Search Results (7)

The influence of vanadium substitution on the structure, elastic, mechanical, and magnetic behavior of lithium ferrite (Li_0.5+xV_xFe_2.5−2xO₄; x = 0.00–0.2) was systematically studied. X-ray diffraction (XRD) was used to investigate the crystal structure, and infrared spectroscopy (IR) was used to determine the cation distribution between the two ferrite sublattices, in addition to the elastic and mechanical behavior of Li_0.5+xV_xFe_2.5−2xO₄ ferrites. X-ray analysis revealed a monotonic decrease in lattice parameter from 8.344 Å to 8.320 Å with increasing V⁵⁺ content, confirming lattice contraction and stronger metal–oxygen bonding. Despite a moderate increase in porosity (from 6.9% to 8.9%), the elastic constants C₁₁ and C₁₂ increased, indicating improved stiffness and reduced compressibility. The derived Young’s, bulk, and rigidity moduli rose with the doping of V⁵⁺. Correspondingly, the longitudinal, shear, and mean velocities (V_l, V_s, and V_m) increased. The Debye temperature also showed a linear rise from 705 K to 723 K with V⁵⁺ doping, directly reflecting enhanced lattice stiffness and phonon frequency. Furthermore, both the saturation magnetization (M_S) and the initial permeability (μ_i) increased up to V⁵⁺ concentration x = 0.1 and then decreased. Curie temperature (T_C) decreased with increasing V⁵⁺ concentration, while both the saturation magnetization (M_S) and the initial permeability (μ_i) increased up to V⁵⁺ concentration x = 0.1 and then decreased, while the coercivity (H_C) showed the reverse trend. These results confirm that V⁵⁺ incorporation significantly enhances the Li ferrite, improving its elastic strength, lattice energy, thermal stability, and magnetically controlling properties and making them suitable for a variety of daily uses such as magneto-elastic sensors, high-frequency devices, and applications requiring mechanically robust ferrite materials. Full article

X-ray diffraction analysis of the pseudo-binary SrFe_1−xV_xO_3−δ system showed that the solid solution formation limit at atmospheric oxygen pressure corresponds to x ≈ 0.1. SrFe_0.9V_0.1O_3−δ has a cubic perovskite-type structure with the Pm$\overline{3}$m space group. The oxygen nonstoichiometry variations in SrFe_0.9V_0.1O_3−δ, measured by coulometric titration in the oxygen partial pressure range of 10⁻²¹ to 0.5 atm at 1023–1223 K, can be adequately described using an ideal solution approximation with V⁵⁺ as the main oxidation state of vanadium cations. This approach was additionally validated by statistical thermodynamic modeling. The incorporation of vanadium decreases both oxygen deficiency and the average iron oxidation state with respect to undoped SrFeO_3−δ. As a result, the electrical conductivity, thermal expansion and chemical expansivity associated with the oxygen vacancy formation all become lower compared to strontium ferrite. At 923 K, the conductivity of SrFe_0.9V_0.1O_3−δ is 14% lower than that of SrFeO_3−δ but 21% higher compared to SrFe_0.9Ta_0.1O_3−δ. The area-specific polarization resistance of the porous SrFe_0.9V_0.1O_3−δ electrode deposited onto 10 mol.% scandia- and 1 mol.% yttria-co-stabilized zirconia solid electrolyte with a protective Ce_0.9Gd_0.1O_2−δ interlayer, was 0.34 Ohm×cm² under open-circuit conditions at 1173 K in air. Full article

