Diffusion Of Mg Research Articles

The dichotomous nature of Mg partitioning between plagioclase and melt: Implications for diffusion chronometry

Compositional zoning in plagioclase feldspar is an important archive of the temporal, compositional and thermal evolution of magmatic systems. Modelling diffusion of Mg in plagioclase is commonly used to estimate the timescales of magmatic processes that operate weeks to decades before eruption. To do this, however, requires knowledge of how the anorthite composition influences plagioclase-melt partitioning of Mg. The nature of this relationship has yet to be properly constrained, with inconsistencies between early empirical models, natural observations and more recent thermodynamic models. Here we compiled a data base of 965 calculated plagioclase-melt partition coefficients of Mg using mineral rim-melt pairs from phase equilibria experiments and natural samples. The data set includes a comprehensive range of plagioclase compositions (An13–An92), melt compositions (46.5–78.2 wt% SiO2) and temperatures (720–1430 °C). We find that the dependence of the partition coefficient on anorthite content has a major inflection at compositions that correspond to the C1¯–I1¯ structural phase transition (An60 at 1000 °C): with a positive dependence in the C1¯ domain, and a negative dependence in the I1¯ domain. We also find that this change in partitioning behaviour can explain Mg distributions in natural plagioclases observed in mafic to silicic systems including the Galápagos, Santorini, Krakatau, Toba and Cerro Galán. We have developed a new empirical model for the partitioning of Mg in plagioclase that takes into account this structural transition, in addition to the effects of temperature and melt composition. The dichotomous nature of the partitioning of Mg between plagioclase and melt has significant implications for diffusion chronometry, with the shape of Mg ‘quasi steady state’ profiles being controlled by the structural state of plagioclase. Compositional profiles that were previously interpreted to show little diffusion, may be close to a quasi steady state and vice versa. This re-evaluation will be highly influential for understanding thermal states and magmatic histories at a range of tectonic settings.

Influence of annealing temperature and isostatic pressure on microstructure and superconducting properties of isotopic Mg11B2 wires fabricated by internal Mg diffusion method

Here, we report superconducting Mg11B2 wires made by using the internal Mg diffusion technique with isotopic amorphous nano boron (11B) as the precursor material. We show the influence of annealing temperature and isostatic pressure of 0.1 MPa and 1.1 GPa on Mg diffusion into 11B layer, microstructure of superconducting filament, critical current density (Jc) at 20 K and 25 K, critical temperature (Tc) and irreversible magnetic induction (Birr) in mono (single-core) - and multi-filament Mg11B2 wires. Our research shows that thermal treatment at 700 °C and 0.1 MPa for 60 min yields a superconducting phase with low Tc, Birr and Jc in single-core Mg11B2 wire. A higher annealing temperature (740 °C and 0.1 MPa for 60 min) significantly accelerates the diffusion of Mg into the 11B layer and increases the Tc, Birr and Jc. However, the distribution of Mg in 11B layer is very heterogeneous (places with high and low Mg concentration). This leads to heterogeneity in the superconducting material and inhomogeneous Tc, Birr and Jc. Further studies showed that higher annealing temperatures at 770 °C and 800 °C significantly accelerates the diffusion of Mg into the 11B layer and leads to the increase of Tc, Birr and Jc in single-core Mg11B2 wire. In single-core wire annealing treatment under isostatic pressure of 1.1 GPa for 60 min at temperature of 800 °C it causes Mg penetrates into the 11B layer very heterogeneously and large amount of 11B remains unreacted. However, the same heat treatment at 800 °C and 1.1 GPa for 60 min in multi-filament wires leads to a complete Mg synthesis reaction with the 11B layer. This leads to increase Birr and Jc. This work shows that the formation and accumulation of pinning centers is essential to further increase Jc in Mg11B2 wires.

