The feasibility of tunable p-type Mg doping in a GaN monolayer nanosheet

Based on density functional theory, the electronic structures, formation energy and transition energy level of a p-type Mg-doped GaN nanosheet are investigated. Numerical results show that the transition energy level decreases monotonously with increasing Mg doping concentration in Mg-doped GaN nanosheet systems, which is lower than that of the Mg-doped bulk GaN case. Moreover, the formation energy calculations indicate that Mg-doped GaN nanosheet structures can be realized under N-rich experimental growth conditions.     

Hydrogen storage properties of Mg-doped Ti_(1.2)Fe alloys synthesized by mechanical alloying

1　INTRODUCTIONHydrogenstoragematerials ,usedinhydrogensourcesystemsforfuelcellshavebeeninvestigatedduetotheirhighvolumetricdensity ,safety ,easyminiaturizationandconvenientoperation .Consider ingallkindsofhydrogenalloysasawhole ,AB typeTiFealloysareknowntobemuchmoresuitableforusingin portableormobilePEMFCbecauseofitshighreversiblehydrogenstoragecapacity ,whichismuchhigherthanthatofAB5 typealloys.Ontheotherhand ,theactivationpropertiesoftheTiFeal loysare poor .Forexample ,typically ,…     

Effect of Zn Addition on the Microstructure and Mechanical Properties of Cast Mg-10Gd-3.5Er-xZn-0.5Zr Alloys

In this work, the effects of Zn content (0-2 wt%) on microstructural evolution and mechanical properties of cast Mg-10Gd-3.5Er-0.5Zr alloys are studied. The results show that the as-cast Mg-10Gd-3.5Er-xZn-0.5Zr alloys are mainly composed of Mg matrix and secondary (Mg, Zn)₃(Gd, Er) phases distributed along grain boundaries. With the increase in Zn content, the volume fraction of secondary (Mg, Zn)₃(Gd, Er) phases increases and the grains get refined. In the process of solid solution treatment, Zn addition can lead to the formation of long-period stacking ordered (LPSO) structures and the volume fraction of LPSO structures increases with Zn content. In addition, the Zn addition can reduce the vacancy formation energy and accelerate the diffusion rate of RE elements in Mg matrix. Because of the comprehensive effect of secondary phases and the accelerated diffusion rate, the base alloy and 2Zn alloy have less grain growth after solid solution treatment than that of the 0.5Zn alloy and 1Zn alloy. The precipitation process is also accelerated by enhanced diffusion rate. At room temperature (RT), the strengthening effect of β^'+ β₁ precipitates is more effective than that of LPSO structures, so the peak-aged 0.5Zn alloy exhibits the most excellent mechanical performance at RT, with yield strength of 219 MPa, ultimate tensile strength 296 MPa and elongation of 6.4%. While LPSO structures have stronger strengthening effect at elevated temperature than that of β^'+ β₁ precipitates, so the 1Zn alloy and 2Zn alloy have more stable mechanical performance than that of the base alloy and 0.5Zn alloy with the increase in tensile temperature.     

Microstructure and growth morphology of Frank-Kasper phase in rapidly solidified Mg32Al17Zn32 ternary alloys

In the present investigation, the microstructures and growth morphology of Mg32(Al,Zn)49 Frank-Kasper phase in rapidly solidified Mg32Al17Zn32 ternary alloys were studied in detail. The samples were characterised by X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), field-emission scanning electron microscopy (FE-SEM) and energy dispersive spectrum (EDS). The results show that the microstructures mainly consist of Mg32(Al,Zn)49 Frank-Kasper phase and interdendritic Mg-rich φ-phase. Under rapid solidification con-dition, Mg32(Al,Zn)49 Frank-Kasper phase reveals a perfect faceted dendritic characteristic in the shape of a three-fold symmetric micro-structure with doublet tips in the axes direction. Observations for fracture surfaces show that the growth morphology of Mg32(Al,Zn)49 grains was truncated cubic, and its growth mechanism was also discussed.     

