Nb-O Bonds Research Articles

A Study on the Microstructure Regulation Effect of Niobium Doping on LiNi0.88Co0.05Mn0.07O2 and the Electrochemical Performance of the Composite Material under High Voltage.

High-nickel ternary materials are currently the most promising lithium battery cathode materials due to their development and application potential. Nevertheless, these materials encounter challenges like cation mixing, lattice oxygen loss, interfacial reactions, and microcracks. These issues are exacerbated at high voltages, compromising their cyclic stability and safety. In this study, we successfully prepared Nb5+-doped high-nickel ternary cathode materials via a high-temperature solid-phase method. We investigated the impact of Nb5+ doping on the microstructure and electrochemical properties of LiNi0.88Co0.05Mn0.07O2 ternary cathode materials by varying the amount of Nb2O5 added. The experimental results suggest that Nb5+ doping does not alter the crystal structure but modifies the particle morphology, yielding radially distributed, elongated, rod-like structures. This morphology effectively mitigates the anisotropic volume changes during cycling, thereby bolstering the material's cyclic stability. The material exhibits a discharge capacity of 224.4 mAh g-1 at 0.1C and 200.3 mAh g-1 at 1C, within a voltage range of 2.7 V-4.5 V. Following 100 cycles at 1C, the capacity retention rate maintains a high level of 92.9%, highlighting the material's remarkable capacity retention and cyclic stability under high-voltage conditions. The enhancement of cyclic stability is primarily due to the synergistic effects caused by Nb5+ doping. Nb5+ modifies the particle morphology, thereby mitigating the formation of microcracks. The formation of high-energy Nb-O bonds prevents oxygen precipitation at high voltages, minimizes the irreversibility of the H2-H3 phase transition, and thereby enhances the stability of the composite material at high voltages.

Mössbauer, optical and structural properties of [formula omitted] ion in borate glass

Lanthanum-bearing iron lithium borate glass is a quaternary system for oxide glasses and was prepared via the melt-quenching method. The present article correlates the structure, optical, ligand field and Mössbauer data on iron lithium borate glass containing La3+. The density was measured, while the molar volume was calculated. Other physical parameters are well-described. With increasing the La2O3 content within the glass network, infrared spectra analysis reveals structural modifications such as the increase in BO4 units and the decline in both BO3 units and NBO bonds content. Furthermore, optical absorption spectra were measured. The absorption spectra disclose a plethora of electronic transitions that are related to Fe3+ in tetrahedral and octahedral sites, however, Fe2+ phase is not observed in optical spectra, but it has a clear signature in Mössbauer spectra. Besides, the glass absorption edges undergo a clear blue shift, reflecting an increased band gap energy (1.96–2.28 eV). The decline in NBO bonds justifies this trend. Bewitchingly, the values of crystal field splitting are increased, while the values of Racah parameters are decreased. This trend is justified by the decline in NBO bonds and increases electron localization around Fe cations. Mössbauer spectra confirm the existence of Fe3+ in tetrahedral and octahedral sites, while Fe2+ exists in only a tetrahedral state. With increasing La2O3 content, the isomer shift of Fe3+ in tetrahedral sites changes to be 0.312–0.329 mm/s, while the isomer shift of octahedral Fe3+ is 0.424–0.456 mm/s. These findings coincide with optical data. While the isomer shift of tetrahedral Fe2+ is 0.902–0.911 mm/s. Our results of structural, optical and ligand field associated with Mössbauer spectra open more vistas toward the utility of these samples in the optics realm.

(Ni1/3Nb2/3)4+-Improved High-K Ba3Ti4Nb4O21 Microwave Dielectric Ceramics for Miniaturized All-Ceramic Radomes with 5G Beam-Splitting Function.

