Decrease In Lattice Parameter Research Articles

Enhancing SrBi₂Nb₂O₉ ceramics: The role of neodymium substitution in structural, dielectric, and ferroelectric properties

This study investigates the impact of neodymium substitution for bismuth in SrBi2Nb2O9 (SBN) ceramics, a potential lead-free alternative for ferroelectric applications. X-ray diffraction analysis reveals a decrease in lattice parameters and volume with increasing Nd content. Scanning electron microscopy examines the influence of neodymium on grain morphology, showing a transition from characteristic SBN plate-like grains to a mix of plates and micro-spheres. Dielectric properties are evaluated, showing an increase in room-temperature permittivity for Nd-doped samples compared to the undoped counterparts. Additionally, the influence of Nd doping on relaxor ferroelectric behavior is studied. The Curie temperature (Tc) increases with Nd concentration, while the temperature dependence of relaxation time weakens. Ferroelectric properties exhibit significant changes due to Nd doping. Inverse permittivity versus temperature (ϵr−1 vs. T) measurements suggest an unconventional response, potentially due to lattice strain induced by the larger ionic radius of Nd. The potential influence of doping concentration on the order of the ferroelectric transition is also explored. Overall, neodymium substitution in SBN ceramics enhances their ferroelectric properties, making them promising for advanced electronic applications.

Structural and electrical properties of Ni-doped MnZn ferrite synthesized via solid state reaction

Abstract MnZn ferrite is commonly studied due to its exceptional magnetic, electric, and catalytic properties, making it a promising material for hyperthermia applications, magnetic fluid, memory storage devices, drug delivery, virus detection, and photocatalysis. It was identified that divalent nickel cation substitution increases the ferrite conductivity and dielectric constant. This study targets to synthesize Ni-doped MnZn ferrite by a simpler, more convenient, and economic solid state reaction, and to investigate its influence on the structural and electrical properties of MnZn ferrite. Mn0.5-xNixZn0.5Fe2O4 (x=0.1 and 0.2) was synthesized via solid state reaction with calcination and sintering temperature at 1000 °C and 1200 °C, respectively. The structural and electrical properties of the resulting pellet were characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), and electrochemical impedance spectroscopy (EIS). The XRD profile, indexed as cubic spinel, indicated good crystallinity and no impurity peaks were detected. As Ni2+ dopant concentration increases, a decrease in lattice parameter and an increase in theoretical and apparent densities were observed. This is attributed to the smaller ionic radius and greater mass of Ni2+ relative to Mn2+. Varying Ni2+ concentration significantly modified the morphology of the ferrite. At higher Ni2+, less uniformity in shape and size was evident in the SEM micrograph since Ni promotes aggregation at the surface. An increase in dielectric constant was also observed with increasing Ni2+ molar concentration. Since Ni2+ presents a high tendency to occupy B sites, its substitution promotes Fe2+ migration to A sites, augmenting Fe2+/Fe3+ hopping resulting in an increase in polarization and dielectric constant.

Exploring the Impact of Elevated Pressure on the Structural Dynamics of TlInS2 Crystal (I): A First-Principles Investigation with XRD, Raman, and Hirshfeld Topology

The structural dynamics of Thallium Indium Disulfide (TlInS2) crystal under elevated pressures were comprehensively investigated using a combination of X-ray diffraction (XRD), Raman spectroscopy via first-principles calculations, and Hirshfeld surface (HS) analysis. This study aims to elucidate pressure-induced modifications in the crystal structure and their associated properties of TlInS2 crystal. The findings reveal significant structural transformations as pressure increases, with XRD patterns indicating lattice compression and a critical transition from semiconductor to conductor at pressure P=6.25GPa [42]. The calculations predict a reduction in bond lengths, specifically S1-In1 and S1-Tl2, alongside a corresponding decrease in lattice parameters and unit cell volume. Raman spectroscopy corroborates these changes through shifts in phonon modes. The HS analysis provides further insights into pressure-dependent alterations in intermolecular interactions, revealing changes in voids and surface characteristics. The data gained from TlInS2's structural behavior under pressure, contributing to the optimization of its functional properties for pressure-tunable applications in high-performance electronic and optoelectronic devices.