Process engineering of GaN power devices via selective-area p-type doping with ion implantation and ultra-high-pressure annealing

P-type doping in selected areas of gallium nitride (GaN) using magnesium (Mg)-ion implantation and subsequent ultra-high-pressure annealing (UHPA) are investigated to improve the performance of vertical GaN power devices. UHPA allows a high-temperature process without decomposition of the GaN surface and virtually complete activation of the implanted Mg ions in GaN. In the present paper, we provide an overview of recent challenges in making UHPA more realistic as an industrial process. Instead of UHPA at more than 1400 °C for a short duration, prolonged UHPA at 1300 °C demonstrates a comparable acceptor activation of Mg-ion-implanted GaN. This can reduce the annealing pressure to approximately 300 MPa and enlarge the processable wafer diameter. The second challenge is controlling the doping profiles in the lateral and vertical directions. We demonstrate fine patterning of the p-type regions, which indicates the limited lateral diffusion of Mg through UHPA. However, controlling the vertical doping profile is challenging. The nitrogen vacancies formed by ion implantation reduce the effective acceptor concentration near the surface, which can be compensated for by sequential nitrogen ion implantation. Defect-assisted Mg diffusion to the deeper region causes a redistribution of the Mg atoms and should be considered in the design of a device. Such anisotropic diffusion of Mg to the c-axis has potential applications in the fabrication of unique vertical device structures such as super junctions.

Effect of grain size on the mechanical properties and bio-corrosion resistance of pure magnesium

In addition to grain size, the mechanical properties and corrosion resistance of magnesium alloys depend on other factors such as texture, distribution of alloying elements, and homogeneity of the microstructure. These attributes might change during grain refining processes, making the situation more complex and masking the real effect of grain size. Accordingly, in the present work, the grain size of commercially pure (CP) Mg was adjusted by grain growth annealing after casting and deformation by hot rolling (for grain refinement via dynamic recrystallization during thermomechanical processing) to investigate the effect of grain size on tensile properties, hardness, and bio-corrosion resistance in simulated body fluid (SBF) for biomedical implant applications. The grain growth kinetics of commercially pure Mg was studied, where the grain growth activation energy (Q) was found to be consistent with that of the grain boundary diffusion in Mg. Based on the Hall–Petch plots, it was revealed that the yield stress (YS), ultimate tensile strength (UTS), and hardness of pure Mg are highly sensitive to average grain size in comparison to common Mg alloys. Moreover, based on the polarization curves and Nyquist plots obtained from electrochemical impedance spectroscopy (EIS) analysis, grain coarsening led to the enhanced corrosion resistance due to the decreased grain boundary regions, where a simple linear formula was obtained for correlating corrosion current density to average grain size.

Correlation between Interface Microstructure and Bond Strength of Al6061/Al6061 HIP-Bonded Plates for Fuel Cladding Application

The effects of hot isostatic pressing (HIP) processing parameters on microstructure and bond strength of Al6061/Al6061 plate interfaces were systemically investigated at the micro- and nanoscale. The HIP bonding of the two aluminum plates was performed at four temperatures: 350°C, 400°C, 450°C, and 560°C. The results reveal the formation of micron scaled Mg2Si precipitate and uniform nano scaled Mg2Al2O5 oxide at the interface. The formation of Mg2Al2O5 is closely associated with the fast bulk diffusion of Mg from the Al matrix to the amorphous Al2O3/Al interface and subsequent reaction between Mg and Al2O3. The highest and lowest bond strengths were observed in samples HIP bonded at 450°C and 350°C, respectively.

Effect of Cr elimination on flow behavior and processing map of newly developed ECO-7175 aluminum alloy during hot compression

ECO-Al alloys are introduced as a game-changer for the aluminum industry and it is of utmost importance to determine the role of alloying elements in their processing characteristics. In this study, the effects of Cr on the hot deformation behavior of newly-developed ECO-7175 alloy were investigated. ECO-7175 samples with and without Cr were hot-compressed using a Gleeble simulator (temperature range of 350−500 °C and strain rates of 0.001−1 s−1). The results were used to study the constitutive equations, the processing maps, and the microstructural evolution of the alloys. In Cr-containing alloy, the analysis of the deformation activation energy reveals that the rate-controlling mechanisms of the deformation change gradually from self-diffusion of Al (or diffusion of Mg in Al) to diffusion of Cr in Al by decreasing the Zener−Hollomon parameter. The analysis of the processing maps of Cr-containing alloy shows that the dynamic recrystallization (DRX) zone is limited to the deformation at high temperatures and low strain rates and expands with increasing applied strain. On the other hand, it is found that the self-diffusion of Al (or Mg in Al) is the only rate-controlling mechanism during hot deformation of Cr-free alloy in all processing conditions and its DRX zone is independent of the plastic strain.

