Dopant Radius Research Articles

Cation doping for enhanced layer spacing and electrochemical performance in Li-rich Mn-based lithium-ion cathode materials

Lithium-rich manganese-based cathode materials offer promising research avenues owing to their high capacity. This study delved into the impact of cation doping on Li1.2Ni0.13Co0.13Mn0.54O2(LNCMO). A range of layered Li1.2BXNi0.13Co0.13Mn0.54O2 (LNCMOxB, B = Ca, Na, Al) cathode materials were produced utilizing calcium, sodium, and aluminum chloride as dopants. Combining these elements with the lithium-rich materials improves the capacity retention of the positive electrode and mitigates voltage decay. X-ray diffraction analysis, Rietveld structural refinement, SEM, and XPS verified the inclusion of Ca, Na, and Al in the synthesized samples. Electrochemical analysis revealed that the LNCMO-0.01Na sample, possessing the largest dopant radius, exhibited favorable cyclic stability at 0.2C. Conversely, the LNCMO-0.01Al sample, featuring the smallest doped cation radius, demonstrated superior rate performance. Specifically, after 30 cycles at varying rates, the capacity reached 170 mAh·g−1 at 0.2C. The LNCMO-0.007Ca sample exhibited the highest residual capacity, maintaining 151.4 mAh·g−1 after 100 cycles at 0.2C. Doping Li sites in Li1.2Ni0.13Co0.13Mn0.54O2 materials with appropriately sized divalent cations significantly enhances their overall electrochemical performance. This enhancement is attributed to ion doping within the Li and TM layers, expediting the diffusion kinetics of Li ions, and augmenting ion and electronic conductivity. Investigating the doping modification of lithium-rich manganese-based oxide microspheres is instrumental in advancing positive electrode materials for lithium-ion batteries, aiming for increased specific capacity and more stable material structures.

Effect of ionic radius and valence state of alkali and alkaline earth metals on promoting the catalytic performance of La2O3 catalysts for glycerol carbonate production

Alkali metals and alkaline earth metals have been used to promote the catalytic performance of metal oxides in transesterification of glycerol and dimethyl carbonate, however, the promotional roles of the dopants in influencing the catalytic performance of the metal oxides have not been fully investigated which hinder the development of low-cost and high-efficiency catalysts in transesterification of glycerol and dimethyl carbonate. This paper, for the first time, systematically studied the influence of ionic radius and valence state of dopants, surface concentration of dopants and the basicity of the catalysts on the catalytic performance of La2O3 in transesterification of glycerol and dimethyl carbonate. Our results suggest that the ionic radius and valence state of the dopants are the determining factors, while the basic site density is not a crucial factor, although the basicity of catalyst surface is important in activating glycerol and dimethyl carbonate. Among alkali and alkaline earth metals, 25 mol% Na/La2O3 catalyst achieved the highest glycerol conversion (85 %) and glycerol carbonate yield (60 %) in the 70 °C and 2-hour reaction. After the detailed investigation, a plausible mechanism of glycerol and dimethyl carbonate transesterification on Na/La2O3 catalyst has been proposed. This research could help understand the promotional role of alkali metals and alkaline earth metals and the results may guide future design of metal oxide catalysts.

Charge-density based evaluation and prediction of stacking fault energies in Ni alloys from DFT and machine learning

A combination of high strength and high ductility has been observed in multi-principal element alloys due to twin formation attributed to low stacking fault energy (SFE). In the pursuit of low SFE alloys, a key bottleneck is the lack of understanding of the composition–SFE correlations that would guide tailoring SFE via alloy composition. Using density functional theory (DFT), we show that dopant radius, which have been postulated as a key descriptor for SFE in dilute alloys, does not fully explain SFE trends across different host metals. Instead, charge density is a much more central descriptor. It allows us to (1) explain contrasting SFE trends in Ni and Cu host metals due to various dopants in dilute concentrations, (2) explain the large SFE variations observed in the literature even within a given alloy composition due to the nearest neighbor environments in “model” concentrated alloys, and (3) develop a machine learning model that can be used to predict SFEs in multi-elemental alloys. This model opens a possibility to use charge density as a descriptor for predicting SFE in alloys.

