Polyhedron Morphology Research Articles

Enhancing the durable performance of LiMn2O4 at high-rate and elevated temperature by nickel-magnesium dual doping

Various nickel and magnesium dual-doped LiNixMg0.08Mn1.92−xO4 (x ≤ 0.15) were synthesized via a modified solid-state combustion method. All as-prepared samples show typical spinel phase with a well-defined polyhedron morphology. The Ni-Mg dual-doping obviously decreases the lattice parameter that gives rise to the lattice contraction. Owing to the synergistic merits of metal ions co-doping, the optimized LiNi0.03Mg0.08Mn1.89O4 delivers high initial capacity of 115.9 and 92.9 mAh·g−1, whilst retains 77.1 and 69.7 mAh·g−1 after 1000 cycles at 1 C and high current rate of 20 C, respectively. Even at 10 C and 55 °C, the LiNi0.03Mg0.08Mn1.89O4 also has a discharge capacity of 92.2 mAh·g−1 and endures 500 cycles long-term life. Such excellent results are contributed to the fast Li+ diffusion and robust structure stability. The anatomical analysis of the 1000 long-cycled LiNi0.03Mg0.08Mn1.89O4 electrode further demonstrates the stable spinel structure via the mitigation of Jahn-Teller effect. Hence, the Ni-Mg co-doping can be a potential strategy to improve the high-rate capability and long cycle properties of cathode materials.

Structural, magnetic, dielectric and optical properties of double-perovskite Bi2FeCrO6 ceramics synthesized under high pressure

We report on double-perovskite Bi2FeCrO6 ceramics synthesized by solid-state reaction under high pressure of 6 GPa and temperature of 1000 °C. Its crystal structure was refined by X-ray powder diffraction data, and the Bi2FeCrO6 ceramics crystallized in rhombohedral structure with R3c space group. The ceramic grains exhibited polyhedron morphology with average size of 2.80 μm. The atomic ratio of Bi:Fe:Cr was determined to be 2.04:1.00:1.00, close to the nominal value. X-ray photoelectron spectra confirmed the dual oxidation states of ion (Fe2+ and Fe3+) and chromium (Cr3+ and Cr6+) in the Bi2FeCrO6 ceramics and oxygen in the forms of lattice oxygen and oxygen vacancies. Bi2FeCrO6 ceramics exhibits both antiferromagnetic and ferromagnetic orders, which are reflected in the unique temperature dependent magnetization curves. In addition, Bi2FeCrO6 ceramics also have large dielectric constant (∼508 at 1 kHz) and small dielectric loss (0.38 at 1 MHz) at room temperature. The direct band gap of the Bi2FeCrO6 ceramics deduced from their UV–Vis–NIR absorption spectra, was ∼1.50 eV, which was small enough to absorb the sunlight at wavelengths below 829 nm. A strong absorption peak was also observed at 600 nm in the absorption spectra of the Bi2FeCrO6 ceramics. These findings demonstrate that the Bi2FeCrO6 ceramics with a narrow direct band gap can effectively absorb the main portion of the sunlight spectrum (i.e., visible lights) and have promising applications in the fields of photoelectrochemical devices and photovoltaic devices.

High performance zeolitic imidazolate framework-8 (ZIF-8) based suspension: Improving the shear thickening effect by controlling the morphological particle-particle interaction

A novel shear thickening fluid (Z-STF) was developed via dispersing zeolitic imidazolate framework-8 (ZIF-8) nanoparticles into ethylene glycol (EG). By varying the morphologies of the ZIF-8 nanoparticles, the rheological properties of the Z-STF were controlled. In comparison to the traditional SiO2 based STF (S-STF), the Z-STF showed a superior shear thickening behavior because of the porous nature and polyhedron morphology of the ZIF-8 nanoparticles. Firstly, the EG molecule could be incorporated into the micropores of ZIF-8, which increased the volume fraction of the dispersing phases and enhanced the hydrodynamic forces between the particles. Secondly, the poor relative sliding of truncated cubic particles led to easily form a more robust structure of frictional contact network in truncated cube ZIF-8 based STF (TCZ-STF) than in truncated rhombic dodecahedron ZIF-8 based STF (TRDZ-STF) and S-STF, thus the TCZ-STF showed smaller critical shear rates and higher maximum viscosities. This work provides a morphology turning method to design high performance STF and supplies a good understanding of the relationship between ST behavior and particles' structure. In view of the easy preparation and wonderful mechanical properties, the Z-STF possessed broad application in damping, body armor, and safe energy.

