Octahedral Sites Research Articles

Sol-gel synthesis of Cobalt-Bismuth substituted strontium hexaferrites and insight into structural refinement, Microstructural, dielectric and spectroscopic properties

Bi and Co-substituted strontium (SrFe12O19) hexaferrites were synthesized using the auto-combustion sol–gel method. The structural, Rietveld refinement, microstructural, spectroscopic, and dielectric characterizations were analyzed with X-ray powder diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR) and Dielectric analysis, respectively. The XRD investigation of Sr1-xBixFe12-yCoyO19 with (x = 0–0.5, y = 0–1.0) confirmed the single phase of M−type hexagonal ferrites. The change in the value of lattice constant ‘a’ in between 5.87 and 5.95 and ‘c’ 22.07 to 23.81 to be noted. The crystallite size of prepared specimens was determined in (20–29) nm range. The specific stretching vibrations in the FTIR results approves (Fe/Co-O and Bi-O) at three different positions 437.59, 549.94, and 587.53 cm−1. The existence of these band from 437 to 588 cm−1 confirmed the hexagonal structure of these ferrites. The force constants at octahedral sites increased from 1.75 to 2.02 (Dyne cm−1) x 105 and shows insignificant behavior at tetrahedral sites in between (3.33–3.54) Dyne cm−1 x 105 with Bi-Co substitution. The first band 582 cm−1 (ʋ1), is due to the maximum restoring force and vibrations at the tetrahedral site. The second band at a lower wavenumber of ∼ 402 cm−1 (ʋ 2) is due to the vibrations at the octahedral site. The microstructure of all synthesized samples of M−type hexagonal ferrites confirmed using the SEM analysis. The dielectric measurements in 0 to 3 GHZ frequency was done and effect of Bi-Co has been observed. The dielectric constant of all specimens shows the increasing trend from 1.5 GHz to 2.5 GHz with the frequency of the applied AC field. A slight increase was observed in the AC conductivity of these ferrites with the increasing concentration of Bi and Co ions.

ODIFICATION OF PINDIGA BENTONITE CLAY WITH DIDODECYLDIMETHYLAMMONIUM BROMIDES SURFACTANT FOR FOUNDRY USE

Bentonite clay from Pindiga, Gombe State, Nigeria, was surface modified with didodecyldimethylammonium bromides (DDAB) by the Base Exchange (cation exchange capacity) method for its possible use in foundries. The surfaces of the unmodified and modified Pindiga bentonite clay were characterised by means of spectroscopic, diffraction, and scanning methods (X-Ray fluorescence spectrometry (XRF)Fourier-transformed infrared spectroscopy (FTIR), X-ray diffraction (XRD), and scanning electron microscopy (SEM).XRF showed that unmodified sample was rich of montmorillonite (MMt) with ca +2 as exchangeable cation, FTIR analysis revealed that unmodified water absorption causes stretching and bending vibrations for hydroxyl groups, with the most intense bands in the low-frequency region, while DDAB organo-bentonites showed slight changes in wave bands, with a strong methyl band and a weak methyl band indicative of long-chain linear aliphatic structure. The basal spacing of the unmodified bentonite sample was 1.52 nm, and after modification with DDAB, it improved to 2.1 nm as determined from the X-ray diffraction (XRD) analysis. Results of the SEM images revealed rougher surfaces with uniformly dispersed small particles of grain-like structures characteristic of the unmodified, while theorgano-modified bentoniterevealed clusters of different sizes and shapes, larger Fe 3+ ions replacing smaller Al 3+ ions at octahedral sites, discontinuous layers enveloping large grains, polygonal growth foams with octahedral and tetrahedral shapes, mixed layers of calcium bentonite, and particle sizes less than 200nm. The study concluded that modified bentonite with didodecyldimethylammonium bromides gives good microstructure, increases rigidity, and improve thermal stability, to the organoclays. Therefore, it is recommended that DDAB bentonite be used as binder for foundries.

