Modification Of Crystal Structure Research Articles

Influence of Vacancies in Manganese Hexacyanoferrate Cathode for Organic Na-Ion Batteries: A Structural Perspective.

Manganese hexacyanoferrates (MnHCF) are promising positive electrode materials for non-aqueous batteries, including Na-ion batteries, due to their large specific capacity (>130 mAh g-1 ), high discharge potential and sustainability. Typically, the electrochemical reaction of MnHCF associates with phase and structural changes, due to the Jahn-Teller (JT) distortion of Mn sites upon the charge process. To understand the effect of the MnHCF structure on its electrochemical performance, two MnHCF materials with different vacancies content are investigated herein. The electrochemical results show that the sample with lower vacancy content (4 %) exhibits relatively higher capacity retention of 99.1 % and 92.6 % at 2nd and 10th cycles, respectively, with respect to 97.4 % and 79.3 % in sample with higher vacancy content (11 %). Ex-situ X-ray absorption spectroscopy (XAS) and ex situ X-ray diffraction (XRD) characterization results show that a weaker cooperative JT-distortion effect and relatively smaller crystal structure modification occurred for the material with lower vacancies, which explains the better electrochemical performance in cycled electrodes.

Low-temperature ground state structure of PbTiO3

${\mathrm{Mn}}^{4+}$, ${\mathrm{Cr}}^{3+}$, and ${\mathrm{Fe}}^{3+}$ electron paramagnetic resonance and $^{47,49}\mathrm{Ti}$ and $^{207}\mathrm{Pb}$ nuclear magnetic resonance (NMR) measurements are carried out in $\mathrm{PbTi}{\mathrm{O}}_{3}$ single crystals at temperatures from 300 K down to 20 K. It was found that the tetragonal crystal-field parameter of the ${\mathrm{Mn}}^{4+}$ and ${\mathrm{Cr}}^{3+}$ impurity ions undergoes an unexpected change in its temperature dependence at $T<170$ K: it increases with decreasing temperature to 150--170 K and then strongly decreases with further temperature lowering. Electric-field gradient at Ti site measured from $^{47,49}\mathrm{Ti}$ NMR shows nonuniform change with decreasing temperature: it sharply increases with decreasing temperature to 150--170 K and is practically temperature independent below these temperatures. Moreover, substantial broadening of NMR linewidth is seen for Ti and Pb nuclei at $T<170$ K due to essential increase of lattice parameters fluctuations. All these facts may indicate proximity of a transition to another phase with barely perceptible crystal-structure modification as reported in the paper by Kobayashi et al. [Phys. Rev. B 28, 3866 (1983)] while, actually, it was not detected in NMR. The experimental data are compared with those obtained from ab initio calculations.

Crystal structure and performance modification of a novel triclinic CaMgP2O7 microwave dielectric ceramic with low sintering temperature

In this study, crystal structure and microwave dielectric properties of phosphate CaMgP2O7 were comprehensively investigated. As a novel microwave dielectric ceramic, CaMgP2O7 consists of highly dense structure with optimal microwave dielectric properties (εr = 7.8 ± 0.124, Q×f = 13,165 ± 836 GHz, and τf = −85.04 ± 1.205 ppm/℃) at a low sintering temperature (950 ℃). The Rietveld refinement of XRD patterns revealed that CaMgP2O7 belongs to a triclinic system with P-1 symmetry type. Moreover, the substitution of Zn2+ for Mg2+ in CaMgP2O7 can further reduce the sintering temperature, effectively promote the densification process, and improve the Q×f value. The effects of porosity (or density) and chemical bond characteristics on the performance of CaMg1-xZnxP2O7 ceramics were carefully analyzed as well. Outstanding performance (εr = 8.05 ± 0.12, Q×f = 20,670 ± 923 GHz, and τf = −87.59 ± 3.24 ppm/℃) can be achieved for the CaMg0.84Zn0.16P2O7 ceramic sintered at 875 ℃ for 3 h.