Metallic Organic Framework-Derived Fe, N, S co-doped Carbon as a Robust Catalyst for the Oxygen Reduction Reaction in Microbial Fuel Cells

Oxygen reduction reaction (ORR) provides a vital role for microbial fuel cells (MFCs) due to its slow reaction kinetics compared with the anodic oxidation reaction. How to develop new materials with low cost, high efficacy, and eco-friendliness which could replace platinum-based electrocatalysis is a challenge that we have to resolve. In this work, we accomplished this successfully by means of a facile strategy to synthesize a metallic organic framework-derived Fe, N, S co-doped carbon with FeS as the main phase. The Fe/S@N/C-0.5 catalyst demonstrated outstandingly enhanced ORR activity in neutral PBS and alkaline media, compared to that of commercial 20% Pt-C catalyst. Here, we started-up and operated two parallel single-chamber microbial fuel cells of an air cathode, and those cathode catalysts were Fe/S@N/C-0.5 and commercial Pt-C (20% Pt), respectively. Scanning electron microscopy (SEM) elaborated that the Fe/S@N/C-0.5 composite did not change the polyhedron morphology of ZIF-8. According to X-ray diffractometry(XRD) curves, the main crystal phase of the resulted Fe/S@N/C-0.5 was FeS. The chemical environment of N, S, and Fe which are anticipated to be the high-efficiency active sites of ORR for MFCs were investigated by X-ray photoelectron spectroscopic(XPS). Nitrogen adsorption/desorption techniques were used to calculate the pore diameter distribution. In brief, the obtained Fe/S@N/C-0.5 material exhibited a pronounced reduction potential at 0.861 V (versus Reversible Hydrogen Electrode(RHE)) in 0.1M KOH solution and –0.03 V (vs. SCE) in the PBS solution, which both outperform the benchmark platinum-based catalysts. Fe/S@N/C-0.5-MFC had a higher Open Circuit Voltage(OCV) (0.71 V), stronger maximum power density (1196 mW/m2), and larger output voltage (0.47 V) than the Pt/C-MFC under the same conditions.

Fabrication of nanostructured magnesium ferrite polyhedrons and their applications in heat transfer management and gas/humidity sensors

In this paper we report the sol–gel synthesis of MgFe2O4 nanostructures of polyhedron morphology. X-ray diffraction (XRD) patterns revealed the presence of pure phase MgFe2O4 crystalline materials whereas Energy dispersive X-ray analysis (EDX) confirmed the presence of Mg, Fe and O in the compound. Scanning electron microscopy (SEM) image shows the porous scenery on the surface of the material whereas transmission electron microscopy (TEM) image displays polyhedron morphology of the particles. Sensor films fabricated utilizing these nanostructures were tested for gas/humidity sensing with notable success as the average sensitivity of the humidity sensor was found to be ~ 0.0237 MΩ/%RH over the entire range of humidity tested for and maximum % sensor response was found to be 27.19 corresponding to exposure of 4 vol% LPG. Minimum response and recovery times were found to be 79 and 60 s respectively for 0.5 vol% LPG. The magnesium ferrite nanoparticles were tested for heat transfer applications as ethylene glycol based nanofluid component. The result shows that the thermal conductivity of ethylene glycol nanofluid was significantly increased compared to pure ethylene glycol due to the presence of suspended MgFe2O4 nanoparticles.

