Conductivity Of Mg Research Articles

The Influence of Reorientational and Vibrational Dynamics on the Mg2+ Conductivity in Mg(BH4)2·CH3NH2.

Reorientational dynamics in solid electrolytes can significantly enhance the ionic conductivity, and understanding these dynamics can facilitate the rational design of improved solid electrolytes. Additionally, recent investigations on metal hydridoborate-based solid electrolytes have shown that the addition of a neutral ligand can also have a positive effect on the ionic conductivity. In this study, we investigate the dynamics in monomethylamine magnesium borohydride (Mg(BH4)2·CH3NH2) with quasielastic and inelastic neutron scattering, density functional theory calculations, and molecular dynamics simulations. The results suggest that the addition of methylamine significantly speeds up the reorientational frequency of the BH4 - anion compared to Mg(BH4)2. This is likely part of the explanation for the high Mg-ion transport observed for Mg(BH4)2·CH3NH2. Furthermore, while the dynamics of both the BH4 - anion and the CH3 group of the methylamine ligand is rapid, the NH2 group of the methylamine ligand exhibits much slower reorientations, as confirmed by both experimental and computational investigations. Notably, molecular dynamics calculations reveal mean square displacements of 0.387 Å2 for NH2, 1.503 Å2 for CH3, and 1.856 Å2 for BH4 - using a trajectory of 10 ps. This study confirms the simultaneous presence of fast dynamics and high ionic conductivity in a metal borohydride-based system and can function as an experimental foundation for future studies on dynamics in hydrogen-rich solid electrolytes.

Effect of Cu addition on the thermal conductivity and mechanical properties of Mg–Zn-xCu-Ce alloys

Thermal conductivity and mechanical properties of Mg–Zn-xCu-Ce alloys with different Cu contents under low extrusion temperature were systematically investigated in this work. The results shows that MgZnCu and Ce-rich (Mg, Zn, Cu, Ce) phase were formed in Mg–Zn-xCu-Ce alloys with high Cu content, which have significantly effect on the thermal conductivity and dynamic recrystallization (DRX). The distribution of grain morphology and LAGBs indicates that CDRX is the main mechanism. The addition of Cu element has an inhibitory effect on the DRX behavior, greatly refining the DRXed grains. After extrusion, a large amount of nano-phase is dispersed in the MZEC alloy, which has a strong pinning effect on dislocations. The formation of MgZnCu phase with high thermal conductivity sacrifices the solute atoms of Zn and Cu in α-Mg matrix, which leads to reduction of lattice distortion of Mg matrix, thereby ensuring high thermal conductivity of Mg–Zn–Cu–Ce ternary magnesium alloys. With the increase of Cu content, the strength and thermal conductivity of the alloy gradually increases. When the Cu content is 3.6 wt%, UTS (ultimate tensile strength), YS (yield strength), EL (elongation) and thermal conductivity are 350 MPa, 317 MPa,15.8% and 135 W/m∙K, respectively.

The effects of substitution of yttrium for Ce-rich mischmetal on the mechanical properties and thermal conductivity of Mg–4Al–4Zn–4RE alloy

Mechanical properties and thermal conductivity are the key parameters for Mg alloys used as the structural components for heat dissipation, balancing good mechanical properties and high thermal conductivity is still a long-term challenge. Here, we investigated the influence of Y contents on the microstructure and mechanical properties of the as-cast Mg–4Al–4Zn–(4–x)RE–xY (x: 0, 1, 2, 3, 4 wt%), where RE was the Ce-rich misch metal. Compared with Mg–4Al–4Zn–4RE alloy, the strength and ductility were significantly enhanced due to the well-optimized microstructure by the suitable substitution of Y for Ce-rich RE. Especially, the ultimate tensile strength and elongation were significantly improved from 201 MPa to 244 MPa and 8.0% to 16.8%, respectively, when the Y content was increased from 0 to 3.0 wt%. Meanwhile, the thermal conductivity still kept a high level within the range of 84.2–89.6 W(m·K)−1. The significantly improved elongation was mainly attributed to the reduction and refinement of coarse lamellar Al11RE3 intermetallic phases with increasing Y contents. The as-cast Mg–4Al–4Zn–1RE–3Y alloy exhibited high performance with a combination of high tensile properties and good thermal conductivity.