Design of K2SrCa(PO4)2-x(BO3)x:Eu2+ phosphors with full-visible spectrum by crystal structure modification

In recent years, much attention has been paid to the development of rare-earth-activated borophosphate phosphors for white light-emitting diodes (LEDs). Herein, Eu2+ single-doped K2SrCa(PO4)2-x (BO3)x white phosphors with full-visible-spectrum continuous emission in the range of 400 nm–720 nm were developed by the modification of the local structure in the crystal. The structural variation resulted from the substitution of (PO4)3- ions by (BO3)3- in host lattice were investigated in detail by X-ray powder diffraction and Fourier transform infrared spectroscopy. Furthermore, the phase structure of sample was also confirmed by the Rietveld method, indicating its Rhombohedral structure with the R-3c space group and the occupation of K and Ca sites by Eu2+ ions, then combined luminescence lifetime decay, revealing insights of site-selective occupation of Eu2+ in the borophosphate white light phosphors. The emission spectra of K2SrCa(PO4)1.4(BO3)0.6:0.05Eu2+ phosphor exhibited full-visible-spectrum continuous emission centered at 455 and 595 nm by adjusting the concentration of the (BO3)3- groups under near ultraviolet excitation at 365 nm. Especially, the WLEDs obtained from the broad-spectrum phosphors showed ultra-high color quality of color rendering index (CRI) values (Ra = 95, R9 = 66, and R13 = 95) and excellent fidelity/gamut index values (Rf = 94 and Rg = 98), which was almost similar to sunlight streaming. The investigation results indicated that the device by using as-prepared K2SrCa(PO4)1.4(BO3)0.6:0.05Eu2+ phosphor could be a potential candidate for full-spectrum lighting.

Ti-Al3Ti metal-intermetallic laminate (MIL) composite with a cubic titanium trialuminide stabilized with silver: Selection of fabrication regimes, structure, and properties

Ti-Al 3 Ti metal-intermetallic laminate (MIL) composites are known as promising structural materials due to the unique combination of their specific properties. However, their application is still limited due to the extremely high brittleness of the Al 3 Ti phase. In this study, we attempt to address this issue by changing the D0 22 crystal structure of Al 3 Ti to the more ductile L1 2 structure by alloying it with silver. To select the best fabrication regimes of Ti-Ti(Al 1−x Ag x ) 3 composites, in situ synchrotron X-ray diffraction analysis was performed to reveal the chemical reactions occurring upon heating the Ti-Al-Ag sample. The analysis showed that the highest amount of Ti(Al 1−x Ag x ) 3 phase with the L1 2 structure appears at 930 °C. This temperature was chosen for subsequent spark plasma sintering experiments. Scanning electron microscopy, energy dispersive X-ray analysis, and X-ray diffraction analysis revealed that the sintered sample consisted mainly of Ti, Ti(Al 1−x Ag x ) 3 , and a minor fraction of the Ag-Al compound distributed in the central parts of the intermetallic layers and at the grain boundaries. Modification of the titanium trialuminide crystal structure positively affected the properties of the composite, providing a 60% increase in fracture toughness. The Ag-Al phase also contributed to toughening, causing an additional crack deflection effect. • Ag stabilizes L1 2 crystal structure of Al 3 Ti in Ti-Al 3 Ti multilayer composite. • The maximum fraction of L1 2 phase in the composite is reached at 930 °C. • Modification of the Al 3 Ti provides 60% increase of the composite fracture toughness. • Minor Al-Ag phase causes the additional crack deflection effect.

A microbial driver of clay mineral weathering and bioavailable Fe source under low-temperature conditions.