Structural stability and superior electrochemical performance of Sc-doped LiMn2O4 spinel as cathode for lithium ion batteries

Scandium doped LiScxMn2-xO4 compounds are synthesized by solid-state method, which show single phase with rod-like polyhedron morphology. The Sc-doping decreases the lattice parameter ‘a’ marginally due to the change in the inter-atomic distance of the metal oxide bonds as confirm by Rietveld refinement. In addition, the expansion of LiO4 tetrahedron and contraction of MnO6 octahedron by ∼0.01 Å upon doping are observed. The Sc2p3/2 peak at 402.5 eV and Sc2p1/2 peak at 407.2 eV in the XPS spectrum of LiSc0.06Mn1.94O4 confirms the presence of Sc in the spinel structure. The symmetric stretching of MnO bond of LiSc0.06Mn1.94O4 shifts lower value (∼4 cm−1) than that of LiMn2O4 indicating the occupancy of Sc3+ ion in the octahedral site. The diffusion coefficient value of LiSc0.06Mn1.94O4 (1 × 10−12cm2s−1) is one-order higher than that of undoped LiMn2O4 (1 × 10−13 cm2s−1). LiMn2O4 delivers a discharge capacity of 117 mAhg−1 at 1C with a capacity retention of 74% after 500 cycles, whereas under similar condition LiSc0.06Mn1.94O4 delivers a discharge capacity of 114 mAhg−1 with a capacity retention of >90%. LiSc0.06Mn1.94O4 also delivers excellent rate capability due to high diffusion coefficient and less charge transfer resistance compared to the parent compound. The structure and morphology of the Sc-doped electrode after 500 cycles remains intact without any formation of Mn-rich agglomeration suggest that the reduction of Mn2+ ion dissolution as well as Jahn-Teller distortion. Hence LiSc0.06Mn1.94O4 can be a potential cathode material for lithium ion batteries.

Fe and S co-doped N-enriched hierarchical porous carbon polyhedron as efficient non-noble-metal electrocatalyst toward oxygen reduction reaction in both alkaline and acidic medium

N-enriched porous carbon materials represent a kind of effective electrocatalysts for oxygen reduction reaction (ORR), which have received extensive attention owing to their low-cost, advantageous catalytic activity and stability. However, exploring non-noble-metal catalysts for replacing high-cost notable metal catalysts remains a major challenge. Herein, iron and sulfur co-doped N-enriched hierarchical porous carbon polyhedron (NC) derived from metal-organic framework (Fe/S-NC) was successfully prepared by a facile strategy, including a direct pyrolyzation of zeolitic imidazolium framework (ZIF-8) and a further pyrolysis of the impregnated NC with Fe(SCN)3 solution. Electron microscopic studies showed that Fe/S co-doping has not changed the polyhedron morphology of NC. The resulted Fe/S-NC demonstrated obviously enhanced ORR activity, excellent durability and methanol tolerance in both alkaline and acidic media. The half-wave potential of the Fe/S-NC exhibited 32 mV positive shift in 0.1 M KOH, and only 25 mV negative shift in 0.5 M H2SO4, respectively, as compared to that of the commercial Pt/C (20% Pt loading) catalyst. The superior performance is attributable to the combined roles of the unique hierarchical porous structure of NC and the Fe/S co-doping by endowing Fe/S-NC with great specific surface area, rich active sites, excellent conductivity and synergistic effect between Fe-Nx-C active sites and a thiophene-like structure (C-S-C).

Orientational Ag nanoparticle alignment from a facile ‘TEG‐sol’ method

Super-aligned conductive material is a hotspot in the research of flexible and transparent conductive films. This work introduces a facile and rapid ‘TEG-sol’ method to synthesise Ag nanoparticles and their orientational alignment. Pure, well-crystallised Ag nanoparticles with polyhedron morphology are fabricated by reducing silver nitrate in TEG (triethylene glycol) solvent. Fourier transform infrared spectroscopy result reveals an organic coating layer on the surface of the Ag nanoparticles, which promotes the excellent dispersibility of these nanoparticles in TEG solvent. Orientational Ag nanoparticle alignment is obtained by spin coating the dispersion on copper foil. This proposed process provides a brand new idea for the design and fabrication of conductive microstructures.