Distribution of Sc3+ at the octahedral sites and its effect on the crystal structure of synthetic Sc-bearing clinozoisite on the Ca2Al3Si3O12(OH)-Ca2Al2ScSi3O12(OH) join

Distribution of Sc3+ at the octahedral sites and its effect on the crystal structure of synthetic Sc-bearing clinozoisite on the Ca2Al3Si3O12(OH)-Ca2Al2ScSi3O12(OH) join

Refinement of the crystal structure of christofschäferite-(Ce) and the modular aspect of the chevkinite polysomatic series with the general formula of {A<sub>4</sub>B(T<sub>2</sub>O<sub>7</sub>)<sub>2</sub>}{C<sub>2</sub>D<sub>2</sub>O<sub>8</sub>}<sub>m</sub> (m = 1, 2)

Research subject. The crystal structure of christofschäferite-(Ce) was previously refined in terms of the P21/m low-symmetrical space group, which allowed the local features of cationic arrangements to be determined. In this work, we set out to refine the crystal structure of christofschäferite-(Ce) in terms of the P21/a high-symmetrical space group based on the previously collected diffraction data. A topology-symmetrical analysis of the members of the chevkinite group with the general formula of A4BC2D2(Si2O7)2O8 was conducted. Materials and methods. A magmatic rock sample with christofschäferite-(Ce) inclusions was found in the vicinity of the Laacher See volcano, near Mendig, Eifel Mountains, Rhineland-Palatinate (Rheinland-Pfalz), Germany. The crystal structure was studied using single-crystal X-ray analysis. Results. Despite an increase in the symmetry to the P21/a space group (in comparison with the previous data with the P21/m space group), the main patterns of cation distribution between the octahedral and tetrahedral sites are preserved. However, due to the lover number of cationic sites, this distribution becomes more disordered. Based on a crystal chemical analysis of the crystal structures of natural and synthetic members of the chevkinite group in the framework of the OD theory, it is possible to combine them into a united OD family with the same OD groupoid. Conclusions. According to the OD theory, there are two structural OD-subgroups of the chevkinite group (chevkinite and perrierite). The crystal structure and symmetry of possible MDO-polytypes are predicted.

Two-Site Occupation for Constructing Double Perovskite BaLaMgNbO6:Cr3+ Ultrabroadband NIR Phosphors.

Given the escalating significance of near-infrared (NIR) spectroscopy across industries, agriculture, and various domains, there is an imminent need to address the development of a novel generation of intelligent NIR light sources. Here, a series of Cr3+-doped BaLaMgNbO6 (BLMN) ultrabroadband NIR phosphor with a coverage range of 650-1300 nm were developed. The emission peak locates at 830 nm with a full width at half maximum of 210 nm. This ultrabroadband emission originates from the 4T2→4A2 transition of Cr3+ and the simultaneous occupation of [MgO6] and [NbO6] octahedral sites confirmed by low photoluminescence spectra (77-250 K), time-resolved photoluminescence spectra, and electron paramagnetic resonance spectra. The fluxing strategy improves the luminescence intensity and thermal stability of BLMN:0.02Cr3+ phosphors. The internal quantum efficiency (IQE) is 51%, external quantum efficiency (EQE) can reach 33%, and thermal stability can be maintained at 60%@100 °C. Finally, we successfully demonstrated the application of BLMN:Cr3+ ultrabroadband in the qualitative analysis of organic matter and food freshness detection.

Enhanced High Voltage Stability of Spinel‐Type Structured LiNi0.5Mn1.5O4 Electrodes: Targeted Octahedral Crystal Site Modification

High‐voltage spinel‐type structured LiNi0.5Mn1.5O4 (LNMO) shows promise as a next‐generation high‐energy‐density lithium‐ion battery cathode material, however, capacity decay on extended cycling hinders its widespread adoption, underscoring an urgent need for further development. In this work, we introduce Zn at octahedral 16c crystal sites in LNMO with Fd‐3m space group to improve rate capability and reduce the rapid capacity decay otherwise experienced during extended cycling. The current work resolves the detailed influence of isolated modification at octahedral 16c crystal sites, unveiling the mechanism for these performance improvements. We show that occupation of Zn at previously empty 16c sites prevents the migration of Ni/Mn to adjacent 16c sites, eliminating transformation to a rock‐salt type structured Ni0.25Mn0.75O2 phase above 4.8 V, preventing structure degradation and suppressing voltage polarization. This study provides insights into the fundamental structure‐function relationship of the LNMO battery cathode, pointing to pathways for the crystal structure engineering of materials with superior performance.

