn2V2O7 elliptical nanoparticles were acquired by a subsequent calcination process at 400 °C for 1 h. With a series of structural and morphological characterization techniques, we found that the surfactant glycine played a key role in controlling the composition and morphologies during the synthesis process: adding 0.15 M glycine to the mixed solution was identified to be the appropriate condition through a series of studies. More importantly, the as-synthesized Zn2V2O7 electrode exhibited a superior specific capacitance of 427.7 F g−1 (at 1 mA cm−2) and enhanced cycling performance, with 83.71% capacitance retained after 1000 cycles. Additionally, the Zn2V2O7/Ni-foam//AC ASC device displayed an energy density of 18.7 W h kg−1 at a power density of 272.7 W kg−1. The Zn3(OH)2V2O7·2H2O nanowires and Zn2V2O7 elliptical nanoparticles synthesized under microwave-assisted conditions were used as electrode materials in supercapacitors for the first time, which paved the way for zinc vanadate's application in the energy storage field. [ABSTRACT FROM AUTHOR]

This paper analyzes the vibration due to magnetostriction in axial flux (AF) permanent magnet (PM) machines with amorphous metal cores (AMCs). First, an analytical model is developed to predict the vibration due to magnetostriction. The solution regions of the analytical model are divided into yoke and teeth subdomains. Then, the effect of processing technics on the vibration of AMCs which is unable to consider in the analytical model was examined using measurements of vibration of AMCs. Through comparing the analytical results and experimental results, the correction factors of vibration acceleration are obtained. Finally, the vibration analysis of a 7 kW AF PM motor with AMCs is carried out by the analytical model. [ABSTRACT FROM PUBLISHER]

Chemical composition directly determines the structure and properties of almost all bulk inorganic solids, which are however popularly dismissed in the literature as a cause of property changes when studying multi-component oxide nanostructures by solution chemistries. The current work focuses on this subject through a systematic case study on CaWO4nanocrystals. CaWO4nanocrystals were prepared using room-temperature solution chemistry, in which a capping agent of citric acid was employed for kinetic grain size control. Sample characterizations by a set of techniques indicated that 5–7 nm CaWO4was obtained at room temperature, showing a pure-phase of tetrahedral scheelite structure. The molar ratio of Ca2+to W6+was found to be 1.2 : 1, apparently deviating from the unity expected for the stoichiometric CaWO4. Such nonstoichiometry was further modulated viaiso-valent incorporation of smaller Zn2+to the Ca2+-sites in CaWO4. It is found that with increasing the Zn2+content, there appeared transformation from high to low nonstoichiometry, though a pure scheelite-typed structure was retained. Such a nonstoichiometry was primarily represented by excessive cations like Zn2+and/or Ca2+within the surface disorder layers, which in turn showed a great impact on the structure and properties as demonstrated by a lattice contraction, band-gap narrowing, luminescence quenching, as well as improved conductivity. The property changes were rationalized in terms of surface structural disorder, electro-negativity discrepancy, and effective activation on the mobile protons. Consequently, systematic control over the non-stoichiometry for single-phase multi-component oxide nanostructures by solution chemistry is proven fundamentally important, which may help to achieve quantitatively the structure–property relationship for materials design and performance optimization. [ABSTRACT FROM AUTHOR]

What's the difference when water molecules are confined in a rather limited space? This work addresses this question by decorating water molecules within the scrolled titanate nanotubes. Both scrolled nanotubes Na0.96H1.04Ti3O7·nH2O and Na0.036H1.964Ti3O7·nH2O were first prepared to show large specific areas around 200 m2g−1, within which quantities of water molecules were confined to form H2O tubes that are alternatively arranged with the titanate nanotubes. This unique double-tube structure exhibited remarkable polarization and dielectric performance, yielding a huge dielectric constant around = 14 000, comparable to some known giant-dielectric-constant ceramics. Depending on the measurement frequency and temperature, the dielectric relaxation peaks were monitored by the content of the water molecules confined within the nanotubes. A two-layer dielectric model that involves the distinct anisotropy and confinement effect of the double-tube structure was proposed to explain this dielectric behavior. The findings reported in this work may pave the way for optimizing many subtle hydrated nanostructures in nature that could create an abundance of confined water molecules for a broad class of applications. [ABSTRACT FROM AUTHOR]

This work initiated a systematic study on the chemical nature of organic coating for monodispersed nanoparticles and its impact on the defect chemistry and the relevant properties. Monodispersed TiO2nanoparticles were prepared by a nonhydrolytic sol–gel reaction, which showed features of uniform diameter distribution around 5.2 nm, high crystallinity, and single anatase structure. These nanoparticles were terminated by oleate-related molecules, which stabilized the surface oxygen vacancies and further generated intense photoluminescence and co-existence of ferromagnetism and diamagnetism. After removal of organic coating, the nanoparticles became highly aggregated with no apparent changes in particle size, while the oxygen vacancy concentration was significantly reduced, as followed by energy position shift towards the deeper-levels which promoted the separation of photogenerated electrons and holes for improved photocatalytic activity. The results reported here are fundamentally important, which may be extended to comprehend the size-dependent defects and structure–property correlations of monodispersed nanoparticles for applications. [ABSTRACT FROM AUTHOR]