Biotic and abiotic Fe(III) reduction of clay minerals (illite IMt-1) under low-temperature (0 and 4°C, pH 6) was studied to evaluate the effects of bioalteration on soil properties including clay structure and elemental composition. The extent of Fe reduction in bioreduced samples (∼3.8 % at 4°C and ∼3.1 % at 0°C) was lower than abiotic reduction (∼7.6 %) using dithionite as a strong reductant. However, variations in the illite crystallinity value of bioreduced samples (°Δ2θ = 0.580–0.625) were greater than those of abiotic reduced samples (°Δ2θ = 0.580–0.601), indicating that modification of crystal structure is unlikely to have occurred in abiotic reduction. Moreover, precipitation of secondary-phase minerals such as vivianite [Fe2+3(PO4)2⋅8H2O] and nano-sized biogenic silica were shown as evidence of reductive dissolution of Fe-bearing minerals that is observed only in a bioreduced setting. Our observation of a previously undescribed microbe–mineral interaction at low-temperature suggests a significant implication for the microbially mediated mineral alteration in Arctic permafrost, deep sea sediments, and glaciated systems resulting in the release of bioavailable Fe with an impact on low-temperature biogeochemical cycles.

On the assignment of quartz-like LiAlSi2O6 - SiO2 solid solutions in dental lithium silicate glass-ceramics: Virgilite, high quartz, low quartz or stuffed quartz derivatives?

ObjectivesHere we aim to provide a background on X-Ray Diffraction analysis of quartz-like crystal structures with varying amounts of Al3+ and Li+ substitution, existing confusions on their nomenclature and its implications for novel lithium silicate glass-ceramics. MethodsWe reviewed the literature dealing with modifications of the quartz crystal structure and their stuffed LiAlSi2O6 derivates, LiAlSi2O6 – SiO2 solid solutions, the terminology of such phases and criteria used to define the structure known as virgilite. Based on this information, we attempted to allocate the quartz-like phases found in CEREC TesseraTM, InitialTM LiSi Block and Amber® Mill in the range of LiAlO2 - SiO2 solid solutions. For this purpose, their lattice parameters obtained from Rietveld refinement were compared with the lattice parameters of members of the corresponding solid solutions with defined SiO2 molar fraction found in the literature. ResultsBased on the lattice parameters available for low quartz, high quartz and its stuffed derivatives, including LiAlSi2O6 and the mineral virgilite, a plot of the a- and c-parameters vs. the mol% SiO2 related to LiAlO2 was constructed with the literature data and the data found for the three dental lithium silicates. As per the definitions of virgilite as either LixAlxSi3-xO6, with 0.5 < x < 1 or especially as members of the LiAlSi2O6 – SiO2 solid-solution series with more than 50 mol% LiAlSi2O6, the crystal structures in CEREC TesseraTM, InitialTM LiSi Block and Amber® Mill failed to fall within the ranges of mol% SiO2 confined for virgilite. SignificanceBased on available literature and definitions, the quartz-like phases found in the three dental lithium silicates should be addressed as stuffed (probably low) quartz solid solutions instead of “virgilite”. However determined by mineralogical practices, the term “virgilite” for parts of the LiAlSi2O6 – SiO2 solid solution is ambiguous and can be considered as arbitrary.

Enhanced rate performance and specific capacity in Ti-substituted P2-type layered oxide enabled by crystal structure and particle morphology modifications