Combining experimental and modelling approaches to understand the expansion of lattice parameter of epitaxial SrTi1-xTaxO3 (x = 0–0.1) films

Cubic SrTiO3 is widely used as a model perovskite oxide due to its exotic optical, electronic, magnetic, superconducting, and ferroelectric properties, which are dominantly influenced by its lattice parameter. This paper reports on the experimental observation of Ta5+ dopant-induced expansion of the perpendicular lattice parameter (a⊥) of (001) heteroepitaxial SrTixTa1-xO3 (x = 0–0.1) films grown at substrate temperature (Tg) of 750 °C under 5 × 10-5 mbar oxygen partial pressure (pO2). The experimental results demonstrate the synthesis of very high-quality epitaxial thin films in which almost all the Ta5+ dopants are substituted. However, not all the carriers are activated due to compensating defects. All these films have smooth surfaces and are stoichiometric in compositions. The value of a⊥ increases linearly with increasing Ta or free carrier concentrations. This expansion is modelled via density functional theory (DFT). The influences of three effects are considered in the present modelling: (i) ionic radius of Ta dopant (ii) deformation potential due to hydrostatic strain energy (iii) concentration of free carrier. Further calculations of a⊥ are also performed by considering the influence of substrate and the results overestimate the experimental values by ∼ 1 %. Further experiments on other perovskite systems are required to establish the efficacy of these modelling approaches.

Phase Stability of Ta-Doped Tetragonal Li7La3Zr2O12 (t-LLZO) Solid-State Electrolyte: A First-Principle Cluster Expansion Study

Using first-principles calculations and cluster expansion, this study generates new possible stable phases of t-LLZO containing a supervalent cation, Ta, on the Zr-site as a way to enhance the conductivity of the tetragonal crystal structure. The Monte-Carlo simulation was then used to provide further insight into the behaviour of the Ta-doped phases as a function of temperature under the canonical ensemble. The cluster expansion binary ground-state diagram generated 28 new multi-component Li5La3Zr2-xTaxO12 structures that are miscible. It is found that all the structures are thermodynamically stable with negative enthalpy of formation. The Monte-Carlo temperature profile shows no phase separation, and the system mixes well at ~900K. Further density functional theory calculations were performed on the most stable generated Ta-doped LLZO structures to determine the structural properties of the structures for their application as active solid-state electrolytes. It is found that the generated structures exhibit good structural stability due to the smooth decrease in calculated lattice parameters, which indicates that the smaller the difference between the dopant ionic radius and the critical dopant radius, the higher the conductivity. Therefore, the findings provide a better understanding of the phase stability of the generated Ta-doped LLZO structures, which paves the way for further analysis of the rate of lithium-ion diffusion and the mobility of the lanthanum, zirconium, tantalum, and oxygen ions in the systems at high temperatures.

Effects of coupling ability of dopants on NbO6 vibration and piezoelectric properties of KNN lead-free ceramics

In the work, the lead-free (K0.5Na0.5)NbO3, (K0.5Na0.5)0.95Li/Ag0.05NbO3 and (K0.5Na0.5)Nb0.95Sb/Ta0.05O3 piezoelectric ceramics were prepared by a solid-state method. The relationships between the coupling ability of the dopants and NbO6 vibration of the ceramics were investigated. The intensity of NbO6 vibration is ascribed to the dopant's radius. However, the distortion of NbO6 is independent of the vibration. The dopants with high coupling ability (i.e., Ag and Ta) give rise to more severe distortion of NbO6, resulting in bigger piezoelectric enhancement for KNN–Ag and KNN–Ta. Furthermore, the NbO6 vibration plays an indispensable role in ferroelectric phase transition while the c/a accounts for the Curie temperature.

Structural differences and adsorption behaviour of alkaline metals doped zinc oxide nanoparticles

Nanotechnology plays a vital role in all the scientific fields including environmental research due to their surface: volume ratio compared to bulk materials. Recent studies prove their effectiveness as pollutant removal and remediation practices. Zinc oxide (ZnO) nanoparticles a multifunctional material with distinct properties and their doped counterparts were widely being studied in different fields of science. However, its application in environmental waste treatment is starting to gain attention due to its low cost and high productivity. Heavy metal pollution is one of the major pollutants affecting aquatic and terrestrial life forms. Pollution in water bodies has also raised alarming concerns in the past decades. Most of the heavy metals are essential elements in trace amounts and omnipresent in the environment, causing toxicity for living organisms, for instance, nickel. In our work, we analysed the prospect of selective removal of nickel ions by different alkaline metals (K+, Rb+, and Cs+) doped zinc oxide nanoparticles fabricated by different treatment methods (as-prepared and heat-treated). We found morphological variations from flower like to rod like owing to the alkaline cations of the dopants. In addition, the crystal structure and its different fractions presented amorphous content of the fabricated samples increased from 2 to 10 wt% with respect to the atomic radius of dopant in as-prepared samples and not present in heat-treated samples. We report, how the structure and the sample composition directly affected their adsorption behaviour towards Nickel ions in aqueous solutions based on the micro and nano zincite ratio of the ZnO particles.

