Effect Of Al-substitution Research Articles

Effect of Al substitution on the magnetocaloric properties of Ni-Co-Mn-Sn multifunctional alloys

Ni-Mn-based metamagnetic shape memory alloys have been extensively studied due to their multifunctional properties including magnetocaloric effect (MCE), magnetoresistance effect, and magnetic-field-induced strain. However, the large intrinsic thermal hysteresis of these alloys sets a limit on further development for practical applications. Here, with a few atomic percent Al substitution, we greatly reduced the thermal hysteresis and transformation temperature interval while maintaining the large magnetization difference (ΔM) between austenite and martensite. The simultaneous achievement of a large ΔM and low thermal hysteresis leads to a remarkable enhancement in MCE upon Al substitution, and a maximum magnetic entropy change of 31.6 J/kg K is achieved under a field of 5 T in Ni39Co11Mn40Sn8Al2. Furthermore, our in situ high-energy X-ray diffraction experiments show that the Ni39Co11Mn40Sn8Al2 has good geometric compatibility between austenite and martensite, which accounts for the reduced thermal hysteresis in this alloy. This study is instructive for the development of high-performance magnetocaloric materials in the metamagnetic shape memory alloys.

Unraveling the Role of Al Substitution in Anionic Oxygen Activity of Ni-Rich Layered Oxide Cathodes

Ni-based layered oxides have attracted great attention for the development of high energy and high capacity Li-ion cathodes. The most popular Ni-based cathodes, LiNi x Mn y Co1-x-y O2 (NMC) and LiNi x Co y Al1-x-y O2 (NMC), are indeed derivatives of LiNiO2 by partially substituting Ni with Co, Mn or Al. The current trend to develop high-Ni and low-Co or Co-free layered Ni-based oxide cathodes, makes a strong push to the limit of Ni content in such layered oxides, leading to many common properties with their parent compound, LiNiO2. In fact, lithium nickel oxide often exists off-stoichiometry because of the presence of Ni2+ in the Li layer, which blocks the Li+ diffusion pathway upon lithiation/delithiation. Therefore, a second metal of a minimal content, such as Co or Al, which can somehow facilitate the formation of layered structure is still needed, although they are not strongly favored due to cost and sacrifice upon the use of inactive Al. In this work, a number of Al substituted lithium nickel oxides, LiAl x Ni1-x O2 (0 ≤ x ≤ 0.20), have been synthesized via a solid state reaction, showing good R m layered structure. Along with their parent LiNiO2, the oxygen activity in these compounds have been studied using combined synchrotron X-ray absorption spectroscopy (XAS), resonant inelastic X-ray scattering (RIXS) and differential electrochemical mass spectrometry (DEMS). The goal of this research is to elucidate the role of Al on the anionic oxygen activity in Ni-based layered oxides, including both reversible anionic oxygen redox and irreversible oxygen release during the electrochemical process. The electronic structure of transition metal and O was investigated at different states of charge to obtain a complete picture of cationic and anionic redox during the charge/discharge process. Beyond the redox chemistry, the effect of Al substitution on the phase transformation at highly delithiated states, dominated by H2 to H3 phase transformation for LiNiO2, as well as thermal stability was carefully studied. We hope this work helps provide a comprehensive picture of the role of Al substitution on the overall performance of Ni-based layered oxide cathodes.

Ga for Al substitution effects on the garnet phase stability and luminescence properties of Gd3GaxAl5-xO12:Ce single crystals

This research deals with the luminescence and physical properties of Gd3(Ga,Al)5O12:Ce single crystal set and it is a complementary study to analogous (Y,Gd)3Al5O12:Ce and (Gd,Lu)3Al5O12:Ce single crystal sets. Those three groups of materials show similar luminescence and physical properties. In this research, the influence of substitution Ga for Al in Gd3(Ga,Al)5O12:Ce single crystals on the luminescence and scintillation characteristics as well as thermodynamical stability of the garnet phase is studied, and it is compared to (Y,Gd)3Al5O12:Ce and (Gd,Lu)3Al5O12:Ce single crystal sets. The unbalanced substitution Ga for Al makes garnet phase thermodynamically unstable and leads to the formation of the multiphase system with luminescence centers in UV and visible spectral ranges. The wavelength-dispersive X-ray spectroscopy, X-ray powder diffraction analysis, photoluminescence and decay kinetic measurements reviled all phase types within multiphase crystals. Temperature dependent measurements were applied to determine the quenching mechanism for Ce3+ luminescence. The timing characteristics are studied as the function of Ga content.