Quantitative Investigation of MgO, Al2O3 and SiO2 Effects on Solid-State Formation of Secondary Hematite in Sintering Process of Iron Ore Fines

Secondary hematite (SH) is a serious factor resulting in reduction degradation of iron ore sinter in a blast furnace; however, until now, a quantitative study for SH formation had not been reported. In this work, the effects of gangue composition, including MgO, Al2O3 and SiO2, on the solid-state formation in the sintering process of iron ore fines were investigated quantitatively. It shows that the SH formation decreased from 67.84% to 46.11%, 35.44% and 22.37% after adding 1.0%, 3.0% and 5.0% MgO, respectively, while for Al2O3, the amount increased to 69.38%, 69.98% and 70.56%, respectively. For SiO2, the amount changed to 68.14%, 61.59% and 47.96%, respectively. Simultaneously, the magnetite (magnesioferrite) formation increased from 8.24% to 34.79%, 50.26% and 70.45% after adding 1.0%, 3.0% and 5.0% MgO, respectively. For Al2O3 and SiO2, the amount changed to 8.95%, 8.37%, 7.62% and 7.62%, 11.10%, 18.77%, respectively, compared with no gangue. This indicates that the SH formation increased with decrease in magnesioferrite. It was found that the decrease in SH formation relates to the diffusion of Mg2+ in magnesioferrite, which inhibits the solid-state formation of SH kinetically. A supposition was suggested that a maghemite existed at a high temperature, and decreased with an increase in MgO addition. This would be another reason to improve the degradation performance of iron ore sinter.

Thermodynamic prediction of thermal diffusivity and thermal conductivity in Mg–Zn–La/Ce system

• Heat dissipating Mg–Zn–La/Ce alloys were designed based on thermodynamic database. • τ 1 phases have more negative influence on thermal diffusivity than REMg 12 . • Solute atom is dominant factor affecting thermal conductivity of Mg–Zn–RE alloys. • The thermal diffusivities of Mg–Zn–La/Ce alloys were predicted by CALPHAD method. Basic thermal properties and mechanical properties are critical parameters for the structural magnesium alloys. Solute atoms and second phases can improve mechanical properties, but are deteriorating the heat dissipation performance. Through experimental determination of alloys, it is found that REMg 12 phases have fewer negative impacts on thermal diffusivities than τ 1 phases. With the same intermetallic compound, the solute atom Zn have more negative influences on thermal diffusivities of Mg–Zn–La/Ce alloys than the content of second phases. In order to quantitatively evaluate thermal conductivities and further design Mg alloys with both high strength and high thermal conductivity, a calculated method is provided to describe the thermal diffusivity of alloys as a function of alloy composition and phase constitution. A set of parameters for expression of thermal diffusivity of Mg–Zn–La/Ce alloys were obtained through assessing the experimental data. The thermal conductivities of Mg–Zn–La/Ce system were predicted and agreed well with experimental values with calculation error of 1.6% and standard error of ±3.0 W/(m K). The calculation method considering thermal diffusivity resistivity improves the calculation accuracy and would be physically significant.