Mg-7Gd-5Y-1Nd-xZn-0.5Zr(x=0,1,2)挤压态合金微观组织和力学性能

采用扫描电子显微镜、电子背散射衍射、透射电子显微镜、高角度环形暗场-扫描透射,分析了Mg-7Gd-5Y-1Nd-xZn-0.5Zr(x=0,1,2,质量分数,％)挤压态合金微观组织结构和力学性能,旨在探索Zn对于合金性能影响的微观机制.结果表明:在Mg-7Gd-5Y-1Nd-0.5Zr合金中添加Zn元素,不仅形成LPS...     

Al-5Zn-1.6Mg合金焊缝中Zn与Mg比值的研究

本文采用钨极氩弧焊并在焊后热处理条件下,通过变动焊丝成分,研究了Al-5Zn-1.6Mg 合金焊缝中Zn Mg 含量和Zn 与Mg 比值对接头性能,特别是对接头应力腐蚀性能的影响规律.指出,接头的抗应力腐蚀性能不仅与焊缝中Zn Mg 含量有关,而且也取决于其中Zn 与Mg 的比值。如果焊缝中Zn Mg 含量一定,则以Zn 与Mg 比值接近2.7时的抗应力腐蚀性能为最好。这些研究结果已经用于海洋构件的试制中.本文还介绍了采用对热裂比较敏感的Al-5Zn-1.6Mg 合金,建造具有多种接头型式的复杂构件时.防止焊接开裂的一些成功经验。     

Oxidation of etched Zn foil for the formation of ZnO nanostructure

Oxidation of Zn foil at temperatures of 100-400 °C was carried out in air to produce ZnO with various nanostructures. The final morphology of the oxidised Zn foil is largely dependent on the oxidation temperatures. At less than 300 °C, spherical oxide grains are seen. At 400 °C, 50 nm thick, porous nanosheets were formed after 30 min of oxidation. In portions of the samples, nanorods can be seen with diameters <10 nm and lengths reaching 1 μm. The nanosheets were formed in accordance to a vapour-solid mechanism whereas the nanorods were formed by diffusion of Zn through a certain path leading to the rod structure. At 450 °C, the nanorods became much more uniform. Oxidation at 500 °C resulted in ZnO nanorods. The rods are also blunt with smaller rods seen to branch out from the main rod. The luminescence properties of the ZnO were investigated as a function of the morphology of the oxide. Both green and blue emissions are seen for the samples with nanosheets whereas the nanorods ZnO has mostly green emission.     

Low-temperature growth and optical properties of ZnO nanorods

Zinc oxide (ZnO) nanorods were grown on ITO conducting glass by the chemical solution deposition method (CBD) in an aqueous solution that contained zinc nitrate hexahydrate (Zn(NO₃)₂·6H₂O) and methenamine (C₆H₁₂N₄). The size of ZnO nanorods increased with molar concentration of zinc nitrate, and the nanorods with different aspect ratios also formed through tuning the reaction time when the molar concentration was 0.1 M. The length of nanorods increased significantly with the reaction time, but the thickness of the film deposited on the substrate only slightly increased. From the X-ray measurement results, it can be seen that the growth orientation of the as-prepared ZnO nanorods was [0 0 2]. Photoluminescence measurements were also carried out, the result showed a blue shift in violet emission with the reduction in crystal size.     

