Ion Substitution Research Articles

Exploring the structural and magnetic properties of La-doped nickel ferrite for microwave absorbing application

The intrinsic properties of microwave absorbing materials are influenced by the permeability and permittivity of the material with indicators of changes in reflection loss characteristics. Nickel ferrite is a magnetic material with very high permeability, so the presence of La3+ ion substitution in nickel ferrite can increase the permittivity of this material and is denoted by increased reflection loss. The magnetic material NiLaxFe(2−x)O4 was synthesized effectively through co-precipitation techniques using NiCl2, FeCl3, and LaCl3 powders, with mole ratios varying from x = 0.01 to 0.04, then continued with the sintering process at a temperature of 1200 °C for 5 h.The X-ray diffraction (XRD) analysis indicates that all NiLaxFe(2−x)O4 samples consist of a single phase of NiFe2O4 with a cubic spinel structure. The scanning electron microscope (SEM) image of NiLaxFe(2−x)O4 powders reveals that all samples exhibit a consistent morphology, however, the powder doesn’t look uniform yet, with particle sizes ranging from 100-800 nm. The magnetic properties of the samples were examined using a vibrating sample magnetometer (VSM). The sample shows ferromagnetic behavior, but the Ms value decreases from 35.89 to 21.54 emu/g and the Hc value increases from 249 to 416 Oe as the La3+ ion content in the material increases. Meanwhile, the microwave absorption capacity measured using the vector network analyzer (VNA) shows that reflection loss increases from 11.16 dB to 15.41 dB as the La3+ ion content in the material increases. So, the substitution of La3+ ions in nickel ferrite structure up toa concentration of x = 0.04 can increase microwave absorption up to 97.11 %.

Sr-doped CuFe2O4 nanoparticles: Exploring structural, magnetic, and blood compatibility characteristics

The aim of this study is to investigate the structural, magnetic, and blood compatibility properties of Sr2+ substituted for Cu2+ in Cu1−xSrxFe2O4 (x = 0.0 to 1 with a 0.25 increment) nanoparticles synthesized via the sol-gel auto-combustion technique. Regardless of the substitution rate, the sol-gel auto-combustion method consistently yields powders with sizes ranging from 20 to 40 nm. The specific surface area of the produced powders is determined as 12 m2/g. X-ray diffraction analysis reveals that CuFe2O4 exhibits a singular phase; however, as the Sr2+ ion substitution increases, the emergence of various secondary phases becomes apparent, with their proportions increasing with the substitution rate. The magnetic characteristics of the synthesized powders exhibit variations in magnetization, correlating with the distribution of cations in the sublattice points. Coercivities are influenced by both anisotropy and secondary phases. Saturation magnetization decreases from 31.3 (CuFe2O4) to 7.6 (SrFe2O4) emu/g with Sr replacement. The lowest observed coercivity is 429.5 Oe in powders prepared with CuFe2O4 composition, while the highest is measured at 583.8 Oe in nanopowders prepared with Cu0.5Sr0.5Fe2O4 composition. Moreover, blood compatibility experiments indicate significantly low hemolysis ratios for Cu1−xSrxFe2O4 nanoparticles. Additionally, all examined samples exhibit an increase in Soret band intensity compared to the negative control test, suggesting potential biocompatibility.

Impact of Cr Doping on the Structural, Optical, and Magnetic Properties of Sol-Gel-Synthesized Bi0.80Ba0.10Pr0.10FeO3 Nanopowders.