Determine elastic parameters and nanocrystalline size of spinel ferrites MFe2O4 (M = Co, Fe, Mn, Zn) through X-ray diffraction and infrared spectrum: Comparative approach

MFe2O4 (M = Co, Fe, Mn, Zn) nanoparticles were successfully synthesized by coprecipitation. Analyzing the X-ray diffraction by the Rietveld method confirmed the spinel ferrite structure of the samples. Rietveld refinement results show that Co, Mn and Zn occupy both the tetrahedral and octahedral sites. Variation in elastic parameters was determined by Fourier transform infrared spectroscopy, and cation distribution was deduced from X-ray diffraction. X-ray diffraction peak expansion was analyzed by employing a variety of calculating methods such as modified Scherrer, Williamson–Hall, size–strain, and Halder–Wagner to determine the crystallite size and elastic parameters of the cubic-structured MFe2O4 nanoparticles, including intrinsic strain, stress, and energy density. Comparison of the results obtained from these different methods revealed that they are ideally suited to each other. Moreover, the transmission electron microscopy image confirmed that the average size of MFe2O4 (M = Co, Fe, Mn, Zn) nanoparticles ranges from 10 to 14nm, consistent with the dimensions obtained from the preceding methods.

Machine learning model for deep exploration: Utilizing short wavelength infrared (SWIR) of hydrothermal alteration minerals in the Qianchen gold deposit, Jiaodong Peninsula, Eastern China

The Jiaodong Peninsula in the eastern North China Craton is renowned globally as a major gold province. Notably, the Jiaojia orefield is an important gold-producing district in this region, and its depths are inferred to offer substantial prospecting potential, underscoring the need for innovative exploration tools to uncover concealed orebodies. The Qianchen gold deposit in the southern part of the Jiaojia orefield is characterized by the disseminated-stockwork-style orebodies at depths of ca. –1000 to –1800 m, with three mineralization stages, namely (I) pre-ore K-feldspar-quartz stage, (II) quartz-sericite-gold-polymetallic sulfide stage (main Au mineralization stage), and (III) post-ore quartz-calcite stage. Systematic short-wavelength infrared (SWIR) spectral analysis reveals that sericite group minerals developing in Stage II are the predominant and wide-distributed alteration minerals at Qianchen. Their spectral characteristics demonstrate a shift in the Al-OH absorption feature wavelength positions (Pos2200) to longer wavelengths (>2205 nm) within the orebodies. This shift is likely due to strong water–rock interactions leading to Fe and Mg substituting for Al in octahedral sites. Orthogonal partial least squares discriminant analysis (OPLS-DA) indicates that the H2O, OH, and FeOH spectral bands (Variable Importance in the Projection (VIP) ≥ 1) of sericite are crucial for distinguishing between gold ores and barren wall rocks. Additionally, Long Short-Term Memory (LSTM) models demonstrate that spectral data of sericite can be used to predict ore samples with an accuracy of 82 %, validated by receiver operating characteristic analysis (84 %), and blind test results demonstrate that the predicted grade closely aligns with the actual grade. Therefore, it is concluded that SWIR spectral characteristics of sericite group minerals can serve as an effective indicator for prospecting the Qianchen concealed gold mineralization. This study highlights the potential of coupling between machine learning and SWIR spectral data of alteration minerals to uncover the concealed lode gold mineralization.

Crystal structures and photoluminescence properties of undoped and Fe3+ doped Li2Ba3(P2O7)2 pyrophosphate nanopowders

Undoped and Fe3+ doped Li2Ba3(P2O7)2 pyrophosphate nanopowders were produced by a solid-state reaction process. The prepared samples underwent characterizations using XRD, SEM with EDS, HR-TEM with SAED, FTIR, Raman, UV-Vis, EPR and PL techniques. The XRD analysis confirms the orthorhombic crystal structure of the prepared samples and unit cell parameters were evaluated. The samples exhibited stone-like structures with low aggregation based on the micrographs obtained from SEM and HR-TEM images. Additionally, the grain and particle sizes of the powder samples were evaluated. The elements Li, O, P, Ba and Fe were confirmed to be present in the produced samples by EDS spectra. FT-IR and Raman spectral investigation revealed the fundamental vibrational and bending modes of various phosphate groups. The energy bands, identified as characteristic bands of Fe3+ ions, were produced in the UV–visible region of the optical absorption spectrum for the doped sample. The crystal field and inter-electronic parameters (Dq = 915, B = 700 and C = 2715 cm−1) were also evaluated. Furthermore, the refractive index and metallization criteria properties were calculated using energy bandgap values of 4.46 and 4.38 eV of the produced samples. The doping of Fe3+ ions led to a reduction in the bandgap energy, resulting in a red-shift. A resonance signal was observed in the EPR spectrum at g = 2.05, which can be ascribed to iron ions entering the host lattice at a distorted octahedral symmetry sites and this was also supported by optical absorption studies. The produced sample showed emission peaks at 354, 440 and 530 nm in the ultraviolet, blue and green regions of its photoluminescence spectrum. Photometric parameters, such as CCT, CRI and CIE chromatic coordinates, reveal that the prepared samples could bee used in LEDs applications. This work offers novel visions into diphosphate compounds doped with transition metal ions.