MECHANOSYNTHESIS, CRYSTAL STRUCTURE, MAGNETIC AND ABSORPTION PROPERTIES OF Al SUBSTITUTED BaFe12O19

The Aluminums (Al) substituted on M-type barium ferrite (BaFe12O19) is one of the magnetic materials, which can be applied to the microwave band working at high frequencies. The purpose of this paper is to investigate the effect of Al substitution for Fe3+ ions on the structure, magnetic and absorption behavior of M-type barium ferrite. The sample was prepared by mechano-synthesis using high-energy milling (HEM). In this research, Fe ion in BaFe12O19 was substituted by Al ion to form BaFe12-xAlxO19 for x = 0.0,BaFe10Al2O19 for x = 2.0 and BaFe8Al4O19 for x = 4.0 which is called as BAl-0, BAl-2 and BAl-4 sample, respectively. The stainless steel balls were used for the milling with a ball-to-powder sample ratio of 5. The mixing and milling for each the sample was conducted for 5 hours in ethanol medium and dried at 100oC in oven for 24 hours and then followed by heat treatment at 1100°C during 1h in the atmosphere media. The sample was characterized using X-rays diffractometer (XRD), Scanning Electron Microscope (SEM), Vibrating Sample Magnetometer (VSM) and Vector Network Analyzer (VNA). The result indicates that the addition of Al ion lead to the change cell parameters, volume, and the particles size. The magnetic behavior such as magnetic coercivity (Hc), magnetization saturation (Ms) and remanent (Mr) changed significantly with the substitution of Al ions. The optimum reflection loss (RL) is found to be –35dB at 14GHz for BaFe10Al2O19 (BAl-2) sample. It is shown that Al substitutions change the particle size, ferromagnetic resonant frequency, and structural and magnetic behavior of M-type barium ferrite.

Effect of Al Substitution on Structural Stability and Topotactic Oxygen Release Rate of LaNi1–xAlxO3 with Perovskite Structure

Oxygen storage materials (OSMs) composed of transition metals are promising in the field of environment protection and energy conversion. In this study, we synthesized LaNi1–xAlxO3 (0 ≤ x ≤ 1.0) solid solutions with a rhombohedral perovskite structure and investigated the effect of Al substitution on their structural stability and oxygen release rate. X-ray diffraction measurements and thermogravimetric analysis revealed that Ni-containing LaNi1–xAlxO3 released/stored oxygen atoms topotactically and reversibly via the Ni3+ ↔ Ni2+ redox reaction. LaNiO3 decomposed into La2O3 and Ni0 at 470 °C in a reducing atmosphere (H2). However, Al-substituted LaNi1–xAlxO3 maintained their perovskite structure even at high temperatures (>800 °C for 0.6 ≤ x ≤ 1.0). The high structural stability of these compounds can be attributed to the suppression of oxygen vacancy ordering. Furthermore, LaNi0.2Al0.8O3 (x = 0.8) exhibited higher oxygen release rate (9.35 × 10–3 mol-O mol-Ni–1 s–1) than LaNiO3 (x = 0; 2.59 × 10–3 mol-O ...

Electronic Structure of LiCoO2 Surfaces and Effect of Al Substitution

The surface properties of LiCoO2 nanoplatelets, and their chemical modifications with Al3+, were studied using combined experimental and theoretical approaches. Our model shows that the electronic ...