Structure and stacking faults in layered Mg–Zn–Y alloys: A first-principles study

We use first-principles density functional theory total energy calculations based on pseudo-potentials and plane-wave basis to assess stability of the periodic structures with different stacking sequences in Mg–Zn–Y alloys. For pure Mg, we find that the 6-layer (6l) structure with the ABACAB stacking is most stable after the lowest energy hcp (2l) structure with ABAB stacking. Addition of 2 at.% Y leads to stabilization of the structure to 6l sequence whereas the addition of 2 at.% Zn makes the 6l energetically comparable to that of the hcp. Stacking fault (SF) on the basal plane of 6l structure is higher in energy than that of the hcp 2l Mg, which further increases upon Y doping and decreases significantly with Zn doping. SF energy surface for the prismatic slip indicates activation of non-basal slip in alloys with a 6l structure. Charge density analysis shows that the 2l and 6l structures are electronically similar which might be a cause for better stability of 6l structure over a 4l sequence or other periodic structures. Thus, in an Mg–Zn–Y alloy, Y stabilizes the long periodicity, while its mechanical properties are further improved due to Zn doping.     

溶剂热法水热后处理合成ZnS纳米棒

采用水热后处理方法将片状、共价键结合的有机-无机复合硫化物ZnS·0.5en放入热液中热解,制备六方纤锌矿结构ZnS纳米棒,利用X射线衍射仪、透射电子显微镜、红外吸收光谱仪分析了水热后处理对ZnS的晶体生长和结构形貌的影响.结果表明ZnS纳米棒是单晶结构,长度达1μm,直径约有30～40nm.纳米ZnS纳米棒的生长符合溶剂配位分子模板机理.     

Zn与Mg质量比对热挤压Al-Zn-Mg-Sc显微组织及力学性能的影响

制备了Al-2Mg-0.4Sc、Al-5Mg-0.4Sc、Al-5Mg-2Zn-0.4Sc和Al-5Zn-2Mg-0.4Sc等4种合金并在350℃进行热挤压,通过光学显微镜(OM),X射线衍射(XRD),扫描电子显微镜(SEM)、室温拉伸测试,研究了Zn/Mg比对于Al-Zn-Mg-Sc合金组织与力学性能的影响。结果表明,Zn/Mg比的提高对于铸态晶粒具有细化作用,挤压后发生动态再结晶,晶粒尺寸显著减小,但挤压态晶粒尺寸并未随Zn/Mg比的提高而减小。另一方面,Zn/Mg比的提高使Mg32(Al,Zn)49第二相数量增加,且呈现更明显的网状结构。挤压态Al-Zn-Mg-Sc合金屈服强度随Zn/Mg比的提高而提升,主要由于大量Al3Sc粒子与碎化的第二相呈网状分布于晶界,使第二相强化起到主导作用。     

熔盐电解制备四元Mg-Zn-Li-Ca合金(英文)

在LiCl-KCl-MgCl2-ZnCl2-CaCl2熔盐体系中,以钼为惰性电极,在温度为943K时,直接电解制备Mg-Zn-Li-Ca四元合金。循环伏安研究表明,在LiCl-KCl熔盐体系中,添加MgCl2、ZnCl2和CaCl2后,Li的析出电位明显正移。计时电位研究表明,当阴极电流密度等于或者更负于-1.55A/cm2时,Mg、Li/Zn和Ca能够实现四元沉积。X射线衍射研究表明,恒电流电解可以制备出由不同相组成的Mg-Zn-Li-Ca合金。采用金相显微镜和电子扫描显微镜对合金样品进行表征。能谱分析结果表明,Mg元素和Ca元素在合金中分布均匀,而Zn元素主要分布在基体的边缘。     

Tensile fracture of as-cast and hot rolled Mg-Zn-Y alloy with long-period stacking phase

