Correlation of the crystal features,magnetic parameters,and electronic structure of Bi-substituted BaFe12-xBixO19 hexaferrites: Theoretical background

Herein, using first-principles density functional theory (DFT) calculations, we have investigated the effects of Bi substitution on the structural, electronic, and magnetic properties of barium hexaferrite (BaFe_12-xBi_xO₁₉, x = 0; 0.5; 1.5 and 2). As a result of the calculation, it was determined that the most stable structure exists if the spin of the Fe atom on the 2a, 2b, and 12k positions of the barium hexaferrite compound is taken in the upward direction. The calculated lattice constant $\left(\raisebox{1ex}{$\mathrm{c}$}\!\left/ \!\raisebox{-1ex}{$\mathrm{a}$}\right.=3.9\right)$ and magnetic moment $\left(4.24{\mu }_{\mathrm{B}}\right)$ of iron ions are in reasonable agreement with other experimental works. Moreover, the presence of bismuth reduces the electronic band gap. Energy gain and magnetic anisotropy energy calculations for FIM, FM, and NM states were performed for the most stable states. It has been established that the most stable structural state is characteristic of х = 0.5. It has been calculated that substitution by the large Bi³⁺ ion dramatically changed the electronic structure and sharply reduced the band gap. This paper is the first step towards establishing the nature of the distribution of ions in M-type hexaferrites under conditions of substitution by ions with a large ionic radius.     

Spectroscopic characterizations and investigation of Judd-Ofelt intensity parameters of Dy3+-doped Ba2La8(SiO4)6O2 near white light emitting phosphor

A series of Dy³⁺-activated Ba₂La₈(SiO₄)₆O₂ phosphors were synthesized using the solid-state method with the objective of developing single host white light emitting phosphors for use in solid state lighting applications. The Dy³⁺ concentration varied between 0.01 and 0.05 mol%. The as-prepared phosphors crystal structure, optical, and photoluminescent properties (PL), along with energy transfer mechanism and luminescence decay, were investigated. The production of a single-phase Ba₂La₈(SiO₄)₆O₂ with hexagonal symmetry was verified by the findings of the X-ray diffraction analysis. When the Ba₂La₈(SiO₄)₆O₂: Dy³⁺ phosphors are exposed to ultraviolet light, they emit the characteristic yellow PL emissions caused by the ⁴F_9/2 → ⁶H_13/2 transition. The Judd-Ofelt (J-O) parameters (Ω₂, Ω₄, Ω₆) were computed using the excitation spectra. The characteristics of the Dy³⁺ transition indicate that the asymmetric environment around the ligand was suggested by the trend, which was followed by J-O parameters. Due to the dominance of the electric-dipole transition in the luminescence spectrum, the Ba₂La₈(SiO₄)₆O₂:0.03Dy³⁺ phosphor displayed yellowish white emission with CIE coordinates of (0.358, 0.398) and a CCT of 4724 K. The synthesized phosphor may be a useful material in the fabrication of white-emitting phosphor for LEDs application.     

Morphotropic phase boundary,polymorphic phases and enhanced electrostrain/piezoelectricity in Ag1-xKxNbO3 solid-solution ceramics

Ag_1−xK_xNbO₃(AKNx (x ≤ 0.12) ceramics were prepared to understand the relationship of structure-properties driven by compositions and temperatures. The results suggested that this binary system possessed a morphotropic phase boundary (MPB) consisted of ferrielectric and ferroelectric phases with iso-symmetry at room temperature, in which domains switching together with electric-field-induced irreversible phase transition achieved a much higher electrostrain (S_max = 0.4%) than other compositions. But this MPB was destroyed after poling, leading to inferior piezoelectricity. A phase diagram was drawn after analyzing in situ XRD and dielectric data, where an almost vertical ferrielectric/antiferroelectric ↔ polymorphic ferroelectric MPB line starting from a triple point was proposed. As temperature increased, the piezoelectricity significant enhanced near ferroelectric orthorhombic ↔ monoclinic phase boundary, while the highest piezoelectricity was achieved near the monoclinic ↔ paraelectric phase boundary with d₃₃ = 200 pC/N. The enhanced piezoelectricity is intimately related to the ferroelectric monoclinic possessing Pm symmetry.     

Air-stable manganese based cathode material enabled by organic protection layer for Na-ion batteries

Layered manganese oxide represents one most potential cathode for sodium-ion batteries thanks to high theoretical specific capacity, low cost and environmental friendliness. Nevertheless, its surface structure degrades owing to the hydration reaction when being stored in the humid air. Herein, Na_0.67Mn_0.92Cu_0.04Fe_0.04O₂ (NMCFO) cathode material is functionalized by tetradecylphosphonic acid (TPA) on the surface to enhance the air stability. It is demonstrated that the TPA protection layer could improve the surface hydrophobicity, and further inhibit the hydration reaction to produce residual alkali, effectively maintaining modified material’s crystal structure and electrochemical performance. After 28 days of placement in the humid air, the modified material delivers a specific capacity of 94.0 mAh g⁻¹ at 5C, and exhibits a capacity retention of 92.22% after 100 cycles at 1C. In summary, we provide an effective pathway to protect layered manganese oxide and other moisture-sensitive materials without sacrificing cell performance.     

Recent research progress of alloy-containing lithium anodes in lithium-metal batteries

Lithium metal is regarded as one of the most ideal anode materials for next-generation batteries, due to its high theoretical capacity of 3860 mAh g⁻¹ and low redox potential (−3.04 V vs standard hydrogen electrode). However, practical applications of lithium anodes are impeded by the uncontrollable growth of lithium dendrite and continuous reactions between lithium and electrolyte during cycling processes. According to reports for decades, artificial solid electrolyte interface (SEI), electrolyte additives, and construction of three-dimensional (3D) structures are demonstrated essential strategies. Among numerous approaches, metals that can alloy with lithium have been employed to homogenize lithium deposition and accelerate Li ion transportation, which attract more and more attention. This review aims to summarize the lithium alloying applied in lithium anodes including the fabricating approaches of alloy-containing lithium anodes, and the action mechanism and challenges of fabricated lithium anodes. Based on summarizing the literature, shortcomings and challenges as well as the prospects are also analyzed, to impel further research of lithium anodes and lithium-based batteries.     

Multi-scale characteristics of magnesium potassium phosphate cement enhanced by waste concrete powder

Using recycled concrete powder (RP) as an alternative binder can effectively reduce construction and demolition waste and contribute to developing eco-friendly repair materials. However, the effect of RP on magnesium potassium phosphate cement (MKPC) has not been sufficiently studied. In this study, MKPC pastes were prepared by replacing different contents of MgO with RP, and the evolution of the structural behavior was explained from nanoscale to microscale. The results show that incorporating an appropriate amount of RP can increase the fluidity and setting time of the MKPC mixture and improve its mechanical properties. The drying shrinkage and water resistance of MKPC specimens also improve with the increasing RP content. Incorporating an appropriate amount of RP can refine the pore structure of MKPC samples, while the generation of gel-like products can compensate for the adverse effects of reduced struvite-K content. The nanoscale characteristics of the MKPC samples also indicate that incorporating RP results in a decrease in the residual MgO and pore phase content, an increase in the content of the hydrated phase, and a decrease in the loss of the hydrated phase volume fraction due to water soaking. Upon optimizing the RP content, the MKPC mixture exhibits a lower cost and carbon footprint, with the 28-d compressive strength of the sample mixed with 10% RP increased by 7.36% relative to the plain sample, indicating that recycling RP is feasible in an eco-friendly MKPC system.