Al substitution effects on phase stabilities and magnetic properties of tetragonal Mn3Ge

We have investigated Al substitution effects on phase stabilities and magnetic properties of Mn3Ge with tetragonal D022 structure. The lattice constant a is expanded, and the c is contracted by substituting Al for Ge. Consequently, the unit cell volume slightly increases with the increasing Al content, although Al atom has smaller ionic radius than Ge atom. These composition dependencies of the structural parameters are influenced by the number of the valence electrons rather than the ionic radius. Thermal stability of the D022 structure is enhanced by the Al substitution. The magnetic curves of the Al-substituted system mostly unchanged, suggesting that the structural properties such as the unit cell volume and the atomic distance between the Mn atoms play an important role for the magnetic properties of the alloy.

Characterization of metal hydrides for thermal applications in vehicles below 0 °C

Metal hydrides promise great potential for thermal applications in vehicles due to their fast reaction rates even at low temperature. However, almost no detailed data is known in literature about thermochemical equilibria and reaction rates of metal hydrides below 0 °C, which, though, is crucial for the low working temperature levels in vehicle applications.Therefore, this work presents a precise experimental set-up to measure characteristics of metal hydrides in the temperature range of −30 to 200 °C and a pressure range of 0.1 mbar–100 bar. LaNi4.85Al0.15 and Hydralloy C5 were characterized. The first pressure concentration-isotherms for both materials below 0 °C are published. LaNi4.85Al0.15 shows an equilibrium pressure down to 55 mbar for desorption and 120 mbar for absorption at mid-plateau and −20 °C. C5 reacts between 580 mbar for desorption and 1.6 bar for absorption at −30 °C at mid-plateau.For LaNi4.85Al0.15, additionally reaction rate coefficients down to −20 °C were measured and compared to values of LaNi5 for the effect of Al-substitution. The reaction rate coefficient of LaNi4.85Al0.15 at −20 °C is 0.0018 s−1. The obtained data is discussed against the background of preheating applications in fuel cell and conventional vehicles.

Effect of Al substitution on the structural, electric and impedance behavior of cobalt ferrite

Cobalt ferrite nanoparticles doped with Al ions, Co1-x AlxFe2O4 (x = 0, 0.1, 0.3 and 0.5) were prepared by sol-gel method. An attempt is made to understand if and how the Al substitution affect the structural and electrical properties of cobalt ferrite. The X-ray diffractometer (XRD) analysis confirmed the single phase cubic spinel structure of the nanocrystals. Crystallite size, lattice constant and x-ray density were calculated from the XRD data. A reduction in crystallite size and lattice parameter values were found with increased dopant concentration. Tetrahedral and octahedral hopping lengths and other related parameters were also calculated from the XRD data. The effect of doping on morphological features were monitored using Field emission scanning electron microscope (FESEM) images. The Fourier transform infrared spectrometer (FTIR) spectral analysis confirmed the cubic spinel structure of cobalt ferrite nanoparticles with the occurrence of characteristic absorption bands. Improved values of dielectric constant, low dielectric loss and resistivity were displayed by Al doped ferrite samples. Detailed impedance spectroscopy analysis with the help of Cole-Cole plot explored the capability of the Al doped cobalt ferrite to be suitable for high frequency applications and magnetic memory devices.

Average, electronic, and local structures of LiMn2-xAlxO4 in charge-discharge process by neutron and synchrotron X-ray

The effect of Al substitution in LiMn2-xAlxO4 on the charge-discharge process was investigated by average, local, and electronic structure analyses. A Rietveld analysis of the neutron and synchrotron X-ray diffractions was performed for LiMn2O4 and LiMn1.8Al0.2O4 during the charge-discharge process. The change range of the distortion parameters, λ and σ2, of the (Mn, Al)O6 in LiMn1.8Al0.2O4 during the charge-discharge was smaller than that of LiMn2O4. Using the Maximum Entropy Method, the covalent change between the 16d site and 32e site was mitigated by the Al substitution, which indicated stabilization of the MO6 octahedra during the charge-discharge process. The PDF analysis of the neutron total scattering data was performed for LiMn2O4 and LiMn1.8Al0.2O4 before the charge-discharge. The σ2 of AlO6 was smaller than that of MnO6, which indicated that distortion of the MO6 octahedra was locally mitigated by the Al substitution. The distortion range of MnO6 was reduced by the Al substitution that improved the cycle performance.