Non-layer-transformed Mn3O4 cathode unlocks optimal aqueous magnesium-ion storage via synergizing amorphous ion channels and grain refinement

Aqueous rechargeable magnesium ion batteries (ARMBs) have obtained more attention due to the two-electrons transfer nature, low cost and safety. However, the scarcity of cathode materials seriously hinders the development of ARMBs because of the unfavorable strong interaction between Mg2+ and cathode material. Herein, we choose a pre-treated spinel Mn3O4 cathode for aqueous Mg2+ storage. The pre-treatment in Na2SO4 solution induces the grain refinement decorated with tortuous amorphous ion diffusion channels, facilitating the production of electrochemical reaction active sites and the diffusion of Mg2+, respectively, which achieve a (sub-)surface pseudocapacitance reaction between Mn (II) and Mn (III). As a result, the pre-treated Mn3O4 cathode exhibits a package of optimal performances, i.e., a capacity of 98.9 mAh g−1 and a high capacity retention rate of 99.4% after 2000 cycles. To the best of our knowledge, our work not only provides a new reaction mechanism of spinel Mn3O4 in aqueous batteries system, but also affords a high cycle stability electrode material for rechargeable Mg2+ energy storage.

Sectoral and growth rate control on elemental uptake by individual calcite crystals

Heterogeneous distribution of trace elements (impurities) within individual calcite crystals is a phenomenon commonly observed in natural and laboratory systems. Changes in thermodynamic intensive parameters (mostly chemical potential and temperature) cannot always explain the inhomogeneous impurity patterns in calcite crystals and it has been suggested that growth rate and crystallographic orientation may exert strong effects on elemental incorporation into calcite. In addition, there are a number of experimental studies on micro-scale element (E) distribution between non-equivalent pairs of calcite vicinal faces (known as sectoral zoning); however, the variability of partition coefficients (e.g., KE = (E/Ca)calcite/(E/Ca)fluid) within individual crystals remains undetermined.In this study, we have extended the work on elemental distribution between crystal sectors to evaluation of partition coefficients of trace and minor elements (Li, B, Mg, and Sr) in calcite crystal faces (10–14) and (01−12), whose growth rates were assessed. Growth entrapment model (GEM) and lattice strain theory were applied to explain KE heterogeneity by varying near-surface diffusivity of Mg and Sr and by varying surface enrichment factor for Li, B, Mg, and Sr. Decoupling of sectoral and growth rate effects reveals that sectoral zoning plays a key role in elemental distribution. More specifically, KLi and KB vary by more than one order of magnitude and KMg varies by a factor of two within individual crystal faces. Strontium sectoral distribution is different from those of Li, B, and Mg and KSr varies by up to a factor of two. These behaviors likely reflect different mechanisms of incorporation of Li, B, Mg, and Sr into calcite.

Eliminating intermetallic compounds via Ni interlayer during friction stir welding of dissimilar Mg/Al alloys

There is a substantial demand in transportation industries to join dissimilar Al and Mg alloy to reduce the structural weight further. However, it is challenging to produce high-strength joints of Al/Mg even with friction stir welding due to the formation of intermetallic compounds (IMCs). In a quest to suppress/eliminate the IMCs, we propose to add a Ni interlayer in a sandwich form between the Mg and Al plates. Widely used and industrially applicable AA6061-T6 and AZ31B Mg alloys are taken for experimentation in the present study. The Ni interlayer's effects on microstructure, mechanical properties, and IMCs characterization are studied. The Ni interlayer can drastically cease the molecular diffusion of Mg and Al across their interfaces, and typical IMCs Al3Mg2 and Al12Mg17 are eliminated. Significant dispersion of Ni with Al and Mg is found in the weld zone, which forms Al3Ni and Mg2Ni compounds. The energy-dispersive X-ray spectroscopy confirms the efficacy of Ni addition to wipe out the β and γ IMCs phases. The localized fracture analysis of Ni interlayered joint suggests dual-mode failure, i.e., ductile and brittle. The mechanical testing advocates better weld quality for Ni interlayered joints compared to its conventional ones.