The lanthanide doping effect on toluene catalytic oxidation over Pt/CeO2 catalyst

The present work was undertaken to know the lanthanide doping effect on the physicochemical properties of Pt/CeO2 catalysts and their catalytic activity for toluene oxidation. A series of lanthanide ions (La, Pr, Nd, Sm and Gd) were incorporated into ceria lattice by hydrothermal method, and the Pt nanoparticles with equal quality were successfully loaded on various ceria-based supports. Their catalytic performance toward toluene oxidation shows a remarkable lanthanide-doping effect, and the activity is much dependent on the ion radius and valence state of dopants. Owing to smaller ion radius and low valence state, the dopant of Gd would form more Gd-Ce complex and less GdO8-type complex, generating more oxygen vacancies and then promoting oxygen replenishment. Furthermore, the high concentration of oxygen vacancy would drive electrons to transfer from support to metal, and thus electron-rich and under-coordinated Pt particles that are favorable for toluene adsorption and dissociation are obtained. Attributing to above positive factors, the doping of Gd would effectively enhance the catalytic oxidation of toluene over Pt/CeO2 catalyst. In addition, the Pt/CeGdO2 sample exhibits an excellent reaction stability and resistance of concentration impact.

Photocatalytic Degradation of Remazol Brilliant Blue R and Remazol Yellow FG using TiO2 doped Cd, Co, Mn

TiO2 and TiO2 doped Cd, Co, Mn (TiO2-M) were synthesized with a sol-gel method, and the photocatalytic activity of Remazol Brilliant Blue R and Remazol Yellow FG has been conducted. TiO2-M (Cd, Co, Mn) was synthesized with the mol Ti:M ratio of 3:1, and the materials were calcined at 300, 400, and 500 °C. The materials were characterized by X-ray Diffraction (XRD), Scanning Electron Microscopy-Energy Dispersive X-ray (SEM-EDX), and UV-Vis Reflectance. The XRD result shows that at the temperature of 300 °C TiO2 and TiO2-M formed tend to be amorphous. At 400 °C the anatase phase is formed, while at 500 °C the rutile phase begins to form. And overall, the crystallinity of TiO2 is higher than metal-doped TiO2. The UV-Vis Reflectance result showed that the bandgap energy of all doping materials (TiO2-M) decreased. The larger the metal ion radius of dopant, the larger the crystal size obtained and then the higher the bandgap obtained. The results of SEM-EDX showed that the morphology of TiO2 was spherical and regular, whereas the morphology of TiO2-M had a smoother surface due to the influence of metal doping. Photocatalytic activity of TiO2-M on Remazol Brilliant Blue R and Remazol Yellow FG was greater than TiO2. The optimum pH of the solution was obtained at pH 5 and the optimum catalyst phase was obtained at the anatase phase. The percentages degradation for 30 min of Remazol Brilliant Blue R were 67.34% (TiO2), 92.12% (TiO2-Co), 85.47% (TiO2-Mn), and 83.91% (TiO2-Cd), while for Remazol Yellow FG they were 58.84% (TiO2), 74.61% (TiO2-Co), 67.93% (TiO2-Mn) and 64.19% (TiO2-Cd), respectively. Copyright © 2021 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Non‐Classical Electrostriction in Hydrated Acceptor Doped BaZrO3: Proton Trapping and Dopant Size Effect