Manganese- and iron-rich P2-type ${\mathrm{N}\mathrm{a}}_{0.67}{\mathrm{F}\mathrm{e}}_{0.5}{\mathrm{M}\mathrm{n}}_{0.5}{\mathrm{O}}_2 \left(\mathrm{N}\mathrm{F}\mathrm{M}\right)$ has garnered significant interest as a promising cathode candidate due to the natural abundance of Fe and Mn along with a high redox couple of Fe³⁺/Fe⁴⁺ and Mn³⁺/Mn⁴⁺. Despite all these merits, NFM suffers from structural instability during cycling, arising from the destructive Jahn-Teller (JT) distortion effect of Mn³⁺/Mn⁴⁺ during charging and Fe⁴⁺/Fe³⁺ during discharging. In this research, a novel P2-type transition metal-oxide cathode Na_0.67Fe_0.5−2xMn_0.5Ti_xV_xO₂ was synthesized by doping a tiny fraction of two electrochemically inactive elements, Titanium (Ti) and Vanadium (V), into Mn-rich Na_0.67Fe_0.5Mn_0.5O₂ (NFM) that mitigated the JT effect substantially and ameliorated the stability of the SIB during cycling. These exhaustive structural and morphological comparisons provided insights into the effects of V and Ti doping on stabilizing surface structures, reducing Jahn Teller distortion, enhancing stability and capacity retention, and promoting the Na⁺ carrier transport mechanism. Moreover, the electrochemical analysis, such as the galvanostatic charge/discharge profile, validates the capacity improvement via Ti and V co-doping into NFM cathode. The initial discharge capacity of the 2% Ti/V-doped ${\mathrm{N}\mathrm{a}}_{0.67}{\mathrm{F}\mathrm{e}}_{0.48}{\mathrm{M}\mathrm{n}}_{0.5}{{\mathrm{T}\mathrm{i}}_{0.01}{\mathrm{V}}_{0.01}\mathrm{O}}_2 \left(2\mathrm{N}\mathrm{F}\mathrm{M}\mathrm{T}\mathrm{V}\right)$ was found to be 187.12 mAh g⁻¹ at a rate of 0.1 C, which was greater than the discharge capacity of 175.15 mAh g⁻¹ observed for pure NFM ${(\mathrm{N}\mathrm{a}}_{0.67}{\mathrm{M}\mathrm{n}}_{0.5}{\mathrm{F}\mathrm{e}}_{0.5}{\mathrm{O}}_2).$ In contrast, 2NFMTV exhibited a noteworthy capacity retention of 46.1% when evaluated for its original capacity after undergoing 150 cycles at a rate of 0.1 C. This research also established a structural doping approach as a feasible technique for advancing the progress of next-generation Sodium-ion Batteries. Full article

Hydrothermal leaching vanadium using oxalic acid is a novel method reported recently to overcome the serious environmental problems caused by traditional extracting processes. In view of its promising application potential, the hydrothermal leaching kinetics of vanadium from a concentrate mainly composed of Fe_3−xV_xO₄ mineral via oxalic acid were investigated in this study. Firstly, the effects of the temperature and concentration of oxalic acid on the leaching behavior of vanadium were studied by measuring the leaching efficiency of vanadium at various times. Then, by fitting the measured leaching efficiency data to the proposed kinetic model, the leaching mechanism was analyzed and the rate-controlling step of the leaching process, the apparent activation energy, and the order of the chemical reactions were determined. Finally, a kinetic model was proposed to describe the present investigated leaching process. Detailed results are as follows: (1) an interfacial chemical reaction was the rate-controlling step of the present hydrothermal leaching process within temperatures ranging from 363 to 403 K, and the leaching efficiency was less than 85%; (2) the apparent activation energy of the interfacial chemical reaction was 45.6 kJ/mol; (3) the order of the interfacial chemical reaction to the concentration of oxalic acid was around 1.66. Full article