With the rapid development of 5G communication technology, microwave dielectric ceramics with high dielectric constants are very conducive to the miniaturization of passive devices. Here, Ba3Ti4-x(Ni1/3Nb2/3)xNb4O21 (BTN ∼ NN, 0.03 ≤ x ≤ 0.15) ceramics with hexagonal phases are synthesized via the solid-phase route. The composite (Ni1/3Nb2/3)4+ ion substitution strategy can substantially improve the microwave dielectric properties of the Ba3Ti4Nb4O21 (BTN) ceramic. The εr and Q × f values depend on the ionicity (Nb-O bonds) and lattice energies (Nb(1)-O3 and Nb(1)-O2(1) bonds). The microwave dielectric properties of the BTN ∼ NN (x = 0.09) ceramic sintered at 1250 °C are εr = 60.3, Q × f = 22073 GHz, and τf = 78.1 ppm/°C. A miniaturized all-ceramic radome (@400 mm × 400 mm × 8 mm) for 5G beam-splitting function is designed and demonstrated using this ceramic. Compared to other radomes designed for other work utilizing low εr, the size of this radome has been reduced by 3/7. The reflection coefficients of the beam splitting function are all 0.73, and the phase shifts are all 360°. This work contributes to the development of miniaturized passive devices from a materials point of view.

Simultaneously promoting the surface/bulk structural stability of Fe/Mn-based layered cathode for sodium ion batteries

Layered sodium iron manganese oxide cathodes have attracted great interest owing to their high specific capacity and cost-effective metal resources, while the detrimental phase transitions and surface structural degradation severely limit their commercial applications. In this work, the bulk and surface structure stability of a P2-Na0.67Fe0.5Mn0.5O2 cathode can be synergically enhanced by a one-step Li/Nb co-doping strategy. Structural characterizations reveal that Li doping promotes the formation of P2/O3 biphasic structure and makes the unfavorable P2-OP4 phase transition convert into a smooth solid-solution reaction. Nb doping enhances the mobility of sodium ions and forms strong Nb-O bonds, thereby enhancing the stability of the TMO2 layer structure. In particular, the Nb element induces the surface reorganization of an atomic-scale NaNbO3 coating layer, which could effectively prevent the dissolution of metals and surface side reactions. The synergistic mechanism of enhanced electrochemical performance is proved by multiple characterizations during cycling. As a result, the as-prepared Na0.67Li0.1Fe0.5Mn0.38Nb0.02O2 exhibits improved capacity retention of 85.4 % than raw material (45.7 %) after 100 cycles at 0.5C (1C = 174 mA g−1) within 2.0–4.0 V. This co-regulating strategy provides a promising approach to designing highly stable sodium-ion battery cathodes. Furthermore, a full cell of Na0.67Li0.1Fe0.5Mn0.38Nb0.02O2 with hard carbon displays excellent cycling stability (85.1 % capacity retention after 100 cycles), making its commercial operation possible. This synergistic strategy of biphasic structure and surface reorganization is a critical route to accelerate the application of layer oxide cathodes.

Effect of K2WO4 on structure and properties of low melting glasses in K2O–Fe2O3–P2O5 system as sealing materials

New phosphate glasses based on the K2O–Fe2O3–P2O5 system, with variable K2WO4 content in place of Fe2O3, are prepared through the melt quenching route. The thermal and structural characteristics and water resistance properties are studied for sealing applications by means of XRD, DSC, and FTIR spectroscopic and dilatometry measurements. The results showed an amorphous nature and a linear increase in the parameters of the glass density and molar volume with the addition of K2WO4. While the glass transition (Tg), crystallization (Tc) temperatures, the thermal stability (ΔT), and the relative criterion (H) values were decreased are decreased. Inversely, the ΔCp values were markedly increased with growing NBO bonds that led to markedly increase in the O/P ratio. Also, the coefficient of thermal expansion (CTE) is increased (from 124 to 211 × 10−7/oC). The glass with high K2WO4 content is a suitable sample for excellent sealing properties with a low transition temperature (Tg < 300 °C), a very low melting point, and a high thermal expansion value (211 × 10−7/oC). As well, the durability values of the examined samples decreased, but they were in the range of those for commercial sealing glass. The study offers fresh suggestions for the development of sealant materials that are both low-temperature and environmentally safe.

