Ni Ga Research Articles

In Situ Synchrotron Diffraction Assessment of Reversibility of the Martensitic Transformation in Single-Crystalline Co–Ni–Ga Shape Memory Alloy Under Torsion

AbstractHeusler-type Co–Ni–Ga shape memory alloys attracted significant attention due to their excellent functional properties in single-crystalline state under both compressive and tensile loading. The present study investigates the superelastic deformation behavior under torsion. Using a newly installed torsion testing setup, in situ synchrotron diffraction was carried out on single-crystalline material in order to investigate the martensitic phase transformation. Incremental deformation experiments reveal a fully reversible martensitic transformation under torsional loading at room temperature, leading to excellent strain recovery after deformation to 6.5% shear strain. Furthermore, relevant aspects towards the analysis of powder diffraction data obtained for single-crystalline material in transmission mode under torsional loading are presented and critically discussed.

A Ni(0) Methyl Complex Based on a Bimetallic Ni–Ga Framework

A Ni(0) Methyl Complex Based on a Bimetallic Ni–Ga Framework

Kinetics and mechanistic insights into selective hydrogenation of furfural to furfuryl alcohol over Ni–Ga intermetallics

AbstractFurfural was mainly used to produce furfuryl alcohol, which is a monomer of furan resins with a global market of ~$0.3 billion/year. Industrial production of furfuryl alcohol is via selective hydrogenation over toxic copper chromate under harsh conditions. Therefore, the search for active and non‐toxic alternatives is highly desired. Here, kinetics studies revealed an inhibitive effect caused by strong furfural adsorption on Ni‐based catalysts, resulting in sites blocking and undesired ring hydrogenation. Such an inhibitive effect can be alleviated over Ni‐Ga intermetallic surfaces by tuning the Ni coordination number, from which the Ni1Ga1 showed markedly enhanced furfuryl alcohol yield (~99%) at milder conditions comparing to the referred Ni catalyst. It is found that isolated Ni sites by Ga on the Ni1Ga1 enabled a tilted adsorption configuration through the carbonyl of furfural. In contrast, the stronger flat‐lying adsorption of furfural was favored on the contiguous Ni sites of the referred catalyst.

Selective hydrogenation of 5-hydroxymethylfurfural to 2,5-bis(hydroxymethyl)furan over Ni–Ga intermetallic catalysts and its kinetic studies

5-Hydroxymethylfurfural (HMF) has been listed as the “TOP 14” most important biomass-derived platform molecules, which can be converted into 2,5-bis(hydroxymethyl)furan (BHF) via selective hydrogenation of the carbonyl group on HMF.

The preferred adsorption sites and catalytic mechanism of FCC_CoFeGaNiZn multi-principal element alloy for oxygen evolution reaction catalysis based on site preference of constituent atom on sublattice

The origin of distinguished oxygen evolution reaction (OER) catalytic properties of multi-principal element alloys (MPEAs) is not clear yet due to the rich surface-active sites may exist in MPEAs composed of multiple types of elements, which may bring complex catalytic environment. In this work, four main steps were carried out using computational materials science. The atom distribution of bulk MPEAs was constructed firstly based on the previously predicted site preference of atoms occupying sublattices, which is beyond the traditional hypothesis that the atom distributing randomly on the whole lattice. Then the (111) close-packed surface slab of CoFeGaNiZn MPEA was obtained by cleaving the bulk structure. Subsequently, the OER processes were systematically explored by calculating the free energy change of intermediates *OH, *O, and *OOH at 171 adsorption sites on the (111) surface. Finally, the oxygen evolution reaction catalytic mechanism and its site preference behavior of FCC_CoFeGaNiZn MPEA were discussed in detail. The results show that atoms have obvious site preference, which deviating the ideal randomly distribution, especially Co, Fe and Zn atoms always prefer to 3c sublattice at all temperature, Ga atoms tend to favor 1a sublattice, and the site preferences of Ni atoms and Ga atoms are affected by the heat treatment temperature. At 1273 K, the site occupying configuration is (Co0.0246Fe0.01680Ga0.4550Ni0.4990Zn0.0046)1a (Co0.2580Fe0.2610Ga0.1150Ni0.1000Zn0.2650)3c. The (111) surface of FCC_CoFeGaNiZn MPEA was based on the site occupying configuration at 1273 K, and it was then supposed to quenched to ground state to simulate the experimental status in the available literature. Since *O at hollow sites transforms into *OOH at a higher overpotential, hollow sites may be poisoning surface sites. Three intermediates are found to primarily participate in the catalytic reaction on top sites. In addition, there are no scaling relationships between ΔE*OH and ΔE*O for CoFeGaNiZn MPEA, even for the same type of top sites. It is noteworthy that an average overpotential of 0.349 V was predicted by considering the combinations of three intermediate-tendency elements, which is in better agreement with the experimental overpotential of 0.37 V at 10 mA/cm2 current density than the overpotential of 0.28 V based on the special quasirandom structures (SQS). Current intensive explorations bring new insights into the OER catalytic mechanism of the preferred adsorption sites of MPEAs based on the reasonable consideration concerning the atoms distributing configuration involving the exact site preference of the constituent metallic atoms on the sublattice.