(Invited) Prospects for Magnesium Diffusion Doping of GaN

Ex-situ p-type doping of GaN has been a long-standing challenge and prevented adoption of numerous devices. While regrowth of p-GaN on etched surfaces and ion implantation have made progress, technical challenges remain. Diffusion of Mg into GaN has received considerably less attention, primarily due to the extremely low diffusivity of Mg in GaN as well as the instability of GaN at the temperatures required (typically >1000oC), as well as its propensity to form compensating defects. Recent work at LLNL on GaN grown both on sapphire and n-type GaN substrates has demonstrated the potential for diffusion of Mg at temperatures as low as 700oC. This is theorized to be through enhanced formation of Gallium vacancies, which provide a pathway for rapid diffusion into GaN. Use of a solid Mg source, such as MgF2, capped by a metal has been shown to be effective, with the diffusivity dependent on the specific metal cap (Figure 1).This talk will discuss the chemical thermodynamics of this process, termed Gallidation Assisted Impurity Diffusion or GAID, methods for control, current challenges, and device results including enhanced barrier height Schottky contacts resulting from the process. Prospects for the future of the technique and its applicability to new device concepts will be briefly addressed.This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344, LLNL-ABS-821793. This support does not constitute an express or implied endorsement on the part of the Government. The information, data, or work presented herein was funded in part by the Advanced Research Projects Agency-Energy (ARPA-E), U.S. Department of Energy, PNDIODES program monitored by Dr. Isik Kizilyalli. Figure 1

Insertion of Magnesium into Antimony Layers on Gold Electrodes:Kinetic Behaviour

AbstractMagnesium based secondary batteries are regarded as a viable alternative to the immensely popular Li‐ion systems. One of the largest challenges is the selection of a Mg anode material since the insertion/extraction processes are kinetically slow because of the large ionic radius and high charge density of Mg2+. In an attempt to bridge the gap between insertion measurements in 3D composite electrode materials and that in an idealized pure model system, we studied the insertion and diffusion of Mg in a thin, massive layer of Sb deposited on Au by using PITT, CV, and potential step experiments. Sb has been suggested as an insertion material because magnesium can form intermetallic compound with it. The layered crystal structure of Sb leads should facilitate formation of such an intermetallic phase. Mg insertion from a MACC/tetraglyme electrolyte into Sb starts 300 mV positive of the onset potential of Mg deposition as shown by cyclic voltammetry. The molar ratio of Mg to Sb agrees well with the stoichiometry of Mg3Sb2 alloy (Zintl‐phase). The diffusion coefficient of Mg‐insertion into Sb – layers and the charge transfer rate have been estimated by the above techniques. Such diffusion coefficients, albeit still somewhat “apparent”, are much more closely related to the true diffusion coefficient in the metal or alloy. The solid‐state diffusion coefficient of Mg into the Sb layers is in the range of 4–8×10−14 cm2 s−1. A very high Tafel slope of 370 mV/dec was found in potential step experiments. Mg insertion was further investigated by XPS measurements. Besides Mg and Sb, Al and Cl signals were also detected, particularly at the outer parts of the layer.

Magnesium Diffusion from MgO Substrates in Sol–Gel‐Derived NiO Epitaxial Films: Effects of Heat Treatment Temperature and Li Doping

The effects of heat treatment temperature and Li doping on the structural properties of sol–gel‐derived NiO epitaxial films on MgO (100) substrates are investigated. X‐ray diffraction measurements indicate that the out‐of‐plane lattice parameters of undoped NiO films increase as the heat treatment temperature increases. This increase is particularly significant in films treated above 900 °C, in which out‐of‐plane and in‐plane lattice parameters are larger than the expected values for bulk NiO. This result cannot be explained by the strain originating in the lattice mismatch between NiO and MgO. In addition, the bandgap drastically increases in undoped films treated above 900 °C. Secondary ion mass spectrometry depth profiling demonstrates that undoped films treated above 900 °C are Ni1−xMgxO alloys generated by the diffusion of Mg from MgO substrates into NiO films, resulting in the anomalous characteristics of the prepared films. Furthermore, it indicates that the diffusion of Mg is reduced in Li‐doped films, which can be explained on the basis of defect chemistry, in which Ni vacancies decrease with the increase in Li concentration. Consequently, the increases in the lattice parameter and bandgap at high heat treatment temperatures are reduced in Li‐doped films.

