Substitutional Elements Research Articles

Influence of Fe on the Hydrogen Storage Properties of LaCeNi Alloys.

LaNi5 intermetallic compounds with a hexagonal CaCu5 type structure can react reversibly with hydrogen. The element substitutions in LaNi5 can significantly change the hydrogenation properties, allowing to tune them to a large extent. It could be very advantageous to partially replace Ni or La with other elements to reduce the cost of this alloy as well as the equilibrium pressure of absorption and desorption. The hydrogen storage properties of ball-milled AB5 alloys containing the elements La, Ce (A-rare elements) and Ni, Fe (B-transition metals) were studied in this paper. Although the substitution of Ni (atomic radius 1.49 Å) with Fe atom (atomic radius 1.56 Å) increased the unit cell volume from 86.4149 to 87.947 5 Å3 of the LaNi5 phase, its hydrogen storage capacity was still close to the value 1.4 wt %. The enthalpy (ΔH) of hydride formation for hydrogen absorption and desorption of the experimental alloys was in the range of 29-32.6 kJ/mol. A very favorable effect of Fe on the sorption properties was found in the significant reduction of the equilibrium pressure of absorption and desorption. These studied experimental Fe-containing alloys were able to store hydrogen at 300 K and with pressure under 0.1 MPa. The fastest sorption kinetics of hydrogen was found in alloys with FeNi phase particles located on the surface of the powder. However, if the FeNi phase was segregated at the grain boundaries, it acted as a barrier limiting the growth of the hydride phase. This led to a decrease of the hydride sorption kinetics.

Realidad aumentada en cirugía hepato-bilio-pancreática. Una tecnología al alcance de la mano

Augmented reality is a technology that opens new possibilities in surgery. Its implementation in a hepatobiliary-pancreatic surgery unit is presented in relation to preoperative planning, intraoperative support and teaching.For surgical planning, 3D CT and MRI reconstructions have been used to evaluate complex cases, making the interpretation of the anatomy more precise and the planning of the technique simpler.At an intraoperative level, it has allowed remote holographic connection between specialists, the substitution of physical elements for virtual elements, and the use of virtual consultation models and surgical guides.In teaching, new lessons include the retransmission of a surgery with the support of virtual elements for a better understanding by the students.Being the experience satisfactory, augmented reality could be applied in the future of hepatobiliary-pancreatic surgery to improve its results.

Microstructures and wear behaviors of WC particle reinforced nickel-based composites fabricated by selective laser melting

To improve the mechanical performance of popular Nickel alloys, in this study, selective laser melting method was introduced to print IN718 alloy composites (WC/IN718) by using Tungsten carbide (WC) as reinforcement particles. The effects of WC content (10-20 wt%) on microstructure evolution and mechanical performance of the printed composites were analyzed comprehensively. It was found, with proper addition of WC reinforcement particles, desired microstructures and mechanical properties can be achieved in the printed composites. WC particles could distribute uniformly in the matrix and excellent metallurgical bonding could be obtained at the heterogeneous interface between the WCP and the IN718 matrix. Under strong laser irradiation, the surface of WC particles could be melted and the decomposed W and C atoms could diffuse into the matrix under strong laser irradiation. WC-W2C/MxC/IN718 (M representing Ni, Cr, Fe, Ti, Nb) sandwich structure was formed due to the substitution of matrix element for W and C element in WC particles. When the added WC particle content increases from 0 to 20 wt%, the hardness of the printed WC/IN718 composite can increase from 304.8 HV to 421.3 HV. Its wear resistance was found to first increase and then decrease due to the transition of the wear mechanism. Among all the printed composites, 15 %WC/IN718 has the best wear resistance and smallest coefficient of friction. The ranking of the wear resistance of the printed composites was found to be 15 %WC/IN718 > 10 %WC/IN718 > 20 %WC/IN718 > IN718.

Laboratory and calorimetric monitoring of medical nutrition therapy in intensive and intermediate care units : Second position paper of the Section Metabolism and Nutrition of the German Interdisciplinary Association for Intensive Care and Emergency Medicine (DIVI)

This second position paper of the Section Metabolism and Nutrition of the German Interdisciplinary Association for Intensive Care and Emergency Medicine (DIVI) provides recommendations on the laboratory monitoring of macro- and micronutrient intake as well as the use of indirect calorimetry in the context of medical nutrition therapy of critically ill adult patients. In addition, recommendations are given for disease-related or individual (level determination) substitution and (high-dose) pharmacotherapy of vitamins and trace elements.