Decoupling topological antiskyrmion and non-topological magnetic phases in D2d symmetric Mn–Ni–Ga single crystalline device

Here, we present the finding of two types of distinct Hall signals in the single crystalline Hall devices of a D2d symmetric antiskyrmion host Mn–Ni–Ga sample. The out-of-plane device, where the magnetic field is applied along the [001] direction, exhibits a dip-like anomaly in the Hall resistivity data, signifying the presence of topological Hall signal originating from the antiskyrmion phase. Most importantly, we demonstrate the robustness of the antiskyrmion phase against an oblique field where the topological Hall signal survives up to a tilting angle of 75° with respect to the c-axis. In contrast, the Hall resistivity data for the in-plane device exhibit an aberrant hump-like feature that can be tuned with applying a rotating magnetic field. We show that this hump-like anomaly emerges from the existence of a two-component anomalous Hall effect arising due to the presence of twinning microstructure. The present study provides an important insight into the stability and evolution of the antiskyrmion phase under the oblique magnetic fields and helps in decoupling of anomalous Hall signals in the non-topological magnetic phases.

Ni–Ga and Mg–Ga co-substituted sintered CoFe2O4 ceramics: Studies of their magnetic and magnetostrictive properties

Magnetostrictive smart materials (MSMs) with superior magnetostriction parameters (strain (λ) and strain sensitivity (dλ/dH)) are indispensable components for device applications in actuators, torque sensors, and transducers. This study investigates the magnetostrictive characteristics of sintered CoFe2O4 (CFO), Co0.85Ni0.15Fe1.85Ga0.15O4 (CNFGO15) and Co0.85Mg0.15Fe1.85Ga0.15O4 (CMFGO15) ceramics synthesized via a solution combustion method, followed by palletisation and sintering (1350 °C for 2 h). It is revealed from interpretation of XRD data of as-synthesized samples that ferrite powders are single phase and nanosized. This means that post-synthesis calcination is not requisite. According to Rietveld refinement analysis performed on powder data of sintered samples, sintered compositions are single phase, and unit cell parameters are 8.38501, 8.37585 and 8.37664 Å for CFO, CNFGO15 and CMFGO15, respectively. Raman bands, more than five, have been detected in the samples' Raman spectra, due to the mixed spinel structure of the materials. The co-substitution induced substantial grain growth, and the mean grain size follows the order of CMFGO15> CNFGO15>CFO. EDS spectra suggested that compositions stoichiometry is maintained. The chemical state and cation distributions of sintered CFO, CNFGO15 and CMFGO15 samples were studied using their XPS data. Despite high co-substitution in CNFGO15 and CMFGO15 samples, their saturation magnetization (MS) is comparable with the CFO sample value because both tetrahedral (A-site) and octahedral (B-site) sites are diluted equally. However, other magnetic parameters such as coercivity (HC), anisotropy constant (K1), Curie temperature (TC) of CNFGO15 and CMFGO15 are low compared to pristine CFO sample values. The CMFGO15 sample exhibited enhanced λ and dλ/dH at low magnetic fields against the other two samples. Furthermore, the maximum strain sensitivity [dλ/dH]max of CMFGO15 sample is −1.93 × 10−9 m/A at 30 kA/m. This is nearly 160% higher than the values found for other two samples even at remarkable low field.