Origin of multilayer corona textures in mafic granulites from the Sandmata Complex, Aravalli Craton (northwestern India): petrological characteristics and tectonic implications

In Late Proterozoic mafic granulites of the Sandmata Complex in Rajasthan, northwestern India, multilayer corona textures were formed along the interface between orthopyroxene and plagioclase. We examined the metamorphic conditions and processes of formation of these coronae, which provide an insight into the interplay between steady state and sequential diffusion-controlled mineral growth mechanisms. The individual corona–symplectite layers consist of clinopyroxene + quartz|garnet + clinopyroxene|garnet + quartz|K-feldspar, from the inner to the outer margins of the coronae. The single-value decomposition models suggest that the multilayered coronae were formed in a locally closed system, via sequential diffusion of Mg, Fe and Ca into the reaction zone, which has acted as the main driving force for the growth of corona textures. The relict orthopyroxene with exsolved clinopyroxene yields primary crystallization conditions of 8.4 ± 1.5 kbar and ~ 1100–1000 °C. Clinopyroxene in the innermost corona layer grew at ~ 9 kbar and 850–800 °C, whereas clinopyroxene + garnet grew outward at ~ 8 kbar and 700–600 °C. Subsequent hydrous retrogression (~ 6 kbar and 600–550 °C) resulted in the development of rimward zoning in garnet and the growth of amphibole. On combining textural relations and the above conventional P–T estimates, a near-isobaric cooling P–T path was reconstructed using phase equilibria modeling. Further, the near-isobaric cooling path is consistent with the magmatic underplating hypothesis in the Sandmata Complex, where the intrusion of magmatic bodies (i.e., Gyangarh–Asind igneous complex and Anjana granite) favored the development of granulite facies assemblage in norite and gabbronorite protoliths.

Investigation on electrochemical behaviors of MgCl2 impurity in LiCl-KCl melt

In this work, the electrochemical behaviors of impurity Mg(II) in LiCl-KCl melt were investigated at 673 K by using cyclic voltammetry (CV), chronopotentiometry (CP) and square wave voltammetry (SWV) techniques. Results showed that the semi-integral curve derived from CV measurements revealed that the reduction of Mg(II) was a quasi-reversible process. And the standard reaction rate constant of the order ≈10 −3 cm s −1 , calculated by Nicholson method, which showed that the redox reaction of Mg was in the quasi-reversible range of Matsuda-Ayabe standard. The EMF measurements were applied to measure the apparent standard potential and activity coefficient of Mg(II). According to the standard apparent potentials at various temperatures, the values of enthalpy and entropy changes were −673.3302 ± 4.3997 kJ mol −1 and 0.1930 kJ mol −1 K −1 , respectively. Chronoamperometry (CA) results showed that deposition of metal Mg on the W electrode was an instantaneous nucleation process under diffusion control. Additionally, the diffusion coefficients calculated by CP revealed that the temperature dependence obeyed the Arrhenius law. And the activation energy for diffusion of Mg(II) is 44.73 kJ mol −1 .

Comparative Insight into the Interfacial Phase Evolutions during Solution Treatment of Dissimilar Friction Stir Welded AA2198-AA7475 and AA2198-AA6013 Aluminum Sheets.

In the current research, dissimilar friction stir welded (FSW) sheets of AA2198-AA7475 and AA2198-AA6013 were solution treated at 460–580 °C for 1 h. Annealing at 580 °C led to complete degradation of both dissimilar weldments from the AA2198 side. According to the microstructure inspection, solution treatment triggered abnormal grain growth within the stir zone (SZ), and applying higher treatment temperatures enhanced the fraction of transformed grains. SEM analysis revealed that the pre-melting of grain boundaries (GBs) over 540 °C encouraged the diffusion of solute atoms to the GBs. The massive diffusion of Cu to the GBs led to the formation of Cu-rich eutectic phases in AA7475 and AA2198 and dense Cu-rich particles in AA6013. In the meantime, the diffusion of Mg and Zn to the GBs of AA7475 and Fe and Si to the GBs of AA6013 eventuated in the formation of coarse particles at the GBs which, in return, attenuated the bonding adhesion of the grains at SZ. The formation of remarkable Cu-rich phases in the pre-melted regions and significant contraction of the eutectic phase while cooling as well as the formation of particles at GBs resulted in intergranular failure of the joints from the AA2198 side of the SZ.

