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At least 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on Mg(BrO3)2 by Materials Project

Mg(O3Br)2 crystallizes in the monoclinic C2/m space group. The structure is two-dimensional and consists of one Mg(O3Br)2 sheet oriented in the (0, 0, 1) direction. Mg2+ is bonded in an octahedral geometry to six O2- atoms. There are two shorter (2.05 Å) and four longer (2.15 Å) Mg–O bond lengths. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one Mg2+ and one Br5+ atom. The O–Br bond length is 1.68 Å. In the second O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one Mg2+ and one Br5+ atom. The O–Br bond length is 1.67 Å. Br5+ is bonded in a trigonal non-coplanar geometry to three O2- atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Mg(BH4)2 by Materials Project

Mg(BH4)2 crystallizes in the tetragonal I-4m2 space group. The structure is three-dimensional. there are two inequivalent Mg2+ sites. In the first Mg2+ site, Mg2+ is bonded in a 8-coordinate geometry to eight H+0.50+ atoms. There are four shorter (2.00 Å) and four longer (2.09 Å) Mg–H bond lengths. In the second Mg2+ site, Mg2+ is bonded in a body-centered cubic geometry to eight equivalent H+0.50+ atoms. All Mg–H bond lengths are 2.06 Å. B3- is bonded in a tetrahedral geometry to four H+0.50+ atoms. All B–H bond lengths are 1.23 Å. There are three inequivalent H+0.50+ sites. In the first H+0.50+ site, H+0.50+ is bonded in an L-shaped geometry to one Mg2+ and one B3- atom. In the second H+0.50+ site, H+0.50+ is bonded in an L-shaped geometry to one Mg2+ and one B3- atom. In the third H+0.50+ site, H+0.50+ is bonded in an L-shaped geometry to one Mg2+ and one B3- atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Mg(AlGe)2 by Materials Project

MgAl2Ge2 crystallizes in the trigonal P-3m1 space group. The structure is three-dimensional. Mg is bonded to six equivalent Ge atoms to form MgGe6 octahedra that share corners with twelve equivalent AlGe4 tetrahedra, edges with six equivalent MgGe6 octahedra, and edges with six equivalent AlGe4 tetrahedra. All Mg–Ge bond lengths are 2.90 Å. Al is bonded to four equivalent Ge atoms to form AlGe4 tetrahedra that share corners with six equivalent MgGe6 octahedra, corners with six equivalent AlGe4 tetrahedra, edges with three equivalent MgGe6 octahedra, and edges with three equivalent AlGe4 tetrahedra. The corner-sharing octahedra tilt angles range from 15–55°. There are three shorter (2.53 Å) and one longer (2.65 Å) Al–Ge bond lengths. Ge is bonded to three equivalent Mg and four equivalent Al atoms to form a mixture of distorted edge and corner-sharing GeMg3Al4 pentagonal bipyramids.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Mg(BrO3)2 by Materials Project

Mg(O3Br)2 crystallizes in the monoclinic C2/m space group. The structure is two-dimensional and consists of one Mg(O3Br)2 sheet oriented in the (0, 0, 1) direction. Mg2+ is bonded in an octahedral geometry to six O2- atoms. All Mg–O bond lengths are 2.14 Å. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a bent 120 degrees geometry to one Mg2+ and one Br5+ atom. The O–Br bond length is 1.69 Å. In the second O2- site, O2- is bonded in a bent 120 degrees geometry to one Mg2+ and one Br5+ atom. The O–Br bond length is 1.69 Å. Br5+ is bonded in a trigonal non-coplanar geometry to three O2- atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Mg(ScSe2)2 by Materials Project

