Ion Substitution Research Articles

Preparation and Luminescence Property Study of Red-Emitting Na3.6Y1.8(PO4)3:Eu3+,Li+/K+ Phosphors with Excellent Thermal Stability for Light-Conversion Application.

A series of red-emitting phosphors, Na3.6Y1.8-x(PO4)3:xEu3+, have been synthesized by a high-temperature solid-phase method. The impact of the partial Li+/K+ ion substitution on the crystal structure and photoluminescence (PL) performance of Na3.6Y1.05(PO4)3:0.75Eu3+ phosphor have been investigated. Various techniques have been used for characterization of the as-obtained materials. X-ray diffraction (XRD) analysis was utilized to confirm the composites of these samples, and the morphology and element distribution were examined by scanning electron microscope (SEM) and transmission electron microscope (TEM). This study found that the developed Na3.6Y1.8-x(PO4)3:xEu3+ phosphors exhibited a prominent emission peak at ~620 nm when excited at 393 nm, which corresponded to 5D0 → 7F2 transitions of Eu3+ ions. Furthermore, the robust emission peak at ~705 nm (5D0 → 7F4) of these phosphors enables a better match with plant pigment absorption. Beyond that, the partial substitution of Li+/K+ ions probably changed the crystal structure, and reduces the symmetry around Eu3+, leading to significantly enhanced luminous intensities by 23.24% and 18.29%, with the highest quantum yields (QYs) reaching 99.85% and 96.29%, respectively. Additionally, the prepared phosphors show non-thermal quenching and superior thermal stability at elevated temperatures from 298 to 473 K. These findings and results suggest that Li⁺/K⁺-substituted Na3.6Y1.05(PO₄)₃:0.75Eu3⁺ phosphors can serve as promising red-emitting phosphors for plant lighting applications.

Modulating the chemical environment of Ni2+ for the oxidative dehydrogenation of ethane: The formation of LAS(Al3+/Ga3+)-Ni-OH site

The oxidative dehydrogenation of ethane to ethylene (ODHE) usually suffers from the issues of ethane conversion-ethylene selectivity seesaw. Herein, a series of alumina-supported Ni and Ga catalysts with different molar ratios of Ni to Ga were synthesized by facile impregnation method constructing the Lewis acid site (LAS) strategy to obtain great ethylene selectivity (97 %). The variation of Ni:Ga ratio adjusted the ionic substitution ability, redox ability and acidity, thus regulate the chemical environment of Ni2+ to the formation of LAS(Al3+/Ga3+)-Ni-OH structure, which was proposed to be the active site for selective oxidation of ethane to ethylene, as proved by H2-TPR, ToF-SIMS, quasi in-situ XPS and in-situ FTIR. Moreover, the probable mechanism of ODHE reaction was proposed that C2H6 molecules were mainly adsorbed on LAS sites and activated on Ni-OH site of the catalyst. The pulse test further suggested that O- was mainly associated with the generation of CO2 and Ni(2-n)+ was connected with the production of CH4. It is highlighted that adjusting the Ni-related species and oxygen species on the catalyst surface are crucial to further improve the ethylene selectivity.

Low-temperature sintering BCZT-Dy ceramics with low strain hysteresis for actuator application

Ba(Cu0.5W0.5)O3 (BCuW)-doped [(Ba0.85Ca0.15)1-xDyx](Zr0.1Ti0.9)O3 (BCZT-xDy, x = 0.001, 0.03) ceramics were prepared by conventional ceramic processing via low-temperature sintering technique. Rather pure perovskite structure and densified morphology with irregular nearly spherical-shape grains are achieved in all ceramics due to liquid-phase sintering. All BCuW-doped BCZT-xDy ceramics present apparent dielectric frequency dispersion and relaxor ferroelectric characteristic due to ion substitution and adding BCuW. The ceramics prepared at optimized sintering temperatures have rather large strain and small strain hysteresis, showing prospect application in piezoelectric high-precision actuators.

