RESUMEN
The beneficial effects of lanthanide incorporation into 0.94Na0.5Bi0.5TiO3-0.06BaTiO3 (BNT-BT) matrix on its functional properties were investigated. The conventional solid-state method was used for synthesizing samples. The structural refinement revealed that all samples crystallized in R3c rhombohedral symmetry. Raman spectroscopy study was carried out using green laser excitation and revealed that no clear perceptible variation in frequency is observed. Dielectric measurements unveiled that the introduction of rare earth obstructed the depolarization temperature promoted in BNT-BT, the diffusive phase transition decreasing with increasing lanthanide size. Only dysprosium addition showed comparable diffusion constant and dielectric behavior as the unmodified composition. Further, the comparison of the obtained ferroelectric hysteresis and strain-electric field loops revealed that only Dy-phase exhibited interesting properties comparing parent composition. In addition, the incorporation of lanthanides Ln3+ into the BNT-BT matrix led to the development of luminescence characteristics in the visible and near infrared regions, depending on the excitation wavelengths. The simultaneous occurrence of photoluminescence and ferroelectric/piezoelectric properties opens up possibilities for BNT-BT-Ln to exhibit multifunctionality in a wide range of applications.
RESUMEN
Lithium-ion batteries (LIBs) have gained considerable attention from the scientific community due to their outstanding properties, such as high energy density, low self-discharge, and environmental sustainability. Among the prominent candidates for anode materials in next-generation LIBs are the spinel ferrites, represented by the MFe2O4 series, which offer exceptional theoretical capacities, excellent reversibility, cost-effectiveness, and eco-friendliness. In the scope of this study, Ni0.5Mg0.5Fe1.7Mn0.3O4 nanoparticles were synthesized using a sol-gel synthesis method and subsequently coated with a carbon layer to further enhance their electrochemical performance. TEM images confirmed the presence of the carbon coating layer on the Ni0.5Mg0.5Fe1.7Mn0.3O4/C composite. The analysis of the measured X-ray diffraction (XRD) and Raman spectroscopy results confirmed the formation of nanocrystalline Ni0.5Mg0.5Fe1.7Mn0.3O4 before coating and amorphous carbon in the Ni0.5Mg0.5Fe1.7Mn0.3O4/C after the coating. The Ni0.5Mg0.5Fe1.7Mn0.3O4 anode material exhibited a much higher specific capacity than the traditional graphite material, with initial discharge/charge capacities of 1275 and 874 mA h g-1, respectively, at a 100 mA g-1 current density and a first coulombic efficiency of 68.54%. The long-term cycling test showed a slight capacity fading, retaining approximately 85% of its initial capacity after 75 cycles. Notably, the carbon-coating layer greatly enhanced the stability and slightly increased the capacity of the as-prepared Ni0.5Mg0.5Fe1.7Mn0.3O4. The first discharge/charge capacities of Ni0.5Mg0.5Fe1.7Mn0.3O4/C at 100 mA g-1 current density reached 1032 and 723 mA h g-1, respectively, and a first coulombic efficiency of 70.06%, with an increase of discharge/charge capacities to 826.6 and 806.2 mA h g-1, respectively, after 75 cycles (with a capacity retention of 89.7%), and a high-rate capability of 372 mA h g-1 at 2C. Additionally, a full cell was designed using a Ni0.5Mg0.5Fe1.7Mn0.3O4/C anode and an NMC811 cathode. The output voltage was about 2.8 V, with a high initial specific capacity of 755 mA h g-1 at 0.125C, a high rate-capability of 448 mA h g-1 at 2C, and a high-capacity retention of 91% after 30 cycles at 2C. The carbon coating layer on Ni0.5Mg0.5Fe1.7Mn0.3O4 nanoparticles played a crucial role in the excellent electrochemical performance, providing conducting, buffering, and protective effects.