The sol-gel route was used to synthesize a series of compounds of the system Bi0.8Ba0.10Pr0.10Fe1-x Cr x O3 within the 0 ≤ x ≤ 0.15 compositional range. To explore the impact of Cr3+ ion substitution on the structural, dielectric, optical, and magnetic properties, we introduced varying concentrations of Cr3+ while maintaining a fixed 10% atomic concentration of each Ba2+ and Pr2+ in BiFeO3. X-ray diffraction analysis revealed a structural phase transition from rhombohedral (R3c) for an undoped (i.e., without Cr) sample to two coexisting phases, i.e., a mix of rhombohedral and orthorhombic (Pbnm) phases for the Cr-doped samples. Cr3+ doping significantly changes the band gap energy from 1.84 eV (x = 0.0) to 1.93 eV (x = 0.15), which makes this material suitable for photovoltaic applications. Furthermore, each sample exhibited ferromagnetic behavior due to the disruption of the spiral spin structures and adjustments in superexchange interactions, attributed to modifications in the Fe-O and Fe-O-Fe bond lengths. A reduction in magnetization is observed at higher Cr concentrations that can be ascribed to the dilution of magnetic moments due to the increase of the orthorhombic phase percentage and the introduction of nonmagnetic Cr3+ ions. Our results show that Cr doping in the Bi0.8Ba0.10Pr0.10FeO3 system induces enhanced multiferroic properties at room temperature.

Incorporation and substitution of ions and H2O in the structure of beryl

Abstract. Incorporation of ions into the crystal structure of beryl (Be3Al2[Si6O18]) can take place by direct ion-to-ion substitution of the framework components Al3+, Be2+ and Si4+ or by occupation of interstitial or structural channel sites. The most common impurities in beryl include transition metals, alkalis and H2O. It is accepted that the transition metals Mn, Cr and V directly substitute for Al at the octahedral site and induce colour. Similarly, the octahedral site can host Fe instead of Al. Nevertheless, it is shown that it remains disputed whether Fe can also be present at the tetrahedral, interstitial, or channel sites, and opposing hypotheses exist regarding these possibilities. However, in the case of Fe, not only the possible occupation of these sites remains under debate, but also their influence on the subsequent colour of beryl. Similarly, the residence of Li in the channels and at the Be tetrahedral or interstitial tetrahedral sites is still under debate. The presence of more than two types of H2O (type I and type II) in the structural channels of beryl is also unclear. This article aims to give an overview on the consensus and on the current debates found in the literature regarding these aspects. It mainly concentrates on the substitution by and the role of Fe ions and on channel occupancy by H2O.

“Study of structural, optical, morphology and magnetic properties of samarium doped magnesium nanoferrites (MgSmxFe2-xO4) using sol-gel auto-combustion method”

The study presents a comprehensive report on Sm3+-doped magnesium ferrite (MgSmxFe2-xO4) and its properties across various x values (0.025, 0.075, 0.1, 0.125, and 0.150). The study utilized multiple characterization techniques, such as X-ray diffraction (XRD), Fourier transmission infrared spectroscopy (FTIR), vibrating sample magnetometer (VSM), UV–visible spectroscopy (UV–vis), Thermogravimetry Differential Thermal Analysis (TG-DTA), High-resolution transmission electron microscopy (HR-TEM), and scanning electron microscopy (SEM) to investigate the structural, magnetic, thermal, optical, and morphological properties of the material. The study determined various parameters, such as x-ray density, lattice constant, crystallite size, and radii on octahedral and tetrahedral sites. An increase in Sm3+ content resulted in an expansion of lattice parameters and a reduction in crystallite size, observed at 13.342 nm in single-phased samples. FT-IR spectroscopy confirmed Sm3+ ion substitution in octahedral sites, while transmission electron microscopy revealed spherical nanoparticles. The UV–vis spectroscopy observed an increase in Sm3+ leads to a corresponding rise in the energy band gap values transitioning from 2.0864, 2.1090, 2.1410, 2.1517, and 2.1850 eV of x = 0.025 to 0.150 respectively. Magnetic measurements indicated decreased magnetization with doping, attributed to particle size dependence. Overall, this study provides valuable insights into the magnetic properties and structural characteristics of Sm3+-doped magnesium ferrite nanomaterials, potentially advancing the development of advanced materials for diverse applications.