Effect of Carbonate Precipitant on the Microstructure and Electrochemical Properties of LiNi0.5Mn1.5O4 Cathodes

Spinel LiNi0.5Mn1.5O4 cathode materials with Fd3m space group were prepared using the co-precipitation method via adjusting the amount of Na2CO3 precipitant. X-ray diffraction and Rietveld refinement revealed that the impurity phase was effectively inhibited after the addition of more amount of Na2CO3. All samples, including the pristine LiNi0.5Mn1.5O4 sample and that prepared with different extra amounts of Na2CO3, exhibited uniform polyhedron morphology and their average grain sizes increased with the amount of Na2CO3. After adding 5% more Na2CO3, the average grain size of the sample was larger than 500 nm. When compared to other samples, the amount of impurity phase was minimum in the sample prepared with 5% more Na2CO3. Due to the impurity suppression, the LiNi0.5Mn1.5O4 sample prepared with 5% more Na2CO3 exhibited superior electrochemical performance for Li-ion batteries, showing initial discharge capacities of 125.4 mA h g−1 and 126.1 mA h g−1, and high capacity retentions of 90.7% and 87.6% after 200 cycles at 0.1 C and 0.5 C, respectively. It also exhibited the lowest intrinsic resistance and best Li+ diffusion kinetics among all the samples deduced from electrochemical impedance spectroscopy.

Structure induced selective adsorption performance of ZIF-8 nanocrystals in water

Inspired by the surface charge and uniform pore size of Zeolitic Imidazolate Framework-8 (ZIF-8), we prepared ZIF-8 nanocrystals and investigated their selective adsorption performance and potential application in water purification by adsorption of Cr(VI), methyl orange (MO) and phenol in aqueous solution. The obtained ZIF-8 nanocrystals have polyhedron morphology, uniform particle size (∼25nm) and high surface area of 1291m2g−1. The adsorption results indicate that the ZIF-8 adsorption capacity for phenol is less than that for MO and Cr(VI), which exhibits selectivity for anions. Further, the adsorption capacity for Cr(VI) is more than that for MO, exhibiting size selectivity. The adsorption behaviors were investigated to fit well with pseudo-second-order model and Langmuir isotherm model, implying the chemical related adsorption process. Further, the adsorption mechanism was investigated by XPS analysis, which indicating the adsorption was related to electrostatic interaction, hydrogen bonding and chemical reducing process. This work not only gives an insight into the adsorption behavior and adsorption mechanism of ZIF-8, but also provides an excellent adsorbent with selective adsorption performance for the process of water treatment and purification.

In situ synthesizing SiC particles and its strengthening effect on an Al–Si–Cu–Ni–Mg piston alloy

Utilizing the reaction between dissolved Si atoms and Al4C3, SiC particles have been in situ synthesized in Al–Si alloys, which perform multiple–scale ranging from nano– to micro–sized, exhibiting polyhedron morphology. An in situ 2% SiCp reinforced Al–17.5Si–4.5Cu–2Ni–0.65 Mg piston alloy was designed. The hardness, density, wear resistance and thermal expansion coefficient properties are improved, and the ultimate tensile strength can be increased up to 132 MPa tested at 350 °C. Besides, it is regarded that the in situ SiC particulates act on the process of heat treatment, which affect the mechanical properties as a result. The in situ SiCp/Al–Si composites may be promising candidates for high temperature applications.