In-situ Raman unveiled Nb-O-bond-dependency selectivity for methanol electro-oxidation at high current density

Selective methanol oxidation reaction (MOR) to value-added formate can maximize the energy utilization by replacing the high onset-potential and sluggish oxygen evolution reaction. However, to date, only first-row 3d transition metal oxides exhibit the capacity of selective MOR, motivating the design of new kinds of electrocatalysts to further enhance the performance. Here we develop amorphous Nb2O5 as an efficient electrocatalyst, for the first time, for selective MOR to formate, with a low operating potential of 1.47 V vs. RHE to achieve the industry-relevant current densities (>100 mA cm−2) with a formate Faradaic efficiency of ∼100 %. We demonstrate, via operando Raman measurements, that this superior electrochemical MOR capacity originates from the in-situ induced short Nb-O bonds from the amorphous structure. Besides, the interface between amorphous Nb2O5 and nickel foam could also faciltate the MOR. This work may provide insights for designing novel transition metal oxides as efficient catalysts for selective MOR.

Developing high performance, low temperature sintering and temperature stable K40 material in Co2O3/Nb2O5-modified Ba3Ti4Nb4O21 microwave dielectric ceramics for 5G-LTCC communication devices

The comprehensive properties and sintering temperature of microwave dielectric ceramics are the key factors limiting their practical application. In this work, a novel strategy of complex (Co1/3Nb2/3)4+ ions substituted and adding glass (Li2O-B2O3- SiO2-CaO-Al2O3: LBSCA) was proposed to greatly enhance the microwave dielectric properties of Ba3Ti4-x(Co1/3Nb2/3)xNb4O21 (0 ≤ x ≤ 12 mol%, xCN-BTN) ceramics. A new ceramic of (Co1/3Nb2/3)4+ substitution improved hexagonal phase BTN was successfully fabricated and systematically investigated. As the increased of (Co1/3Nb2/3)4+ ions concentration, the Q×f was greatly increased because of higher packing fraction, and the reduction in the [Nb1/Ti1O6] octahedral distortion caused great changes of τf. Besides, the P-V-L theory revealed that the Ti/Nb ratio greatly contributed in permittivity εr, and the Nb-O bonds mainly affected dielectric loss, especially in Nb(1)-O2(1) bond. As a result, the superior microwave dielectric properties were obtained in 6CN-BTN ceramic sintered at 950 °C: εr∼40.99 ± 0.48, Q×f∼17,310 ± 565 GHz, and τf∼8.62 ± 4.34 ppm/°C. More encouragingly, 6CN-BTN showed good compatibility with silver, making it a promising K40 LTCC material for filter and dielectric resonators. This study presented a new strategy to improve the properties of BTN-based materials by complex ions substitution, which was expected to provide a general approach for the design of advanced microwave dielectric ceramics for other material systems.

Effects of magnesium on the structure of aluminoborosilicate glasses: NMR assessment of interatomic potentials models for molecular dynamics

AbstractClassical molecular dynamics simulations have been used to investigate the structural role of Mg and its effect when it is incorporated in sodium aluminoborosilicate glasses. The simulations have been performed using three interatomic potentials; one is based on the rigid ionic model parameterized by Wang et al. (2018) and two slightly different parameterization of the core–shell model provided by Stevensson et al. (2018) and Pedone et al. (2020) The accuracies of these models have been assessed by detailed structural analysis and comparing the simulated nuclear magnetic resonance (NMR) spectra for spin active nuclei (29Si, 27Al, 11B, 17O, 25Mg, and 23Na) with the experimental counterparts collected in a previous work. Our simulations reveal that the core–shell parameterizations provide better structural models. In fact, they better reproduce the NMR spectra of all the investigated nuclei and give better agreement with known experimental data. Magnesium is found to be five coordinated on average with distances with oxygen in between a network modifier (like Na) and an intermediate network formed (like Al). It prefers to lay closer to three‐coordinated B atoms, forming B–NBO bonds, with respect to Si and especially Al. This can explain the formation of AlO5 and AlO6 units in the investigated Na‐free glass, together with a Si clusterization.