Mg(ScSe2)2 crystallizes in the orthorhombic Pca2_1 space group. The structure is three-dimensional. there are two inequivalent Mg2+ sites. In the first Mg2+ site, Mg2+ is bonded to six Se2- atoms to form MgSe6 octahedra that share a cornercorner with one ScSe6 octahedra, corners with two equivalent MgSe6 octahedra, corners with four ScSe7 pentagonal bipyramids, an edgeedge with one MgSe6 octahedra, edges with four ScSe6 octahedra, and edges with three ScSe7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 15–56°. There are a spread of Mg–Se bond distances ranging from 2.66–2.80 Å. In the second Mg2+ site, Mg2+ is bonded to six Se2- atoms to form MgSe6 octahedra that share a cornercorner with one ScSe6 octahedra, corners with two equivalent MgSe6 octahedra, corners with four ScSe7 pentagonal bipyramids, an edgeedge with one MgSe6 octahedra, edges with four ScSe6 octahedra, and edges with three ScSe7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 15–56°. There are a spread of Mg–Se bond distances ranging from 2.68–2.75 Å. There are four inequivalent Sc3+ sites. In the first Sc3+ site, Sc3+ is bonded to six Se2- atoms to form ScSe6 octahedra that share a cornercorner with one MgSe6 octahedra, corners with two equivalent ScSe6 octahedra, corners with four ScSe7 pentagonal bipyramids, an edgeedge with one ScSe6 octahedra, edges with four MgSe6 octahedra, and edges with three ScSe7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 13–56°. There are a spread of Sc–Se bond distances ranging from 2.69–2.75 Å. In the second Sc3+ site, Sc3+ is bonded to six Se2- atoms to form ScSe6 octahedra that share a cornercorner with one MgSe6 octahedra, corners with two equivalent ScSe6 octahedra, corners with four ScSe7 pentagonal bipyramids, an edgeedge with one ScSe6 octahedra, edges with four MgSe6 octahedra, and edges with three ScSe7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 13–56°. There are a spread of Sc–Se bond distances ranging from 2.68–2.79 Å. In the third Sc3+ site, Sc3+ is bonded to seven Se2- atoms to form distorted ScSe7 pentagonal bipyramids that share corners with four MgSe6 octahedra, corners with four ScSe6 octahedra, edges with three MgSe6 octahedra, edges with three ScSe6 octahedra, and faces with two equivalent ScSe7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 18–67°. There are a spread of Sc–Se bond distances ranging from 2.71–2.99 Å. In the fourth Sc3+ site, Sc3+ is bonded to seven Se2- atoms to form distorted ScSe7 pentagonal bipyramids that share corners with four MgSe6 octahedra, corners with four ScSe6 octahedra, edges with three MgSe6 octahedra, edges with three ScSe6 octahedra, and faces with two equivalent ScSe7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 19–66°. There are a spread of Sc–Se bond distances ranging from 2.72–3.00 Å. There are eight inequivalent Se2- sites. In