Assessment of the influence of glycol and alcohol on the morphology and protective properties of iron carbonate in carbon dioxide corrosion of gas pipelines

The potential effect of hydrate formation inhibitors (glycols, alcohols) — components of the liquid phase of gas pipeline operating media — on carbon dioxide corrosion during the transport of aggressive gas has not been sufficiently studied. The paper presents the results of a study of the corrosive effect of glycol (alcohol) present in the liquid phase on the composition and properties of corrosion products on steel when modeling the main aggressive factors under conditions of transport of CO2-containing gas. On a corrosion stand, the aggressive conditions of alternating wetting of gas pipeline walls with water were reproduced. The fluid circulation characteristic of a partially filled pipeline can have an effect on preventing the formation or destruction of films of corrosion products (iron carbonate, siderite) on the steel surface. In places of cracking and peeling of siderite formed in the presence of CO2, conditions will be created for the formation of general and local corrosion damage. During simulation tests, monoethylene glycol and isopropanol, as well as their aqueous solutions of different concentrations, were used. For the first time, data on the formation and composition of non-stoichiometric siderite in water-glycol and water-alcohol media at CO2 partial pressures and temperature were obtained. By processing diffraction patterns obtained by X-ray diffraction, the degree of substitution of iron ions in non-stoichiometric siderites by other cations was determined. The dependence of the degree of substitution on the concentration of alcohol (glycol) in their aqueous solutions was analyzed. It was revealed that with an increase in glycol concentration, a decrease in the rate of local corrosion is observed. With a high glycol content, internal corrosion is completely suppressed in the presence of CO2. It has been established that in aqueous-alcoholic media at elevated temperatures, local carbon dioxide corrosion does not occur. This is apparently due to the uneven distribution of water and alcohol in the mixture. The results obtained can be used in assessing internal carbon dioxide corrosion in the presence of glycol (alcohol), used at gas facilities as an inhibitor of hydrate formation.

Energy band gap tuning of Ba-Ca hexagonal ferrite by Dy3+ ion substitution (0 ≤ x ≤ 0.2) to improve spectral, structural, dielectric and photocatalytic properties

In the present study, Dy3+ substituted M-type Ba0.5Ca0.5DyxFe12-xO19 (0.00 ≤ x ≤ 0.20) hexagonal ferrites were synthesized using sol-gel auto-combustion method with lemon extract as a fuel. The single hexaferrite phase with space group P63/mmc is revealed by the X-ray powder diffraction (XRD) patterns. The Field emission scanning electron microscopy (FESEM) exhibits the agglomeration of nanoplates with vacancies at some places. Energy dispersive X-ray photoelectron spectroscopy (EDAX) mapping confirmed the presence of Ba, Ca, Fe, O, and Dy in the hexaferrite. Fourier Transform Infrared (FTIR) spectroscopy exhibits two characteristic bands at 579 and 429 cm−1 corresponding to tetrahedral and octahedral metal ions-oxygen stretching, revealing the occurrence of the ferrite phase. The optical energy band gap calculated using the Tauc plots was found to increase with the increase in dysprosium substitution to fall within the range of 2.8–3.5 eV. The Raman spectra confirmed the Raman vibration modes and M-type structures of hexagonal ferrites (HFs). The dielectric constant values drop rapidly with increasing frequency up to a few KHz and then gradually for the further higher frequencies. The occurrence of Ba and Ca with 2+, while Dy, and Fe with 3+ oxidation states is confirmed using X-ray photoelectron spectroscopy (XPS). The HFs exhibit remarkable efficiency by degrading the Reactive Brown dye to 99.3 % in just 15 min, equivalent to a high degradation reaction rate constant (k) value of up to 0.0396 min−1. Consequently, the catalyst shows promising potential for environmental remediation.