First principles analysis on the nucleation interface of La2O3[formula omitted]/NbC[formula omitted

Niobium carbide (NbC), as a reinforcement phase, has been applied in the alloy to enhance its service life. It is important to refine the NbC in the alloy. In this paper, the nucleation interface of La2O3(11̅0)/NbC(11̅0) was analyzed and the mechanism of NbC refined by La2O3 was investigated by first principles. Firstly, the mismatch degree of La2O3/NbC interface was calculated. According to the surface convergence, the interface models of La2O3/NbC were established. Then, the combined work and energy of the La2O3/NbC interfaces were calculated. Finally, the interface bonding properties were analyzed by the charge density, differential charge density and projected density of states. The results show that the mismatch degree of La2O3(11̅0)/NbC(11̅0) interface is smallest, which is 7.1%. La2O3(11̅0) and NbC(11̅0) lattice planes were selected to establish four kinds of interface models, which are named as O-Hollow, O-Interface, OLa-Hollow and OLa-Interface in turn. The adhesive work of O-Hollow interface is the largest, which is 0.995J/m2. And its interface energy is the smallest, which is 3.055J/m2. Meanwhile, the bonding types of O-Hollow interface are mainly a combination of La-C and Nb-O bonds. In summary, La2O3 can be as a moderate effective heterogeneous nucleus of NbC, then NbC be refined by La2O3.

Tuning ferroelectric photovoltaic performance in R3c-CuNbO3 through compressive strain engineering: a first-principles study.

Most ferroelectric oxides exhibit relatively wide bandgaps, which pose limitations on their suitability for photovoltaics application. CuNbO3 possesses potential ferroelectric properties with an R3c polar structure that facilitate the separation of charge carriers under illumination, promoting the generation of photovoltaic effects. The optical and ferroelectric properties of R3c-CuNbO3, as well as the effect of strain on the properties are investigated by first-principles calculation in this paper. The calculated results indicate that R3c-CuNbO3 possesses a moderate band gap to absorb visible light. The interaction of Cu-O and Nb-O bonds is considered to have a crucial role in the photovoltaic properties of CuNbO3, contributing to the efficient absorption of visible light. The bandgap of CuNbO3 becomes smaller and the density of states near the conduction and valence bands becomes relatively uniform in distribution under compressive conditions, which improves the photoelectric conversion efficiency to 29.9% under conditions of bulk absorption saturation. The ferroelectric properties of CuNbO3 are driven by the Nb-O bond interactions, which are not significantly weakened by the compressive strain. CuNbO3 is expected to be an excellent ferroelectric photovoltaic material by modulation of compressive strain due to the stronger visible light absorption and excellent ferroelectric behavior.

Electrochemical performances of niobium-doped new spherical low-cobalt Li-rich Mn-based Li1.14Mn0.476Ni0.254Co0.048Al0.016O2 cathode

Here, niobium (Nb) -doped new spherical low-cobalt Li-rich Mn-based Li1.14Mn0.476Ni0.254Co0.048Al0.016O2 cathode materials are reported. It is found that Nb-doping could form strong NbO bonds to stabilize the lattice structure, alleviate structural disorder and maintain the discharge capacity of the cathode during cycling. Moreover, Nb-doping could reduce surface LiOH/Li2CO3 by-product formation during the synthesis process, thereby reducing detrimental side reactions between the electrode and electrolyte resulting in longer cycle life. In addition, the Nb doping also could extend the interlayer spacing, which is conducive to the lithium ion diffusion. The sample (Li1.14Mn0.466Ni0.249Co0.046Al0.015Nb0.02O2, Nb-0.02) doped with Nb at a molar ratio of 2 % in the total transition metals exhibits the best electrochemical performance. It shows the initial coulombic efficiency of 79.6 % and a high discharge specific capacity of 192 mAh g-1 with 92.8 % capacity retention after 200 cycles under C/5 charge and C/3 discharge at the cut-off voltage of 2.0–4.8 V.

Zr-doped silver niobates for photocatalytic degradation of methylene blue and Rhodamine B dyes

Pristine silver niobate and Zr-doped silver niobates as photocatalysts were synthesized by the sol-gel method. The synthesized samples were characterized by X-ray diffraction (XRD) and were found to contain both AgNbO3 and AgNb3O8. Fourier transform infrared (FT-IR) shows that the Nb-O bonds among the samples are different and may be attributed to the two types of silver niobates. Field emission scanning electron microscopy (FESEM) showed changes in morphologies of particles with increasing Zr-doping with average particle size ranging from 0.89 µm to 1.21 µm. The Tauc plots indicate that Zr-doped silver niobates have lower band-gap energies than their undoped counterpart. Furthermore, Zr-doped silver niobates also have a lower rate of electron-hole recombination than the undoped silver niobate as proven by the PL analysis. The photocatalytic degradation studies showed that Zr doping improved the performance of silver niobate for both Rhodamine B and methylene blue dyes. Through the present study, the link between Zr-doping and its role in dye degradation by silver niobates could be established.