Strengthening mechanisms of (Al3Zrmp + ZrB2np)/AA5052 hybrid composites

To establish the correlation between grain size, dislocations, dispersed particles (size and vol.%) along with their solid solution strengthening effects in alloy and combined effect of all on the strengthening of advanced composite materials (Al3Zrmp + ZrB2np)/AA5052 hybrid composites have been selected for the investigation. (Al3Zrmp + ZrB2np)/AA5052 hybrid composites have been synthesized by the direct melt reaction of AA5052 alloy and inorganic salts (K2ZrF6 and KBF4). These composites have been characterised by X-ray diffractometer, optical microscopy, scanning-electron microscopy with energy-dispersive spectroscopy, transmission-electron microscopy, tensile and hardness test. Results indicate the successful formation of second phase reinforcement particles namely Al3Zr and ZrB2 in the AA5052 alloy matrix. Al3Zr particles exhibit rectangular and polyhedron morphology within an average of micron size while ZrB2 show hexagonal and rectangular within an average of nano size. Grain refinement of Al-rich phase observed in the composites, increases with increasing vol.% of reinforcement particles. TEM observation shows the presence of dislocations in the composite matrix which help to improve the strength parameters. Tensile results show the improvement in strength parameters which improve with the increasing amount of particles whereas percentage elongation also improves up to certain vol.% of particles and beyond that decrease. However, bulk hardness shows an increasing trend continuously with vol.% of particles. The strengthening mechanisms, namely dislocation, Orowan, grain-refined and solid solution are quantified for the hybrid (Al3Zrmp + ZrB2np)/AA5052 composites and the total of above are in agreement with experimental results. Solid-solution and Orowan are the predominant strengthening mechanisms in the composites.

Facile one-step in-situ synthesis of type-II CeO2/CeF3 composite with tunable morphology and photocatalytic activity

Ce-based materials have gained considerable prominence in catalysis as a type of the most valuable material for various applications ranging from automotive emission control to CO2 and water splitting. We here report a novel type-II CeO2/CeF3 composite, composed of two paradigms of Ce-based binary compounds, prepared by a facile one-step in-situ hydrothermal method, and explore its potential as a photocatalyst for solar energy conversion. Primarily, the morphologies, particle size and microstructures of CeO2/CeF3 composite can be modulated by the volume ratio of ethanol to water in the precursor solution. The photocatalytic activities firstly increase to a maximum and then decrease with the increased amount of ethanol. The hybrid CeO2/CeF3 particles with large size and polyhedron morphology exhibit superior photocatalytic activity, having a high rate constant k of MB decomposition about 7.6 times faster than that of the lowest one. A multiple synergetic mechanism in CeO2/CeF3 composite, which is featured by obvious promoted separation of photogenerated electrons and holes at the type-II heterojunction interfaces and in particular between the different facets of microcrystals, and the highly reactive facets exposed, has been proposed to account for its distinguished photocatalytic activity. This work provides some new insights for the synthesis and optimization of novel rare earth Ce-based composite photocatalyst with high photocatalytic performance.

Synthesis of a soluble preceramic polymer for ZrC using 2-hydroxybenzyl alcohol as carbon source

A preceramic polymer for ZrC was successfully synthesised by chemical reaction between zirconium oxychloride (ZrOCl2·8H2O) and 2-Hydroxybenzyl alcohol via a one-pot route. The molecular structure, thermal properties and pyrolysis behaviour of the precursor were investigated. The results indicated that the precursor might be Zr–O–Zr chain polymer with 2-Hydroxybenzyl alcohol as ligand. The precursor was air-stable and exhibited excellent solubility in common organic solvents. The conversions from precursor to ZrC powders were investigated by TG-DTA, X-ray diffraction, Scanning electron microscope, TEM and Raman spectrum. The precursor underwent a thermal decomposition in four steps, and ZrC powders were formed at 1300°C via carbothermal reduction reaction of ZrO2 and carbon in argon with ceramic yield of 63.0%. The ZrC particles were fine and exhibited irregular polyhedron morphology with average size in the range of 100–300 nm.

The effects of positional isomers, protonation and solvent on the morphologies and photophysical properties of boron difluoride complex microcrystals

Positional isomers, protonation and solvent provide useful strategies for morphology-controllable fabrication of organic microcrystals. Among them, the solvent unprecedentedly induces a globate polyhedron morphology with unusual orange-red phosphorescence. The changes in morphology also induce interesting changes in the photophysical properties of boron difluoride organic microcrystals.