Tackling toxicity and stability using eco-friendly metal-halide ion substituted perovskite nanocrystals for advanced display color conversion

In recent years organic–inorganic hybrid halide perovskites nanocrystals have made a remarkable impact in display color converting layer application. However, lead toxicity and stability issues always pose arduous challenges. In this regard, the incorporation of a suitable metal ion to reduce toxicity and enhance stability is a widely tested method. In this study, we used a simple ligand-assisted reprecipitation (LARP) technique to simultaneously introduce metal ion and halide ion substitution by synthesizing MAPb1-xZnxBr3-2xCl2x nanocrystals (NCs). Being eco-friendly with a smaller ionic radius than lead ion, zinc metal ion was chosen as a substitute. With the variation of Zn2+ concentration, the highest quantum yield of 95 % was recorded with an emission width of 21 nm. Temperature-dependent photoluminescence (PL) studies revealed the higher optical phonon-exciton interaction after Zn2+ incorporation leading to radiative transition in NCs. Variation of PL peak energy with temperature revealed the reduced thermal chromaticity of Zn2+ incorporated NCs making them suitable for display application. Further, these NCs maintained a stable cubic structure and luminescence up to 150 °C, indicating higher thermal stability. The MAPb0.9Zn0.1Br2.8Cl0.2 (x = 0.1 or 10 mol%) NCs embedded in PMMA (poly (methyl methacrylate) polymer matrix coated LED emits narrow width, green light with color coordinate (0.15, 0.79), which is closer to green coordinate (0.17, 0.79) in Rec.2020. This helps to reproduce close to 97 % color gamut of Rec.2020. This research paves the way for finding less toxic and stable green light-emitting materials instead of cadmium-based molecules.

Structural, Optical, and Morphological Study of Manganese Substituted Cobalt Ferrite and Its Effect on the Magnetic and Dielectric Properties of PVA Composites

Nanopowders of Mn-substituted CoFe2O4 were prepared in different proportions using the sol-gel auto-combustion method and were structurally and morphologically studied. In another step, composites based on polyvinyl alcohol (PVA) with Mn-substituted CoFe2O4 fillers were prepared, and the effect of the Mn-substituted CoFe2O4 on the optical, magnetic, and dielectric properties was studied. X-ray analysis revealed the formation of polycrystalline Mn-substituted CoFe2O4. The results showed a decrease in the lattice constant with Mn2+ substituted and incorporated into the crystal structure of CoFe2O4. The Fourier confirmed the spinel structure of the Mn-substituted CoFe2O4 transform infrared spectrum where absorption bands appeared at 569–561 and 446–407 cm-1, which are attributed to tetrahedral and octahedral groups. The magnetic properties were affected when Mn ions were substituted with CoFe2O4, as shown by the results of VSM. It was observed that the saturation magnetization, remnant magnetization, and coercivity decreased with increasing Mn content. The dielectric constant and loss tangent of PVA/MnxCo1−xFe2O4 were also studied. The difference in the diameters of the substituted and host ions causes the dielectric constant to increase following the substitution of Mn ions.

Effect of Fe3+ ions substitution on electrical and dielectric properties of MgFexCr2-xO4 (x = 0, 0.2, and 0.4 mol%) chromites prepared by solution combustion method

This paper reports the structural, dielectric and electrical properties of Fe3+ ions substituted magnesium chromite with composition MgFexCr2-xO4 (x = 0, 0.2, and 0.4 mol%) synthesized via solution combustion method. The structural analysis was done by XRD pattern which confirmed the formation of cubic crystal symmetry of the samples with Fd-3 m space group. The value of lattice parameters of MgFexCr2-xO4 chromites slightly increased with increasing concentration of Fe3+ ions. The TEM (Transmission electron microscopy) micrographs at different magnifications showed the spherical particles of the sample and average particle size was found to be ≈ 56.22 nm. The dielectric parameters (dielectric constant and dielectric loss) and ac conductivity were investigated in the frequency range of 100 Hz–100 kHz and temperature range of 50 °C–350 °C. The dielectric studies showed that the dielectric parameter decreases in high frequency range which can be explained by Maxwell-Wagner type of space charge polarization. The dielectric constant increases with increasing concentration of Fe3+ ions due to increase in polarization. The frequency and temperature dependent ac conductivity was studied and found that the conductivity value increases with an increase in frequency and temperature, which followed the Jonscher's universal power law. The ac conductivity decreases with increasing Fe3+ ions due to formation of grain boundary defect barrier. The non-Debye type relaxation behavior of the MgFexCr2-xO4 samples was confirmed by the Cole-Cole plot. The obtained result shows the capability of magnesium chromite for fabrication of micro-electronic devices, sensors, and other electronic devices.