AbstractPoint defects such as oxygen vacancies and protonic interstitials are not only essential for ionic conductivity in oxides since they also affect the mechanical and electromechanical properties. These properties of nominally dry and hydrated proton‐conducting BaZr0.85M0.15O2.925+δH2δ (M = Al, Ga, Sc, In, Y, Eu) ceramics are investigated. Doping decreases Young's modulus with increasing ionic radii difference between the dopant and the host. Nominally dry samples show consistently higher Young's moduli than hydrated samples. All samples exhibit large non‐classical electrostriction, with a negative electrostriction coefficient M33<0. M33 shows saturation with the field and a non‐ideal Debye relaxation with frequency. The low‐frequency M33 value for both dry and hydrated samples shows a similar dependence on dopant radius as Young's modulus. For the hydrated samples, the relaxation frequency increases by a factor >100 in the series Ga‐Y, emphasizing the importance of proton trapping, with Y‐doped samples having minimal trapping energy. This coincides with the fact that the saturation strain for Y‐doped samples is also the smallest. In light of these findings, it is concluded that the present data give strong evidence for the existence of defect‐related elastic dipoles in acceptor doped barium zirconate and that the non‐classical electrostriction originates in their reorientation under electric field.

Distribution coefficient of rare-earth dopants in Y3Al5O12 garnet

We present the distribution coefficient for the entire series of rare-earth dopants (RE = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu) in flux-grown Y3Al5O12 garnet crystals. When the distribution coefficient is plotted in a logarithmic scale as a function of dopant radius, it shows a smooth parabolic drop from the smallest dopant (Lu3+) at 1.5 to the largest dopant (La3+) at 0.004. This behavior can be interpreted by the lattice strain model, with Lu3+ having close to the ideal radius for the 8-fold coordination site of the aluminum garnet structure.

Fabrication of different rare earth incorporated ZnCo2O4 matrix via chemical-mechanical hybrid mechanism and study their charge carrier dynamics by Motts VRH model

This work reports how microstructural and electrical property varies with different rare-earth (Nd, Sm, Gd, Dy and Y) incorporation in spinel structured ZnCo2O4 nano-cobaltite. These materials have been synthesized using a combination of both chemical and physical methods. Host spinel material was prepared through chemical co-precipitation method and mechanical milling was used to reinforce the rare earth oxides into the spinel structure. Structural, microstructural, elemental and optical characterization has been carried out using XRD, FTIR, FESEM, EDX and UV-Vis spectroscopy. XRD confirms the formation of the nanocrystalline materials. Different microstructural parameters like lattice parameters, microstrain, crystallite size and x-ray density have been estimated from Rietveld analysis, which shows particle size of the doped samples depends on size of the dopant rare earth. Positions of different bonds have been confirmed from FT-IR analysis. FESEM micrographs confirm particle dimensions of the agglomerated spherical grains are in good agreement with Rietveld output. Optical band gap increases with decreasing dopant radii from 3.48 eV to 3.99 eV. Impedance plots show highest conductivity achieved was 1.151 × 10−3 Ω−1cm−1 at 433 K for Yttrium doped ZnCo2O4 nano-composition with lowest activation energy of 0.34 eV. Temperature dependent frequency exponent explains small polaron hopping transaction. Impedance master curves obey time-temperature superposition principle. Motts VRH model applied to electrical properties to get an insight about electrical conduction mechanism of the prepared samples.

Effect of doping location induced anisotropy on thermophysical properties of dilute Fe2O3‐Y2O3‐ZrO2 solid solutions

AbstractMulti‐element doped zirconia ceramics are of interest as a satisfactory balance in low thermal conductivity, phase stability, and particularly fracture resistance dominated by non‐transformable tetragonal prime phase (t′) for the next generation thermal barrier coatings and catalysis supports. Compared with mass and radius of dopants, dopant location is rarely investigated due to the high complexity. The undersized transition metal oxides (Fe, Co, and Ni) within 2.0 mol% content were selected for doping 3Y‐TZP to improve thermophysical properties by distinctive doping locations. As shown by X‐ray diffraction and Raman spectra, the Fe3+/Fe2+ ions occupied both substitution and interstitial sites simultaneously, which significantly increased tetragonality and local anisotropy of FeY‐TZP polycrystal. The t′ phase transformation mechanism of the FeY‐TZP compounds quantitatively discussed regarding the coercive strain and stress. In opposition to prediction by Kopp's law, the coefficient of thermal expansion and specific heat capacity of the FeY‐TZP compounds unusally decreased, and the maximum reduction of −83% and −22.5% occured in the 1.0 mol% Fe doping. Cp‐T dependency of the specimens above 550 K strongly related with lattice anisotropy in addition to t′ phase content. Thermomechanical properties of the multicomponent zirconia are highly tunable with dopant locations, supplying a novel landscape for designing high‐entropy ceramics.