the first Se2- site, Se2- is bonded to two Mg2+ and three Sc3+ atoms to form distorted SeMg2Sc3 trigonal bipyramids that share corners with two equivalent SeMg2Sc3 square pyramids, corners with three equivalent SeMgSc3 tetrahedra, corners with two equivalent SeMg2Sc3 trigonal bipyramids, edges with three SeMg2Sc3 square pyramids, and edges with five SeMg2Sc3 trigonal bipyramids. In the second Se2- site, Se2- is bonded to two Mg2+ and three Sc3+ atoms to form distorted SeMg2Sc3 trigonal bipyramids that share corners with six SeMg2Sc3 square pyramids, corners with two equivalent SeMgSc3 tetrahedra, corners with two equivalent SeMg2Sc3 trigonal bipyramids, an edgeedge with one SeMg2Sc3 square pyramid, an edgeedge with one SeMgSc3 tetrahedra, and edges with five SeMg2Sc3 trigonal bipyramids. In the third Se2- site, Se2- is bonded to one Mg2+ and three Sc3+ atoms to form distorted SeMgSc3 tetrahedra that share corners with two SeMg2Sc3 square pyramids, corners with ten SeMg2Sc3 trigonal bipyramids, edges with two SeMg2Sc3 square pyramids, and edges with two SeMgSc4 trigonal bipyramids. In the fourth Se2- site, Se2- is bonded in a distorted rectangular see-saw-like geometry to one Mg2+ and three Sc3+ atoms. In the fifth Se2- site, Se2- is bonded to two Mg2+ and three Sc3+ atoms to form distorted SeMg2Sc3 square pyramids that share a cornercorner with one SeMgSc3 tetrahedra, corners with eight SeMg2Sc3 trigonal bipyramids, edges with two equivalent SeMg2Sc3 square pyramids, an edgeedge with one SeMgSc3 tetrahedra, and edges with four SeMg2Sc3 trigonal bipyramids. In the sixth Se2- site, Se2- is bonded to two Mg2+ and three Sc3+ atoms to form distorted SeMg2Sc3 square pyramids that share a cornercorner with one SeMgSc3 tetrahedra, corners with eight SeMg2Sc3 trigonal bipyramids, edges with two equivalent SeMg2Sc3 square pyramids, an edgeedge with one SeMgSc3 tetrahedra, and edges with four SeMg2Sc3 trigonal bipyramids. In the seventh Se2- site, Se2- is bonded to one Mg2+ and four Sc3+ atoms to form distorted SeMgSc4 trigonal bipyramids that share corners with two equivalent SeMg2Sc3 square pyramids, corners with two equivalent SeMgSc3 tetrahedra, corners with two equivalent SeMgSc4 trigonal bipyramids, edges with three SeMg2Sc3 square pyramids, an edgeedge with one SeMgSc3 tetrahedra, and edges with five SeMg2Sc3 trigonal bipyramids. In the eighth Se2- site, Se2- is bonded to one Mg2+ and four Sc3+ atoms to form distorted SeMgSc4 trigonal bipyramids that share corners with six SeMg2Sc3 square pyramids, corners with three equivalent SeMgSc3 tetrahedra, corners with two equivalent SeMgSc4 trigonal bipyramids, an edgeedge with one SeMg2Sc3 square pyramid, and edges with five SeMg2Sc3 trigonal bipyramids.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Tailored Additive Design of Scaffold‐Free Porous Mg for Ultimate Hydrogen Storage