The quaternary system Sm-Fe-Mo-Al and the effect of Al substitution on magnetic and structural properties of its ThMn12 phase

The Fe-rich corner of the quaternary system Sm-Fe-Mo-Al is studied at isothermal conditions. The phase equilibria of ferromagnetic SmAlxFe10−xMo2 with adjacent phases, especially Sm2AlxFe15.7−xMo1.3, are observed for 1000 °C. Existence ranges are studied by SEM/EDX on samples with various compositions. Magnetic and structural properties were obtained by VSM(PPMS) as well as Permagraph measurements while structural relations were tracked by XRD. Al can be substituted for Fe up to x = 6.5 accompanied by a decrease in high field (8 MA/m ≈ 10 T) polarization from 0.66 T (x = 0.0) to 0.44 T (x = 2.0). Respective Curie temperatures of SmAlxFe10−xMo2 and Sm2AlxFe15.7−xMo1.3 initially increase with Al content reaching a maximum of ≈125 °C at x = 0.5 and ≈135 °C at x = 1.0, respectively. Further Al substitution decreases TC. The coercive fields of optimally annealed nanocrystalline powders decrease slightly from 153 kA/m for x = 0.0–139 kA/m for x = 0.8 and drops to 38 kA/m for x = 2.0. XRD data indicates that lattice parameters of SmAlxFe10−xMo2 continuously increase with Al content. The simultaneous refinement of X-ray and neutron diffraction patterns confirms that Mo prefers 8i sites in the ThMn12 structure and that Al occupies equally 8i and 8j in a ratio of 1:2.

Theoretical investigation of C-(A)-S-H(I) cement hydrates

The atomic-level understanding of the correlation of chemical, electronic and bonding behavior to mechanical properties of complex multi-component calcium (alumino)silicate hydrates [C-(A)-S-H] (The Cement Chemist Notation heavily used in this manuscript refers to C=CaO; A=Al2O3; S=SiO2; H=H2O or –OH), which is among the main binding phases of concrete could provide a point of departure for the study of cement behavior. In this paper, models of highly ordered C-(A)-S-H(I) are proposed and investigated. These models have been optimized and constructed in close relation and guidance of relevant experiments. The focus of the work is on illuminating the effect of Al substitution on chemical and mechanical properties of highly ordered synthetic cement phases. Furthermore, we show the importance of hydrogen bonds to mechanical properties in cements. We show, for the first time, that in the absence of vacancies in Dreierketten chains, the Al substitution in bridging sites reduces the mechanical anisotropy of C-(A)-S-H(I) cement. The study also shows the average partial charge of O, H, Si of different structural units are effectively independent of the chemical environment. This finding could have profound implications upon relevant classical molecular dynamics force fields for cements and could lead to further improvements in the modeling capabilities.

Microstructure, Martensitic Transformation, and Inverse Magnetocaloric Effect in Ni48Mn39.5Sn12.5−xAlx Metamagnetic Shape Memory Alloys

The effect of Al substitution on microstructure, martensitic transformation and magnetocaloric properties in Ni48Mn39.5Sn12.5−xAlx (x = 0, 1, 2, 3) alloys is reported. At room temperature, depending on Al concentration, the alloys have typical Heusler L21 austenite structure and/or orthorhombic martensite structure with Pmma space group. A secondary Ni-Mn-Al phase also appears already for low Al concentrations (x ≥ 1). On cooling, irrespective of Al substitution, all the samples show ferromagnetic type ordering below 303 K in the austenite phase. The martensitic transition temperature varies with Al content. All the alloys undergo magnetic field-induced reverse martensitic transformation giving rise to an inverse magnetocaloric effect. The largest magnetic entropy change (8.5 J·kg−1·K−1) is observed near 280 K for the Ni48Mn39.5Sn12.5 alloy.