Luminescence enhancement effects of CaxSr2‒xNb2O7:Er3+,Tm3+ phosphors for temperature sensing and anti-counterfeiting applications

Er3+- and Tm3+-doped CaxSr2‒xNb2O7 (CxS2‒xN, x = 0.6, 0.8, 1.0, 1.2, 1.4) phosphors with layered perovskite structure were designed. These phosphors exhibit a dominant emission peak at 549 nm under 980 nm laser excitation, attributed to the 4S3/2→4I15/2 transition. By increasing the content of Ca2+, the crystal field regulation of rare earth ions is realized and the luminescence enhancement is induced, which is manifested by the increase of 2H11/2,4S3/2→4I15/2 emission. Furthermore, the temperature sensing sensitivities of C0.6S1.4N:Er,Tm and C0.6S1.4N:Er,Tm based on non-thermally coupled energy levels were studied. Finally, an anti-counterfeiting imprint was prepared using phosphors, which have high brightness and excellent photothermal stability. This work not only confirms that closer ionic radii substitution enables to increase the electronic density of states, improve the crystal field symmetry and enhance the luminescence, but also provides a promising phosphor system for temperature sensing and anti-counterfeiting applications, opening up new prospects in the optimization of the optical properties of phosphors.

Dielectric and magnetic response of mechanically activated Mn-doped SrTiO3 ceramics

This research was focused on the influence of manganese (Mn) incorporation at Sr and/or Ti sites on the microstructure, relative dielectric permittivity and specific magnetization of strontium titanate (SrTiO3) ceramics. A solid-state method was used for the preparation of mechanically activated (10, 30 and 120 min) Mn-doped SrTiO3 ceramics with various manganese dioxide (MnO2) weight percentages (1.5, 3 and 6 wt%). Rietveld's analysis showed that the mean crystallite size in doped-activated SrTiO3 ceramics is smaller than in undoped ceramics, which is a consequence of additional crystal structure distortion due to ion substitution. Changes in the Raman spectra indicated dopant incorporation in the SrTiO3 lattice. The microstructural analysis pointed out a decrease in the mean grain size with increasing dopant concentration and time of activation. The highest values of permittivity and magnetization were observed for Mn-doped SrTiO3 ceramic mechanically activated for 120 min. Based on all the above, the optimal electrical and magnetic properties of SrTiO3 ceramics can be achieved by the appropriate choice of mechanical activation time and dopant concentration.

Mixed Metal Amide-Hydride Solid Solutions for Potential Energy Storage Applications.

Mixed solid solutions have played an important role in improving the kinetics and performance of hydrogen storage materials, as reported for the Li-Mg-N-H, K-Mg-N-H, and Rb-Mg-N-H systems. Besides, the formation of a homogeneous solid solution, mostly due to partial ionic substitution, is known to be an effective approach to improve the ionic conductivity of a material, which is an important property in electrochemical applications. We have reported a series of solid solutions based on mixed amide-hydride materials of the Group 1 elements, e.g., K(NH2)xH1-x, Rb(NH2)xH1-x, and Cs(NH2)xH1-x, via the exchange of NH2-/H- anions with the change of the lattice cell of the solid solution. Extending the research in this direction, we study the M-N-H solid solution in the MNH2-MH systems (M = K, Rb, Cs, and their combinations), i.e., KNH2-RbH, RbNH2-KH, RbNH2-CsH, and CsNH2-RbH via ex situ/in situ XRD, IR, and 1H 2D solid-state NMR. The results obtained confirm the formation of mixed metal amide-hydride solid solutions associated with an exchange between both anionic (NH2- and H-) and cationic species (K+, Rb+, and Cs+). With this study, we aim to create an accessible library of M-N-H solid solutions for further studies as additives for hydrogen storage materials or ionic conductors.