CuO and spinel CuCo2O4 supported on mesoporous nanocubes with dual redox-active centers for electrocatalytic H2O2 reduction and sensing

The copper hexacyanoferrate (CuHCF) nanocube and its cobalt-substituted analogue (CoCuHCF) possess numerous micropores; however, they demonstrate limited electrocatalytic performance for H2O2 reduction. Heat treatment of CuHCF in air (CuHCF-ht) results in the formation of CuO and Fe3O4 with noticeable aggregation. In contrast, the heat treatment of CoCuHCF in air (CoCuHCF-ht) preserves its nanocube structure while also forming a spinel CuCo2O4 phase. The partial substitution of cobalt ions for copper ions in CuHCF enhances both thermal and structural stability, leading to the transformation of micropores into mesopores during heat treatment. This transformation improves electrolyte accessibility and structural integrity. The CoCuHCF-ht electrode features dual redox-active centers (Cu+/Cu2+ couple) derived from the CuO and CuCo2O4 phases, serving as catalytic redox mediators for H2O2 reduction. This dual redox activity results in superior performance for H2O2 reduction compared to CuHCF-ht, which only exhibits a single pair of Cu+/Cu2+ couple from CuO as an active mediator. This enhanced performance is evidenced by a lower Tafel slope, a higher catalytic rate constant, and improved mass transfer of analytes. The CoCuHCF-ht catalyst, characterized by dual redox-active centers in mesoporous nanocubes, demonstrates a high sensitivity of 234.03 μA mM−1 cm−2 and a low limit of detection (0.26 μM), along with high selectivity, stability, repeatability, and reproducibility.

Triggering Asymmetric Layer Displacement Polarization and Redox Dual-Sites Activation by Inside-Out Anion Substitution for Efficient CO2 Photoreduction.

Sluggish bulk charge transfer and barren catalytic sites severely hinder the CO2 photoreduction process. Seeking strategies for accelerating charge dynamics and activating reduction and oxidation sites synchronously presents a huge challenge. Herein, an inside-out chlorine (Cl) ions substitution strategy on the layered polar Bi4O5Br2 is proposed for achieving layer structure-dependent polarization effect and redox dual-sites activation. Cl ions in the bulk phase shrink the halogen layer interspace by 8‰, triggering asymmetric [Bi4O5]2+ layer displacement polarization, prolonging the average photocharge lifetime to 201.8ps. Meanwhile, surface substituted Cl ions enhance the electron-donating capability of neighboring Bi atoms, activating the intrinsic Bi reduction sites, and increasing H2O molecule adsorption on nearby intrinsic O oxidation site (cal. by 0.105eV), also self-donating as an alien oxidation site. Besides, Cl upshifts the p-band center closer to the Fermi level, facilitating the reactant adsorption. Therefore, the energy barrier for CO2 activation and rate-limiting *COOH intermediate formation steps are significantly decreased. Without cocatalysts and sacrificial reagents, inside-out Cl-substituted Bi4O5Br2 delivers a remarkable CO2-to-CO photoreduction rate of 50.18µmol g-1 h-1, being one of the state-of-the-art catalysts. This finding offers insights into exploiting polarization at the molecular-level and enhances understanding of catalytic site activation.

Metal-organic frameworks with a sulfur-rich heterocycle: synthesis, gas adsorption properties, and metal exchange.

Three new three-dimensional (3D) metal-organic frameworks [M2(ttdc)2(dabco)] (M = Zn(II), 1-Zn; Cu(II), 1-Cu; and Zn/Cu, 1-ZnCu) based on thieno[3,2-b]thiophene-2,5-dicarboxylate (ttdc2-) were synthesized and characterized by a combination of physicochemical methods (single crystal X-ray diffraction, powder X-ray diffraction, chemical and thermogravimetric analyses and IR spectroscopy). 1-Cu demonstrated permanent porosity (Vpore = 0.790 cm3 g-1 and SBET = 1725 m2 g-1) and significant CO2, CH4, C2H2, C2H4 and C2H6 gas uptakes under ambient conditions. The adsorption selectivities for gas mixtures, calculated by IAST, were 10.8 (10.7), 14.6 (9.4), 1.7 (1.6) and 1.5 (1.6) for the equimolar gas mixture compositions CO2/N2, C2H6/CH4, C2H6/C2H4 and C2H6/C2H2 at 1 bar and 273 K (298 K), respectively. The mixed-metal compound 1-ZnCu was prepared by a crystal-to-crystal ion exchange metathesis reaction from 1-Zn with a 52% degree of ion substitution, confirmed by energy-dispersive X-ray spectroscopy, optical microscopy and single crystal X-ray diffraction analysis.