Indirect to direct band gap transition of ABI3 (A = Rb, Cs; B = Ca, Sr) perovskites under hydrostatic pressure for photovoltaic and optoelectronic applications: A DFT study

The objective of this study is to enhance the utilization of ABI3 (A = Rb, Cs; B = Ca, Sr) metal-halide perovskites in multiple forms of technological applications by investigating their structural, electronic, optical, and mechanical characteristics using the ab initio method. At ambient pressure, the geometry-optimized lattice constants for RbCaI3, RbSrI3, CsCaI3, and CsSrI3 are 6.19 Å, 6.45 Å, 6.22 Å, and 6.47 Å, respectively, consistent with prior research. Additionally, a significant decrease in lattice parameters and bond length is observed, which leads to increased levels of atomic interactions. Pressure narrows the band gap from the ultraviolet-to-visible region. This phenomenon promotes the transfer of electrons from the valence-to-conduction band, hence improving the performance of optoelectronic devices. Furthermore, a shift from an indirect to a direct band gap is induced by the application of pressure, which improves the material's suitability for photovoltaic applications. The covalent and ionic nature of Ca/Sr-I and Rb/Cs-I under pressure and without pressure conditions was determined using the charge density maps. Enhanced pressure significantly boosts optical absorption and conductivity in the visible spectrum, implying substantial potential for improving the efficacy of perovskite solar cells and photonic devices. Additionally, applied pressure significantly influences the mechanical properties of the entitled perovskites, leading to higher ductility and anisotropy. As a whole, this study offers insights into the scientific applications of non-toxic perovskites in different pressure environments.

Investigation of kesterite to stannite phase transition and band gap engineering in Cu2Zn1-xCoxSnS4 thin films prepared by sol-gel spin coating

In this study, the Cu2Zn1-xCoxSnS4 (CZn1-xCoxTS) films with partial cation substitution of cobalt are synthetized by sol gel spin coating, followed by sulfurization treatment. The incorporation of cobalt cation in the CZTS crystalline lattice as well as the phase transition from kesterite to stannite were confirmed by the X-ray diffraction (XRD) and Raman spectroscopy data. The XRD pattern shows peak-shifting toward higher 2θ by increasing the Co concentration, indicating a decrease in lattice parameters. The red shift of Raman peaks by increasing x from 0 to 0.6, confirms the phase transition. The CZn1-xCoxTS morphology was observed by scanning electron microscopy, showing large grain size as x increases and a good distribution of elements for all films. X-ray photoelectron spectroscopy was employed to study the valence of cations/anions and to probe the chemical bonds. The optical band gap showed a parabolic behavior versus the molar ratio Co/(Co + Zn), this deviation from Vegard’s law being induced by the difference in electronegativity between cobalt and zinc. The pure CZTS has a band gap of 1.47 eV, while for CZn0.6Co0.4TS the gap is 1.17 eV, which indicates that the incorporation of cobalt cation produces a red-shift of the band to band transition energy.

Investigations on the crystallographic stacking disordering and properties of novel Ga-containing in-plane chemically ordered (Cr2/3R1/3)2GaC (R=Y, Tb - Lu) i-MAX phases

Eight novel transition metal carbides, nanolaminated (Cr2/3R1/3)2GaC (R=Y, Tb, Dy, Ho, Er, Tm, Yb and Lu) with R in-plane chemical ordered occupation, have been synthesized with mainly Cmcm orthorhombic structure and monotonously decreased lattice parameters due to lanthanide contraction. Stacking disorderings and high-density slidings within c plane have been observed. Two characteristic in-plane sliding, along [100] or [1¯30]o directions have been analyzed with former one leading into the structural evolution between Cmcm and C2/c symmetry. Such an atomic scale co-existence of Cmcm and C2/c structures is explained by more negative charge for Ga and anisotropic bonding with Ga compared with A=Al case. Thus, the Vickers hardness, fracture strength and increased wear depth are reduced in representative (Cr2/3Lu1/3)2GaC i-MAX bulk compared with the (Cr2/3Lu1/3)2AlC counterpart.