In recent years, P2-type layered oxides have received considerable attention as potential cathodes for Na-ion batteries owing to their compositional diversity, good specific capacity, and cyclability. However, poor rate performance and low-capacity retention at high discharge rates have limited their use in commercial battery applications. This study aims to mitigate this issue by synthesizing a series of structurally engineered P2-type cathode materials, through Ti substitution, with high cyclability and improved rate performance. P2-type Na0.70Ni0.20Cu0.15Mn(0.65-x)TixO2 were prepared through a sol–gel route and were characterized for their structural, electrical, and electrochemical properties In the Ti-substituted samples, the Rietveld refinement of XRD data revealed an increased size of the bottleneck area of the Na-O6 prism planes, while the SEM images showed a decrease in the aspect ratio of hexagon-type morphology of particles which facilitates faster Na-ion conduction through the material. These changes in the crystal structure and particle morphology induced by Ti substitution have significantly improved electrical and electrochemical performance compared to the parent material. The sample with x = 7.5% exhibited a specific capacity of 126 mAh/g at a discharge rate of 0.1C in the 2.00–4.25 V window, which was about 25% more than that of the undoped material. At a discharge rate of 1C, the specific capacity of Na0.70Ni0.20Cu0.15Mn0.575Ti0.075O2 was 97 mAh/g compared to 74 mAh/g for Na0.70Ni0.20Cu0.15Mn0.65O2 sample. Na0.70Ni0.20Cu0.15Mn(0.65-x)TixO2 samples also exhibited excellent cyclability, with over 95% of original capacity retained after 300 cycles. Complex impedance measurements corroborated the improved Na-ion conductivity in Ti-doped samples and an associated increase in Na-ion transference number from 0.86 for the sample with x = 0 to 0.97 for the sample with x = 0.075.

Incorporation of the Ce3+ activator ions in LaAlO3 crystals: EPR and NMR study

This work reports the results of EPR and NMR study of the Ce3+ incorporation in LaAlO3 single crystals grown by the micro-pulling-down method in the range of the Ce concentrations in the solid solution La1-xCexAlO3 from x ​= ​0.001 up to x ​= ​1.0. From EPR measurements, Ce3+g tensor parameters were determined as a function of Ce concentration. The g tensor has an orthorhombic symmetry even in the trigonal phase (x ​< ​0.1) suggesting that the incorporation of Ce at La site lowers the lattice symmetry near this ion. The local properties of the La1-xCexAlO3 crystals were further studied by 27Al and 139La high-resolution NMR measurements. It was found that 139La chemical shift has the Fermi contact interaction origin. It linearly increases with the Ce concentration from 0 ​ppm up to 165 ​ppm at x ​= ​0.5. Due to this strong Fermi contact interaction, separated peaks corresponding to different Ce–O–La spin transfer passways are resolved in the 139La NMR spectra. On the other hand, no Fermi contact interaction is visible in 27Al NMR spectra. However, these spectra contain a satellite peak whose intensity linearly increases with an increase of the Ce concentration leaving position of this peak unchanged. This was interpreted as manifestation of the crystal structure modification in the vicinity of Ce ions in agreement with EPR data. Thus, optical properties of Ce3+ in LaAlO3 will be determined namely by the local crystal structure near this ion.

“Clay-corn-caprolactone” a novel bioactive clay polymer nanofibrous scaffold for bone tissue engineering

Osteoconductive bone tissue scaffolds are of particular interest. Clay composed of aluminosilicate can play an essential role in bone repair and regeneration, enhancing osteoblastic differentiation and apatite deposition. Current research focuses on the fabrication of illite incorporated polycaprolactone/zein electrospun scaffolds. The prepared scaffolds by varying concentrations of Illite were characterized physiochemically and biologically. The composite scaffolds were analyzed for surface morphology, mechanical properties, thermal characteristic, crystal structure, surface wettability, and chemical modification. Biocompatibility of the composite scaffold was checked against the MC3T3-e1 cell line as a model. The biomineral apatite deposition was determined by incubating the scaffolds in simulated body fluid. The alkaline phosphatase staining evaluated osteoblastic differentiation. The results show that the clay composite scaffolds showed reduced fiber diameters and enhanced wettability. The addition of Illite improved the tensile strength and the Youngs Modulus of the composite scaffolds. The in vitro biomineralization of the composite scaffolds improved calcium deposition with the maximum Ca/P ratio of 1.55. The WST-1 assay and ALP staining show that the composite scaffolds have better cell viability and osteoblastic differentiation than the PCL/zein scaffolds. The overall results show that the clay-corn-caprolactone scaffold is a promising material for bone tissue engineering.