Effect of Al substitution on the enhanced electrochemical performance and strong structure stability of Na3V2(PO4)3/C composite cathode for sodium-ion batteries

In this study, a promising cathode material in Na-ion batteries, Al-doped NASICON-type Na3V2-xAlx(PO4)3/C (0≤ × ≤0.03) samples are synthesized and characterized. The doping effects on the crystal structure are investigated by XRD and XPS, indicating that low dose of Al3+ doping generates no damage on the structure of the material, and aluminum is substituted for the vanadium site successfully. Electron microscopy and Raman data show that amorphous carbon coated on the matrix can enhance the electron conductivity. The electrochemical kinetic response of Al3+ doping are tested based on “slow-charge and rapid-discharge” electrochemical mode, results from before and after the cycles show that the doping samples have strong structure stability and excellent electrochemical performance because of low internal resistances and high ion conductivity. Thus, Na3V1.98Al0.02(PO4)3/C exhibits an initial reversible capacity of 102.7 mAh g−1 at 10 mA g−1 in the potential range between 2.3 and 3.8 V and delivers a discharge value of 95 mAh g−1vs. 59.9 mAh g−1 of NVP/C at current density of 70 mA g−1 discharge after 50 cycles. The ionic conductivity of Na3V1.98Al0.02(PO4)3/C sample at 3.4 V after 50 cycles at 10 mA g−1 charge 200 mA g−1 discharge is 1.31 × 10−12 cm2s−1, four orders of magnitude higher than the undoped one(7.79 × 10−17 cm2s−1).

Effect of Al substitution on the structural and magnetic properties of Co-Zn ferrites

In this work we investigate the effect of aluminum (Al) substitution on the structural, morphological and magnetic properties of Co0.5Zn0.5AlxFe2−xO4 (x = 0.0, 0.05 and 0.1) prepared by sol-gel method. The structural and magnetic properties are performed by using X-ray powder diffraction (XRD), scanning electron microscope (SEM), Fourier transform infrared spectra (FT-IR) and Vibrating Sample Magnetometer (VSM) studies. The XRD data revealed the formation of single phase cubic spinel with crystallite sizes around 45.83–51.84nm for Al substituted samples. Two significant absorption bands around 600 and 400cm−1 are observed from FT-IR spectra of the samples under investigation, which confirmed the formation of a single-phase cubic spinel. Interionic bond lengths and bond angles confirm the solubility of Al in the spinel lattice and support the observed variation in magnetic properties. Using a vibrating sample magnetometer (VSM), saturation magnetization and coercivity are measured. A decrease in lattice parameter and saturation magnetization with increasing Al concentration is attributed to the difference in the ionic radii and weakening of exchange interactions.

The effect of Al substitution on the structural and magnetic properties of epitaxial thin films of epsilon ferrite

Epitaxial growth of aluminum substituted epsilon ferrite by pulsed laser deposition on strontium titanate and yttrium-stabilized zirconium substrates is demonstrated for a wide range of aluminum substitution. Linear decrease of the out-of-plane lattice parameter with aluminum substitution correlates with the decrease of the coercive magnetic field, while the magnetization first increases and then decreases with increasing aluminum concentration. A characteristic inflexion in the hysteresis loops has been attributed to the presence of a small quantity of magnetite. Epitaxial growth on yttrium-stabilized zirconium is technologically significant due to its use as buffer layer for the growth of complex oxides on silicon.

Effect of Al Substitution in Structural and Magnetic Properties of MnCr2O4

Single-phase samples of Mn(Cr1−x Al x )2O4 (x = 0 – 0.30) with cubic spinel structure were prepared and the lattice constant is found to decrease from a = 8.4396 A for x = 0 to a = 8.3801 A for x = 0.30. The substitution of Al at Cr site is confirmed from the blue shift of Raman modes. Magnetization measurements and analysis show all the prepared samples exhibit ferrimagnetic transition with transition temperature in the range of 46 K for x = 0 to 33 K for x = 0.30. The saturation magnetization (M s ) and the estimated anisotropy constant (K) show an anomalous behavior up to x = 0.10 and beyond that they decrease monotonously. They are explained by considering different site preferences of Al 3+ ions as the doping concentration is increased. The theoretical and experimental effective magnetic moment of the samples is found to be comparable and it decreases with increase in Al concentration.