Structural and Magnetic Properties of Barium-Strontium-Hexaferrite Material Ba0.6Sr0.4Fe10-xCoxMnTiO19 (x = 0.5; 1.0; and 1.5) as Microwave Absorbers

We discuss the structure properties of Ba0.6Sr0.4Fe10-xCoxMnTiO19(BSFCMTO) for x = 0.5, 1.0, and 1.5 that influence its magnetic properties as a microwave absorber. A solid-state reaction method using high-energy milling was used to synthesize hexaferrite. There were no structural changes when the Co2+ ion was substituted for the Fe3+ ion; the structures of all samples were hexagonal and the space group was P63/mmc. The surface morphology had heterogeneous particles with a size of 300 to 600 nm. The magnetic properties tended to decrease with an increasing number of Co2+ ion substitutions. The reflection loss (RL) had a minimum value of -14.89 dB. This value was reached at a frequency of 10.96 GHz and had a bandwidth at 1.24 GHz with a sample thickness of 1 mm in the Ba0.6Sr0.4Fe9.9Co0.1MnTiO19 sample.

Mechanism of antimony ion doping to optimize microwave dielectric properties of zinc zirconate tantalate ceramic

Herein, first-principles calculations predicted the atomic-scale variation of Sb5+ substitution for ZnZrTa2O8, and combined with the solid-phase reaction method to prepare ZnZr(Ta1-xSbx)2O8 (0.0 ≤ x ≤ 0.10) ceramics. ZnZr(Ta0.94Sb0.06)2O8 ceramics demonstrated the optimum microwave dielectric properties after sintering at 1350 °C for 6 h: εr = 24.92, Q × f = 134053 GHz (@7.18 GHz), and τf = −46.21 ppm/°C. For the non-intrinsic factors, the relative density increased from 96.54 % to 97.74 % and the average grain size increased from 19.88 μm to 21.85 μm, both of which reduced the dielectric loss. Regarding intrinsic factors, the progressive elevation of the Raman characteristic peak wave number and the heightened ionicity of Ta/Sb–O bonds predominantly account for the observed enhancement in εr. In addition, the attenuation of lattice vibrational damping behavior, the augmentation in electron cloud density, and the escalation of lattice energy collectively contribute to a decrement in dielectric loss. This study refines the examination of ionic substitution in ZnZrTa2O8 ceramics, offering theoretical insights for optimizing their dielectric properties and promoting their application in microwave communications.

Static Magnetic Properties and Morphological Behaviour of Mn and Zn Substituted Ca-hexaferrite by Ceramic Technic

Synthesis of M-type hexagonal ferrite compounds, Ca(CoTi)0.5(MnZn)x/2Fe11-xO19 (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0, 1.2) prepared by ceramic technic. Mn and Zn ions substituted to find the magnetic characterizationat magnetic field of 10 kOe. XRD and SEM study have been done for getting the hexagonal structure of these samples. Due to the substitution of Mn and Zn ions saturation magnetization increases and magnetocrystalline anisotropy decreases. Due to the sub-latice site distribution the variations in magnetic parameters have been observed. Because of Mn and Zn ions substitution Curie temperature decreases by weakening of superexchange interaction. These materials can be used for various applications such aspermanent magnetic material, magnetic recording media, ferrofluids, sensors, microwave absorbing materials, ceramic magnets in loud speakers and rotors in small DC motors by studying various magnetic parameters from VSM characterization.

Preparation and properties of cordierite-based multi-phase composite far-infrared emission ceramics by fine-grained tailings

In this paper, cordierite ceramics with high far-infrared emission properties are synthesized by a high-temperature solid-phase method using molybdenum tailings and vanadium-titanium magnetite tailings. The microstructure, physical properties and far-infrared emission mechanism of ceramics are investigated. The results show that the ceramics synthesized with 10 wt% molybdenum tailings and 30 wt% vanadium-titanium magnetite tailings have a flexural strength of 67 MPa, a bulk density of 2.531 g/cm3 and a maximum far-infrared emissivity of 0.958 when the sintering temperature is 1200 °C. The crystal phase of the ceramic are 21.4 % cordierite and 58.7 % magnesia-alumina spinel. In the sintering process, the Fe3+ in vanadium-titanium magnetite tailings doped into the cordierite to substitute the Mg2+, which has the similar ionic radius with Fe3+, to form a substitutional solute. Ionic substitution causes the lattice parameters of cordierite larger, reducing the symmetry of the lattice vibrations and leading to lattice distortion. In addition, the composition of a large amount of magnesia-aluminum spinel is attributed to the far-infrared emission properties of ceramics.