An experimental Mg97Zn1Y2(molar fraction,%)alloy was produced by rolling the as-cast alloy.The microstructure of the alloy is composed of theα-Mg(also marked as 2H-Mg with reference to long-period stacking structure according to hexagonal close packed structure)and long-period stacking(LPS)phase.Tensile tests of Mg97Zn1Y2 alloy in comparison with pure Mg were conducted.The fracture morphologies of the tensile specimens were characterized and the microstructures near fracture surface were observed.The results show that the rolled Mg97Zn1Y2 alloy shows a mixed fracture mode including dimples indicating a ductile fracture pattern and a small fraction of cleavage planes indicating a brittle fracture pattern,which is different from the single brittle fracture of the as-cast alloy.In addition,the plastic deformation is mainly from dislocations induced strain with small strengthening effect during plastic deformation in the as-cast Mg97Zn1Y2 alloy,and the strain hardening rate is similar to that of the as-cast pure magnesium.The deformation mechanism of Mg97Zn1Y2 alloy is different from that of the pure magnesium according to a metallographical observation that whether twins are found or not.The strengthening effect hardly exists in the rolled Mg97Zn1Y2 alloy under the same dislocations induced strain,which is different from that of the as-cast alloy with moderate strengthening effect.     

Formation of oxidation-resistant Cu-Mg coatings on (001) Cu for oxide superconducting tapes

The formation of oxidation-resistant buffer layers on (001) oriented Cu for coated high-temperature superconducting tape applications was investigated. The approach employed Cu/Mg multilayer precursor films that were subsequently annealed to form either Mg-doped fcc Cu or intermetallic Cu₂ Mg. The precursor consisted of an Mg/Cu multilayer stack with 5 each of 25 nm thick Mg and 25 nm thick Cu layers which were grown at room temperature by sputter deposition. At annealing temperature of 400 °C, formation of the intermetallic Cu₂ Mg was observed. X-ray diffraction showed that the Cu₂ Mg (100) oriented grains were epitaxial with respect to the underlying Cu film, possessing a cube-on-cube orientation. In order to test oxidation resistance, CeO₂ films were deposited at elevated temperature on Ni/(Cu,Mg)/Cu/MgO structures. In case of the CeO₂ film on Ni/Cu/MgO, significant surface roughness due to the metal oxidation is observed. In contrast, no surface roughness is observed in the SEM images for the CeO₂/Ni/(Cu,Mg)/Cu/MgO structure.     

Preparation and characterization of Mg-doped CaCu3Ti4O12 thin films

Mg-doped CaCu_3?xMg_xTi₄O₁₂ (x=0, 0.05, 0.1, 0.15, 0.2, at.%) thin films were prepared by a modified sol?gel method. A comparative study on the microstructure and electrical properties of Mg-doped CaCu₃Ti₄O₁₂ (CCTO) thin films was carried out. The grain sizes of the Mg-doped CCTO thin films were smaller in comparison to the undoped CCTO films. Furthermore, compared to undoped CCTO films, Mg-doped CCTO thin films obtained higher dielectric constant as well as excellent frequency stability. Meanwhile, Mg doping could reduce the dielectric loss of CCTO thin films in the frequency range of 10⁴?10⁶ Hz. The results showed that the Mg-doped CCTO thin films had the better electrical characteristics compared with the undoped CCTO films. The nonlinear coefficient of Mg-doped CCTO thin films at x=0.15 and x=0.1 was improved to 7.4 and 6.0, respectively.     

Microstructures and properties of rapidly solidified Mg-Zn-Ca alloys

Ternary alloys based on the Mg-Zn-Ca system were produced by twin-roll rapid solidification.The alloys were characterized by OM,SEM,HRTEM,XRD,EDS and Micro-hardness.The results show that the rapidly solidified flakes are of fine dendritic cell structures with the cell size ranging from 1 to 5μm.The Mg-6Zn-5Ca alloy in RS and annealing(200℃for 1 h) states are mainly composed ofα-Mg,Mg_2Ca,Ca_2Mg_6Zn_3 and a small quantity of Mg_(51)Zn_(20),MgZn_2 and Mg_2Zn_3.Micro-hardness increases with the increment of...     