Viability and antibacterial properties of Ba2-x AgxFeMoO6(x=0.0, 0.05) double perovskite oxides

Double perovskite Ba2FeMoO6 (BFMO) and doped with Ag ions were synthesized via the sol-gel method. The structural and antibacterial properties and viability of the samples were systematically investigated. The results of the Rietveld refinement indicated that both samples exhibited a single phase with cubic structure and space group Fm-3m. The substitution of Ag ions led to an increase in the unit cell and lattice parameters of BFMO, resulting in a change in the sample's morphology. The direct band gap (∼2eV) was measured for samples by Diffuse Reflectance Spectroscopy (DRS). Antibacterial activity of the Ba2FeMoO6 and Ba1.95Ag0.05FeMoO6 samples was assessed on the Gram-positive bacteria (Staphylococcus aureus) and the Gram-negative bacteria (Escherichia coli) using the spread plate method. The results showed that the samples were effective against Staphylococcus aureus but not against Escherichia coli. The sample doped with Ag ions showed a higher antibacterial effect than the pristine sample. An MTT assay of the normal fibroblast cell line treated with an Ag-doped sample showed a higher percentage of viability.

Dilution induced magnetic localization in Rb(Co[formula omitted]Ni[formula omitted])2Se2 single crystals

We report experimental studies on a series of Rb(Co1−xNix)2Se2 (0.02 ≤x≤ 0.9) powder and single crystal samples using x-ray diffraction, neutron diffraction, magnetic susceptibility, and electronic transport measurements. All compositions are metallic and adopt the body-centered tetragonal structure with I4/mmm space group. Anisotropic magnetic susceptibilities measured on single crystal samples suggest that Rb(Co1−xNix)2Se2 undergo an evolution from ferromagnetism to antiferromagnetism, and finally to paramagnetism with increasing Ni concentration. Neutron diffraction measurements on the samples with x = 0.1, 0.4, and 0.6 reveal an A-type antiferromagnetic order with moments lying in the ab plane. The moment size changes from 0.69 (x=0.1) to 2.80μB (x=0.6) per Co ions. Our results demonstrate that dilution of the magnetic Co ions by substitution of nonmagnetic Ni ions induces magnetic localization and evolution from itinerant to localized magnetism in Rb(Co1−xNix)2Se2.

Enhancing structural strength and microwave dielectric properties of the Ba4(Sm1-xCex)9.33Ti18O54 ceramics

Herein, microwave dielectric ceramics of the Ba4Sm9.33Ti18O54 ceramics are substituted at A sites by partially replacing Sm at A1 sites with Ce, and the effects of ionic substitution at A sites on ceramic crystal structure and microwave dielectric properties are investigated. The Ba4(Sm1-xCex)9.33Ti18O54 (BSCT) ceramics prepared through the solid phase method has a typical tungsten–bronze structure, and its lattice spacing increases gradually with the increase in Ce content x. This increase is reflected in the increase in the cell volume and growth of ceramic grains. However, the excess Ce after Ce content exceeds 0.25 leads to the growth of ceramic grains and increase in porosity between grains, which in turn increases the dielectric loss of the ceramic. Under optimal sintering conditions, the ceramic crystal has a maximum atomic packing density of x = 0.25, which corresponds to its most stable structural properties, and the highest Q × f value of 9013 GHz. Raman spectroscopy results indicate that in titanium oxygen octahedrons, an increase in Ce substitution can effectively weaken the bending and tensile vibration intensities of titanium oxygen bonds, further enhancing structural strength.

Sol-Gel Spin Coating Synthesis and Characterization of Cadmium Zinc Phosphate Thin Films: Structural, Optical, and Electrical Properties

This study successfully implemented the sol-gel and spin coating technique to grow cadmium zinc phosphate cadmium zinc phosphate (CZP) thin films on a glass substrate and p-Si wafer. Structural and morphological analyses were conducted via X-ray diffraction (XRD) and field-emission scanning electron microscopy (SEM). Additionally, the films’ linear and nonlinear optical properties, encompassing absorbance performance, energy gap, refractive index, dielectric, conductivity, and electronegativity, were systematically studied through UV–vis spectroscopy. XRD analysis uncovers the zinc ions substitution by cadmium ions in zinc phosphate’s unit cell, generating oxygen vacancies crucial for maintaining charge neutrality. SEM images then showcase the intricate and organized nano CZP framework. Shifting to optical studies, CZP film analysis spanning 190–2500 nm reveals an indirect energy band gap of 2.92 eV. Transitioning to electrical characteristics, the CZP/p-Si junction undergoes dark mode I-V-T analysis, elucidating the ideality factor, series resistance, and barrier height.