Effect of Al Substitution on Structural, Magnetic, and Magnetocaloric Properties of Er6Fe23−xAlx (x = 0 and 3) Intermetallic Compounds

The structural, magnetic, and magnetocaloric properties of Er6Fe23−xAlx (x = 0 and 3) intermetallic compounds have been studied systematically. Samples were prepared using the arc furnace by annealing at 1073 K for one week. Rietveld analysis of XRD shows the formation of pure crystalline phase with cubic Fm-3m structure. Refinement results show that the unit cell volume decreases with increasing Al content. The Curie temperature Tc of the prepared samples was found to be strongly dependent on the aluminum content. This reduces magnetization and the ferrimagnetic phase transition temperature (Tc) from 481 K (for x = 0) to 380 K (for x = 3), is due to the substitution of magnetic element (Fe) by non-magnetic atoms (Al). With the increase of the Al content, a decrease in the values of magnetic entropy is observed. The magnitude of the isothermal magnetic entropy (|∆SM|) at the Tc decreases from 1.8 J/kg·K for x = 0 to 0.58 J/kg·K for x = 3 for a field change 14 kOe. Respectively, the relative cooling power (RCP) decreases with increasing Al content reaching 42 Jkg−1 for x = 0 to 28 Jkg−1 for x = 3.

Structural and electronic properties of Fe(AlxGa1–x)3 system

FeGa3 is a well known intermetallic semiconductor with a band gap, which is induced by d-p hybridization. In this work, we present the results of experimental and theoretical studies on the effect of Al substitution in FeGa3, obtained by X-ray diffraction (XRD) study, temperature dependent resistivity measurement, room temperature Mössbauer measurement, and density functional theory based electronic structure calculations. It is observed that up to x = 0.178 in Fe(AlxGa1–x)3, which is the maximum range studied in this work, Al substitution reduces the lattice parameters a and c, preserving the parent tetragonal P42/mnm crystal structure of FeGa3. Rietveld refinement of the XRD data shows that Al atoms replace Ga atoms located at the 8j sites in FeGa3. A comparison of the trends of the lattice parameters and energy band gap obtained from the calculations and experimental measurements also confirms that Al atoms primarily replace the Ga atoms in the 8j site. The band gap of Fe(AlxGa1–x)3 for x = 0.178 is reduced by ≈24% as compared to FeGa3. The system thus has a lot of promise for applications in band gap engineering in infra-red devices.

Effect of Al substitution for Ga on the mechanical properties of directional solidified Fe-Ga alloys

Alloys of Fe82Ga18−xAlx (x=0, 4.5, 6, 9, 12, 13.5) were prepared by directional solidification technique and exhibited a <001> preferred orientation along the axis of alloy rods. The saturation magnetostriction value of the Fe82Ga13.5Al4.5 alloy was 247ppm under no pre-stress. The tensile properties of alloys of Fe82Ga18−xAlx at room temperature were investigated. The results showed that tensile ductility of binary Fe-Ga alloy was significantly improved with Al addition. The fracture elongation of the Fe82Ga18 alloy was only 1.3%, while that of the Fe82Ga9Al9 alloy increased up to 16.5%. Addition of Al increased the strength of grain boundary and cleavage, resulting in the enhancement of tensile ductility of the Fe-Ga-Al alloys. Analysis of deformation microstructure showed that a great number of deformation twins formed in the Fe-Ga-Al alloys, which were thought to be the source of serrated yielding in the stress-strain curves. The effect of Al content in the Fe-Ga-Al alloys on tensile ductility was also studied by the analysis of deformation twins. It indicated that the joint effect of slip and twinning was beneficial to obtain the best ductility in the Fe82Ga9Al9 alloy.