Mesocrystalline structure and mechanical properties of biogenic calcite from sea urchin spine.

Using X-ray scattering, we measured detailed maps of the diffuse scattering intensity distribution and a number of phonon dispersion branches for a single crystal of inorganically formed natural calcite and for high-quality mesocrystals of biogenic calcite from a Mediterranean sea urchin spine. A comparison shows that the known differences in the mechanical properties between the `strong' biogenic and `brittle' abiotic material should be attributed to the mesoscopic architecture of the crystal rather than to a modification of the calcite crystal structure. The data are rationalized by comparing them to the results of ab initio model calculations of lattice dynamics. For the mesocrystal, they are augmented by the evaluation of the faceting of the constituent nanocrystals.

Water-Processable and Multiscale-Designed Vanadium Oxide Cathodes with Predominant Zn2+ Intercalation Pseudocapacitance toward High Gravimetric/Areal/Volumetric Capacity.

Layered vanadium oxides have great potential as cathode materials for recently surged aqueous zinc-ion batteries (AZIBs). However, achieving high energy/power densities simultaneously is challenging, and side reactions related to more frequently than disclosed Zn2+ /proton co-insertion mechanism aggravate stability concerns. Herein, an engineered binder-free cathode configuration based on water-processable and high packing-density sheet-shaped composites of carbon nanotubes network, surface poly(3,4-ethylenedioxythiophene) (PEDOT) bridging coating, and ultrasmall PEDOT-intercalated V2 O5 nanoflakes is developed, and therein, large pseudocapacitance via predominant (≈91%) Zn2+ intercalation is revealed. Besides competitive gravimetric/areal capacity, the binder-free cathodes exhibit high volumetric capacity of 1106.1mAhcm-3 and high-rate capability of 180.0mAg-1 at 30Ag-1 as well as long-cycling stability. Such combined level of performance and unwanted reaction mechanism are attributed to the contained multiscale material/electrode design formula from crystal structure modification to 3D architecture construction of whole electrode, which endows the binder-free cathodes with abundant accessible sites for Zn2+ storage, but theleast hydroxyl terminated surface for H+ insertion, as well as highly conductive network for electron transfer and fast Zn2+ diffusion kinetics throughout the electrode. Combined with scalable fabrication protocols, this study opens up great opportunities for high-performance vanadium oxide cathodes practically applicable to AZIBs.

Incorporation of the Ce3+ Activator Ions in Laalo3 Crystals: EPR and Nmr Study

This work reports the results of EPR and NMR study of the Ce3+ incorporation in LaAlO3 single crystals grown by the micro-pulling-down method in the range of the Ce concentrations from x=0.1 at.% up to 100 at.%. From EPR measurements, Ce3+ g tensor parameters were obtained as function of Ce concentration. The g tensor has orthorhombic symmetry even in the trigonal phase (x < 10 at.%) suggesting that the incorporation of Ce at La site lowers lattice symmetry near this ion. The local properties of the La1-xCexAlO3 crystals were further studied by 27Al and 139La high-resolution NMR measurements. It was found that 139La chemical shift has the Fermi contact interaction origin. It linearly increases with Ce concentration up to 165 ppm at x = 0.5. Due to this strong Fermi contact interaction, separated peaks corresponding to different Ce-O-La spin transfer passways are resolved in the 139La NMR spectra. On the other hand, no Fermi contact interaction is visible in 27Al NMR spectra. However, these spectra contain satellite peak which intensity linearly increases with increase of Ce concentration leaving position of this peak unchanged. This was interpreted as manifestation of crystal structure modification in vicinity of Ce ions in agreement with EPR data. Thus, optical properties of Ce3+ in LaAlO3 will be namely determined by the local crystal structure near this ion.