Manipulating the mechanical strength and thermal conductivity of a Mg–4Zn-0.6Zr alloy through Ca addition

In this study, the microstructure, mechanical properties, and thermal conductivity of as-extruded Mg–4Zn-0.6Zr-xCa (x = 0, 0.3, 0.6, 0.9 wt%) alloys were investigated. The results revealed a bimodal grain size distribution in all the alloys due to incomplete dynamic recrystallization (DRX), characterized by the coexistence of elongated deformed grains and equiaxed DRX grains. The bimodal grain size distribution enhanced the mechanical properties of the studied alloys. Furthermore, Ca alloying facilitated the formation of Ca2Mg6Zn3 phases, through which the DRX extent was also enhanced. The precipitation of secondary phases, along with the increased DRX induced by Ca addition, was beneficial in eliminating the lattice distortion of the alloys, resulting in improved thermal conductivity compared to the Ca-free Mg–4Zn-0.6Zr alloy. The optimum combination of mechanical properties and thermal conductivity was achieved in the Mg–4Zn-0.6Zr-0.6Ca alloy, with yielding strength, ultimate tensile strength, tensile fracture elongation, and thermal conductivity values of 271 MPa, 318 MPa, 17.6 %, and 123.9 W/(m‧K), respectively. This work demonstrates that Mg–Zn–Zr–Ca-based alloys can be developed with high strength and high thermal conductivity, significantly expanding the industrial application of magnesium alloys.

Thermoelectric Properties of N-type Mg<sub>3</sub>La<sub>0.005</sub>Mn<sub>x</sub>SbBi Materials Doped with La and Mn

Mg<sub>3</sub>Sb<sub>2</sub>-based n-type materials are consisted of earth-abundant elements and possess comparable thermoelectric properties with n-type Bi<sub>2</sub>Te<sub>3</sub> at low temperatures, which make them promising candidates for cooling and power generation applications in terms of cost and performance. Substitution of Sb atom with chalcogen elements (Te, Se S) is a conventional method for n-type doping, but doping cations such as rare-earth elements and transition metals is also widely studied for its unique advantages. In this study, La and Mn were selected for co-doping of Mg3SbBi, and the thermoelectric performances of the doped materials were investigated. Mg<sub>3</sub>La<sub>0.005</sub>Mn<sub>x</sub>SbBi (0  <i>x</i>  0.015) polycrystalline samples were made by sintering the fine powders of the mother alloy after arc melting, in which elemental Mn and LaSb compound were included for n-type dual doping. Considering the loss of Mg at elevated temperatures by vaporization, the molar ratio of Mg, Sb, and Bi in the mixture for arc melting was set to 4 : 1 : 1 with excess Mg. Analysis shows that all the samples are n-type, and the electrical conductivity of Mg<sub>3</sub>La<sub>0.005</sub>Mn<sub>0.015</sub>SbBi increased by 62% from the Mn-free Mg<sub>3</sub>La<sub>0.005</sub>SbBi at 298 K. In addition, the lattice thermal conductivity (<i><sub>lat</sub></i>) decreased with increasing Mn content in the measured temperature range of 298-623 K. The minimum value of <i><sub>lat</sub></i> was about 0.60 W m<sup>-1</sup>K<sup>-1</sup> in Mg<sub>3</sub>La<sub>0.005</sub>Mn<sub>0.015</sub>SbBi at 523 K, which is about 19% smaller than that of the Mn-free sample. As a result of these enhancements in thermoelectric performance, the maximum figure of merit (<i>zT<sub>max</sub></i>) of 1.12 was obtained in Mg<sub>3</sub>La<sub>0.005</sub>Mn<sub>0.01</sub>SbBi and Mg<sub>3</sub>La<sub>0.005</sub>Mn<sub>0.015</sub>SbBi at 573 K, and the <i>zT</i> at 298 K increased by 73% to 0.35 in Mg<sub>3</sub>La<sub>0.005</sub>Mn<sub>0.015</sub>SbBi compared to Mn-free Mg<sub>3</sub>La<sub>0.005</sub>SbBi, which is beneficial to room-temperature applications.