(Invited) Proton Transport Properties of Yb-Doped BaZrO3 and Its Application to High Efficiency Proton Ceramic Fuel Cell

Barium zirconate have high chemical stability with CO2 comparison with barium cerate. Acceptor doped barium zirconate show high proton conductivity [1]. The proton conductivity of yttrium doped barium zirconate is 1×10-2 Scm-1 at 600 ℃ and it is attracted as the electrolyte of fuel cell and water vapor electrolysis cell. The fuel cell using proton conducting oxide was called to PCFC (proton ceramic fuel cell) and work at the intermediate temperature. PCFC is expected to be the energy conversion device in future because of high efficiency [2] and low production cost [3]. Generally, nickel is used as anode of PCFC. The anode overpotential of nickel is lower than that of the other metals. However, the nickels dissolve to the proton conducting oxide and possibly increase the ohmic resistance of electrolyte. Moreover, the nickel and the electrolyte possibly form the blocking layer such as the complex oxide. Although the proton conductivity of yttrium doped barium zirconate is highest in the zirconate-type proton conductor, BaY2NiO5 is formed between the nickel and the yttrium doped barium zirconate [4] and it might work as the blocking layer of proton. In this study, the reaction product between NiO and BaZr0.8 M 0.2O3-δ (M=Sc, In, Yb, Y, Gd) were confirmed by X-ray diffraction analysis. In order to clarify the NiO dissolution effect on the proton transport properties of BaZr0.8 M 0.2O3-δ (M=Sc, In, Lu, Yb, Y), the partial conductivity of the proton and the hole for BaZr0.8 M 0.2O3-δ (M=Sc, In, Lu, Yb, Y) with NiO were measured at temperature range of 200-600 ℃ by impedance analysis. The current efficiency on the polarization properties, then was examined for the fuel cell system using Acceptor-doped barium zirconate with NiO as electrolyte. Moreover, we investigated the effect of dopants on the ease of cell fabrication. The conventional ceramic tape-casting and firing process for fabricating laminated ceramic electronic devices was used, which is important for practical use. The power generation performance of planer cells fabricated by this process was also measured. The X-ray diffraction patterns of 0.4 mol% NiO doped BaZr0.8 M 0.2O3-δ (M= Sc, In, Yb, Y, Gd) were measured for the the samples as-sintered and annealed under 1%H2 at 873K. The peak of the NiO or Ni phase except the barium zircanate phase was observed for 0.4 mol% NiO doped BaZr0.8 M 0.2O3-δ (M= Sc, In, Yb). On the other hand, the BaM 2NiO5 phase was observed for M=Y, Gd. When the ionic radius of dopant is in excess of the size of Yb, the BaM 2NiO5 was formed as the reaction product between NiO and BaZr0.8 M 0.2O3-δ. The proton conductivity of the series of BaZr0.8 M 0.2O3-δ containing no NiO increased in the order of In<Sc<Lu<Yb<Y. On the other hand, there was no distinct difference of the hole conductivity for dopant. PCFC using BZM20 (M=Lu, Yb, Tm, Y) has an energy efficiency of more than 0.8 at 873 K. The proton conductivity decreased and the hole conductivity did not change for all series of BaZr0.8 M 0.2O3-δ due to NiO dissolution in BaZr0.8 M 0.2O3-δ. Therefore, proton transport number and the efficiency of the fuel cell decrease by addition to NiO. Considering the above, the ytterbium-doped barium zirconate did not form a complex oxide with NiO and might have high proton conductivity. The performance of PCFC using BZYb20 as electrolyte was measured. The maximum power density values at 600 and 700 °C were 0.50 and 0.70 Wcm−2 for the planar cells using BZYb20, respectively. Electrochemical impedance spectroscopy of the cell showed that the ohmic resistance was 0.28 Ωcm2 at 600 °C, which was approximately three times larger than the resistance value calculated using the bulk conductivity of BZYb20 and the electrolyte thickness and was in agreement with the resistance value of BZYb20 with NiO.[1] K.D. Kreuer et al., Solid State Ionics 145(2001)295-306.[2] Y. Matsuzaki et al., Scientific Reports, 5:12640(2015)1-10.[3] A. Doubois et al., ECS Transaction 78(1) (2017)1963-1972.[4] J. Tong et al., J. Mater. Chem. , 20(2010)6333.