Strategy for Co-Enhancement of Remanence-Coercivity of RE-Fe-B Sintered Magnets with High Ce-Content: Appropriate La Substitution.

The development of low-cost RE-Fe-B sintered magnets with large La/Ce content is of great significance for the balanced utilization of rare earth (RE) resources, but it is limited by reduced magnetic properties. In this work, the coercivity (Hcj ), remanence (Br ), maximum energy product [(BH)max ], and temperature stability are simultaneously enhanced for magnets with LaCe accounting for 40wt% of the total RE. The synergistic regulation of the REFe2 phase, Ce-valence, and grain boundaries (GBs) in RE-Fe-B sintered magnets is realized for the first time by introducing appropriate La elements. The La elements inhibit the generation of the REFe2 phase and tend to stay in the triple junctions, promoting the segregation of the RE/Cu/Ga elements and contributing to the formation of Ce/Nd/Cu/Ga-rich continuous thicker lamellar GBs, and as a result, weakening the detrimental effect on HA caused by La element substitution and enhancing Hcj . In addition, partial La atoms entering the RE2 Fe14 B phase are beneficial for improving the Br and temperature stability of the magnets and promoting the Ce3+ ion ratio, which also provides additional benefit for Br . The findings provide an effective and feasible way to co-enhance the remanence and coercivity of RE-Fe-B sintered magnets with high Ce content.

Positive correlation of Nb/Cr doping with dehydrogenation performance of ZrCo-based hydrides

It is well known that element substitution is vital to an improvement of hydrogen storage capacity degraded by hydrogen-induced disproportionation of zirconium-cobalt (ZrCo) alloy. Contrary to other studies, this work is devoted to investigating the hydrogen desorption behavior of Zr1-xNbxCo1-yCryH3 (x = 0–0.25 and y = 0–0.125) systems formed by Nb substitution and Nb/Cr co-substitution in the ZrCoH3 crystal using the first-principles calculations based on the density functional theory. Firstly, the preferred positions of Nb and Nb/Cr substitutions are determined through the minimum total energy. Lattice constants and the density of states are employed to characterize the bonding behavior between atoms. The thermodynamic properties of Zr1-xNbxCo1-yCryH3 are also assessed by the enthalpy of formation and equilibrium hydrogen pressure. It is shown that both the thermodynamic stability and dehydrogenation temperature of ZrCoH3 decrease by increasing the Nb content, which is attributed to the fact that the Zr–H and Co–H binding capabilities are weakened by the presence of Nb. In addition, there are weaker thermal stability, lower dehydrogenation temperature, smaller volume of 8e site, and comparable volume of the hydride after ZrCoH3 is co-substituted by Nb and Cr, thereby promoting the hydrogen release and enhancing the anti-disproportionation performance. Clearly, both Nb doping and Nb/Cr co-doping possess a positive effect on the hydrogen desorption ability of ZrCoH3. More importantly, it is discoverable that compared to other substitution systems, the dehydrogenation temperature is the least for the Zr0.75Nb0.25Co0.875Cr0.125 hydride, highlighting that Nb and Cr co-substitution is more beneficial to improving the dehydrogenation performance of ZrCo-based alloy.

Cold welding adhesion for spacecraft repair: Experiment design and roadmap

Collisions with micrometeoroids and space debris can perforate spacecraft shields and hulls; in-situ repair or substitution of the damaged elements is currently considered a complex task, in particular the case of crewed modules with pressurized elements. In this context, cold-welding can overcome the current technological difficulties allowing fast and safe repairing procedures. To date, it has been shown that similar metallic materials can fuse or weld at ambient temperatures provided that there are sufficiently high contact forces. In the space environment this fusion is aided by the fact that the joint surfaces do not re-oxide after wear and, as a consequence, atomic diffusion of the metal occurs at lower contact forces. It has also been demonstrated that, even under terrestrial conditions, the action of a low fretting load can nearly double this adhesion force.In this paper, the suggested utilization of cold-welding phenomenon for spacecraft hull repair is described, as well as a verification road map to demonstrate its feasibility. It is proposed to develop an experimental test rig to apply custom repair patches of different materials to pre-damaged metallic structures and monitor the performance the adhered joint in low orbit and during re-entry. The test samples will include simple plates, Whipple shields, and sandwich panels that have been subjected to hypervelocity impacts. In the first phase, the cold-welding phenomena will be investigated in ground laboratories and validated in a vacuum chamber; afterwards, it is proposed to repeat the experiment in microgravity conditions, during a sounding rocket flight. Results will include an assessment of the contact forces necessary to apply the repair patch and an evaluation of the structural properties of the refurbished systems.