Research On Mg Doping in Nitride Semiconductor Materials

Summarized the achievements of various model research directions in nitride Mg doped semiconductors in this thesis. Due to the Internal properties of Mg acceptors which resulting the low ionization rate of acceptor, and the low hole mobility in heavily Mg doped nitrides, the conductivity of Mg doped nitrides is limited. At present, research is divided into three categories of models, one is a new type of polarization model. This model adopts a built-in electron polarization ionization acceptor dopant in the bulk uniaxial semiconductor crystal, and provides an attractive solution for the problem of P-type and n-type doping in broadband gap semiconductors. The other two are the traditional thermal activation model. There are mainly ultra-high-pressure-annealing (UHPA) and multicycle rapid thermal annealing (MRTA) respectively. Both of these schemes can activate more Mg impurities, resulting in higher conductivity in nitrides. The principles, advantages and disadvantages, and future development prospects will be explained of these three models in this thesis.

Relationship between microstructure evolution and thermal conductivity of Mg–Sn–Ca alloys

Relationship between microstructure evolution and thermal conductivity of Mg–Sn–Ca alloys

First-principles investigation of mechanical properties, elastic anisotropy, and ultralow lattice thermal conductivities of ductile Mg–Bi alloys

The crystal structures, mechanical properties, anisotropic properties, and lattice thermal conductivities of Mg–Bi alloys have been investigated by particle swarm optimization structure prediction method and first-principles calculations. Apart from the well-known stoichiometry of Mg3Bi2, the novel stable stoichiometry of Mg4Bi, as well as several metastable stoichiometries (i.e., Mg3Bi, Mg2Bi, and MgBi) are predicted. Meanwhile, the calculated phonon dispersion curves and elastic constants show that the above five Mg–Bi alloys are dynamically and mechanically stable, respectively. Moreover, the calculated mechanical properties indicate that the studied Mg–Bi alloys with various stoichiometries behave ductility. Simultaneously, they exhibit obvious anisotropic characters and the degree of anisotropy follows the order of MgBi > Mg2Bi > Mg3Bi > Mg4Bi > Mg3Bi2. More importantly, the minimum lattice thermal conductivities of MgBi and Mg2Bi are smaller than that of the well-known Mg3Bi2. The adsorption of O atom on the Mg3Bi (001) surface is more sensitive compared with other four Mg–Bi (001) surfaces.

Microstructure evolution and improvement of thermal conductivity in Mg–2Sn alloy induced by La addition

Rare earth elements are commonly used to improve the properties of magnesium alloys. In this paper, the effects of various La contents on the microstructure and thermal properties of Mg–2Sn alloys were investigated. Cooling curve thermal analysis technique was adopted to reveal the microstructure evolution of Mg-2Sn-xLa alloys. La addition contributed a new eutectic reaction to occur at 639 °C and the eutectic structure was determined to be LaMgSn phase. Mg12La, Mg2Sn and matrix precipitated phases may be generated in the microstructure with further increase of La content. The thermal conductivity of Mg–2Sn alloy can be effectively improved by La addition and the maximum value 149 W/(m·K) was achieved at the Sn/La atomic ratio of 1. The thermal conductivity of Mg-2Sn-2.3La alloy could further increase to 152 W/(m·K) after solution heat treatment. The addition of La reduced the amount of solute atoms and eliminated the Sn enriched region, resulted in a rapid increase in the thermal conductivity of the Mg–2Sn alloy. The spheroidization of Mg12La phase contributed to the further improvement of the thermal conductivity after solution treatment.

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.

Microstructure, mechanical properties, and electrical conductivity of Mg-8Li-2Y-Zn/Al multilayered composites fabricated by cross asynchronous accumulative roll bonding.