Role of Rare Earth Metal Ions Doping on Structural, Electrical, Magnetic, and Dielectric Behavior of Spinel Ferrites: a Comparative Study

In current studies, we have compared the doping effect of different rare earth metal ions on structural, electrical, magnetic, and dielectric properties in three different series of spinel ferrites. The cubic spinel structure for all the synthesized nanoferrites had been confirmed by XRD scans and further with FTIR analysis. Crystallite size, grain size, and lattice constant are found significantly affected by nature of dopant RE3+ ions and decrease with decreasing ionic radii of dopants. Lanthanum doping showed appearance of secondary phases at dopant concentration above 0.2 that was attributed to its larger ionic radii than cerium. The magnetic parameters for all the prepared samples were discussed by tracing hysteresis curves of all synthesized samples at room temperature. Decreasing crystallite size effected spin orders which associated with ionic radii of RE3+ ions resulted in decrease in magnetization. Dopants having smaller ionic radii greatly reduced coercivity and improved initial permeability. In the temperature range 423 to 823 K, the composition-dependent DC resistivity and activation energy ranges between 109 to ~ 1010 Ωcm and ~ 2.85 eV respectively. Both dielectric loss and dielectric constant decrease with decrease in frequency. The reported characteristics made these prepared nanoferrites suitable candidates for high-frequency and microwave absorber devices.

Effect of the bivalent dopant ionic radius, electronegativity and concentration on the physical properties of the sol–gel-derived ZnO thin films

This study deals with the influence of the concentration and ionic radius of the bivalent dopant on the structural, morphological and optical properties of the sol–gel-derived ZnO thin films. For that, different concentrations of dopants with different radii (Ni2+, Cu2, Fe2+) have been chosen to synthesize many ZnO thin films. The X-ray diffraction confirms that all the obtained films exhibit a pure hexagonal wurtzite structure. Meanwhile, it appears that both the preferential film orientation and the crystal quality are strongly affected when varying the ionic radius or the concentration of dopant. We note also that the lattice parameters decrease when the electronegativity of the dopant increases. This behavior has been explained at the light of a simple schematic model, based on the electrostatic forces involved in chemical bonding. The Scherer formula reveals that the average size of the crystallites is ranged between 20 and 35 nm. On the other hand, as confirmed by the SEM analysis, all the deposited films present a compact, uniform and nanocrystalline morphology. Nonetheless, the optical analysis indicates that the Ni- and Fe-doped films are highly transparent (greater than 90%) in the visible region, while the Cu-doped ones exhibit the lowest transmission (about 76%). Additionally, a blue shift of the bandgap is noticed when doping with Ni or Fe, whereas the doping with Cu induces a red shift.

Synthesis, structure, optical and magnetic properties of Nd1−xAxMn0.5Co0.5O3−δ (A = Ba, Sr and Ca; x = 0 and 0.25)

The structural, optical, and magnetic properties of polycrystalline Nd1-xAxMn0.5Co0.5O3−δ (A = Ba, Sr and Ca; x = 0 and 0.25) perovskite oxides were investigated. The powder XRD pattern demonstrates that the unit cell volume decreases with the changing A-site dopant type. The estimated bandgap energy (Eg) from UV–vis spectroscopic for NdMn0.5Co0.5O3−δ, Nd0.75Ba0.25Mn0.5Co0.5O3−δ, Nd0.75Sr0.25Mn0.5Co0.5O3−δ and Nd0.75Ca0.25Mn0.5Co0.5O3−δ are 3.27, 3.82, 3.79 and 3.53 eV respectively. The substitution of divalent element alters the absorption spectrum, while the redshift optical transition was observed with an increasing ionic radius of dopant. Temperature-dependent magnetization exposes that the Curie temperature (TC) gradually decreases with the decreasing size of alkaline earth metals, and glassy nature was observed at a lower applied magnetic field. The observation of TC can be well explained by the considering of the cationic size disorder parameter in A-site than the random distribution of B-site ions.