Anion substitution strategy for constructing abundant oxygen vacancies in perovskites enables efficient nitrate electroreduction

Perovskite oxides have emerged as promising candidates for electrocatalytic nitrate reduction (ERN) catalysts due to their unique electronic structures and tunable chemical compositions. In this work, we employed a fluorine ion substitution strategy to modulate the oxygen site of LaCoO3 (LCO), resulting in the construction of F-substituted LaCoO3 (LCOF0.5) catalyst for efficient ERN. The incorporation of fluorine ions leads to a weakening of the hybridization between the O 1 s orbital and Co 3d orbital of the catalyst, thereby inducing an increase in oxygen vacancies. The abundant oxygen vacancies can facilitate the electron transfer and surface adsorption energy of the ERN reaction intermediates. This leads to a reduction in the energy barriers for both the reduction of *HNO3 to *NO2 and the reduction of *HNO2 to *NO, thereby enhancing the performance of ERN. As excepted, LCOF0.5 exhibits a rapid reaction rate of k = 5.48 × 10−3 min−1, which is 1.70 times faster than that of pristine LCO, and its catalytic activity approaches that of the state-of-the-art electrocatalysts for ERN. Applying this strategy to LaFeO3 and LaMnO3 also yields similar results, demonstrating its general applicability. The F-anion substitution strategy offers new opportunities for significantly enhancing ERN performance.

Exploring dielectric and electrical characteristics in Sr0.5Ba0.5SnxFe12-xO19/CoFe2O4 nanocomposites

This study examined the morphological, structural, electrical, and dielectric characteristics of hard-soft (H-S) Sr0.5Ba0.5SnxFe12-xO19/CoFe2O4 (x ≤ 0.10) ferrite nanocomposites (NCs), created using one-pot sol-gel combustion route. This study systematically investigated the electrical/dielectric features of H-S Sr0.5Ba0.5SnxFe12-xO19/CoFe2O4 NCs where x is within the range of 0.00 ≤ x ≤ 0.10. The examination realizes frequencies that reach 3.0 MHz, conducted within 20 °C–120 °C. A detailed analysis was performed to investigate various conduction mechanisms linked with dielectric constant, dissipation factor, AC/DC conductivity, loss of dielectric capacity, and real/imaginary modulus, which were explored across the entire range of Sn ion substitution ratios. Observations reveal that the conductivity variations adhere to power law dynamics concerning frequency, predominantly influenced by the Sn ion substitution ratios within the NCs. Furthermore, the frequency dependency of the dielectric coefficient across all NCs substantiates the common propagation of dielectric behavior, prominently contingent upon the substitution ratio of "x". Notably, the majority of dielectric parameters observed in H-S Sr0.5Ba0.5SnxFe12-xO19/CoFe2O4 (x ≤ 0.10) NCs are attributable to grain-to-grain boundaries, elucidated by conduction mechanisms similar to those observed in most compositional ferrites, explicable through Koop's model.

Crystal structure and spectral tuning of Eu2+/Eu3+ co-activated Na2Ba1-xSrxCa(PO4)2 phosphors with high thermal stability