Mg-Li alloy is a material with great potential for development but its application in multiple fields is limited due to disadvantages, such as low strength and poor molding properties. In this study, Mg-8Li-2Y-Zn/Al multilayered composites were prepared by the Al layer cladding Mg-Li alloys using a cross asynchronous accumulative roll banding (CAARB) method, and the changes in microstructural characterization, mechanical properties, and electrical conductivity after rolling were evaluated. The results showed that the asynchronous rolling introduced additional shear variables, which provided the conditions for the aluminum layers to fracture to form wave patterns and improve the formability of the composites. The change in the rolling direction caused the grain orientation to be dispersed along the TD direction. The microhardness and tensile strength of the Mg-8Li-2Y-Zn/Al composites increased during the CAARB and reached a maximum after four cycles. In addition, calculations based on the skin depth indicate that the addition of Al layers benefits the composites in terms of improved electrical conductivity. Overall, the addition of Al layers allows more flexibility in the design and extension of Mg-Li alloys, and these findings provide insights into the control of microstructure and improvement of properties of Al/Mg-Li multilayered composites using the CAARB process.

Different Effects of Mg and Si Doping on the Thermal Transport of Gallium Nitride

Mg and Si as the typical dopants for p- and n-type gallium nitride (GaN), respectively, are widely used in GaN-based photoelectric devices. The thermal transport properties play a key role in the thermal stability and lifetime of photoelectric devices, which are of significant urgency to be studied, especially for the Mg- and Si-doped GaN. In this paper, the thermal conductivities of Mg- and Si-doped GaN were investigated based on first-principles calculations and phonon Boltzmann transport equation. The thermal conductivities of Mg-doped GaN are found to be 5.11 and 4.77 W/mK for in-plane and cross-plane directions, respectively. While for the Si-doped GaN, the thermal conductivity reaches the smaller value, which are 0.41 and 0.51 W/mK for in-plane and cross-plane directions, respectively. The decrease in thermal conductivity of Mg-doped GaN is attributed to the combined effect of low group velocities of optical phonon branches and small phonon relaxation time. In contrast, the sharp decrease of the thermal conductivity of Si-doped GaN is mainly attributed to the extremely small phonon relaxation time. Besides, the contribution of acoustic and optical phonon modes to the thermal conductivity has changed after GaN being doped with Mg and Si. Further analysis from the orbital projected electronic density of states and the electron localization function indicates that the strong polarization of Mg-N and Si-N bonds and the distortion of the local structures together lead to the low thermal conductivity. Our results would provide important information for the thermal management of GaN-based photoelectric devices.

The performance conductivity of Mg/Graphene nanosheet as anode of battery

Research on performance conductivity of magnesium (Mg)/graphene nanosheet (GNS) as anode of batteries was carried out. This research is an experimental laboratory research. The purposes of this research are to synthesize anode material on battery and to evaluate performance of GNS and Mg/GNS as a supporting material and a candidate of electrode on battery anode, respectively. First, GNS was synthesized by using graphite as a raw material (modified Hummer’s method) and electrode of Mg/GNS was prepared with impregnation method. The characterization of GNS and Mg/GNS was carried out by using XRD and conductometer, respectively. The XRD data shows a weak and broad peak on GNS (2θ = 26.0°) indicating GNS was synthesized well and on 2θ = 43.79° indicating that the Mg was deposited inside of the graphene nanosheet. The conductivity data showed that Mg 2.02%/GNS has the highest electric conductivity of Mg (63.6945μS/cm) among to graphite and commercial battery anodes. Mg 1.91%/GNS has the lowest electric conductivity. Based on those data, GNS and Mg/GNS are potentially be used as an anode on battery.