The Local Structure and Metal-Insulator Transition in a Ba3Nb5-xTixO15 System.

The local structure of the filled tetragonal tungsten bronze (TTB) niobate BaNbTiO (x = 0, 0.1, 0.7, 1.0), showing a metal-insulator transition with Ti substitution, has been studied by Nb K-edge extended X-ray absorption fine structure (EXAFS) measurements as a function of temperature. The Ti substitution has been found to have a substantial effect on the local structure, that remains largely temperature independent in the studied temperature range of 80–400 K. The Nb-O bonds distribution shows an increased octahedral distortion induced by Ti substitution, while Nb-Ba distances are marginally affected. The Nb-O bonds are stiffer in the Ti substituted samples, which is revealed by the temperature dependent mean square relative displacements (MSRDs). Furthermore, there is an overall increase in the configurational disorder while the system with Nb 4d electrons turns insulating. The results underline a clear relationship between the local structure and the electronic transport properties suggesting that the metal-insulator transition and possible thermoelectric properties of TTB structured niobates can be tuned by disorder.

Niobium speciation in minerals revealed byL2,3-edges XANES spectroscopy

AbstractThe systematic mineralogy of niobium (Nb) is complex, with more than one hundred species dominated by multicomponent oxides of similar chemistry. The determination of Nb speciation in solids (i.e., the distribution between the phases and the crystal-chemical environment of Nb) is thus a challenge in geological contexts. Here, we present the first Nb L2,3-edges X-ray absorption near-edge structure (XANES) measurements on various Nb minerals and synthetic oxides with geological relevance. The interpretation of Nb L2,3-edges XANES spectra in the light of crystal-field theory shows the sensitivity of spectra to local site symmetry and electronic environment around Nb atoms. Crystal-field multiplet simulations give estimates of the 10Dq crystal-field parameter values for Nb5+, which range from 2.8 to 3.9 eV depending on Nb coordination and Nb—O distances. Rather than a 10Dq vs. R–5 relationship (where R represents the average Nb-O bond distance) expected in a point-charge model, we find a R–3 dependence with the crystal-field splitting for reference materials with octahedrally coordinated Nb. Complementary ligand-field multiplet simulations provide evidence of charge transfer between Nb and O. The contribution of the ionic and covalent characters to the Nb-O bonds is equivalent, unlike more ionic 3d metal–O bonds. This systematic characterization of the L2,3-edges XANES spectral properties of Nb provides information on the mechanisms by which Nb5+ substitutes for Fe3+, Ti4+, or Ce4+ in oxides common in geological contexts. Whereas the substitution of Nb5+ for Ce4+ does not modify the local structure of the cation site in cerianite, the substitution of Nb5+ for Ti4+ in rutile and anatase results in an increase of the cation-ligand distance and a decrease in the symmetry of the cation site. Conversely, the substitution of Nb5+ for Fe3+ in hematite and goethite results in a smaller cation site distortion. Our study demonstrates the usefulness of L2,3-edges XANES spectroscopy to determine Nb speciation in minerals to understand the processes of enrichment of this critical metal.

Low loss and good chemical compatibility with silver electrodes of Cu2+-substituted Ba3Ti4Nb4O21 ceramics realizing low temperature co-fired ceramics technology: Crystal structure, vibration modes and chemical bonds studies