Effects of spherical quasi-crystal on microstructure and mechanical properties of ZA155 high zinc magnesium alloy

Effects of spherical quasi-crystal contained in Mg-Zn-Y-Mn master alloy on the microstructure and as-cast mechanical properties of ZA155 high zinc magnesium alloy have been investigated by means of optical microscopy, XRD, SEM, EDS, tensile test, impact test and hardness test. Experimental results show that the addition of spherical quasi-crystal contained in the Mg-Zn-Y-Mn master alloy into the ZA155 high zinc magnesium alloy resulted in grain refinement of the matrix, changing the morphologies of φ-Al2Mg5Zn2 phase and τ-Mg32(Al,Zn)49 phase from continuous net-like structures to discontinuous strip-like structure and blocky one, respectively.In the present research, the best comprehensive mechanical properties of reinforced ZA155 high zinc magnesium alloy has been obtained when 5.0wt% spherical quasi-crystal was introduced from the Mg-Zn-Y-Mn master alloy into the target alloy system. In such case, the room-temperature tensile strength reached 207 MPa, about 23% higher than that of the base alloy; the impact toughness peaked at 5.5 J/cm2, about 40% higher than that of the base alloy; and the elevated-temperature tensile strength reached 203 MPa, indicating improved heat resistance.     

Effects of secondary phases on texture and mechanical properties of as-extruded Mg–Zn–Er alloys

The effects of kinds of secondary phases on texture and mechanical properties of Mg–Zn–Er alloys were investigated. The results suggest that the I-phase has a great effect on modification of the texture via the discontinuous dynamic recrystallization mechanism (DDRX), which tends to form well-developed equiaxed recrystallized grains. Meanwhile, the W-phase plays an important role in refining the grain size via continuous dynamic recrystallization (CDRX), companied with a higher maximum texture intensity. Thus, the Mg–6Zn–1Er alloy containing I-phase shows a performance of higher elongation of 20.4%. The Mg–2Zn–2Er alloy including W-phase displays a better tensile strength, and the yield strength (YS) is about 247 MPa.     

Synthesis of ZnO nanorods and their optical absorption in visible-light region

Single crystalline ZnO nanorods were prepared by the hydrothermal method with synthesized ZnCl2·4Zn(OH)2 as the precursor. Morphologies of the nanorods were controlled by various reaction conditions with cetyltrimethylammo-nium bromide (CTAB) as the modifying agent. The nanorods were characterized by XRD, TEM, UV-Vis spectra, and IR spectra. The microstructure of holes in nanosize was observed on the surface of the nanorods. The UV-Vis spectra indicate that the as-prepared ZnO nanorods have absorption of visible-light as well as ultraviolet-light. Therefore, these nanorods may be good candidates for visible-light photocatalysis materials from the viewpoint of practical applications. The reason for visible-light absorption was discussed in this article.     

Effect of Zn and Y Additions on Grain Boundary Movement of Mg Binary Alloys During Static Recrystallization

Texture evolution in rolled Mg–1 wt% Zn and Mg–1 wt% Y binary alloys was analyzed by quasi-in situ electron backscatter diffraction (EBSD) during static recrystallization. Mg–1 wt% Zn and Mg–1 wt% Y alloys exhibited strong basal texture at the initial recrystallization state. After grain growth annealing, the basal texture component {0001} < $11\overline{2}0$ > was increased in Mg–1 wt% Zn alloy and that of Mg–1 wt% Y alloy was decreased to be a random texture. Zn and Y atoms segregated strongly to the recrystallized grain boundaries in Mg–1 wt% Zn alloy and Mg–1 wt% Y alloy, respectively. Thus, Zn and Y elements facilitated the grain boundary movements along contrary directions during grain growth. In Mg–1 wt% Zn alloy, due to the Zn element segregation on grain boundaries, the grains consisted of a strong texture grew more easily because the grain boundary migration tended to move from the orientation close to normal direction to the orientation near to transverse direction or rolling direction. Therefore, after grain growth, the volume fraction of texture component {0001} < $11\overline{2}0$ > was increased by consuming the neighboring grains, leading to a stronger basal texture. On the contrary, in the Mg–1 wt% Y alloy, the Y element segregation caused the opposite direction of grain boundary migration, resulting in a random texture.