High‐Density Frenkel Defects as Origin of N‐Type Thermoelectric Performance and Low Thermal Conductivity in Mg3Sb2‐Based Materials

AbstractMg3Sb2‐based intermetallic compounds with exceptionally high thermoelectric performance exhibit unconventional n‐type dopability and anomalously low thermal conductivity, attracting much attention to the underlying mechanisms. To date, investigations have been limited to first‐principle calculations and thermodynamic analysis of defect formation, and detailed experimental analysis on crystal structure and phonon modes has not been achieved. Here, a synchrotron X‐ray diffraction study clarifies that, against a previous view of a simple crystal structure with a small unit cell, Mg3Sb2 is inherently a heavily disordered material with Frenkel defects, charge‐neutral defect complexes of cation vacancies and interstitials. Ionic charge neutrality preserved in Mg3Sb2 is responsible for exotic n‐type dopability, which is unachievable for other Zintl phase materials. The thermal conductivity of Mg3Sb2 exhibits deviation from the standard T−1 temperature dependency with strongly limited phonon transport due to a strain field. Inelastic X‐ray scattering measurement reveals enhanced phonon scattering induced by disorder. The results will draw renewed attention to crystal defects and disorder as means to explore new high‐performance thermoelectric materials.

Towards P-Type Conduction in Hexagonal Boron Nitride: Doping Study and Electrical Measurements Analysis of hBN/AlGaN Heterojunctions

Reliable p-doped hexagonal boron nitride (h-BN) could enable wide bandgap optoelectronic devices such as deep ultra-violet light emitting diodes (UV LEDs), solar blind photodiodes and neutron detectors. We report the study of Mg in h-BN layers as well as Mg h-BN/AlGaN heterostructures. Mg incorporation in h-BN was studied under different biscyclopentadienyl-magnesium (Cp2Mg) molar flow rates. 2θ-ω x-ray diffraction scans clearly evidence a single peak, corresponding to the (002) reflection plane of h-BN with a full-width half maximum increasing with Mg incorporation in h-BN. For a large range of Cp2Mg molar flow rates, the surface of Mg doped h-BN layers exhibited characteristic pleats, confirming that Mg doped h-BN remains layered. Secondary ion mass spectrometry analysis showed Mg incorporation, up to 4 × 1018 /cm3 in h-BN. Electrical conductivity of Mg h-BN increased with increased Mg-doping. Heterostructures of Mg h-BN grown on n-type Al rich AlGaN (58% Al content) were made with the intent of forming a p-n heterojunction. The I-V characteristics revealed rectifying behavior for temperatures from 123 to 423 K. Under ultraviolet illumination, photocurrent was generated, as is typical for p-n diodes. C-V measurements evidence a built-in potential of 3.89 V. These encouraging results can indicate p-type behavior, opening a pathway for a new class of wide bandgap p-type layers.

Magnesium-doped Na2FeP2O7 cathode materials for sodium-ion battery with enhanced cycling stability and rate capability

Magnesium doping is successfully utilized to enhance the electrochemical performance of Na2FeP2O7 for sodium-ion batteries (SIBs). A series of morphological and electrochemical tests indicate that Mg doping does not affect the structures of the host phase and the abundant defects in carbon coating are beneficial for electronic conductivity. A new peak at ~2.70 V during the first few cycles in CV curves is observed, which is related to the increase of specific capacity during the lifespan test. DFT calculation results reveal the enhanced electronic conductivity in Mg doped Na2FeP2O7, which is consistent with experimental observations. The Na2FeP2O7 with an appropriate Mg doped of 5% exhibits an initial reversible capacity of 90 mAh g−1 at 0.1 C without an obvious decline after 2000 cycles at 9 C. The specific capacity of Mg doped Na2FeP2O7 does not decrease fatally even the amount of Mg doped comes to 20%. The Coulombic efficiency is very high, close to 100% in all samples. The excellent electrochemical performance of Mg doped Na2FeP2O7 presents great potential as cathodes for advanced SIBs.