In the present study, an approach of determining the standard Gibbs energy of formation of Fe_3–xV_xO₄ was proposed firstly, then the standard Gibbs energies of formation of a variety of Fe_3–xV_xO₄ were determined experimentally, and finally, a calculating model of the standard Gibbs energy of formation of Fe_3–xV_xO₄ was established. The detailed results are as follows: (1) the standard Gibbs energy of formation of Fe_3–xV_xO₄ can be determined successfully by two steps; the first is to measure the chemical potential of Fe in Fe_3–xV_xO₄ under fixed oxygen partial pressure, the second is to derive the chemical potential of V in Fe_3–xV_xO₄ by Gibbs–Duhem relation; (2) the standard Gibbs energies of formation of Fe_3–xV_xO₄ are mainly decided by the Fe/V molar ratio, and almost not influenced by the oxygen partial pressure in the range from 2.39 × 10⁻¹² to 3.83 × 10⁻¹¹ atm; (3) in this oxygen partial pressure range, the standard Gibbs energies of formation of Fe_3–xV_xO₄ can be calculated satisfactorily by the following model: ${\Delta }_f{G}_{F{e}_{3-x}{V}_x{O}_4}^{\theta }\left(J/mol\right)=\left(1-x/2\right){\Delta }_f{G}_{F{e}_3{O}_4}^{\theta }+\left(x/2\right){\Delta }_f{G}_{Fe{V}_2{O}_4}^{\theta }+\left(1-x/2\right)RTln\left(1-x/2\right)+\left(x/2\right)RTln\left(x/2\right)$$- 168627.48\left(1-x/2\right)\left(x/2\right)$. Full article

Mn-Ferrite with a nanostructure is a highly valuable material in various technological fields, such as electronics, catalysis, and sensors. The proposed article presents the hydrothermal synthesis of Mn-ferrite doped with V (V) ions. The range of the doping level was from 0.0 to x to 0.20. The fluctuation in tetrahedral and octahedral site occupancies with Fe (III), Mn (II), and V (V) ions was coupled to the variation in unit cell dimensions, saturation magnetization, and LPG sensing sensitivity. The total magnetic moment shows a slow decrease with V-doping up to x = 0.1 (M_s = 51.034 emu/g), then sharply decreases with x = 0.2 (M_s = 34.789 emu/g). The dimension of the unit cell increases as x goes up to x = 0.1, then lowers to x = 0.2. As the level of V (V) ion substitution increases, the microstrain (ε) also begins to rise. The ε of a pure MnFe₂O₄ sample is 3.4 × 10⁻⁵, whereas for MnFe_{2−1.67 x}V_xO₄ (x = 0.2) it increases to 28.5 × 10⁻⁵. The differential in ionic sizes between V (V) and Fe (III) and the generation of cation vacancies contribute to the increase in ε. The latter is created when a V (V) ion replaces 1.6 Fe (III) ions. V-doped MnFe₂O₄ displays improved gas-sensing ability compared to MnFe₂O₄ at lower operating temperature. The maximum sensing efficiency was observed for 2 wt% V-doped MnFe₂O₄ at a 200 °C optimum operating temperature. Full article

Solid-solution Li-ion cathode materials transform through a single-phase reaction thus leading to a long-term structural stability and improved cyclability. In this work, a two- to single-phase Li⁺-extraction/insertion mechanism is studied through tuning the stoichiometry of transition-metal Fe/V cations to trigger a transition in the chemical reactivity path. Tavorite triclinic-structured LiFe_1−xV_xPO₄F (x = 0, 0.1, 0.3, 0.5, 0.7, 0.9, 1) solid-solution powders were prepared by a facile one-step solid-state method from hydrothermal-synthesized and commercial raw materials. The broad shape of cyclic voltammetry (CV) peaks, sloping charge/discharge profiles and sloping open-circuit voltage (OCV) profiles were observed in LiFe_1−xV_xPO₄F solid-solution cathodes while 0 < x < 1. These confirm strongly a single-phase behavior which is different from the two-phase behavior in the end-members (x = 0 or 1). The electronegativity of M (M = Fe_1−xV_x) for the redox potential of Fe^2+/3+ couple or the M–O₄F₂ bond length for the V^3+/4+ couple plays respectively a dominant role in LiFe_1−xV_xPO₄F solid-solution cathodes. Full article