Characterizing the defects and ferromagnetism in metal oxides: The case of magnesium oxide

Defects play an essential role in controlling the phenomenon of d0 ferromagnetism in nonmagnetic oxides. Defects can have significant impact on behavior, especially d0 ferromagnetism of oxide materials at room temperature (RT). Defects in magnesium oxide can be created by various phenomena like ion implantation, swift heavy ion/laser/gamma or UV irradiation, etc. This review focuses on the various characterization tools that are helpful to identify the nature of defects in the materials. Microscopic studies infer about the crystal structure modification via doping concentrations in metal oxides. Tools like ultra-violet visible (UV–Vis) spectroscopy and photoluminescence (PL) spectroscopy enrich the information on defects as well as depict the kind of vacancy. Electron paramagnetic resonance (EPR) is suitable to get information on spin centers in the materials. In addition to this, synchrotron radiation-based techniques like X-ray absorption spectroscopy (XAS), X-ray magnetic circular dichroism (XMCD) are also helpful to know about the structural defects and nature of vacancy in the materials. Vibrating sample magnetometry (VSM)/superconducting quantum interference device (SQUID) measurements deduce the magnetic properties and cause of the ferromagnetism in the metal oxide. Thus, these characterization tools are covered in this review by addressing the origin of defects as well as the methodology utilized to create and control defects in the materials. A detailed understanding of these issues is focused on magnesium oxide, a well-known candidate of the d0 ferromagnetic category.

Preparation and application of rare earth sulfides

Rare earth sulfides are a new type of functional materials with complex crystal structures, which show unique optical, electrical and magnetic properties. They are widely used in many fields, such as non-toxic pigments and energy storage, and have perspective application in photocatalytic, thermoelectric power generation, permanent magnet and other fields. Based on our group’s work in these fields, this review systematically summarizes the research progress and milestone on synthetic methodology, crystal structure modification and composite construction of rare earth sulfide in recent years. The performance enhancement strategies of rare earth sulfide in inorganic pigment, energy storage and photocatalysis are comprehensively sorted out. The structure-activity relationship of rare-earth sulfide is discussed and their positive prospects are proposed. Finally, this review summarizes the existing problems in current research and puts forward the prospects for its research direction.

Modification in crystal structure of copper ferrite fiber by annealing and its hyperthermia application

The copper ferrite fiber has been synthesized using the electrospinning technique by optimizing the electric voltage and viscosity of the polymer solution. Physical properties of copper ferrite fiber have been tuned with annealing at different temperatures (550, 750, and 950 °C for 2 h). The crystal structure has been confirmed by X-ray-diffraction pattern analysis and studied by using Rietveld refinement technique. The morphology of fibers was explored with the help of field emission scanning electron microscopy. The fibers annealed at 550 °C crystallize to cubic structure, and the tetragonal phase has been observed for 750 °C, and 950 °C annealed fibers. Sample annealed at 750 °C shows the highest magnetocrystalline anisotropy constant at 300 K (3 × 105 erg/cc). The SAR (Specific absorption rate) and ILP (intrinsic loss power parameter) of the 750 °C annealed fibers are 265 ± 5 W/g and 3.412 nHm2/Kg, respectively. The SAR value calculated by using non-adiabatic approach is 335 W/g.

Effect of crystallographic orientation on structural response of silicon to femtosecond laser irradiation

Femtosecond laser has been widely utilized for modification of crystal structure to achieve desired functions. So far, however, the effect of crystallographic orientation on the induced structure by femtosecond laser processing has yet been comprehensively studied. The present work is undertaken in an attempt to fill this gap in our knowledge. To this end, commercial-purity Si is used as a target material and high-resolution transmission electron microscopy as well as electron backscatter diffraction are applied to examine the irradiation-induced microstructural changes. The structural response of the pulsed material is found to be principally influenced by the crystallographic orientation of the target surface. Specifically, at the surface orientation close to {111}, a pronounced amorphization effect is observed whereas no disordered material is detected at the orientations close to {100}. This phenomenon could be explained by the lowest crystallization speed required by the (111) surface due to its smallest surface energy. Compared with nanosecond laser, non-thermal melting induced by femtosecond laser induces mild thermal gradient and favors recrystallization.