Effects of La-Co Co-Substitution and Magnetic Field Pressing on the Structural and Magnetic Properties of SrM Hexaferrites

We carefully investigated the effects of La-Co co-substitution and magnetic field pressing (MFP) on the structural and magnetic properties of SrM hexaferrites. Samples composed of Sr1−xLaxFe12−xCoxO19 were sintered at 1230 °C for 2 h in air with sintering additives composed of 0.7 wt% CaCO3 and 0.7 wt% SiO2. A single M-type phase was confirmed to exist up to x = 0.3. Rietveld refinement revealed a slight decrease in lattice parameter a and the unit cell volume (Vcell) with an increasing x, while parameter c showed a significant decrease. The saturation magnetization (Ms) values increased from 70.90 to 72.40 emu/g with an increasing x from 0.0 to 0.15 and then decreased to 71.38 emu/g with further increasing of x to 0.3, while the anisotropy field (Ha) increased from 17.7 to 25.9 kOe, leading to a continuous increase in the intrinsic coercivity (Hci), from 3.52 to 5.00 kOe, respectively. Using the MFP process, the c-axis of M-type hexaferrite grains could be effectively aligned to the applied field direction, which significantly affected the microstructures and, thus, magnetic properties of samples. Unlike non-MFP samples, exhibiting a significant increase in the average grain size (davg) but almost unaltered average thickness (tavg) with an increasing x from 0.0 to 0.3, MFP-processed samples exhibited almost unaltered davg values but a continuous decrease in tavg. Consequently, the variation in remanent flux density (Br) versus x followed that of Ms versus x and thus exhibited the highest Br of 4.05 kG for x = 0.15, leading to the highest maximum energy product {(BH)max} of 3.62 MGOe. With an increasing x from 0.0 to 0.3, the Hci values continuously increased from 3.14 to 3.84 kOe mainly due to a continuous increase in Ha, although they were significantly lowered in comparison with those of non-MFP samples because of a large increase in Br for a given composition x. A higher Mr/Ms ratio always resulted in a larger (BH)max in our samples regardless of x. A careful comparison of the microstructures and magnetic properties between MFP and non-MFP samples provided valuable insights into a broad area of permanent magnet optimization.

Emergence of Perovskite and Hashemite-type phases in chromium doped (Ba0.90Sr0.10)(Fe1-xCrx)O3±δ oxides: Formation, Rietveld refinement and Raman spectra

Perovskite- and Hashemite-type oxides are relevant due to their applications as oxidizing agent, photocatalyst, nutrient, fuel cells, gas sensors, batteries materials. An attempt has been made here to synthesize (Ba0.90Sr0.10)(Fe1-xCrx)O3±δ(x = 0 – 1.0) and characterized with regards to structure and Raman vibrations. It depicts (a) pure cubic (Ba0.90Sr0.10)FeO3-δ phase, (b) cubic+orthorhombic, and (c) single orthorhombic (Ba0.90Sr0.10)CrO4 phase for x = 0–0.10, 0.20 – 0.80, and 1.0, respectively. It exhibits (i) decrease of cubic lattice parameter (ac)as 4.020 – 3.926 Å, (ii) expansion of orthorhombic unit cell, (iii) complete appearance of chromium in 6+ state for x = 1.0, and (iv) decrease of bond length and angle both with chromium. The bond lengths corresponding to Ba/Sr-O ∼ 2.84 Å, Fe-O ∼2.04 Å and Ba/Sr-O1 ∼ 3.227 Å, Ba/Sr-O2 ∼ 2.893 Å, Ba/Sr-O3 ∼2.859 Å have been derived for cubic (x = 0) as well as orthorhombic structure (x = 1.0), respectively. The bond angles e.g., Cr-O1-Cr ∼ 129°, Cr-O2-Cr ∼ 104.3° and Cr-O3-Cr ∼ 83.3° have been found for x = 1.0. Moreover, the bond Cr-O1 is compressed and Cr-O2 is more stretched than Cr-O3 bond. The morphology has also been changed to bigger size (nm) and shows different nature with chromium content. Raman spectra for Hashemite-type (Ba0.90Sr0.10)CrO4 reveal bands at ∼350, 360, 401, 425, 861, 886 and 904 cm−1 and arise due to symmetric (υ1, υ2) and antisymmetric (υ3, υ4) bending/ stretching mode. The present findings suggest potential applications of (Ba0.90Sr0.10)(Fe1-xCrx)O3±δ oxides.