Role of Substitution Elements in Enhancing the Structural Stability of Li-Rich Layered Cathodes.

Element doping/substitution has been recognized as an effective strategy to enhance the structural stability of layered cathodes. However, abundant substitution studies not only lack a clear identification of the substitution sites in the material lattice, but the rigid interpretation of the transition metal (TM)-O covalent theory is also not sufficiently convincing, resulting in the doping/substitution proposals being dragged into design blindness. In this work, taking Li1.2Ni0.2Mn0.6O2 as a prototype, the intense correlation between the "disordered degree" (Li/Ni mixing) and interface-structure stability (e.g., TM-O environment, slab/lattice, and Li+ reversibility) is revealed. Specifically, the degree of disorder induced by the Mg/Ti substitution extends in the opposite direction, conducive to sharp differences in the stability of TM-O, Li+ diffusion, and anion redox reversibility, delivering fairly distinct electrochemical performance. Based on the established paradigm of systematic characterization/analysis, the "degree of disorder" has been shown to be a powerful indicator of material modification by element substitution/doping.

Modulations in Superconductors: Probes of Underlying Physics.

The importance of modulations is elevated to an unprecedented level, due to the delicate conditions required to bring out exotic phenomena in quantum materials, such as topological materials, magnetic materials, and superconductors. Recently, state-of-the-art modulation techniques in material science, such as electric-double-layer transistor, piezoelectric-based strain apparatus, angle twisting, and nanofabrication, have been utilized in superconductors. They not only efficiently increase the tuning capability to the broader ranges but also extend the tuning dimensionality to unprecedented degrees of freedom, including quantum fluctuations of competing phases, electronic correlation, and phase coherence essential to global superconductivity. Here, for a comprehensive review, these techniques together with the established modulation methods, such as elemental substitution, annealing, and polarization-induced gating, are contextualized. Depending on the mechanism of each method, the modulations are categorized into stoichiometric manipulation, electrostatic gating, mechanical modulation, and geometrical design. Their recent advances are highlighted by applications in newly discovered superconductors, e.g., nickelates, Kagome metals, and magic-angle graphene. Overall, the review is to provide systematic modulations in emergent superconductors and serve as the coordinate for future investigations, which can stimulate researchers in superconductivity and other fields to perform various modulations toward a thorough understanding of quantum materials.

First principles study in two-dimensional antiferromagnetic Mn2Cl8 with strain-controllable and hydrogenation

With the rapid development of spintronics, two-dimensional antiferromagnetic materials have attracted much attention because of their unique physical properties. Here, the monolayer Mn2Cl8 is discovered to be an intrinsically antiferromagnetic semiconductor in current work. The results show that monolayer Mn2Cl8 and Mn2Cl4X4 (X = F, Br) are stable semiconductors with indirect bandgaps of 0.34eV, 0.95eV, and 0.55eV, respectively, and Mn2Cl8 has a Néel temperature (TN) of 245 K. In the systematic study of strain effects, TN changes significantly under strains from −4% to 4% when the antiferromagnetic ground state is not affected. And the compression strain can increase TN to 469 K due to the enhancement of antiferromagnetic coupling of the nearest adjacent magnetic atoms. Moreover, the bandgap and TN of monolayer Mn2Cl8 can be tuned by hydrogenation. This work finds that elemental substitution, strains, and hydrogen passivation is efficient routes to tune the electronic properties of monolayer antiferromagnetic semiconductor Mn2Cl8.

Modification of BaTiO3 for diversified applications by single Nd element substitution with wide doping range

Modification of BaTiO3 for diversified applications by single Nd element substitution with wide doping range

Lu–H–N Phase Diagram from First-Principles Calculations

Employing a comprehensive structure search and high-throughput first-principles calculation method on 1561 compounds, the present study reveals the phase diagram of Lu–H–N. In detail, the formation energy landscape of Lu–H–N is derived and utilized to assess the thermodynamic stability of each compound that is created via element substitution. The result indicates that there is no stable ternary structure in the Lu–H–N chemical system, however, metastable ternary structures, such as Lu20H2N17 (C2/m) and Lu2H2N (), are observed to have small E hull (< 100 meV/atom). It is also found that the energy convex hull of the Lu–H–N system shifts its shape when applying hydrostatic pressure up to 10 GPa, and the external pressure stabilizes a couple of binary phases such as LuN9 and Lu10H21. Additionally, interstitial voids in LuH2 are observed, which may explain the formation of Lu10H21 and LuH3–δ N ε . To provide a basis for comparison, x-ray diffraction patterns and electronic structures of some compounds are also presented.