New low loss and low-sintering temperature co-fired Ba3-xCuxTi4Nb4O21 (BCTN, 0 ≤ x ≤ 0.12) ceramics with 0.60 wt% Li2O-B2O3-SiO2-CaO-Al2O3 (LBSCA) glass were prepared by solid-state reaction methodology. This work showed that CuO and LBSCA were effective sintering aid, which improved the densification and decreased sintering temperature. Thus, the excellent microwave dielectric properties of BCTN ceramics (x = 0.08) were obtained after sintering at 925 ℃ with εr ~ 44.18, Q×f ~ 17,860 GHz (@ 5.6 GHz) and τf ~ 94.76 ppm/℃. Q×f value was increased nearly 3-fold compared to pure BTN ceramics (~ 6090 GHz). Based on the P-V-L bond theory, the Ti-O and Nb-O bonds together contributed greatly to εr. The Nb-O bonds was the main factor affecting the internal loss on Q×f. The τf closely related to the oxygen octahedron [Ti1/Nb1O6]. The BCTN ceramics would not react with Ag electrodes, and had great potential to be used in LTCC microwave devices.

Luminescence and Scintillation of [Nb2O2F9]3--Dimer-Containing Oxide-Fluorides: Cs10(Nb2O2F9)3F, Cs9.4K0.6(Nb2O2F9)3F, and Cs10(Nb2O2F9)3Cl.

We report three novel Nb-containing oxide-fluorides, Cs10(Nb2O2F9)3F, Cs9.4K0.6(Nb2O2F9)3F, and Cs10(Nb2O2F9)3Cl, which were prepared as high-quality single crystals via a HF-based mild hydrothermal route. The compounds all crystallize in the trigonal crystal system with space group P3̅m1. All three compositions form the same framework structure consisting of isolated [Nb2O2F9]3- dimers that create hexagonal channels that are occupied by disordered halide species. Upon excitation by UV light at room temperature, these compounds display broad band emission with a maximum at 440 nm for Cs10(Nb2O2F9)3F. The broad band emission of these compounds is attributed to the charge-transfer transitions of Nb-O bonds within the [Nb2O2F9]3- dimers. All three compounds scintillate blue under X-ray irradiation. Radioluminescence (RL) measurements performed on Cs10(Nb2O2F9)3F demonstrate that the RL emission intensity decreases with increasing temperature and that the integrated RL emission (300-750 nm) is 4% of Bi4Ge3O12 (BGO) powder. Thermogravimetric analysis confirms that Cs10(Nb2O2F9)3F has excellent thermal stability up to 600 °C and no structural phase transition is observed prior to sample decomposition.

Properties of strontium-containing BG 58S produced by alkali-mediated sol-gel process

Among many bioglass (BG) compositions, gel-BG 58S has been indicated in the literature for applications as bone graft due to its promising use to repair bone defects. However, its physical and biological properties also depend of choice of precursors. The use of phosphoric acid as a source of P2O5 changes the thermal behavior of BG and in the presence of HNO3 increases the rate of hydrolysis and reduces the size of sol particles, thus influencing the surface area and in turn rate of apatite formation of bioactive glasses. In addition, the addition of concentrated NH4OH decreases the gelation time and new bioactive materials have been produced using Ca/Sr substitution in BG compositions. Thus, the aim of this work was to prepare BG 58S by the sol-gel technique at room temperature using phosphoric acid (PA) as the phosphorus precursor compared with conventional precursor triethylphosphate (TEP) and to evaluate the effect of the adding NH4OH (1 or 2 M) as gelation catalyst in order to select the better route to Sr incorporate. The products were characterized using XRD, FTIR and confocal Raman spectroscopy. The composition prepared with 1M NH4OH (PA-1M) presented more evidence of NBO bonds, and the absence of crystallinity. Thus, BG 58S-5 wt% Sr was prepared using the alkali-mediated sol-gel process (PA-1M) and characterized as the techniques mentioned in addition to bioactivity and cytotoxicity assays. Both compositions showed the development of a layer of apatite when treated in a simulated body fluid (SBF). Strontium composition showed higher cell viability and more evidence of calcium phosphate formation while calcium carbonate is mainly identified in strontium-free composition.

Insights into the Enhanced Structural and Thermal Stabilities of Nb-Substituted Lithium-Rich Layered Oxide Cathodes.