Experimental and DFT studies of structural and optoelectronic properties of CdS, Zn doped CdS, and (Zn-Ni) co-doping CdS nanomaterials

Abstract This paper presents experimental and theoretical studies of binary semiconductor CdS, Zn:CdS, and (Zn-Ni) co-doped CdS. Thin films of pure CdS, Cd35ZnS36, and Cd34ZnNiS36 alloys grown by sol-gel spin coating were analyzed using X-ray diffraction, EDX, and UV-vis spectroscopy. The experimental results show the success of growing nanomaterials in hexagonal structures with crystallite sizes ranging from 1.6 to 2.11 nm and possessing band gaps in the region 2.30 -2.49 eV. Additionally, we investigate the structural and optoelectronic properties of these materials in the ground state using the density functional theory implemented in the WIEN2k software. The first principles calculations confirmed that the structural and optical properties of CdS align with the experimental results. For nanostructure Cd35ZnS36, the lattice parameters decrease, and the band gap increases to 2.85 eV with Zn doping. The (Zn-Ni) co-doped CdS structure optimization shows that the ferromagnetic configuration is more stable than the non-magnetic structure. The spin-polarized band structure investigations reveal that the majority spin-up channel is about 2.79 eV while the minority spin-down channel is around 2.19 eV. These results increase the importance of Zn:CdS and CdZnNiS alloys for optoelectronic and spintronic applications. The calculated optical properties of CdS, Zn:CdS, and (Zn-Ni) co-doped CdS show slight changes in refractive index and extinction coefficient with the doping and a quantitative agreement with the experimental findings.

Effects of Co on the microstructure evolution and mechanical properties of Ti-4Al-6Cr-5Mo-8 Nb alloy by ultrasonic vacuum melting

An investigation was conducted into the impact of low cobalt content on the microstructure and mechanical properties of titanium alloys. Ti-4Al-6Cr-5Mo-8 Nb-xCo (x = 0, 2, 3, 4, and 5) alloys were prepared by ultrasonic-assisted melting and casting. The changes in microstructure, mechanical properties, and the strengthening and toughening mechanisms were researched. Results show that, when the cobalt content increases from 0 to 5 wt%, the as-cast structure is all β phase. The lattice parameter of the β phase decreases from 0.3663 to 0.3114 nm, a 15% decrease. The size of primary β grains decreases from 676.8 to 310.7 μm, a 54% decrease. When the cobalt content exceeds 3 wt%, the segregation energy of cobalt increases and grain boundary segregation occurs. Grain refinement is due to constitutional supercooling caused by the β-stable element cobalt, as well as the solute drag caused by the differences in intragranular and grain boundary compositions. In addition, the size mismatch between cobalt and titanium atoms leads to lattice distortion. As the cobalt content increases from 0 to 3 wt%, the tensile strength increases from 918.1 to 1147.8 MPa, a 25% increase, while the fracture toughness increases from 51.7 to 59.7 MPa·m1/2, a 15% increase. At 5 wt% cobalt, the tensile strength and fracture toughness diminished to 247.5 MPa and 14.8 MPa·m1/2, respectively. The decrease in lattice parameters mainly lead to an increase in strength. The secondary crack leads to an increase in toughness. The decline in strength and toughness results from cobalt segregating at grain boundaries, leading to embrittlement.