Role of Bi3+ ion substitution on the piezocatalytic degradation performance of lead-free BaTi0·89Sn0·11O3 at low vibrational energy

Harnessing low ultrasonic vibration energy to initiate piezocatalytic-based reactions is increasingly becoming a significant focus due to the current environmental energy crisis. In this study, we report on the potential of heterovalent ion substitution in improving piezocatalytic degradation of Rhodamine B dye (RhB) under the application of low-power ultrasonic vibration. For this purpose, bismuth ions Bi3+ are substituted into the lead-free ferroelectric BaTi0·89Sn0·11O3 (BTSn11-xBi, x = 0, 0.02, 0.04) submicrocubes synthesized using sol-gel method. The structural, morphological, optical and piezocatalytic properties of the prepared materials appear to be significantly influenced by the substituting content. Compared to pure BTSn11 and BTSn11-0.04Bi, BTSn11-0.02Bi exhibits the lowest band gap energy value of 3.22 eV, the smallest particle size value of 283 nm, the strongest piezoelectric current of about 8 μA/cm2, and the lowest required applied field for piezoresponse force microscopy hysteresis loops. The degradation efficiency and the kinetic rate constant are substantially higher for BTSn11-0.02Bi, indicating its enhanced piezocatalytic efficiency. Total organic carbon (TOC) measurements revealed good RhB mineralization using BTSn11-xBi piezocatalysts. Furthermore, the BTSn11-0.02Bi sample demonstrates good reusability and stability by maintaining effective RhB dye degradation for five consecutive cycling tests. These findings suggest that the BTSn11-0.02Bi piezocatalytic system holds significant potential for environmental remediation applications.

Colossal Ferroelectric Photovoltaic Effect in Inequivalent Double-Perovskite Bi2FeMnO6 Thin Films.

Double perovskite films have been extensively studied for ferroelectric order, ferromagnetic order, and photovoltaic effects. The customized ion combinations and ordered ionic arrangements provide unique opportunities for bandgap engineering. Here, a synergistic strategy to induce chemical strain and charge compensation through inequivalent element substitution is proposed. A-site substitution of the barium ion is used to modify the chemical valence and defect density of the two B-site elements in Bi2FeMnO6 double perovskite epitaxial thin films. We dramatically increased the ferroelectric photovoltaic effect to ∼135.67 μA/cm2 from 30.62 μA/cm2, which is the highest in ferroelectric thin films with a thickness of less than 100 nm under white-light LED irradiation. More importantly, the ferroelectric polarization can effectively improve the photovoltaic efficiency of more than 5 times. High-resolution HAADF-STEM, synchrotron-based X-ray diffraction and absorption spectroscopy, and DFT calculations collectively demonstrate that inequivalent ion plays a dual role of chemical strain (+1.92 and -1.04 GPa) and charge balance, thereby introducing lattice distortion effects. The reduction of the oxygen vacancy density and the competing Jahn-Teller distortion of the oxygen octahedron are the main phenomena of the change in electron-orbital hybridization, which also leads to enhanced ferroelectric polarization values and optical absorption. The inequivalent strategy can be extended to other double perovskite systems and applied to other functional materials, such as photocatalysis for efficient defect control.

Optimizing the sulfur-resistance and activity of perovskite oxygen carrier for chemical looping dry reforming of methane

Perovskite oxides has been attracted much attention as high-performance oxygen carriers for chemical looping reforming of methane, but they are easily inactivated by the presence of trace H2S. Here, we propose to modulate both the activity and resistance to sulfur poisoning by dual substitution of Mo and Ni ions with the Fe-sites of LaFeO3 perovskite. It is found that partial substitution of Ni for Fe substantially improves the activity of LaFeO3 perovskite, while Ni particles prefer to grow and react with H2S during the long-term successive redox process, resulting in the deactivation of oxygen carriers. With the presence of Mo in LaNi0.05Fe0.95O3−σ perovskite, H2S preferentially reacts with Mo to generate MoS2, and then the CO2 oxidation can regenerate Mo via removing sulfur. In addition, Mo can inhibit the accumulation and growth of Ni, which helps to improve the redox stability of oxygen carriers. The LaNi0.05Mo0.07Fe0.88O3−σ oxygen carrier exhibits stable and excellent performance, with the CH4 conversion higher than 90% during the 50 redox cycles in the presence of 50 ppm H2S at 800 °C. This work highlights a synergistic effect in the perovskite oxides induced by dual substitution of different cations for the development of high-performance oxygen carriers with excellent sulfur tolerance.