Effect of alloy elements on the morphology transformation of TiB2 particles in Al matrix

To reveal the effect of alloy element on the morphology of in situ TiB2 particles, a series of TiB2 particles with various morphology were obtained via controlling synthesis process. Si and Cu can affect the morphology transformation of TiB2 particles significantly. Si preferentially adsorbed on (1 0 1¯ 1), (1 1 2¯ 0) and (1 2¯ 1 3¯) planes resulting in the polyhedron morphology of TiB2. Cu adsorbed on (1 0 1¯ 0) preferentially leading to the minimum aspect (the ratio of the diameter and thickness).

Properties of aniline-modified strontium titanyl oxalate-based electrorheological suspension

Aniline-modified strontium titanyl oxalate (STO) particles were fabricated with a precipitation method. The structures of the particles were analyzed by x-ray diffraction analyses, Fourier transform infrared spectrometry and thermogravimetric analysis. Scanning electron microscopy was used to analyze the morphology of the particles. The results indicate chemical bonds are formed between STO and aniline. By tuning the molar ratio of aniline to Ti, the morphology of the aniline-modified STO particles can be sphere, polyhedron and a mixture composed of clusters of nano particles and micro rod-like particles. Electrorheological (ER) properties, temperature effect, thixotropy and sedimentation stability of the ER fluids based on the pure STO and the aniline-modified STO were tested. The results indicate all the properties strongly depend on the content of the aniline during the fabrication process of the particles. The ER fluid with a molar ratio of aniline/Ti of 2 presents the highest shear stress, yield stress, leak current density and the most stable ER behavior at changing temperatures. The reason is the particles have polyhedron morphology and absorbed polar aniline molecules. Because of the stable space grid structure formed by the particles with a molar ratio of aniline/Ti of 3, the ER fluid exhibits better thixotropy and sedimentation stability than the others.

Preparation of Magnetic Iron Oxide by Hydrothermal Method

Abstract. Iron oxide particles with spherical, date-pit like, or polyhedron morphology were obtained by hydrothermal method. The morphology, thermal analysis, crystal structure of the products was characterized by FESEM, thermogravimetry (TG), X-ray diffraction (XRD), respectively. The measured results reveal that the product of three different shapes is hematite (α-Fe2O3).

Molten salt synthesis and photoluminescence properties of novel red emitting phosphors Ba5(VO4)3Cl:Eu3+,K+

A series of Ba5(VO4)3Cl:Eu3+,K+ phosphors have been synthesized by the molten salt synthesis method. The crystalline structure, morphology, photoluminescence properties and lifetimes were characterized using X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM) and photoluminescence spectroscopy, respectively. XRD indicates that the Ba5(VO4)3Cl:Eu3+,K+ phosphors are synthesized successfully via molten salt method. SEM image demonstrates that the obtained phosphors have hexagonal polyhedron morphology. The photoluminescence spectra reveal that the as-prepared phosphors exhibit a bright red emission under the excitation of blue or near ultraviolet light. The concentration quenching was also investigated, and the dipole–dipole interaction is responsible for the concentration quenching of fluorescence emission of Eu3+ ions in Ba5(VO4)3Cl phosphor. The present work suggests that the Ba5(VO4)3Cl:Eu3+,K+ phosphors would be a potential candidate for light emitting devices.

Effect of Silver Content on Bulk Properties and Interfacial Morphology of Sn-xAg-Cu Solders

The bulk microstructure, melting behavior, mechanical property, and interfacial Intermetallic compound (IMC) morphology were investigated on Sn-Ag-Cu (SAC) lead free solders with different Ag content (0.3,1.0,2.0,3.0,3.8wt%). The result indicates that SAC solders with higher Ag content present finer and denser intermetallic particles in the bulk solder, as a result that the tensile strength of SAC solders increased with the increasing of Ag content, while the ductility decreased. The melting temperature of SAC305 and SAC387 solders are close to eutectic point from the narrow melting range. It was found that the interfacial IMC morphology didnt appear obvious difference regardless of Ag content for as-soldered. Furthermore, the higher Ag contained solders present smaller IMC grain at the interface of aged joints and all aged joints have a tendency of polyhedron morphology.