For hydrogen storage materials to become practically viable, comprehensive improvements in key properties—kinetics, thermodynamics, thermal transport, and durability—are crucial. Porous Mg structure has been proposed as a promising strategy due to its high storage capacity and ability to accommodate volume expansion. However, challenges such as sluggish kinetics and structural degradation resulting from instability due to vacant sites still remain. In this study, a tailored design of porous Mg structure with site-specific transition metal dual-doping and structure-reinforced carbon nanotube (CNT)-framework is presented for optimal hydrogen storage. Ti and Ni are strategically deposited on the surface to synergistically enhance hydrogen sorption kinetics by facilitating hydrogen dissociation and diffusion, while CNTs are interpenetrated into 3D Mg structure for improving thermal conductivity and maintaining the porous structure. The resulting composite demonstrates exceptional performance, achieving hydrogen absorption and desorption of 4.8 and 5.8 wt%, respectively, within 10 min with an impressively low activation energy for absorption of 46 kJ mol −1 H 2 . Even after 50 cycles, its capacity and porous structure are well preserved, showing excellent cyclability in comparison with previously reported materials. In conclusion, this delicate design strategy based on a comprehensive understanding of structural and chemical characteristics is key to maximizing the targeted performance.

CNT embedding↗
DOE OSTI2020

Structural Stabilization of P2-type Sodium Iron Manganese Oxides by Electrochemically Inactive Mg Substitution: Insights of Redox Behavior and Voltage Decay

Layered P2-type Na 0.8 Mn 0.5 Fe 0.5 O 2 cathode material is a promising candidate for next-generation sodium-ion batteries due to the economical and environmentally benign characteristics of Mn and Fe. The poor cycling stability of the material, however, is still a problem that must be solved. To address the problem, here, electrochemically inactive Mg 2+ was introduced into the structure by substituting some of the Fe ions. It was shown that Mg substitution led to a smoother voltage profile with improved cycling performance and rate capability. These observations were attributed to the suppressed structural changes during electrochemical processes. Detailed redox mechanisms, associated local structural changes, and phase transitions were investigated by X-ray absorption spectroscopy and X-ray diffraction. From the detailed analysis of electrochemical behaviors, it was also identified how the redox reactions and structural disordering occurred in the high-and low-voltage regions and how Mg substitution stabilized the structure.

25 ENERGY STORAGE↗
NASA NTRSDate not supplied

Al-Cu-Zn-Mg Alloy for Additive Manufacturing by Electron Beam Deposition

The application of fusion-based additive manufacturing (AM) to aircraft structural components is limited by the lack of high-strength aluminum alloys optimized for AM processing. High strength aluminum alloys (such as 7050-T7451) are difficult to process by AM because of their solidification cracking susceptibility and loss of volatile alloying elements such as Zn and Mg. The performance of a proprietary Al-Cu-Zn-Mg alloy wire feedstock was evaluated for AM utilizing electron beam deposition. Deposit microstructure, composition, occurrence of porosity and cracking, and post-heat treatment tensile and fracture toughness were correlated with deposition parameters. Post-heat treatment strength, ductility, and fracture toughness were lower than typical values for wrought 7050-T7451, related to significant losses of Zn and Mg and to porosity. Recommendations are offered for modifications to wire feedstock composition and adjustments to deposition conditions and heat treatment to enable AM of electron beam deposited material that has strength comparable to 7050-T7451 wrought products.

Al-Cu-Zn-Mg alloy, electron beam deposition, mecha↗
DOE OSTI2023

Large Enhancements in Optical and Piezoelectric Properties in Ferroelectric Zn 1- x Mg x O Thin Films through Engineering Electronic and Ionic Anharmonicities

Multifunctionality as a paradigm requires materials exhibiting multiple superior properties. Integrating second-order optical nonlinearity and large bandgap with piezoelectricity can, for example, enable broadband, strain-tunable photonics. Though very different phenomena at distinct frequencies, both second-order optical nonlinearity and piezoelectricity are third-rank polar tensors present only in acentric crystal structures. However, simultaneously enhancing both phenomena is highly challenging since it involves competing effects with tradeoffs. Recently, a large switchable ferroelectric polarization of ≈80 μC cm –2 was reported in Zn 1-x Mg x O films. Here, ferroelectric Zn 1-x Mg x O is demonstrated to be a platform that hosts simultaneously a 30% increase in the electronic bandgap, a 50% enhancement in the second harmonic generation (SHG) coefficients, and a near 200% improvement in the piezoelectric coefficients over pure ZnO. These enhancements are shown to be due to a 400% increase in the electronic anharmonicity and a ≈200% decrease in the ionic anharmonicity with Mg substitution. Precisely controllable periodic ferroelectric domain gratings are demonstrated down to 800 nm domain width, enabling ultraviolet quasi-phase-matched optical harmonic generation as well as domain-engineered piezoelectric devices.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Superatomic nature of metal encapsulated dodecahedrane: The case of M@ C 20 H 20 (M = Li, Na, Mg + )

The idea of designing unprecedented materials made of superatomic building blocks, motivated the present study on endohedral M@C 20 H 20 (M = Li, Na, Mg + ) species. Here, ground and excited electronic structures of M@C 20 H 20 (M = Li, Na, Mg + ) were analyzed by means of high-level quantum calculations. In their ground states, one electron occupies a defuse superatomic s-orbital that lies around the C 20 H 20 cage. These entities populate higher angular momentum p-, d-, f-, g-superatomic orbitals in their low-lying electronic states. The proposed superatomic Aufbau shell model for Li@C 20 H 20 and Na@C 20 H 20 is 1s, 1p, 1d, 2s, 1f, 2p, 2d, 1g, 2f slightly different from that of Mg@C 20 H 20 + which is 1s, 1p, 1d, 2s, 1f, 2p, 2d, 1g, 3s, 2f, 2g, 3p. These introduced superatomic orbital series resemble the Aufbau principle of solvated electron precursors.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Direct Nano‐Synthesis Methods Notably Benefit Mg‐Battery Cathode Performance