Optimization of near-infrared luminescence performance in Cr3+-doped double perovskite Sr2ScTaO6 phosphor by Nb5+ ion substitution

Here, Nb5+ were partially substituted for Ta5+ in the double perovskite Sr2ScTaO6: Cr3+ phosphor to improve its luminescence performance and finally obtained the optimized phosphor Sr2ScTa0.6Nb0.4O6: Cr3+. The structure, substitution mechanism, luminescence optimization mechanism, crystal field, and thermal stability of the phosphor were all thoroughly explored. The results indicate that introducing Nb5+ into Sr2ScTaO6: Cr3+ can cause lattice distortion in the host, and the distorted crystal lattice can break the forbidden transition of Cr3+, thereby enhancing its absorption of excitation light. At the same time, the full width at half maximum of the phosphor emission increased from 176.4 nm to 179.7 nm. And the internal quantum efficiency, absorption efficiency, and external quantum efficiency of the optimized Sr2ScTa0.6Nb0.4O6: Cr3+ phosphor can reach 86.3%, 49% and 42.3%, respectively. The photoelectric conversion efficiency of the optimized pc-LED increased from 5.63% to 7.80%@100 mA, indicating the introduction of Nb5+ in Sr2ScTaO6: Cr3+ improved the luminescence performance of phosphor. The above results provide directions for the development of more efficient and promising double-perovskite NIR phosphors.

Altered spinels act as a mirror of multi-episodic fluid metasomatism in the forearc mantle: An example from the Minhe ophiolite in Qilian Orogen, NW China

Forearc mantle peridotites commonly undergo complex melt/fluid metasomatism, which inevitably has a considerable influence on their geochemical compositions at the whole-rock scale. Serpentinites predominantly comprise the Minhe ophiolite, which is a fragment of the Proto-Tethys Ocean that outcrops in the Qilian Orogen in NW China. These serpentinites contain zoned spinels that vary compositionally from the centers to the margins, with a spinel core overgrown by ferritchromite layer and magnetite at the outermost rim. The mineral chemistry of the spinel cores (i.e., Cr#, Mg#, Cr2O3, and Al2O3) suggests that the protolith of the serpentinites was an oceanic mantle remnant in a forearc setting. Moreover, the ferritchromite exhibited increases in Fe, Mn, Sc, and Ni contents and decreases in Mg, Cr, Al, V, Zn, and Ga contents. Considering the linear correlation among elements (e.g., Co, Ni, and Zn) and the absence of mineral inclusions, the ferritchromite likely formed through ionic substitutions induced by slab fluids. The magnetite was enriched in Cr, Ni, V, Zn, Co, and Cu, but did not have a magmatic origin owing to low V concentrations. All evidence indicates that the peridotites underwent at least two episodes of fluidic metasomatism in the subduction zone. During early slab subduction, aqueous fluids released from the dehydration of the subducted slab directly serpentinized the forearc mantle peridotites, thereby altering the olivine and orthopyroxene to lizardite/chrysotile. During this process, certain mobile elements (e.g., Fe, Ni, and Mn) in the fluids and/or olivine serpentinization were incorporated into existing spinels, favoring ferritchromite growth. The second fluidic episode was dependent on prograde metamorphism at greater depths in the subduction channel, which not only produced antigorite via the recrystallization of lizardite and chrysotile, but also drove the fluids towards a more oxidizing state, thereby facilitating the growth of Cr-magnetites. Subsolidus re-equilibration controlled by fluid infiltration further promoted the inter-diffusion of elements (e.g., Cr, V, Co, Ni, Cu, and Zn) in the zoned spinels.