Hydrotalcite-derived nickel–gallium alloy catalysts with enhanced resistance against metal sintering for methane decomposition

Catalytic methane decomposition is a promising way to convert methane into COx-free hydrogen and value-added carbon nanomaterials, but the development of a sintering-resistant catalyst is a challenge. In this study, Ni–Ga/Al2O3 alloy catalysts with different Ga/Ni atomic ratios were prepared from Ni3−xGaxAl (x = 0–1.2) hydrotalcite-like compounds (HTlcs) as precursors and tested for methane decomposition. Structural and physicochemical properties of the as-prepared and used catalysts were characterized by ICP, N2 physical adsorption, XRD, H2-TPR, H2 chemisorption, STEM-EDX, SEM, TEM, and Raman techniques. The results indicate that upon calcination at 500 °C, Ni–Ga–Al HTlcs are transferred to rock-salt Ni(Ga,Al)O oxide solid solutions, and reduction with H2 at 800 °C leads to single-phase and composition-uniform Ni–Ga alloy particles with an average crystal size of 8–10 nm. In catalytic methane decomposition at 600 °C, the alloying Ni with a suitable amount of Ga effectively enhances the catalyst life and carbon yield. Especially, Ni2.4Ga0.6Al shows the highest carbon yield of 61.1 g-C/g-cat, approximately 4.4 times that of the Ga-free Ni counterpart. Meanwhile, Ni–Ga alloying has a marked influence on the CNTs geometry, giving herringbone-like CNTs with small diameters and thin walls. It is gratifying to find that the Ni–Ga/Al2O3 catalyst exhibits good resistance against sintering under the adopted reaction condition, which accounts for the formation of uniform CNTs of smaller size. The findings provide guidelines for the control of carbon morphology and geometric size in methane decomposition.

Ultra-wide-temperature-range superelasticity and intrinsic two-way shape memory effect in Co–Ni–Ga microwires

We demonstrate perfect superelasticity and inherent two-way shape memory effect in Co49Ni21Ga30 microwires fabricated by a Taylor–Ulitovsky method. With the formation of an almost complete [001]A-oriented single crystal along the axis of the wire, the as-drawn microwire displays great superelastic behaviors with a large reversible tensile strain of >8% over an ultra-wide temperature window of 550 K (223–773 K). Simultaneously, an excellent intrinsic two-way shape memory effect with a considerably large strain output (∼6.3%) was also obtained in this Co49Ni21Ga30 microwire. After mechanical training, the two-way shape memory strain can reach up to 6.8% at a low operating temperature. With the combination of above extraordinary functional properties and the low cost of fabrication, the Co49Ni21Ga30 microwire holds a significant potential for applications in miniature sensing and self-actuating devices in the future.

On the Impact of Additive Manufacturing Processes on the Microstructure and Magnetic Properties of Co–Ni–Ga Shape Memory Heusler Alloys

Microstructure design allows to prevent intergranular cracking and premature failure in Co–Ni–Ga shape memory alloys. Favorable grain boundary configurations are established using additive manufacturing techniques, namely, direct energy deposition (DED) and laser powder bed fusion (L‐PBF). L‐PBF allows to establish a columnar grain structure. In the Co–Ni–Ga alloy processed by DED, a microstructure with strong ⟨001⟩ texture is obtained. In line with optimized microstructures, the general transformation behavior is essential for performance. Transition parameters such as transition temperature and thermal hysteresis depend on chemical composition, homogeneity, and presence of precipitates. However, these parameters are highly dependent on the processing method used. Herein, the first‐order magnetostructural transformation and magnetization properties of Co–Ni–Ga processed by DED and L‐PBF are compared with single‐crystalline and as‐cast material. In the alloy processed by L‐PBF, Ga evaporation and extensive formation of the ferromagnetic Co‐rich γ'‐phase are observed, promoting a very wide transformation range and large thermal hysteresis. In comparison, following DED, the material is characterized by minor chemical inhomogeneity and transition and magnetization behavior being similar to that of a single crystal. This clearly renders DED‐processed Co–Ni–Ga to become a promising candidate material for future shape memory applications.

Signatures of superconducting triplet pairing in Ni–Ga-bilayer junctions

Ni–Ga bilayers are a versatile platform for exploring the competition between strongly antagonistic ferromagnetic and superconducting phases. We characterize the impact of this competition on the transport properties of highly-ballistic Al/Al2O3(/EuS)/Ni–Ga tunnel junctions from both experimental and theoretical points of view. While the conductance spectra of junctions comprising Ni (3 nm)–Ga (60 nm) bilayers can be well understood within the framework of earlier results, which associate the emerging main conductance maxima with the junction films’ superconducting gaps, thinner Ni (1.6 nm)–Ga (30 nm) bilayers entail completely different physics, and give rise to novel large-bias (when compared to the superconducting gap of the thin Al film as a reference) conductance-peak subseries that we term conductance shoulders. These conductance shoulders might attract considerable attention also in similar magnetic superconducting bilayer junctions, as we predict them to offer an experimentally well-accessible transport signature of superconducting triplet pairings that are induced around the interface of the Ni–Ga bilayer. We further substantiate this claim performing complementary polarized neutron reflectometry measurements on the bilayers, from which we deduce (1) a nonuniform magnetization structure in Ga in a several nanometer-thick area around the Ni–Ga boundary and can simultaneously (2) satisfactorily fit the obtained data only considering the paramagnetic Meissner response scenario. While the latter provides independent experimental evidence of induced triplet superconductivity inside the Ni–Ga bilayer, the former might serve as the first experimental hint of its potential microscopic physical origin. Finally, we introduce a simple phenomenological toy model to confirm also from the theoretical standpoint that superconducting triplet pairings around the Ni–Ga interface can indeed lead to the experimentally observed conductance shoulders, which convinces that our claims are robust and physically justified. Arranging our work in a broader context, we expect that Ni–Ga-bilayer junctions could have a strong potential for future superconducting-spintronics applications whenever an efficient engineering of triplet-pairing superconductivity is required.