Proton absorption and penetration behaviors in Pt‐supported graphene

AbstractThe proton (H+) conductivity is very crucial for graphene applications in the field of proton membrane fuel cell (PEMFC), and the absorption and penetration of H+ are fundamental steps for the H+ conduction. In order to improve the H+ conductivity in graphene, loading catalytically active metals such as Pt on the graphene surface is an effective method. First‐principles calculations were thus employed to investigate the absorption and penetration behaviors of H+ on Pt‐supported graphene, and the doping effect of substitutional elements such as B, N, and S were also involved. It is found that the absorption and penetration behaviors of H+ on Pt‐supported graphene depend strongly on the loaded Pt atoms and doped elements. From the viewpoint of absorption energy, N is favorable for the H+ absorption in Pt‐supported graphene, while B and S are unfavorable. From the perspective of penetration barrier, B‐doping is beneficial for the penetration of H+ in Pt‐supported graphene, while N‐ and S‐doping are unbeneficial. On the other hand, Pt loading has a positive effect on the H+ absorption on pristine, B‐ and N‐doped graphene, while has a negative effect on S‐doped graphene. Meanwhile, Pt loading has a positive effect on the penetration of H+ in pristine, B‐, N‐ and S‐doped graphene. The absorption and penetration behaviors of H+ in Pt‐supported graphene are closely dependent on electronic properties, and will be influenced by the introduction of impurity elements.

Manipulate the magnetic and electronic states in NiCo2O4 films through protonation

Element doping and substitution have been widely used for the engineering of the electronic structure and macroscopic magnetic properties of various materials. However, traditional doping process does not allow further optimization after preparation of the samples. Hydrogen annealing-induced protonation has emerged as a powerful method for the efficient control of uniaxial lattice expansion to modulate the physics properties of the otherwise inaccessible novel correlated phases in oxide thin-films. Here, we report the modulation of the magnetic moment, magneto-transport and electrical-transport in inverse-spinel NiCo2O4 (NCO) by protonation. Strong dependence of saturation magnetic moment and electrical conduction on deposition temperature and proton doping parameters has been systematically investigated. The magnetoresistance ratio of the protonated NCO could be increased by 400% by engineering of the doping condition and thus the phase configuration. These findings indicate that protonation is one effective strategy for regulation and optimization of NCO-based magnetic and electric devices.

Atomistic insights into the inhomogeneous nature of solute segregation to grain boundaries in magnesium

In magnesium alloys with multiple substitutional elements, solute segregation at grain boundaries (GBs) has a strong impact on many important material characteristics, such as GB energy and mobility, and therefore, texture. Although it is well established that GB segregation is inhomogeneous, the variation of GB solute composition for random boundaries is still not understood. In the current study, atomic-scale experimental and simulation techniques were used to investigate the compositional inhomogeneity of six different GBs. Three-dimensional atom probe tomography results revealed that GB solute concentration of Nd in Mg varies between 2 and 5 at.%. This variation was not only seen for different GB orientations but also within the GB plane. Correlated atomistic simulations suggest that the inhomogeneous segregation behavior observed experimentally stems from local atomic rearrangements within the GBs and introduce the notion of potential excess free volume in the context of improving the prediction of per-site segregation energies.

First-principles phonon calculations of neodymium-magnet compounds

We report first-principles investigations of the light-element effect on phonon states in neodymium-magnet compounds. It is found that B in Nd2Fe14B contributes to acoustic phonon hardening. As for the substitution of other light elements for B, frequencies of phonons that originate from light elements decrease with increasing the atomic number. However, imaginary phonons in Nd2Fe14F are attributed to the electronic states and the atomic configurations, not to the heavier mass of F. In addition, as the effect of the magnetic disordering on the phonon state, we show that the phonons of the paramagnetic Nd2Fe14B are softer than those of the ferromagnetic Nd2Fe14B. This suggests that the phonon effect decreases the Curie temperature through the stabilization of the paramagnetic state.