Pressure-induced DFT evaluation of MSnI3 (M = K, Rb) perovskites for electronic phase transition and enhanced optoelectronic utilization

In optoelectronic device applications, perovskite materials have overtaken other compounds because of their exceptional power conversion efficiencies. Lead-based perovskites have found extensive use; however, their widespread adoption is hindered by the inherent toxicity associated with lead content. In contrast, lead-free metal halide perovskites have taken the dominant position in the commercialization of optoelectronic devices by offering high efficiency, affordability, flexibility, tunability, and environmental benefits. To better understand the structural, electronic, bonding, optical, elastic, and mechanical properties of the non-toxic MSnI3 (M = K, Rb) metal halides under different hydrostatic pressures, a first-principles simulation has been carried out with the use of density functional theory (DFT). Lattice parameters and electronic band structures have been computed using both the Generalized Gradient Approximation (GGA) and the non-local hybrid sX (Hartree-Fock screened exchange) functional. Utilizing the sX method results in enhanced band gap values for MSnI3 (M = K, Rb) perovskite compounds. The application of pressure has led to a decrease in both lattice parameters and band gaps, marking a transition from a semiconductor to a metallic state. The projection of the density of states and their electronic orbital contributions are also explored to evaluate the band structure tuning of MSnI3 (M = K, Rb) under pressure. The bond length calculation and the charge density mapping confirm the existence of both the ionic and covalent bonds in MSnI3 (M = K, Rb). Additionally, the pressure-induced calculation suggests that the bonds between both compounds will be stronger at high pressure. Increasing hydrostatic pressure causes a dramatic movement of the absorption edge of MSnI3 (M = K, Rb) perovskites into the low energy region (a red shift), which is revealed by the analysis of optical functions. The optical functions’ investigation indicates that the hydrostatic pressure allows the compounds even better for a number of possible uses. The mechanical qualities are a direct reflection of the ductile and anisotropic nature of the compounds, both of which are significantly influenced by the external pressure.

Study on the pathway of performance improvement and mechanism of Gd2O2S:Tb3+ green phosphor

To improve the luminescence performance of Gd2O2S:Tb3+, Gd2O2S:Tb3+, Tm3+, Gd2O2S:Tb3+, Dy3+, Tm3+ and Gd2O2S:Tb3+, Dy3+, Tm3+@SiO2 phosphors have been prepared by molten salt method. The samples are characterized using XRD, SEM, TEM, FT-IR, UV-Vis absorption spectroscopy, photoluminescence, cathodoluminescence and thermal stabilization tests. XRD tests and refinement results show that the crystal structure of the phosphor is still the hexagonal Gd2O2S crystalline phase and the lattice parameter decrease due to Dy3+/Tm3+ occupying the Gd3+ sites. SEM images and mapping of each element show that the particle grain and all expected elements distribute uniformly. TEM results illustrate that SiO2 coating is in an amorphous form on the surface of the powder grains. FT-IR tests indicate that SiO2 is present on the powder surface through Si-O-Gd bonding. The results of photoluminescence and cathodoluminescence show that the luminescence intensity increase 50% while adding Tm3+ into Gd2O2S:Tb3+, Gd2O2S:Tb3+, Dy3+ phosphors caused mainly by the energy transfer from Dy3+/Tm3+ to Tb3+. The core-shell structure of Gd2O2S:Tb3+, Dy3+, Tm3+@SiO2 has better photoluminescence and cathodoluminescence and the fluorescence lifetime remains unchanged while SiO2 coats phosphor. And it has good thermal stability. Its luminescence intensity at 425 K reaches 71.4% of that at room temperature, which is better than the corresponding value (46.4%) for the uncoated sample.