Abstract: This work explored the selective synthesis of polymorphs of CdWO4 in either tetragonal or monoclinic phase by optimizing the experimental parameters. Systematic characterization indicated that both polymorphs possessed similar spherical morphologies but different structural building blocks. Electronic structures calculations for both polymorphs demonstrated the same constructions of conduction band or valence band, while the conduction band widths of both polymorphs were quite different. Both CdWO4 polymorphs exhibited good photocatalytic activity for degradation of methyl orange under UV light irradiation. When comparing to some other well-known tungstate oxide materials, the photocatalytic activity was found to follow such a consequence, monoclinic CdWO4≈monoclinic ZnWO4>tetragonal CdWO4>tetragonal CaWO4. The specific photocatalytic activity of monoclinic CdWO4 was even higher than that of commercial TiO2 photocatalyst (Degussa P25). The increased activity from the tetragonal CdWO4 to the monoclinic was consistent with the trend of the decreased symmetry, and this could be explained in terms of the geometric structures and electronic structures for both polymorphs. [Copyright &y& Elsevier]

In recent years, ternary transition metal oxides (TTMOs), especially spinel type TTMOs have attracted widespread attention as promising candidates for electrode materials. Among all of the popular TTMOs, MgCo 2 O 4 is an outstanding one, owing to its superior theoretical capacitance. In this work, MgCo 2 O 4 nanosheet arrays (NSAs) grown directly on nickel foams were fabricated through a facile hydrothermal process at 120 °C for 4 h. With a series of structural and morphological characterization techniques, it was found that the ethanol played a key role in controlling the composition and morphology during the synthesis process. The MgCo 2 O 4 NSAs exhibited a superior specific capacitance of 853.06 C g -1 (at 1 mA cm -2 ) and enhanced cycling performance, with 94.65 % of initial capacitance retained after 3000 cycles when used as a binder-free integrated electrode for electrochemical supercapacitors; much higher than other reported data for MgCo 2 O 4 as well. The excellent electrochemical properties mainly came from the unique morphology of the MgCo 2 O 4 NSAs. This study will demonstrate the applications of MgCo 2 O 4 NSAs based large-scale supercapacitors grown on low-cost nickel foams., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The phenomenon of symmetry breaking-in which the order of symmetry of a system is reduced despite manifest higher-order symmetry in the underlying fundamental laws-is pervasive throughout science and nature, playing a critical role in fields ranging from particle physics and quantum theory to cosmology and general relativity. For the growth of crystals, symmetry breaking is the crucial step required to generate a macroscopic shape that has fewer symmetry elements than the unit cell and/or seed crystal from which it grew. Advances in colloid synthesis have enabled a wide variety of nanocrystal morphologies to be achieved, albeit empirically. Of the various nanoparticle morphologies synthesized, gold nanorods have perhaps been the most intensely studied, thanks largely to their unique morphology-dependent optical properties and exciting application potential. However, despite intense research efforts, an understanding of the mechanism by which a single crystal breaks symmetry and grows anisotropically has remained elusive, with many reports presenting seemingly conflicting data and theories. A fundamental understanding of the symmetry breaking process is needed to provide a rational framework upon which future synthetic approaches can be built. Inspired by recent experimental results and drawing upon the wider literature, we present a mechanism for gold nanorod growth from the moments prior to symmetry breaking to the final product. In particular, we describe the steps by which a cuboctahedral seed particle breaks symmetry and undergoes anisotropic growth to form a nanorod. With an emphasis on the evolving crystal structure, we highlight the key geometrical and chemical drivers behind the symmetry breaking process and factors that govern the formation and growth of nanorods, including control over the crystal width, length, and surface faceting. We propose that symmetry breaking is induced by an initial formation of a new surface structure that is stabilized by the deposition of silver, thus preserving this facet in the embryonic nanorod. These new surfaces initially form stochastically as truncations that remove high-energy edge atoms at the intersection of existing {111} facets and represent the beginnings of a {011}-type surface. Crucially, the finely tuned [HAuCl 4 ]:[AgNO 3 ] ratio and reduction potential of the system mean that silver deposition can occur on the more atomically open surface but not on the pre-existing lower-index facets. The stabilized surfaces develop into side facets of the nascent nanorod, while the largely unpassivated {111} facets are the predominant site of Au atom deposition. Growth in the width direction is tightly controlled by a self-sustaining cycle of galvanic replacement and silver deposition. It is the [HAuCl 4 ]:[AgNO 3 ] ratio that directly determines the particle size at which the more open atomic surfaces can be stabilized by silver and the rate of growth in the width direction following symmetry breaking, thus explaining the known aspect ratio control with Ag ion concentration. We describe the evolving surface faceting of the nanorod and the emergence of higher-index facets. Collectively, these observations allow us to identify facet-size and edge-atom effects as a simple fundamental driver of symmetry breaking and the subsequent development of new surfaces in the presence of adsorbates.