Limits of Solid Solution and Evolution of Crystal Morphology in (La1–xREx)FeO3 Perovskites by Low Temperature Hydrothermal Crystallization

The crystallization of a new series of A-site substituted lanthanum ferrite materials (La1-xREx)FeO3 was explored by the hydrothermal method at 240 °C, for rare earth (RE) = Nd, Sm, Gd, Ho, Er, Yb, and Y, with 0 ≤ x ≤ 1. The effect of elemental substitution on the morphological, structural, and magnetic properties of the materials was studied using high-resolution powder X-ray diffraction, energy dispersive spectroscopy (EDS) on the scanning electron microscope, Raman spectroscopy, and SQUID magnetometry. If the radius of the La3+ and the substituent ions is similar, such as for Nd3+, Sm3+, and Gd3+, homogeneous solid solutions are formed, with the orthorhombic GdFeO3-type structure, and a continuous evolution of Raman spectra with composition and distinct magnetic behavior from the end members. When the radius difference between substituents and La3+ is large, such as for Ho3+, Er3+, Yb3+, and Y3+, then instead of forming solid solutions, crystallization in separate phases is found. However, low levels of element mixing are found and intergrowths of segregated regions give composite particles. In this case, the Raman spectra and magnetic behavior are characteristic of mixtures of phases, while EDS shows distinctive elemental segregation. A-site replacement induces an evolution in the crystallite shape with an increasing amount of substituent ions and this is most evident for RE = Y from cube-shaped crystals seen for LaFeO3 to multipodal crystals for (La1-xYx)FeO3, providing evidence for a phase-separation-driven evolution of morphology.

Evaluating some design criteria for TiFe-based ternary hydrogen storage alloys

Elemental substitution is widely practised to fabricate TiFe-based alloys with enhanced hydrogen storage characteristics. While some hydrogen storage properties can be improved others are usually adversely affected by this method. Hence, establishing sensible alloying design criteria is important for further developing Ti-Fe-based alloys. Here, the effects of substitutional elements in Ti-Fe-based ternary alloys are assessed based on several factors such as hydrogen bond dissociation energy, lattice parameters, interstitial site size, and intermetallic phase formation. Our calculations show that all the substitutional elements studied in this work (except Ni and Co) increase the lattice parameter compared to the TiFe alloy, while they have a diverse effect on the interstitial site sizes. The thermodynamic stability of the alloys could not be adequately described based on the lattice parameter and factors such as interstitial site sizes along the local atomic environment should be also considered. Hydrogen storage capacity of the Ti-Fe-based ternary alloys also appears to be influenced by the metal-hydrogen bond dissociation energy of the substitutional elements and their capability to form intermetallic phases with Ti. TiFe-based ternary alloys were modified by V and Zr substitutions according to the above criteria. The modified alloys were mostly composed of the B2 TiFe phase, offering significantly easier activation and a higher reversible hydrogen storage capacity compared to the binary alloy.

A comprehensive review of synthesis, properties, and applications of BaFe12O19 hexaferrites

BaFe12O19, also known as barium hexaferrite (BHF), is a magnetic compound that became increasingly popular in numerous fields of science due to its unique set of characteristics. One of the key advantages of barium hexaferrite is that its properties can be easily tuned through the use of doping, synthesis techniques, and heat treatment methods. Therefore, by introducing small amounts of other elements (transition elements, rare earth elements, etc.) into the hexaferrite structure, its magnetic and structural properties can be altered to suit the specific requirements of a particular application. This review paper gives a detailed literature on the numerous methodologies for the development of BaFe12O19 hexaferrites along with the impact of different elemental substitution on the magnetic as well as structural traits of the BHF. Lastly, the potential use of BHF in various research sectors were addressed.

Machine learning-based Curie temperature prediction for magnetic 14:2:1 phases

The TM14RE2B-based phases (TM = transition metal, RE = rare earth metal; hereafter called 14:2:1) enable permanent magnets with outstanding magnetic properties. Novel chemical compositions that represent new 14:2:1 phases necessitate that they do not demagnetize at application-specific operating temperatures. Therefore, an accurate knowledge of the Curie temperature (Tc) is important. For magnetic 14:2:1 phases, we present a machine learning model that predicts Tc by using merely chemical compositional features. Hyperparameter tuning on bagging and boosting models, as well as averaging predictions from individual models using the voting regressor, enables a low mean-absolute-error of 16 K on an unseen test set. The training set and a test set have been constructed by randomly splitting, in an 80:20 ratio, of a database that contains 449 phases (270 compositionally unique) mapped with their Tc, taken from distinct publications. The model correctly identifies the relative importance of key substitutional elements that influence Tc, especially in an Fe base such as Co, Mn, and Al. This paper is expected to serve as a basis for accurate Curie temperature predictions in the sought-after 14:2:1 permanent magnet family, particularly for transition metal substitution of within 20% in an Fe or Co base.