Harnessing the brilliance of Cr3+ doped LaAlO3–Al2O3 phosphors with exceptional responsiveness to far-red phytochrome for plant growth LEDs

Perovskite-based materials have recently gained significant attention due to their unique properties. Herein, the deep and far-red-emitting LaAlO3–Al2O3:Cr3+ perovskite-based phosphors with particle sizes of 2–5 μm have been reported for the first time, demonstrating excellent responsiveness to far-red phytochrome. The synthesized phosphors exhibited a sharply defined deep and far-red emission, peaking at 735 nm, and significant absorptions in the violet (∼410 nm) and green (∼565 nm) regions. The distinct lines at 735 nm can be attributed to the robust crystal field effect of surrounding Cr3+ ions, wherein the 3+ oxidation state substitutes smaller-sized Al3+ ions in the [AlO6] octahedral site of the LaAlO3–Al2O3 lattice. The optimized LaAlO3–Al2O3:0.6%Cr3+ phosphor, annealed at 1400 °C, demonstrated exceptional characteristics, including a color purity of 100 %, a prolonged lifetime of 32.26 ms, a high activation energy of 0.501 eV, and an impressive internal quantum efficiency of 68.1 %. Moreover, a prototype of a violet-pumped LaAlO3–Al2O3:0.6%Cr3+ phosphor-coated LED showcased a well-matched emission spectrum with the absorption spectrum of far-red phytochrome, underscoring its significant potential for applications in LED-based plant growth systems.

Construction of Co1-xZnxFe2xGa2-2xO4 (0

Solid solutions are garnering substantial attention in the realm of solar energy utilization due to their tunable electronic properties, encompassing band edge positions and charge-carrier mobilities. In this study, we designed and synthesized Co1-xZnxFe2xGa2-2xO4 (0<x≤0.6) as a photocatalyst for CO2 conversion using H2O. Careful optical and photo/electrochemical characterizations unveiled that the relative content of CoGa2O4 and ZnFe2O4 not only substantially influences light absorption in the full solar spectrum but also modulates valence and conduction band positions. We thoroughly assessed the photocatalytic activity of Co1-xZnxFe2xGa2-2xO4 and found that when x=0.35, the solid-solution catalyst achieved a remarkable CO2 reduction rate to CH4 and CO (31.5 μmol g-1 h-1). Furthermore, this optimized solid-solution catalyst demonstrated impressive photostability. Characterization and DFT calculations revealed that the formation of a solid solution not only reduces the band gap and promotes the separation of electron-hole pairs to accelerate efficient CO2 photoreduction, but also the introduction of more FeO6 octahedral active sites in Co1-xZnxFe2xGa2-2xO4 solid solutions enhanced the effective photoreduction of CO2. This design results in high conversion efficiencies for producing solar fuels through CO2 reduction with H2O.

Tuning benzene activity of cobalt-based spinel catalysts with cation substitution

Cobalt-based spinel oxides are promising low-cost catalysts for volatile organic compounds (VOCs) elimination. Herein, we prepared the cobalt-based spinel oxides (MCo2O4: M = Ni, Cu, Co, Zn) by a one-step solvothermal method to evaluate the influence of cation substitution on benzene combustion. The cation distribution on tetrahedral and octahedral sites could influence the degree of inversion in cobalt-based spinel oxides, thus achieving the regulation of Co-O bond strength. NiCo2O4 catalyst with the inverse spinel structure had the weak Co-O bond strength, which is conducive to the activation of lattice oxygen to improve the activity of benzene degradation. This work provides deep insights into the influence of the cation substitution on the cobalt-based spinel catalysts for the efficient benzene oxidation.