Formation of anisotropic nanocrystals from isotropic single-crystal precursors requires an essential symmetry breaking event. Single-crystal gold nanorods have become the model system for investigating the synthesis of anisotropic nanoparticles, and their growth mechanism continues to be the subject of intense investigation. Despite this, very little is known about the symmetry breaking event that precedes shape anisotropy. In particular, there remains limited understanding of how an isotropic seed particle becomes asymmetric and of the growth parameters that trigger and drive this process. Here, we present direct atomic-scale observations of the nanocrystal structure at the embryonic stages of gold nanorod growth. The onset of asymmetry of the nascent crystals is observed to occur only for single-crystal particles that have reached diameters of 4-6 nm and only in the presence of silver ions. In this size range, small, asymmetric truncating surfaces with an open atomic structure become apparent. Furthermore, {111} twin planes are observed in some immature nanorods within 1-3 monolayers of the surface. These results provide direct observation of the structural changes that break the symmetry of isotropic nascent nanocrystals and ultimately enable the growth of asymmetric nanocrystals.

Metastable monoclinic ZnMoO4 was successfully synthesized via a hydrothermal route with variation of reaction temperatures and time at pH value of 5.7. Systematic sample characterizations were carried out, including X-ray powder diffraction, scanning electron microscopy, Fourier transformed infrared spectra, UV-visible diffuse reflectance spectra, and photoluminescence spectra. The results show that all as-prepared ZnMoO4 samples were demonstrated to crystallize in a pure-phase of monoclinic wolframite structure. All samples were formed in plate-like morphology. Six IR active vibrational bands were observed in the wave number range of 400-900 cm(-1). The band gap of as-prepared ZnMoO4 was estimated to be 2.86 eV by Tauc equation. Photoluminescence measurement indicates that as-prepared ZnMoO4 exhibits a broad blue-green emission under excitation wavelength of 280 nm at room temperature. Photocatalytic activity of as-prepared ZnMoO4 was examined by monitoring the degradation of methyl orange dye in an aqueous solution under UV radiation of 365 nm. The as-prepared ZnMoO4 obtained at 180 degrees C for 40 h showed the best photocatalytic activity with completing degradation of MO in irradiation time of 120 min. Consequently, monoclinic ZnMoO4 proved to be an efficient near visible light photocatalyst.

Chemical composition directly determines the structure and properties of almost all bulk inorganic solids, which are however popularly dismissed in the literature as a cause of property changes when studying multi-component oxide nanostructures by solution chemistries. The current work focuses on this subject through a systematic case study on CaWO(4) nanocrystals. CaWO(4) nanocrystals were prepared using room-temperature solution chemistry, in which a capping agent of citric acid was employed for kinetic grain size control. Sample characterizations by a set of techniques indicated that 5-7 nm CaWO(4) was obtained at room temperature, showing a pure-phase of tetrahedral scheelite structure. The molar ratio of Ca(2+) to W(6+) was found to be 1.2:1, apparently deviating from the unity expected for the stoichiometric CaWO(4). Such nonstoichiometry was further modulated via iso-valent incorporation of smaller Zn(2+) to the Ca(2+)-sites in CaWO(4). It is found that with increasing the Zn(2+) content, there appeared transformation from high to low nonstoichiometry, though a pure scheelite-typed structure was retained. Such a nonstoichiometry was primarily represented by excessive cations like Zn(2+) and/or Ca(2+) within the surface disorder layers, which in turn showed a great impact on the structure and properties as demonstrated by a lattice contraction, band-gap narrowing, luminescence quenching, as well as improved conductivity. The property changes were rationalized in terms of surface structural disorder, electro-negativity discrepancy, and effective activation on the mobile protons. Consequently, systematic control over the non-stoichiometry for single-phase multi-component oxide nanostructures by solution chemistry is proven fundamentally important, which may help to achieve quantitatively the structure-property relationship for materials design and performance optimization., (This journal is © the Owner Societies 2011)

This work initiated a systematic study on the chemical nature of organic coating for monodispersed nanoparticles and its impact on the defect chemistry and the relevant properties. Monodispersed TiO(2) nanoparticles were prepared by a nonhydrolytic sol-gel reaction, which showed features of uniform diameter distribution around 5.2 nm, high crystallinity, and single anatase structure. These nanoparticles were terminated by oleate-related molecules, which stabilized the surface oxygen vacancies and further generated intense photoluminescence and co-existence of ferromagnetism and diamagnetism. After removal of organic coating, the nanoparticles became highly aggregated with no apparent changes in particle size, while the oxygen vacancy concentration was significantly reduced, as followed by energy position shift towards the deeper-levels which promoted the separation of photogenerated electrons and holes for improved photocatalytic activity. The results reported here are fundamentally important, which may be extended to comprehend the size-dependent defects and structure-property correlations of monodispersed nanoparticles for applications.