Abstract Rechargeable magnesium batteries are promising candidates for next‐generation electrochemical energy storage, but their development is severely hindered by sluggish solid‐state diffusion and significant desolvation penalties of the divalent cation. Studies suggest that nano‐sized electrode materials alleviate these issues by shortening diffusion lengths and increasing electrode/electrolyte interaction. Here, the effect of particle size and synthetic methodology on the electrochemical performance of four sulfide cathode materials in Mg batteries is investigated: layered TiS 2 , CuS, spinel Ti 2 S 4 , and CuCo 2 S 4 . In these sulfide hosts, the direct preparation of nano‐dimensional crystallites is critical to activate or improve electrochemistry. Even promising cathode materials can appear electrochemically inert when micron‐sized particles are investigated (e.g., CuCo 2 S 4 ), and mechanical milling leads to surface degradation of active material which severely limits performance. However, nano‐sized CuCo 2 S 4 prepared directly reaches a capacity nearly double that of ball‐milled material and delivers 350 mAh g −1 at 60 °C. This work provides synthetic considerations which may be crucial in the discovery and design of novel Mg cathode materials, so that promising candidates are not overlooked. By extension, in oxide materials where Mg 2+ diffusion is expected to be much more sluggish, this factor is anticipated to be even more important when screening for new hosts.

Blanc, Lauren E.↗
DOE OSTI2020

NASICON Li 1.2 Mg 0.1 Zr 1.9 (PO 4 ) 3 Solid Electrolyte for an All‐Solid‐State Li‐Metal Battery

Abstract A thin solid electrolyte with a high Li + conductivity is used to separate the metallic lithium anode and the cathode in an all‐solid‐state Li‐metal battery. However, most solid Li‐ion electrolytes have a small electrochemical stability window, large interfacial resistance, and cannot block lithium‐dendrite growth when lithium is plated on charging of the cell. Mg 2+ stabilizes a rhombohedral NASICON‐structured solid electrolyte of the formula Li 1.2 Mg 0.1 Zr 1.9 (PO 4 ) 3 (LMZP). This solid electrolyte has Li‐ion conductivity two orders of magnitude higher at 25 °C than that of the triclinic LiZr 2 (PO 4 ) 3 . 7 Li and 6 Li NMR confirm the Li‐ions in two different crystallographic sites of the NASICON framework with 85% of the Li‐ions having a relatively higher mobility than the other 15%. The anode–electrolyte interface is further investigated with symmetric Li/LMZP/Li cell testing, while the cathode–electrolyte interface is explored with an all‐solid‐state Li/LMZP/LiFePO 4 cell. The enhanced performance of these cells enabled by the Li 1.2 Mg 0.1 Zr 1.9 (PO 4 ) 3 solid electrolyte is stable upon repeated charge/discharge cycling.

Zhou, Qiongyu↗
DOE OSTI2025

Stimulating β -Series Precipitation in Mg–Nd Alloys Via Microalloying: A Comparison of Electron Microscopy and Small-Angle Scattering Techniques