RESUMEN
Due to the low capacity, low working potential, and lithium coating at fast charging rates of graphite material as an anode for Li-ion batteries (LIBs), it is necessary to develop novel anode materials for LIBs with higher capacity, excellent electrochemical stability, and good safety. Among different transition-metal oxides, AB2O4 spinel oxides are promising anode materials for LIBs due to their high theoretical capacities, environmental friendliness, high abundance, and low cost. In this work, a novel, porous Zn0.5Mg0.5FeMnO4 spinel oxide was successfully prepared via the sol-gel method and then studied as an anode material for Li-ion batteries (LIBs). Its crystal structure, morphology, and electrochemical properties were, respectively, analyzed through X-ray diffraction, high-resolution scanning electron microscopy, and cyclic voltammetry/galvanostatic discharge/charge measurements. From the X-ray diffraction, Zn0.5Mg0.5FeMnO4 spinel oxide was found to crystallize in the cubic structure with Fd3¯m symmetry. However, the Zn0.5Mg0.5FeMnO4 spinel oxide exhibited a porous morphology formed by interconnected 3D nanoparticles. The porous Zn0.5Mg0.5FeMnO4 anode showed good cycling stability in its capacity during the initial 40 cycles with a retention capacity of 484.1 mAh g-1 after 40 cycles at a current density of 150 mA g-1, followed by a gradual decrease in the range of 40-80 cycles, which led to reaching a specific capacity close to 300.0 mAh g-1 after 80 cycles. The electrochemical reactions of the lithiation/delithiation processes and the lithium-ion storage mechanism are discussed and extracted from the cyclic voltammetry curves.
RESUMEN
Throughout extensive research endeavors, SrTiO3 has emerged as a promising photocatalytic material for utilizing solar energy and facilitating hydrogen production via water splitting. Yet, the pursuit of enhanced efficiency and amplified hydrogen generation has prompted researchers to delve into the realm of advanced doping strategies. In this work, using experimental characteristics and DFT calculations, we studied the effect of cobalt substitution on the structural, electronic, optical, and magnetic properties as well as the photocatalytic activity of SrTi1-xCoxO3-δ (x = 0, 0.125, 0.25, 0.375, and 0.5) perovskites. The samples were successfully prepared by using the solid-state reaction method. Based on X-ray diffraction and the Rietveld refinement method, the elaborated samples were shown to preserve the absorption range up to the visible region. Moreover, the position of band edge levels after cobalt doping becomes more appropriate for water splitting. Our findings report that all cobalt-doped compounds exhibit good photocatalytic activities and could be used as suitable photocatalyst materials for hydrogen production.
RESUMEN
Calcium manganite (CaMnO3-δ) has been extensively utilized in many applications due to its unique physical and chemical properties. In this study, the effect of Sr-substitution at the Ca-site on the structural, magnetic, electronic and electrical properties of CaMnO3 manganite perovskites is investigated in detail. The perovskite compounds Ca1-xSrxMnO3-δ (x = 0, 0.25, 0.5, 0.75 and 1) were synthesized through the sol-gel method at 1200 °C. From the patterns of X-ray diffraction, it was observed that all of the synthesized compounds show a pure perovskite phase at room temperature. The refinement results of the perovskite series suggest that a structural transformation from an orthorhombic (Pnma) to a hexagonal (P63/mmc) system occurred for 0.50 < x ≤ 0.75. We note however that the sample with the composition x = 0.50 showed a phase mixture of orthorhombic (Pnma) and hexagonal (P63/mmc). Based on DFT calculations, we have demonstrated the energetic stability of all compounds by negative formation energy and confirmed the semiconductor behavior by the presence of a band gap. The change in the band gap value with the Sr content suggests the potential tuning of the electronic behavior of CaMnO3-SrMnO3 solid solution. Furthermore, as the temperature increases from 300 to 1000 K, the electrical resistivity exhibits a reduction while the Seebeck coefficient (S) shows an augmentation. The negative values of S indicated the n-type-semiconductor nature of all compounds. The obtained values of the activation energy from thermal evolution of resistivity suggested that the electrical transport behavior of all the compounds followed the mechanism of small polaron hopping. Power factor is greatly affected by the Sr amount and reached a maximum value at x = 0.50. Overall, introducing Sr into the CaMnO3-δ matrix improved the power factor and reduced electrical resistivity. According to the obtained results, the studied manganite perovskites could be proposed as suitable materials for photocatalytic and thermoelectric applications.