Exploring the impact of annealing temperature on morphological, structural, vibrational and electron paramagnetic resonance properties of starch-mediated spinel CoAl2O4: Experimental and DFT study

In the present work, CoAl2O4 nanoparticles were successfully synthesized using the simple auto-combustion sol-gel method employing starch as an organic fuel source. The effect of the annealing temperature on the structural, vibrational, morphological, and magnetic properties is studied. The obtained spherical nanoparticles have grain sizes ranging from 23.54 nm to 46.50 nm. X-ray diffraction (XRD) patterns reveal the formation of a face centered cubic (fcc) spinel phase with the Fd-3m space group for all prepared samples. The calculated average crystallite sizes exhibit an increase from 24.65 nm to 56.27 nm, consistent with the observed grain sizes. Density Functional Theory (DFT) calculations are applied to reach the optimized cell parameters as well as to confirm the structural properties of the synthetized CoAl2O4 nanoparticles. Geometry optimization of the CoAl2O4 spinel oxide is performed using the CASTEP module of Materials Studio software. The optimized unit cell, lattice parameter and unit cell volume were obtained from this simulation. The combined experimental and density functional theory study of structural properties of CoAl2O4 revealed that an increase in the calcination temperature leads to an increase in the volume of the unit cell and hence to an increase in the particles size. Fourier-transform infrared spectroscopy (FTIR) further corroborated these findings by demonstrating subtle shifts in characteristic CoAl2O4 absorption peaks with varying annealing temperatures. These peak shifts suggest a potential redistribution of Al³⁺ and Co2⁺ ions between tetrahedral and octahedral sites within the spinel structure. Electron paramagnetic resonance (EPR) spectroscopy revealed a magnetic state transition as a function of both the annealing temperature and the resulting crystallite size. Occupancy fluctuations of Al³⁺ and Co2⁺ ions at specific sites have also impacted on the nanoparticles color since the hue of the material depends on the valence state and the cationic coordination environment in the CoAl2O4 crystal lattice. Correlations between structural, vibrational, magnetic and color properties are presented to understanding how synthesis parameters influence CoAl2O4 characteristics which is essential for tailoring materials for specific applications.

Can large lattice volume always facilitate ion diffusion in solids?

Large lattice volume is usually expected to expand the bottleneck size and enlarge free volume for fast Li ion transport in solids. But the universality of lattice expansion decreasing activation energy barrier for Li ion migration is still debatable. Herein, our molecular dynamics simulations and density functional theory calculations detect the unconventional phenomenon of lattice expansion increasing activation energy barrier for Li ion migration in β-Li3PS4, Li4SnS4 and Li4GeS4 sulfides with the hcp-type anion sublattice, and discover the underlying mechanism. On one hand, lattice expansion enlarges the relative energies between the octahedral and tetrahedral Li sites, and correspondingly increase activation energy barrier for tetrahedral Li ions migration along the Tet-Oct-Tet migration paths in β-Li3PS4, Li4SnS4 and Li4GeS4. On the other hand, the lattice dynamics calculations show Li energy landscapes of β-Li3PS4, Li4SnS4 and Li4GeS4 are anharmonic and enlarging lattice volume make the local minimum of Li potential energy surface flatter, simultaneously reduce the relative energy of Li occupation site, eventually resulting in the higher activation energy barrier for Li ion migration. Thus, understanding the effect of lattice volume on ion migration in solids should not only consider the factor of bottleneck size and free volume, but also combine the aspects of Li ion occupation type, Li ion migration path and anion sublattice type. These new understandings of the lattice expansion increasing activation energy barrier for ion migration would further promote the further optimization and rational design of superionic conductors by element doping or strain engineering.

Strong nonlinear-polarization in ZnMgO epitaxial thin-films with Li incorporation