An effective doping strategy to improve the cyclic stability and rate capability of Ni-rich LiNi0.8Co0.1Mn0.1O2 cathode

Ni-rich LiNi0.8Co0.1Mn0.1O2 (NCM811) is considered as a promising cathode material for high-capacity power batteries. Nevertheless, the rapid capacity fading during the charge/discharge process and inferior rate capability hinder their successful realization. Elemental doping plays a critical role in stabilizing the structure, inhibiting Li/Ni disorder, reducing polarization, improving electronic conductivity and enhancing Li-diffusion coefficient from the viewpoints of dopant radius, valence state and bonding energy. Herein, niobium (Nb), with optimal radius (0.64 Å), high valence state (Nb5+) and strong Nb-O bonding energy (753 kJ/mol), is introduced into NCM811 structure to improve the electrochemical performance and to evaluate this strategy. Then, X-ray diffraction, transmission electron microscopy, field emission scanning electron microscopy, energy dispersive spectroscopy, X-ray photoelectron spectroscopy and electrochemical characterization are carried out to comprehensively evaluate the influence of Nb-doping on structure and electrochemical performance of NCM811 cathodes. Consequently, NCM811 cathode, with 1 at.% Nb, exhibited the highest capacity retention of 94.55% after 100 charge/discharge cycles (1 C) and rendered a superior charge storage capacity of 151.46 mAh/g at a high current rate of 5 C, demonstrating the effectiveness of the proposed strategy.

Structural and Electrical Properties of Cerium Oxides Doped by Sb3+ and Bi3+ Cations

The addition of low melting point trivalent ions in ceria-based electrolyte systems results in a new composite with better oxygen ion conduction at reduced temperature. The present work discusses the synthesis and characterization of co-doped ceramic electrolyte Ce0.8Sm0.1M0.1O2−δ (M = Bi, Sb) prepared by coprecipitation. This study mainly focuses on the effect of the ionic radius of the dopants on the structural and electrical properties of doped ceria. The structural studies of the samples by X-ray diffraction, field emission scanning electron microscopy and transmission electron microscopy show nanosized particles with a cubic fluorite structure. Raman spectroscopy confirmed the presence of O2− vacancies introduced into the lattice due to the substitution of a large ionic radius of Bi3+ for Ce4+. The electrical survey by electrochemical impedance spectroscopy suggests that the dopant ionic radius has a significant influence on the ionic conductivity and activation energy of the doped ceria. There is an enhancement in conductivity noted for bismuth-co-doped samarium-doped ceria due to the larger ionic radius of the bismuth dopant compared to antimony-co-doped samarium-doped ceria.

Optical field enhancements and applications by epsilon-near-zero medium with dielectric dopant

Field enhancement is an interesting and important topic in electromagnetic study. Electromagnetic field concentration and enhancement devices have wide applications in high directional antenna design, laser ignition, optical control, etc. At present, there are usually two ways of implementing the field enhancement, one is to use the artificial electromagnetic materials to realize the radiation direction control and energy concentration, which is more suitable for the applications at microwave or lower frequencies, and the other is to use the materials with high permittivity or high permeability. However, the latter is extremely sensitive to the position and characteristic of the radiation source and the cross-sectional area of the material, and depends heavily on the value of the relative permittivity or the relative permeability of the material. Therefore, both methods cannot fully meet the application requirements of creating high field intensity in optical band, such as laser ignition, etc. In this paper, based on the theory of photonic crystal doping, the strong electromagnetic field enhancement has been successfully realized by epsilon-near-zero medium filled with ordinary dielectric dopant. We first make the comprehensive theoretical analysis of the field enhancement in the structure of epsilon-near-zero medium with dielectric dopant. The method of calculating the central magnetic field in the doped medium is then rigorously derived, and the formula for the ratio of the central magnetic field in the doped medium to the external radiation field is deduced. We find that the optimal magnetic field enhancement occurs only when the proposed structure is equivalent to an epsilon-mu-near-zero medium. Subsequently, under the above condition, various parameters (radius of the cylindrical dopant, number of sources, etc.) are studied to analyze the magnetic field enhancement performance inside the doped medium. The theoretical analysis and simulation results show that the proposed structure can significantly enhance the magnetic field which is applicable in a broad frequency band from microwave to optical region, and meets the application requirements of providing high field intensity. Finally, as a practical realization example, an ultraviolet ignition device working at 270 nm is designed, which presents an efficient and alternative way of developing electromagnetic (optical) devices for producing strong field enhancement.