Lithium-rich manganese-based layered oxides (LLOs) are considered to be the most promising cathode materials for next-generation lithium-ion batteries (LIBs) for their higher reversible capacity, higher operating voltage, and lower cost compared with those of other commercially available cathode materials. However, irreversible lattice oxygen release and associated severe structural degradation that exacerbate under high temperature and deep delithiation hinder the large-scale application of LLOs. Herein, we propose a strategy to stabilize the layered lattice framework and improve the thermal stability of cobalt-free Li1.2Mn0.53Ni0.27O2 by doping with 4d transition metal niobium (Nb). Detailed atomic-scale imaging, in situ characterization, and DFT simulations confirm that the induced strong Nb-O bonds stabilize the oxygen lattice framework and restrains the fracture of TM-O bonds, thereby inhibiting the release of lattice oxygen and the continuous migration of TM ions to the lithium layer during the cycle. Furthermore, Nb doping also promotes the surface rearrangement to form a Ni-enrichment layered/rocksalt heterogeneous interface to enhance surface structural stability. As a result, the Nb-doped material delivers a capacity of 181.7 mAh g-1 with retention of 85.5% after 200 cycles at 1C, extraordinary thermal stability with a capacity retention of 80.7% after 200 cycles at 50 °C, and superior rate capability.

Effect of Sintering Process on Ionic Conductivity of Li7-xLa3Zr2-xNbxO12 (x = 0, 0.2, 0.4, 0.6) Solid Electrolytes.

Garnet-type Li7La3Zr2O12 (LLZO) is considered as a promising solid electrolyte. Nb-doped LLZO ceramics exhibit significantly improved ion conductivity. However, how to prepare the Nb-doped LLZO ceramics in a simple and economical way, meanwhile to investigate the relationship between process conditions and properties in Li7-xLa3Zr2-xNbxO12 ceramics, is particularly important. In this study, Li7-xLa3Zr2-xNbxO12 (LLZNxO, x = 0, 0.2, 0.4, 0.6) ceramics were prepared by conventional solid-state reaction. The effect of sintering process on the structure, microstructure, and ionic conductivity of LLZNxO (x = 0, 0.2, 0.4, 0.6) ceramics was investigated. Due to the more contractive Nb-O bonds in LLZNxO ceramics, the cubic structures are much easier to form and stabilize, which could induce the decreased preparation time. High-performance garnet LLZNxO ceramics can be obtained by optimizing the sintering process with lower calcining temperature and shorter holding time. The garnet samples with x = 0.4 calcined at 850 °C for 10 h and sintered at 1250 °C for 4 h exhibit the highest ionic conductivity of 3.86 × 10−4 S·cm−1 at room temperature and an activation energy of 0.32 eV, which can be correlated to the highest relative density of 96.1%, and good crystallinity of the grains.

Elastic anisotropy, electronic and magnetic behaviours of ferromagnetic Europium Niobate EuNbO3 in orthorhombic structure: DFT + U, MFA and QTAIM studies

ABSTRACT Recently, previous studies have shown that at room temperature, EuNbO3 adopts an orthorhombic structure of Imma space group with a ferromagnetic behaviour. The relevant idea of ⁣this work is to provide a new insight into some electronic and magnetic behaviours of EuNbO3 in orthorhombic structure, which are still unknown, based on the results already found previously. The structural properties have been determined using two functionals (GGA-PBE and GGA-PBEsol) and the found results are in good agreement with the previous ones. Mechanical behaviour and elastic anisotropy have also been studied in detail from which, it has been confirmed that EuNbO3 is mechanically stable in Imma orthorhombic perovskite structure. The directional analysis of Young’s modulus has shown that it is elastically anisotropic. For the electronic properties, many approaches have been used in order to take all the considerations that are not taken into account by GGA semilocal functional, hence, spin–orbit coupling effect (SOC), Hubbard correction (GGA + U) and Modified Becke–Johnson exchange potential (mBJ) have been adopted. The two adopted mBJ parameterizations gave different results, hence, for that of TB-mBJ, the studied compound is almost halfmetallic, while that of Radi A. Jishi et al. showed a semiconductor behaviour. To estimate Curie temperature, we have employed the mean field approximation (MFA), hence, its estimated value is higher than that of transition to the tetragonal I4/mcm structure, which has been determined previously. The ionic character of Eu-O and Nb-O bonds has been confirmed by The Quantum Theory of Atoms in Molecules (QTAIM).