Influence of Pulsed Flows of Deuterium Ions and Deuterium Plasma on Cu–Ni and Cu–Ni–Ga Alloys

Influence of Pulsed Flows of Deuterium Ions and Deuterium Plasma on Cu–Ni and Cu–Ni–Ga Alloys

Enhanced acetylene semi-hydrogenation on a subsurface carbon tailored Ni–Ga intermetallic catalyst

A subsurface carbon tailored Ni–Ga intermetallic catalyst delivers superior catalytic performance for acetylene semi-hydrogenation.

γ-phase evolution in aged Co–Ni–Ga shape memory alloy

A synchrotron X-ray diffraction study of high-temperature (HT) shape memory alloy 49Co–21Ni–30Ga (in at. pct.) was performed. The volume fraction, cell parameter and temperature evolution of the different secondary phases were analyzed. This study reports reliable experimental data on these parameters to be used as a future reference to adjust the composition of the material.

Insight into the structure of SiO2-supported Ni–Ga nanoparticles for catalytic application via X-ray absorption spectroscopy and total scattering

Insight into the structure of SiO₂-supported Ni–Ga nanoparticles for catalytic application <i>via</i> X-ray absorption spectroscopy and total scattering

Structural studies of ligand stabilized Ni/Ga clusters by means of vibrational spectroscopy and theoretical calculations

AbstractIn order to explain the different catalytic activity in hydrogenation of two new intermetallic Ni/Ga clusters, [Ga7](NiCp*)6 (1A) and [NiGa6](NiCp*)6 (1B) (Cp* = C5Me5), investigations of structure–function relationship have been performed based on Raman and infrared (IR) spectroscopy and theoretical (density functional theory [DFT] and normal coordinate) calculations. Full interpretation of the Raman, far‐IR, and mid‐IR spectra of these dark colored solids has been proposed. Based on the overview of metal–Cp* complexes, all the 14 characteristic Cp*− skeletal fundamental modes have been identified. By comparison of the NiCp* stretching and tilting external modes (350–380 cm−1), their force constants, and bond lengths, cluster 1B exhibited slightly stronger metal–ligand bonding. Vibrations of Ga7 and NiGa6 cluster cores showed that the stretching wavenumbers and force constants of NiGa (100–350 cm−1) and GaGa (60–250 cm−1) bonds are higher for cluster 1B, in agreement with the shorter averaged experimental and calculated bond lengths of GaGa bonds (2.873 and 2823 Å for clusters 1A and 1B, respectively). Cluster hydrogenation experiments with H2 and D2 showed strong NiH and ND stretching features (at 1750 and 1260 cm−1, respectively), and at the same time, characteristic bands of self‐hydrogenated Cp*H and remained nondegraded clusters have been detected. The extent of HD exchange in cluster deuteration was obtained about 1.5 times more effective with cluster 1B than cluster 1A. The stronger hydrogen or deuterium uptake by cluster 1B and the more intensive self‐hydrogenation of Cp* clearly support the higher hydrogenation activity of cluster 1B compared with that of 1A.