Microstructure and thermophysical properties of Mg−2Zn−xCu alloys

Abstract The microstructure and thermophysical properties of Mg−2Zn−xCu alloys (x=0.5, 1.0 and 1.5, at.%) were investigated through microstructural and thermophysical characterization, heat treatment, and first-principles calculations. It was found that the addition of Cu had influence on the microstructure and thermophysical properties of the alloy. As the Cu content increased, the content of the MgCuZn phase increased in the as-cast alloys along with the electrical and thermal conductivities. After solution treatment, the eutectic structure partially decomposed and Zn atoms dissolved into the matrix, leading to the decrease in both the electrical and thermal conductivities of the alloy. During the early stages of the aging treatment, solute atoms precipitated from the matrix, thus increasing the electrical conductivity of the alloy. After aging for 24 h, the thermal conductivity of Mg−2Zn−1.5Cu alloy reached the maximum of 147.1 W/(m·K). The thermostable MgCuZn phases were responsible for increasing the electrical and thermal conductivities. Smaller amounts of Zn atoms dissolved in the matrix resulted in smaller lattice distortion and higher conductivities. The first-principles calculations findings also proved that the MgCuZn phases had very high conductance.

Reduced Thermal Conductivity of Mg2(Si, Sn) Solid Solutions by a Gradient Composition Layered Microstructure.

Solid solutioning of Mg2(Si, Sn) has been a promising approach in reducing thermal conductivity and leads to improvement of thermoelectric performance. In addition to the Mg2(Si, Sn) solid solutions, we have noticed a layered structure with a gradient composition, which is formed by nonequilibrium solidification and peritectic reaction process and can provide further reduction of thermal conductivity of the Mg2(Si, Sn) solid solutions. All layers of the layered structure have the same face-centered cubic-based structure but varying Sn/Si concentration ratios in each layer. The interfaces between the layers are semi-coherent, reticulating with different numbers of misfit dislocations. Such an interfacial structure brings large numbers of phonon-scattering sources, resulting in further reduction of thermal conductivity in the Mg2(Si, Sn) solid solutions. Consequently, the undoped Mg2Si0.75Sn0.25 containing a higher density of the layered structure has relatively lower thermal conductivity, 1.9 W m-1 K-1 at 523 K, than Mg2Si0.25Sn0.75 with a much lower density of the layered structure, 2.3 W m-1 K-1 at 523 K.

Microstructure, Thermal Conductivity and Mechanical Properties of the Mg–Zn–Sb Ternary Alloys

A novel Mg alloys of Mg–xZn–ySb (x = 0, 2, 4, 6; y = 0, 0.2, 0.5, 0.8, 1.2) were designed and their microstructure, thermal conductivity and mechanical properties were systematically investigated in the present study. The as-cast Mg–Zn–Sb ternary alloys consist of α-Mg, Mg4Zn7 and Mg3Sb2 phases. Sb addition can refine the eutectic structure (α-Mg + Mg4Zn7) by the growth of Mg4Zn7 on Mg3Sb2 phases. The thermal conductivity of Mg–Zn–Sb alloys decreased with increasing Sb content. There existed an interactive effect of Zn/Sb on the thermal conductivity of the Mg–Zn–Sb alloys. The negative effect of Sb addition on thermal conductivity of alloys was getting smaller with increasing Zn content in alloys. The negative effect of Mg3Sb2 phases on the thermal conductivity of alloys could be weakened by the formation of weak-scattering Mg4Zn7 coated on Mg3Sb2 phases. The best refinement effect on microstructure could be obtained with 0.8 wt%Sb addition. Mg–4Zn–0.8Sb alloy possess the best comprehensive properties with thermal conductivity of over than 120 W/(m·K) and UTS of 185.6 MPa.

A review on thermal conductivity of magnesium and its alloys

Abstract This review summarizes recent researching works the thermal conductivity of Mg–Zn, Mg–Al, Mg–Mn and Mg–RE alloys. Solute atoms, heat treatment, deformation and temperature, which have significant influence on the thermal conductivity of magnesium alloys, are highlighted. For an individual solute atom, its effects on thermal conductivity are highly dependent on its chemical valence, radius and extra-nuclear electrons. The thermal conductivity of Mg alloys is decreased by solution treatment, but improved by aging and/or annealing treatments. As for the deformed Mg alloys, the thermal conductivity along transverse or normal direction is superior to that of along extrusion or rolling direction. We expect this review is helpful for those who are working on developing Mg alloys with superior thermal conductivity.