Quantum critical behavior of the hyperkagome magnet Mn3CoSi

β-Mn-type family alloys Mn3TX (T=Co, Rh, and Ir; X=Si and Ge) have a three-dimensional antiferromagnetic (AF) corner-shared triangular network, i.e., the hyperkagome lattice. The antiferromagnet Mn3RhSi shows magnetic short-range order over a wide temperature range of approximately 500 K above the Néel temperature TN of 190 K. In this family of compounds, as the lattice parameter decreases, the long-range magnetic ordering temperature decreases. Mn3CoSi has the smallest lattice parameter and the lowest TN in the family. The quantum critical point (QCP) from AF to the quantum paramagnetic state is expected near a cubic lattice parameter of 6.15 Å. Although the Néel temperature of Mn3CoSi is only 140 K, the emergence of the quantum critical behavior in Mn3CoSi is discussed. We study how the magnetic short-range order appears in Mn3CoSi by using neutron scattering, μSR, and bulk characterization such as specific heat capacity. According to the results, the neutron scattering intensity of the magnetic short-range order in Mn3CoSi does not change much at low temperatures from that of Mn3RhSi, although the μSR short-range order temperature of Mn3CoSi is largely suppressed to 240 K from that of Mn3RhSi. Correspondingly, the volume fraction of the magnetic short-range order regions, as shown by the initial asymmetry drop ratio of μSR above TN, also becomes small. Instead, the electronic-specific heat coefficient γ of Mn3CoSi is the largest in this Mn3TSi system, possibly due to the low-energy spin fluctuation near the quantum critical point. Published by the American Physical Society 2024

Gallium induced effect on magnetic, magnetostrictive and electrical properties of sintered NiFe2O4

This study investigates how the incorporation of Ga ions into the tetrahedral coordination sites affects the magnetic, magnetostrictive, and electrical properties of sintered NiFe2O4. All characterization was performed on the sintered NiFe2-xGaxO4 samples, which were synthesized using the autocombustion method. The sintered samples exhibit a single phase, wherein the lattice parameter decreases, and the particle size increases with the augmentation of Ga-content within the Ni-ferrite lattice. Saturation magnetization (MS) was found to be higher for x = 0.25 compared to the parent sample (x = 0), while for x = 0.5, MS was slightly lower than that of the parent sample. Both coercivity (HC) and Curie temperature (TC) exhibited a decrease with increasing 'x,' which can be attributed to the weakening of superexchange interactions (A-O-B) due to the presence of non-magnetic Ga ions. Furthermore, the maximum magnetostriction (λmax) also decreased with increasing 'x,' reflecting a magnetic dilution effect within the system. Electric modulus analysis of the dielectric response and the Jonscher power law fits AC conductivity propounded the long-range hoping for charge transportation. Also, the Cole-Cole fit of impedance spectra showed a combined effect of electrode-grain boundary, grain interior, and grain-grain boundary.

Исследование превращений переохлажденного аустенита при ступенчатой закалке стали 20Cr2Mn2SiNiMo

Currently, step quenching of steels in the temperature range of martensitic transformation, including quenching – partitioning, has found wide application in the automotive industry. Step quenching technology is successfully used to increase a set of properties, which most often include temporary tensile strength and relative elongation. The authors carried out a dilatometric study of the supercooled austenite transformations occurring in the 20Cr2Mn2SiNiMo steel, when implementing various options of step quenching with holding in the martensitic region. It was found that after single-stage quenching, single-stage quenching followed by tempering, and two-stage quenching, primary martensite, isothermal bainite, and secondary martensite are formed in various quantitative ratios. Using X-ray diffraction phase analysis, the amount of residual austenite was determined during step quenching. It has been shown that two-stage quenching makes it possible to stabilise up to 14 % of residual austenite, in the structure of the studied steel, at room temperature. Research has revealed that 20Cr2Mn2SiNiMo steel is characterised by a decrease in the crystal lattice parameter of the residual austenite, with an increase in its content in the steel structure. Uniaxial tensile and impact bending tests were carried out, and the values of the mechanical properties were determined. It has been found that during two-stage quenching, higher strength and elongation values, with lower values of relative contraction and impact strength are achieved compared to oil quenching and low-temperature tempering. The study showed that, with regard to the structural reliability of machine-building parts, step quenching is not the optimal heat treatment mode for the steel under study. The best combination of strength, ductility and impact hardness is achieved after quenching and low-temperature tempering.