The Mg–Nd alloy system is of particular interest in the development of high-strength, lightweight structural alloys due to the formation of strengthening metastable Mg–Nd β-series precipitates during heat treatment. The strengthening is primarily provided by a combination of the β''' and β 1 precipitation. It is therefore important to understand how the precipitation behavior can be enhanced by other common alloying elements. In this work, the effects of 0.2 wt pct Zn and Ca on β-series precipitation were studied. Small-angle/ultra-small-angle X-ray scattering (SAXS/USAXS) techniques in combination with scanning transmission electron microscopy (STEM) were used to study the evolution of precipitation microstructure. Here, it is found that the Zn additions refine the precipitates, leading to an increase in hardness with aging at 200 °C. On the other hand, the Ca additions result in an acceleration in the formation of larger β 1 precipitates and chains which provides less strengthening. The β 1 chains are surrounded by precipitate-free zones (PFZs) that further contribute to the decreases in hardness observed in the over-aged condition. This paper demonstrated that SAXS/USAXS provides a powerful tool for an in situ study of the early stages of precipitation in the Mg–Nd-based alloys.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Impact of Mg on Pd-based Methane Oxidation Catalysts for Lean-burn Natural Gas Emissions Control

More efficient lean-burn, natural gas engines are limited by greenhouse gas emissions due to methane oxidation catalysts (MOC) that suffer from water inhibition and high temperature activation. Herein, we report that the addition of Mg to supported 1 wt.% Pd MOCs improved hydrothermal stability even after severe hydrothermal aging. The superior methane oxidation activity compared to the corresponding Mg-free catalyst was attributed to (1) influence of Mg during surface roughening and restructuring at 700 °C on metal-support interaction, (2) reducibility of PdOx sites and (3) preferential stabilization of active Pd (1 0 0) facets in the sample as was evidenced by H 2 TPR and CO TPD characterization experiments. Methane conversion under synthetic exhaust conditions relevant to natural gas, lean-burn engines were investigated. In conclusion, BET, TPR, CO pulse chemisorption followed by TPD provided valuable insights into the surface area, pore volume, reducibility, Pd dispersion and Pd particle size of the selected catalyst samples.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Spinel high-entropy oxides (FeNiCrMnZnX) 3 O 4 (X = Al, mg) as anode materials for high-performance lithium-ion batteries

To address the high cost, cobalt dependency, and resource constraints typical of conventional high-entropy oxide (HEO) anodes, this study reports the successful synthesis of two Co-free, six-component spinel-type HEOs(FeNiCrMnZnAl) 3 O 4 (HEO-Al) and (FeNiCrMnZnMg) 3 O 4 (HEO-Mg), via a sol-gel method. The distinct effects of Al 3+ and Mg 2+ incorporation on the electrochemical performance and lithium storage kinetics were systematically investigated. XRD, Raman, and TEM characterizations confirm that both materials possess a pure spinel phase, uniform particle size, and homogeneous elemental distribution. Notably, electrochemical evaluations reveal that HEO-Al delivers a superior reversible capacity of 480.7 mAh g −1 after 100 cycles at 0.1 A g −1 , and maintains 354.5 mAh g −1 after 1000 long-term cycles at 1 A g −1 , significantly outperforming HEO-Mg. Kinetic analysis indicates that HEO-Al exhibits lower charge transfer resistance, a higher Li + diffusion coefficient, and a pseudocapacitive contribution of up to 82%. Furthermore, these findings demonstrate that Al substitution effectively optimizes the structural stability and lithium storage kinetics of Co-free HEOs, providing a viable strategy for designing low-cost, highly stable HEO anode systems.

Anode materials↗
DOE OSTI2020

The effects of heat treatment on the response of WE43 Mg alloy: crystal plasticity finite element simulation and SEM-DIC experiment

The present report addressed the effects of heat treatment on the mechanical response of a WE43 Mg alloy using an integrated framework of SEM-DIC experiment and CPFE simulation. Both macroscopic responses including yield strength, ultimate strength, ductility, and microscopic responses, including local displacement and strain maps, were experimentally investigated. The focus of this work is to use the CPFE simulation as an integrated computational tool to study the effects of heat treatment. The CPFE framework was evaluated using the local fields of displacement and strain obtained from the SEM-DIC experiment rather than the conventional scheme of using macroscopic responses at different loading directions. Subsequently, the information which is available using CPFE, such as the critical resolved shear stress (CRSS) and relative slip activity, was used to study the effects of heat treatment on the response of WE43 Mg alloy. The contributions of different strengthening mechanisms on the CRSS were addressed. The results show that effects of heat treatment can be captured using the predominant mechanisms of the grain size effect and the influence of precipitates. Finally, it has been shown that classical Hall-Petch in which one constant can capture the size effects, should be modified. To do so, each deformation mode should have a unique Hall-Petch constant, which are calculated here for the WE43 Mg alloy.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Dislocation cross-slip in precipitation hardened Mg–Nd alloys