The coupling of UV LED chips with phosphors to produce white or color-tunable light is still a challenge. In this work, we propose a simple rare earth occupation site engineering method to adjust the valence of doped Eu ions. Based on the Ba2+ substituted by Sr2+, new Eu2+/Eu3+ co-activated Na2Ba1-xSrxCa(PO4)2 (NB1-xSxCP) phosphors were designed and successfully synthesized. In NB1-xSxCP, the Ba2+/Sr2+ site is occupied by Eu2+, while the Ca2+ site is occupied by Eu3+. The coupled broad blue 448 nm and sharp red 619 nm luminescence under 321 nm excitation has demonstrated the coexistence of Eu2+ and Eu3+. This double emission phenomenon is studied in terms of the fluorescence lifetime as well as lattice distortion induced by the substitution ions. With the increased substitution of Sr, the luminescence of NB1-xSxCP:0.03Eu2+/3+ can be tuned from blue to red crossing the warm-white region. When x = 0.3, the chromaticity coordinates is located at (0.3779, 0.2495). The integrated intensity of Na2Ba0.7Sr0.3Ca(PO4)2:0.03Eu2+/3+ at 150℃ remains 90.9 % of that at room temperature, while the chromaticity shift (ΔE) can be calculated as 15 ×10−3. The Eu2+/Eu3+ co-activated NB1-xSxCP is a potential candidate for single-phase color-tunable phosphors used for light-tunable applications due to the combining contributions from both Eu3+ and Eu2+ ions.

Microstructural Study of the Coloring Variation of Chinese Sauce Glaze Replications

ABSTRACTSauce glazed wares of Yaozhou kilns are famous for their high gloss and distinctive glaze color palette varying from yellowish‐brown to reddish‐brown. In this work, sauce glazes were successfully replicated using the traditional technology of Yaozhou kilns. Micro‐Raman spectroscopy, combined with optical microscopy, scanning electron microscopy, x‐ray fluorescence, and reflective spectroscopy, was systematically applied to analyze the chemical composition, nature and distribution of crystals, and the coloration of the glazes. The results show that the yellowish‐brown glaze is mainly original from dendritic ε‐Fe2O3 crystals, whereas the reddish‐brown color is mainly derived from dendritic hematite crystals. Such dendritic structure could account for slightly color variations of the glaze surface observed in different angles, which also reported in Japanese Bizen ceramics. The principal component analysis (PCA) was further applied to study the Raman spectra of these iron oxides. The PCA results effectively indicates the structural disorders of these crystals introduced by ion substitutions. These substitutions could not only stabilize the crystals but also darken the crystals color. Besides, high Mg in the raw materials was found to benefit the growth of magnesioferrite crystals. The relative low level of Fe2O3, high level of SiO2, and CaO may relate to the formation of ε‐Fe2O3 crystals.

A series of Ba12M0.5Zr0.5Nb9O36 (M=Ni, Mg, Co, and Zn) microwave dielectric ceramics with hexagonal perovskite structure

A series of hexagonal perovskite Ba12M0.5Zr0.5Nb9O36 (M = Ni, Mg, Co, Zn) ceramics were prepared by solid-state reaction method. XRD and Rietveld refinement results showed that all ceramic samples belong to the hexagonal perovskite structure with R-3m space group. With different B-site ion substitution, variation of permittivity (εr) can be ascribed to the average ion polarizability. Ceramics with highest relative density exhibit maximum quality factor (Q×f) values. Among all samples, the optimal microwave dielectric properties of εr = 35.2, Q×f = 57,985 GHz, and τf = 26.4 ppm/°C for Ba12Mg0.5Zr0.5Nb9O36 were obtained, which indicated that Ba12Mg0.5Zr0.5Nb9O36 ceramic is a candidate material for microwave communication applications.

A prediction of high temperature magnetic coupling in transition metal phthalocyanines.

In spintronics, a perennial goal has been the generation of organic spin-bearing semiconductor materials with magnetic ordering stable at room temperature. To this end, the class of transition metal phthalocyanines has shown much promise in fulfilling this ambition. In particular, alpha-phase cobalt (II) phthalocyanine (α-CoPc) exhibits strong antiferromagnetic exchange interactions producing a long range order up to ∼100K. However, the underlying mechanism by which this magnetic interaction proceeds is not well understood. In this report, a simple mechanism has been proposed based on the Hubbard Hamiltonian, which elucidates the exchange coupling in α-CoPc. The mechanism provides stipulations for increasing the magnetic coupling, and this directs to a proposal that substitution of the central cobalt ion for rhodium will lead to a significant increase in coupling strength. The strength of this exchange interaction has been evaluated using broken symmetry hybrid exchange density functional theory and indicates that the novel rhodium (II) phthalocyanine system is indeed predicted to exhibit significantly stronger magnetic ordering. This study, therefore, identifies the coupling mechanism in α-CoPc as primarily attributable to kinetic exchange, explains its previously reported strong coupling relative to its first-row transition metal counterparts, and suggests that rhodium (II) phthalocyanine is likely to exhibit stable magnetic ordering at room temperature.