Structural characterization, optical, and magnetic properties of MgTbxFe2−xO4 nano ferrite particles using a combustion technique

The citrate gel auto-combustion method was utilised to synthesis terbium-doped nanoparticles (NP) with considerable concentrations of magnesium ferrites, using the chemical formula MgTbxFe2−xO4 and an X range of 0.000 to 0.0030 (with an X step of 0.0005). At 300 K, X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transition electron microscopy (TEM), and magnetic characteristics were all determined. The XRD and TEM images indicate nanoscale ranges as well as the cubic spinel structure, which is merely phased, and confirm the normal crystallite size. The lattice parameter and volume decrease as density increases with doping of terbium. The images from the FESEM. It is evident that the grain clusters were found within the material. In the specimen's case, the highly interacting grains were found. The fourier-transformed infrared spectroscopy (FTIR) data clearly suggests that two metallic bands have formed, confirming the cubic spinel ferrites. There are two primary absorption bands visible between 200 and 650 cm−1. The UV–vis investigation demonstrates that the calculated direct band gap energy values have a violet shift. The band gab energy was reported in the range of 415.30 eV to 375.12 eV.The magnetic properties of the hysteresis loops indicate a transition from hard magnetic moments to soft magnetic moments. All magnetic properties were reduced when the Tb3+ ion was substituted. They are excellent for switching memory storage devices as well as telecommunications.

Microwave-Irradiation Suppresses the Jahn-Teller Distortion in Spinel LiMn2O4 Cathode Material for Lithium-Ion Batteries

Jahn-Teller (J-T) distortion remains the key challenge to realizing the full electrochemistry potential of the commercialized LiMn2O4 cathode material for lithium-ion batteries. In this work, the application of microwave irradiation to suppress the limiting J-T distortion in pristine LMO (LMO-p) materials and improve the electrochemistry of lithium-ion batteries has been reported. Unlike thermal heating, microwave irradiation inhibits J-T distortion. To establish the underlying science behind the impact of microwave irradiation, both the pristine (LMO-p) and the microwave-treated counterpart (LMO-m) are subjected to several characterization techniques, including synchrotron XRD, XPS, powder neutron diffraction (PND), MAS 7Li NMR, Raman and BET analysis. These techniques prove that LMO-m possesses the needed physico-chemical properties that explain: i) suppressed J-T distortion (such as an increased average Mn oxidation state (i.e., nMn ≥ 3.5+ or Mn4+/Mn3+ > 50%)), decreased lattice parameter, enhanced BET surface area, and enhanced structural crystallinity), and ii) improved electrochemical performance (such as increased specific discharge capacity, electronic and Li-ion transfer kinetics, and Coulombic efficiency). The findings in this work are relevant for the realization of low-cost and environmentally benign scale-up modification processes for LMO spinel and related cathode materials for the development of high performance lithium-ion batteries.