An integrated experimental characterization and molecular dynamics (MD) simulation approach was used to explore the dislocation-precipitate interactions in a dilute Magnesium–Neodymium (Mg–Nd) precipitation hardened alloy. In situ indentation in a transmission electron microscope (TEM) and postmortem TEM characterization of deformed samples and MD simulations revealed that basal < a > type dislocations interacted differently with β 1 (Mg 3 Nd) and β"(Mg 3-7 Nd) precipitates. For β" precipitates, the basal dislocations directly shear the precipitates. For β 1 precipitates, such shearing becomes much more difficult because it requires the creation of antiphase boundaries in the ordered lattice of β 1 precipitates. Screw dislocations were observed to cross-slip from basal to the prismatic plane, which could be parallel to the broad facet of β 1 precipitates. It is postulated that double cross-slip (basal to prismatic to basal) via the Hirsch mechanism may enable screw dislocations to overcome the β 1 precipitates. MD simulations also revealed that an edge dislocation is unable to bypass the precipitate via the generation of screw dislocation segments plus the double cross-slip mechanism. The edge dislocation can bow around the precipitate, and the segment that adopts a screw character can cross-slip to the prismatic plane but with increasing applied stress, cross-slips back to the original basal plane to continue glide via precipitate shearing. Finally, the implication of glide dislocation - β 1 -precipitate interaction mechanisms on the strength and ductility of β 1 precipitate dominant microstructures is discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Crystal structure, magnetism, and specific heat of lightly depleted layered honeycomb oxides, Na$_2$(Ni$_{2-x}$D$_x$)TeO$_6$ ($D$ = Mg, Ga, Co; 0.10 ≤ $x$ ≤ 0.25)

Layered oxides, in which transition metal atoms form a honeycomb lattice, are known for complex magnetic phase diagrams. In this work we study the doped compounds, Na$_2$(Ni$_{2-x}$D$_x$)TeO$_6$, $D$ = Mg, Ga, and Co (0.10 ≤ $x$ ≤ 0.25), to understand how chemical dilution at the nickel site influences the stability of magnetic exchanges within the honeycomb layer of the parent, Na$_2$ Ni$_2$ TeO$_6$. Here, the studied compounds were found to crystallize in $P6_3/mcm$ space group common to P2 type layered oxides. In general, the lattice parameters and the unit cell volume expanded with increased doping. The oxidation states determined from X-ray photoelectron spectroscopy were consistent with bond valence sum estimates, that confirmed the presence of Ni$^{2+}$, Mg$^{2+}$, Ga$^{3+}$, Co$^{2+}$ in our samples. Irrespective of magnetic or non-magnetic doping, the magnetic phase transition temperature ($T_N$) of the doped compounds were reduced from that of Na$_2$ Ni$_2$ TeO$_6$ or Na$_2$ Co$_2$ TeO$_6$, and lay between 21.7 K and 26.8 K. The effective paramagnetic moments extracted from Curie–Weiss analysis were in the range 3.17 μ B to 3.84 μ B and the Weiss temperatures were between $-15$ K and $-25$ K, suggesting antiferromagnetism. Mg- and Ga-doped compounds showed free spin formation, indicated by Curie–Weiss tails in their magnetic susceptibility. Our results suggest emergence of short-range magnetic correlations in Na$_2$(Ni$_{2-x}$D$_x$)TeO$_6$, enhanced due to the depletion of the Ni honeycomb lattice.

75 - CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY A↗