Jahn–Teller distortions in (Co1–xCux)Cr2O4 (x = 0.5, 0.25) nanoparticles: Structural, magnetic and electronic properties

The spinel ferrimagnetic compound CoCr2O4 demonstrates a spin spiral (TS) ordering at 25 K, as well as an anomaly at 15 K termed as lock-in transition (TL). From crystallographic perspective CoCr2O4 retains the cubic phase down to 11 K. On the other hand, the normal spinel CuCr2O4 crystallizes into the cubic phase above 850 K, below which Jahn-Teller (J-T) activity of the Cu reduces the crystal symmetry by transforming it to a tetragonal phase. Contraction of CuO4 tetrahedra towards the formation of a square planar structure accounts for the tetragonal to orthorhombic structural transition at ∼ 130 K associated with the ferrimagnetic Curie temperature (TC). Considering the differences in crystal structure and magnetism of these two compounds, the current work investigates the modification in crystal structure and magnetic behaviour by mixing Co site with Cu in CoCr2O4. To achieve this, (Co1–xCux)Cr2O4 (x = 0.5, 0.25 and 0.75) nanoparticles were prepared by chemical routes. X-ray diffraction (XRD) revealed the retention of cubic structure for the samples calcined at a temperature of 600 °C for x = 0.25 and 0.5. On the other hand, J-T distortion becomes prominent for x = 0.75. Hence, only the compositions with x = 0.25 and 0.5 were studied in detail as unusual cubic phase retention is observed in these compounds. The temperature dependent magnetization studies revealed that the TC values of both the samples, 103 K for (Co0.5Cu0.5)Cr2O4 and 99 K for (Co0.75Cu0.25)Cr2O4, compare well with the value reported for CoCr2O4. However, the feature related to TS is quite prominent for x = 0.25, whereas it is suppressed for x = 0.5. The electronic properties of the cations associated with these compounds, probed using X-ray photoelectron spectroscopy (XPS), indicate that Cu and Co mostly has a 2+ oxidation state whereas that of Cr is 3+.

Roles of structure and electron mobilization in enhanced ethanol sensing by Al doped SnO2nanoparticles

Enhanced alcohol sensing driven by crystal structure modification, surface charge immobilization and bulk charge mobilization in aluminium doped SnO2nanoparticles.

Boosting Potassium Storage by Integration Advantageous of Defect Engineering and Spatial Confinement: A Case Study of Sb2 Se3.

The potassium ion batteries (KIBs) based on conversion/alloying reaction mechanisms show high theoretical capacity. However, their applications are hampered by the poor cyclability resulting from the inherent large volume variations and the sluggish kinetics during K+ repeated insertion/extraction process. Herein, taken Sb2 Se3 as a model material, by rational design, nickel doped-carbon coated Sb2 Se3 nanorods (denoted as (Sb0.99 Ni0.01 )2 Se3 @C) are prepared through combined strategies of the conductive encapsulation and crystal structure modification. The carbon coating acts as an efficient buffer layer that maintains superior structural stability upon cycling. The introduction of Ni atoms can enhance electrical conductivity, leading to outstanding rate performance, which are confirmed by density functional theory calculation. The (Sb0.99 Ni0.01 )2 Se3 @C displays excellent reversible capacity (410mAhg-1 at 0.1Ag-1 after 100 cycles) and unprecedented rate capability (140mAhg-1 at 10Ag-1 ). Furthermore, KFeHCF//(Sb0.99 Ni0.01 )2 Se3 @C full cell exhibits a high specific capacity (408mAhg-1 at 0.1Ag-1 ), superior rate capability (260mAhg-1 at 2Ag-1 ). This work can open up a new avenue for the design of stable conversion/alloying-based anodes for high energy density KIBs.