Phase decomposition of AlCrFeCoNiCu0.5 HEA thin films by vacuum annealing

The most attractive advantages of high entropy alloy (HEA) thin films are their excellent properties, such as high strength and high corrosion and oxidation resistance, with a lower material cost. However, the thermal stability of the HEA thin films is always controversial. This is critical since the thermal stability of metals and alloys is closely related to the material's performance at high temperatures and also determines the application field of the material. The question of how will the nanocrystalline high entropy alloy thin film perform in terms of thermal stability needs to be clarified urgently. In this research, the thermal stability of AlCrFeCoNiCu0.5 HEA thin film fabricated by cathodic arc deposition was investigated at 500 °C as a function of time during vacuum annealing. X-Ray Diffraction (XRD), High-Resolution Transmission Electron Microscopy (HRTEM) and Transmission Kikuchi Diffraction (TKD) were applied to analyze the chemistry and microstructure of HEA thin films in detail. The results showed that there was no obvious change in the elemental compositions of the films after annealing, but the elemental distribution of the annealed films was different from the as-deposited film, especially at the film surface and film-substrate interface for the 24 h-annealed sample. The existence of the FeCo phase with B2 structure was a significant sign to demonstrate that the spinodal decomposition occurred in the single face-centered-cubic (FCC) phase matrix of the film during annealing. Simultaneously, the segregation of Cu and Cr near the film-substrate interface and the penetration of Ni and Cu towards the Si substrate were clearly observed. These unusual phenomena indicated that the thermal stability of HEA was not always excellent. Also, it was noticed that a few Kirkendall voids forming at the film-substrate interface after 24 h of annealing would affect the adhesion of the film. Additionally, heat recovery and recrystallization were achieved by 500 °C annealing, which were confirmed by the decrease of lattice parameter and the increase of grain size in the 24 h-annealed thin film. Furthermore, the hardness and elastic modulus of the thin films before and after annealing were measured by nanoindentation. The results showed all the thin films exhibited excellent mechanical properties, and the optimal hardness and elastic modulus of 7.7 ± 0.3 GPa and 183.9 ± 4.4 GPa were obtained after 3 h-annealing.

Isotropic pressure induced structural, electronic, photocatalytic, elastic and mechanical properties of RbPbF3: GGA-PBE and HSE03 based computational estimation

The main objective of this study is to present a comprehensive computational analysis, with Generalized Gradient Approximations (GGA) and Heyd–Scuseria–Ernzerhof (HSE03) correlation functionals, of the structural, optoelectronic, photocatalytic and elastic properties of Rubidium Lead Fluoride (RbPbF3) under the systematic isotropic pressure range of 0–55 GPa. Under stress a systematic decrease in lattice parameters and band gap (4.869 eV − 1.105 eV) is observed upto 55 GPa. For comprehensive evaluation of band gap, PDOS and EPDOS have also been determined. Photocatalytic properties of RbPbF3 under stress demonstrate the best photocatalytic water-splitting potential, aligning with the band gap estimation. The significant variation in optical parameters is found with a varying stress array from 0–55 GPa. Optically this compound can be utilized as a UV detector because absorption bands are seen in the UV spectrum. The material exhibits mechanical stability, and ductile behavior, with ionic and covalent bonding. The anisotropic nature is observed in our estimated results.

Effects of Mn doping on the structural, linear and nonlinear optical properties of Gd2O3 nanoparticles

We report on the effects of Mn doping on the structural, linear, and nonlinear optical properties of Gd2-xMnxO3 nanoparticles (x = 0.00, 0.03, 0.05, and 0.10). The Gd2-xMnxO3 powders were prepared using sol-gel process. The x-ray diffraction technique shows that the Mn3+ doping results in a small decrease in lattice parameter and an increase in crystallite size. UV–visible measurements were carried out in the wavelength range of 200–800 nm. The direct optical band gap estimated using Tauc model decreases with increasing Mn content from 5.152 to 5.008 eV, while Urbach energy increases from 0.753 to 1.012 eV. Moreover, the insertion of Mn results in a significant enhancement in the optical parameters (refractive index, extinction coefficient, absorption coefficient, dielectric constants (ε', ε"), optical and electrical conductivity. The dispersion energy (Ed) increases from 24.13 to 30.1 eV, while the single oscillator energy (E0) declines lightly from 10.28 to 9.998 eV with the increase of Mn content. With Mn doping an enhancement in the static linear refractive index (n0) and high-frequency dielectric constant (ε∞) were also observed. Analysis of linear and nonlinear optical parameters shows that the presence of manganese enhanced the linear optical susceptibility (χ(1)), third-order non-linear susceptibility (χ(3)), and non-linear refractive index (n2). These optical results show the potential applications of Gd2-xMnxO3 nanoparticles (x = 0.00, 0.03, 0.05 and 0.10) in various optical devices.