The second-order nonlinear-polarization originated from the interaction between thin-film materials with second-order nonlinear susceptibility (χ (2)) and high-power laser is essential for integrated optics and photonics. In this work, strong second-order nonlinear-polarization was found in a-axis oriented Zn1-x Mg x O (ZnMgO) epitaxial thin-films with Li incorporation, which were deposited by radio-frequency magnetron sputtering. Mg incorporation (x > 0.3) causes a sharp fall in the matrix element χ 33 of χ (2) tensor, although it widens optical bandgap (E opt). In contrast, moderate Li incorporation significantly improves χ 33 and resistance to high-power laser pulses with a little influence on E opt. In particular, a Zn0.67Mg0.33O:Li [Li/(Zn + Mg + Li) = 0.07] thin-film shows a |χ 33| of 36.1 pm V−1 under a peak power density (E p) of 81.2 GW cm−2, a resistance to laser pulses with E p of up to 124.9 GW cm−2, and an E opt of 3.95 eV. Compared to that of ZnO, these parameters increase by 37.8%, 53.4%, and 18.6%, respectively. Specially, the Zn0.67Mg0.33O:Li shows higher radiation resistance than a Mg-doped LiNbO3 crystal with a comparable E opt. First-principle calculations reveal the Li occupation at octahedral interstitial sites of wurtzite ZnO enhances radiation resistance by improving structural stability. X-ray photoelectron spectroscopy characterizations suggest moderate Li incorporation increases χ 33 via enhancing electronic polarization. These findings uncover the close relationship between the octahedra interstitial defects in wurtzite ZnMgO and its nonlinear-polarization behavior under the optical frequency electric field of high-power laser.

Structural, dielectric and magnetic properties of MnFe2O4/ MWCNTs based nanocomposites for technological applications

In this paper, the manganese ferrite/MWCNTs nanocomposites were prepared by functionalizing with MWCNTs in various wt% from x = 0 to x = 25. First the nanoparticles of manganese ferrites have been composed by means of sol-gel self-combustion route. Nanocomposites with manganese ferrite/MWCNTs were synthesized by ultra-sonication. The crystalline structures of the nanocomposites were confirmed using the x-ray diffraction techniques (XRD). The crystallite size of the prepared nanocomposites was determined and found in the range of 9.1 to 9.4 nm. FTIR analysis assisted to get the vibration bands at tetra- and octahedral sites. Furthermore, confirmation of the linkage between MnFe2O4 and MWCNTs and morphology of the prepared was investigated through transmission electron microscopy (TEM). The relaxation mechanism of the prepared nanocomposites for the applied frequency range from 1 MHz to 3 GHz has been investigated. The relaxation behavior due to hopping of electrons in GHz are the interest for this research work. The dielectric constant at high frequency is useful for the nanocomposites that can be used in high frequency devices. The magnetic properties of the prepared nanocomposites were also investigated with applying magnetic field. The soft magnetic nature of the prepared nanocomposites makes the excellent choice for the waste water treatment application.

Persistent production of multiple active species with copper doped zinc gallate nanoparticles for light-independent photocatalytic degradation of organic pollutants

Photocatalysis is considered as an environmentally friendly and sustainable method as it can produce active species to degrade pollutants. However, its applications are hindered by the turbidity of pollutants and the requirements for continuous or repeated in situ irradiation. To avoid the need for continuous in situ irradiation in the photocatalytic process, herein we report the doping of Cu(II) ions into zinc gallate (ZnGa2O4) as traps to capture photo-generated electrons. In this way, long lifetime charge release and separation were effectively achieved for the persistent degradation of organic dyes in wastewater. The Cu(II) doped ZnGa2O4 (ZGC) nanoparticles with a small size about 7.7 nm synthesized via a hydrothermal method exhibited a persistent photocatalytic activity with continuous production of reactive oxygen species for at least 96 h without in situ irradiation due to its unique electronic structure and carrier transport path, and enabled to degrade 82.2 % of rhodamine B in 1 h. Further investigation revealed that the doped Cu(II) ions occupied the octahedral sites of ZGC and highly increased the persistent production and availability of active species for the persistent degradation of organic dyes under pre-illuminated conditions.

Highly Sensitive Temperature Sensors Resulting from the Luminescent Behavior of Sm3+-Doped Ba2MgMoO6 High-Symmetry Double-Perovskite Molybdate Phosphors.