Systematic investigation of the influence of magnetic and non-magnetic ion substitutions in BiFeO3 under similar internal chemical pressure

Polycrystalline Bi1-xRxFeO3 (RHo and Y, x = 0.00, 0.05 and 0.10) compounds were prepared to perform a systematic investigation of the role of chemical nature and effect of internal chemical pressure on the structural, microstructural, magnetic, electric, ferroelectric and optical properties of the compounds. Structural analysis revealed that lattice distortions observed in Ho and Y-substituted compounds were not the same. The lattice parameters were larger in the case of the Y-substitution compared to the Ho-substituted counterpart. Scanning electron micrographs confirmed the formation of dense, well-connected grains exhibiting a reduction in size with increasing substitution. The magnetic properties of BiFeO3 were enhanced through the suppression of the spin structure with the substitution. The substitution of magnetic (Ho3+) ions led to an improvement in remanent magnetization and coercive field, whereas the substitution of non-magnetic (Y3+) ions resulted in enhanced maximum magnetization with negligible coercive field at room temperature. The ferroelectric measurements evidenced that both remanent polarization and coercive fields improved in substituted compounds, attributed to a decrease in charge carriers. Furthermore, the Y3+ ion substitution positively influenced ferroelectric properties by reducing leakage currents compared to the Ho3+ ion substitution. The optical absorption measurements indicated a decrease in the energy band gap of BiFeO3 with substitution, implying alterations in the material's optical characteristics. The ac conductivity studies demonstrated a discernible reduction in the conductivity of the substituted compounds. Specifically, Ho-substitution exhibited a more pronounced magnitude in the decline in conductivity relative to Y-substitution. This outcome signifies the potential efficacy of Ho-substitution in exerting control over the insulating characteristics of the compounds.

Unveiling the structural, optical, electrical, and ferromagnetic properties of Ca2+ doped mixed spinel ferrites for switching field high-frequency device applications

In this paper, the calcium-doped nickel-zinc nano-ferrites [Ni0.5Zn0.5CaxFe2-xO4; x = 0.00, 0.10, and 0.30] were prepared using the chemical co-precipitation synthesis route and studied for switching field high-frequency device applications. The structural analysis has been completed by analyzing X-ray diffraction (XRD) patterns. The Rietveld refined XRD patterns confirmed the formation of cubic spinel structure of Ca2+ substituted nickel-zinc ferrites. The detection of metal-oxygen bonds present at A and B lattice sites has been unveiled by Fourier transform infrared (FTIR) spectroscopy. The morphological studies obtained through FESEM (Field emission scanning electron microscopy) analysis showed a reduction in the particle size from 70 nm to 53 nm when the concentration of Ca2+ ions in Ni-Zn ferrites was increased. Energy dispersive spectra (EDS) confirmed the presence of elements present in the prepared composition. The structure of a cubic spinel-shaped unit cell has been verified from three active prominent Raman modes (A1g, A2g, and T2g). Diffuse-reflectance spectroscopy (DRS) exhibits the increment in the bandgap values (from 1.55 eV to 1.63 eV) which helps fabricate highly efficient photovoltaic devices. The ferroelectric measurements yielded a rise in polarization values from 1.461 μC/cm2 to 18.228 μC/cm2 for 10 % Ca2+ ion substitution. The tangent loss values declined from 24 to 3 in Ni-Zn ferrites upon substituting Ca2+ ions. The Vibrating sample Magnetometer (VSM) technique found the increment in the saturation magnetization (Ms) values from 34.724 emu/g to 54.662 emu/g on substituting up to 30 % Ca2+ ions in Ni-Zn ferrites. These obtained results support the material in switching field distribution for high-frequency applications. The results exhibited that the prepared samples can be applicable for switching devices, filters, and microwave absorption devices. The results revealed the maximum frequency between 12 and 18 GHz which is useful for Ku band absorption.