DFT study of adsorption and diffusion of Mg, K, Ca over monolayer antimonene

Density Functional theory (DFT) based calculations are carried out to investigate adsorption and diffusion properties of Magnesium (Mg), Potassium (K) and Calcium (Ca) over single layer antimony (Sb) i.e. antimonene. Ca has highest value of absolute adsorption energy followed by K and Mg respectively. Charge transfer is greater in case of K adsorbed antimonene as compared to both of the other metals. This affects the electronic properties such as bandstructure and density of states. Antimonene is semiconducting in its pristine form. The adsorption of K leads to a shift to metallic nature, whereas Mg and Ca adsorption still maintain the semiconducting nature after reducing the bandgap. Diffusion of these metals shows that K can easily diffuse through the antimonene surface as compared to the Mg and Ca. The value of diffusion barrier for Mg, K and Ca is 0.30, 0.12 and 0.43 eV respectively. The effective adsorption and charge transfer along with low values of diffusion barrier suggests that phosphorene can be explored further as potential candidate for metal-ion batteries.

Dendrite‐Free Li‐Metal Anode Enabled by Dendritic Structure

AbstractThe practical application of Li‐metal anode in high‐energy rechargeable Li batteries is still hindered by the uncontrollable formation of Li dendrites. Here, a facile way is reported to stabilize Li‐metal anode by building dendrite‐like Li3Mg7 alloys enriched with Li‐containing polymers as the physical protecting layer and LiH as the Li‐ion conductor. This unique dendritic structure effectively reduces local current density and accommodates volume change during the repeated Li plating/stripping process. More importantly, lithiophilic Li3Mg7 alloys not only guide the uniform Li deposition down into the below Li metal upon Li deposition, but also thermodynamically promote the extraction of Li during the reverse Li stripping process, which suppresses the parasitic reactions occurring on the surface of Li metal and hence inhibits the formation of Li dendrites. Moreover, the facile diffusion of Mg from Li3Mg7 alloys toward Li metal below is thermodynamically permitted, which leads to a uniform distribution of LiMg alloys inside the whole electrode and thus benefits long‐term deep cycling stability. As a result, the protected Li‐metal anode delivers stable and dendrite‐free cycling performance at 10 mA h cm−2 for over 900 h. When coupling this anode with LiFePO4 and S cathodes, the thus‐assembled full cells exhibit superior cycling stability.

Interdiffusion and impurity diffusion behavior in polycrystalline Mg-Y binary system

The diffusion behavior in binary Mg-Y system was investigated using polycrystalline Mg/Y diffusion couples at temperatures ranging from 573 to 823 K. For all diffusion couples, electron microprobe analysis was utilized for the measurement of concentration profiles. The interdiffusion coefficients in Mg solid solution and intermetallic phases were determined via the Boltzmann-Matano and Heumann-Matano method, respectively. In addition, the Hall method was employed to extrapolate the impurity diffusion coefficients of Y in pure polycrystalline Mg and Mg in pure polycrystalline Y. The results showed that the interdiffusion coefficient in Mg solid solution increased with an increase of Y concentration, and the corresponding pre-exponential factor and activation energy both increased nearly linearly. The pre-exponential factor and activation energy for Y impurity diffusion in Mg were determined to be 2.36×10−8 (±9.0×10−9) m2/s and 85.61 (±2.0) kJ/mol, while those for Mg impurity diffusion in Y were determined to be 3.47×10−7 (±7.6×10−7) m2/s and 95.90 (±6.7) kJ/mol. Simultaneously, the pre-exponential factor and activation energy for interdiffusion in intermetallic phase Mg24Y5 were determined to be 9.96×10−9 (±2.9×10−9) m2/s and 68.98 (±2.0) kJ/mol；while those for Mg2Y were determined to be 1.18×10−9 (±9.0×10−10) m2/s and 64.54 (±3.2) kJ/mol. Additionally, the vacancy diffusion was dominant mechanism above 723 K, while the grain boundary diffusion mechanism dominated below 723 K in polycrystalline Mg-Y binary system.