We present double-perovskite molybdate with the formula of Ba2MgMoO6 doped with Sm3+ ions as a potential red phosphor to improve the color characteristics of white-light-emitting dioded (wLEDs). The new orange-red phosphor was synthesized using the co-precipitation (CP) method, and then its structural and spectroscopic properties were determined. Red emission at 642.6 nm dominates, which results from the electric dipole (ED) transition of the 4G5/2 → 6H9/2 type, and the materials are characterized by short luminescence decay times. BMM:Sm3+ is, to our best knowledge, the clearest example of dominant red emission of Sm3+ resulting from the location of the dopant in octahedral sites of high-symmetry cubic structure. In the sample containing 0.1% Sm3+, Sm3+ ions are located in both Mg2+ and Ba2+ sites, while at higher concentrations the Ba2+ site is less preferable for doping, as a result of which the emission becomes more uniform and single-site. The relative sensitivity calculated from FIR has a maximum of 2.7% K-1 at -30 °C and another local maximum of 1.6% K-1 at 75 °C. Such value is, to the best of our knowledge, one of the highest achieved for luminescent thermometry performed using only Sm3+ ions. To sum up, the obtained materials are good candidates as red phosphor to improve the color characteristics of wLEDs, obtaining a color-rendering index (CRI) of 91 and coordinated color temperature (CCT) of 2943 K, constituting a warm white emission. In addition to this, a promising precedent for temperature sensing using high-symmetry perovskite materials is the high sensitivity achieved, which results from the high symmetry of the BMM host.

Investigation of structural, electrical, and magnetic variations of Ni-Zn-Co ferrites by substituting rare earth Ho3+ for high-frequency applications

The investigation of structural, magnetic, and electrical properties of Ni0.6Zn0.3Co0.1HoxFe2−xO4 (NZCHF, 0 ≤ x ≤ 0.2) ferrites, synthesized through the sol–gel autocombustion method, has been undertaken. The refined x-ray diffraction (XRD) analysis was performed for XRD data analysis using Fullprof Suite software and it confirmed a single-phase cubic spinel structure, with the determination of crystallite size, refinement parameters and lattice constants. The bulk density of the samples consistently remained lower than the x-ray density, with densities increasing proportionally to the enhancement of Ho concentration. FTIR analysis corroborated the presence of metal-oxygen bonds within the ferrite possessing a spinel cubic structure. 57Fe Mossbauer spectroscopy showed that the hyperfine magnetic field of tetrahedral (A) and octahedral (B) sites decreased with the substitution of Ho3+ ions that preferentially occupy the B site. The impedance analyzer and vibrating sample magnetometer (VSM) were utilized to measure the real and imaginary parts of the complex permeability and magnetic properties of the samples, respectively. Complex impedance plots were scrutinized to discern the contributions of grain and grain boundary resistances, providing insights into the electrical behavior of the ferrite samples. Furthermore, the introduction of Ho concentration led to alterations in other key properties of the ferrites, including coercivity (H c ), retentivity (M r ), anisotropy constant (K), and magnetic moment (μ B ).The impact of the rare-earth content on the magnetic features of the prepared NiZnCo ferrite microspheres was investigated by analyzing magnetic-hysteresis (M-H) loops, which showed soft ferrimagnetism. Concurrently, the dielectric constant and dielectric loss tangent of the studied samples exhibited a decrease with the rise in Ho3+ concentration. The expected reduction in tan loss in the prepared samples is attributed to the increase in ac resistivity associated with the higher Ho3+ content.

Constructing Bipolar Dual-Active Sites through High-Entropy-Induced Electric Dipole Transition for Decoupling Oxygen Redox.

It remains a significant challenge to construct active sites to break the trade-off between oxidation and reduction processes occurring in battery cathodes with conversion mechanism, especially for the oxygen reduction and evolution reactions (ORR/OER) involved in the Zinc-air batteries (ZABs). Here, we propose using a high-entropy-driven electric dipole transition strategy to activate and stabilize the tetrahedral sites, while enhancing the activity of octahedral sites through orbital hybridization in a FeCoNiMnCrO spinel oxide, thus constructing bipolar dual-active sites with high-low valence states, which can effectively decouple ORR/OER. The FeCoNiMnCrO high-entropy spinel oxide (HESO) with severe lattice distortion, exhibits a strong 1s→4s electric dipole transition and intense t2g(Co)/eg(Ni)-2p(OL) orbital hybridization that regulates the electronic descriptors, eg and t2g, which leads to the formation of low-valence Co tetrahedral sites (Coth) and high-valence Ni octahedral sites (Nioh), resulting in a higher half-wave potential of 0.87 V on Coth sites and a lower overpotential of 0.26 V at 10 mA cm-2 on Nioh sites as well as a superior performance of ZABs compared to low/mild entropy spinel oxides (L/MESO). Therefore, entropy engineering presents a distinctive approach for designing catalytic sites by inducing novel electromagnetic properties in materials across various electrocatalytic reactions, particularly for decoupling systems. This article is protected by copyright. All rights reserved.