Superelastic damping at nanoscale in ternary and quaternary Cu-based shape memory alloys

Superelasticity is a characteristic thermomechanical property in shape memory alloys (SMA), which is due to a reversible stress-induced martensitic transformation. Nano-compression experiments made possible the study of this property in Cu–Al–Ni SMA micropillars, showing an outstanding ultra-high mechanical damping capacity reproducible for thousands of cycles and reliable over the years. This scenario motivated the present work, where a comparative study of the damping capacity on four copper-based SMA: Cu–Al–Ni, Cu–Al–Be, Cu–Al–Ni–Be and Cu–Al–Ni–Ga is approached. For this purpose, [001] oriented single-crystal micropillars of comparable dimensions (around 1 µm in diameter) were milled by focused ion beam technique. All micropillars were cycled up to two hundred superelastic cycles, exhibiting a remarkable reproducibility. The damping capacity was evaluated through the dimensionless loss factor η, calculated for each superelastic cycle, representing the dissipated energy per cycle and unit of volume. The calculated loss factor was averaged between three micro-pillars of each alloy, obtaining the following results: Cu–Al–Ni η = 0.20 ± 0.01; Cu–Al–Be η = 0.100 ± 0.006; Cu–Al–Ni–Be η = 0.072 ± 0.004 and Cu–Al–Ni–Ga η = 0.042 ± 0.002. These four alloys exhibit an intrinsic superelastic damping capacity and offer a wide loss factor band, which constitutes a reference for engineering, since this kind of micro/nano structures can potentially be integrated not only as sensors and actuators but also as dampers in the design of MEMS to improve their reliability. In addition, the study of the dependence of the superelastic loss factor on the diameter of the pillar was approached in the Cu–Al–Ni–Ga alloy, and here we demonstrate that there is a size effect on damping at the nanoscale.

Original Fe–Co–Ni–Ga–Nb Multicomponent Alloy with Soft Magnetic Properties

Herein, the study of a multicomponent alloy comprising Fe, Co, Ni, Ga, and Nb is presented. The study begins with analysis of small samples, and these samples results conducted to the production of a laminated alloy with composition FeCoNi(GaNb)0.20, which has its magnetostriction roundly determined. This alloy is found to have longitudinal magnetostriction of less than 5 ppm. In addition, the material shows high values of initial and maximum relative permeabilities of 1160 and 1340, respectively. The saturation magnetization of the alloy is 97.4 Am2 kg−1, and the electrical resistivity is 88 μΩ cm. Moreover, it is demonstrated that this alloy has good mechanical workability. Overall, the studied FeCoNi(GaNb)0.20 alloy has potential to be used in electric machines and magnetic devices that work in the subkilohertz frequency range.

Low-temperature martensite relaxation in Co–Ni–Ga shape memory alloy monocrystal revealed using in situ cooling, transmission electron microscopy and low rate calorimetry

This work presents the results of research on a Co49Ni21Ga30 magnetic shape memory single crystal. Based on a literature review, it was identified that analyses of phase transformations have been limited to specific heating and cooling rates, which could lead to an incomplete description of the resulting phenomena. Differential scanning calorimetry (DSC) performed with different heating/cooling rates enabled the precise determination of enthalpy values, which deviate from literature values. Weak and previously unnoticed thermal phenomena at temperatures below 190 K were also observed. Their presence was confirmed by low-temperature in situ transmission electron microscopy (TEM). Through DSC measurements and TEM observations, a model of the discovered phenomenon was proposed, which may have an impact on a better understanding of the physics of magnetic shape memory materials.

First-principles investigation of Mg substitution for Ga on martensitic transformation, magnetism and electronic structures in Ni2MnGa

The impact of Mg substitution for Ga on the crystal structure, phase stability, magnetism, and electronic structures in the Ni2MnGa1-xMgx (x = 0, 0.25, 0.5, 0.75 and 1) alloys were studied by first-principles calculation. Unlike the elemental substitutions by the transition metals or the main-group elements of III, IV, and V (sp elements) in NiMnGa alloys, very rare knowledge is available on the effect of substitution by the main-group elements of I and II (e.g., Mg) characterized by only s valence electrons. Results show that the substituted Mg prefers to occupy the Ga site directly, and the magnetic atoms tend to be ferromagnetically coupled with each other. The appearance of the minimum global energy with the lattice tetragonality (c/a) larger than one suggests their possibility of being magnetic shape memory alloys. Mg substitution can enhance the austenite stability due to the reduced minority-spin states near the Fermi energy (EF). c/a of martensite decreases linearly when Mg substitutes Ga, which could be meaningful for optimizing transitional hysteresis. For the ferromagnetism, both austenite and martensite are enhanced with Mg substitution, which arises due to the increased moment of Ni owing to its increased eg states above EF. Elastic constant investigations show that Ni2MnGa1-xMgx (x < 0.18 and x > 0.94) alloys are elastically stable. Mg replacement for Ga tends to decrease bulk modulus, Young’s modulus and shear modulus. By contrast, Mg substitution is favorable to improve the ductility of NiMnGa owing to the weaker covalent hybridization of Ni–Mg compared with Ni‒Ga.