Increase Of Mg Content Research Articles

Structural and hydrogenation studies of ZnO and Mg doped ZnO nanowires

In this work, Mg doped zinc oxide (MgxZn1−xO, x = 5, 10 and 20 at. %) nanowires were successfully prepared by two step process. Initially, ZnO nanowires were grown by thermal evaporation of Zn powder under oxygen atmosphere. Mg powder was doped in as grown ZnO through solid state diffusion at low temperature. Energy dispersive x-ray spectroscopy (EDAX), transmission electron microscopy (TEM), X-ray diffraction (XRD) and UV–Visible absorption spectra analysis reveals that the Mg doping on ZnO nanowires induces lattice strain in ZnO. Rietveld analysis of XRD data confirms the wurtzite structure and a continuous compaction of the lattice (in particular, the c-axis parameter) as x increases. The hydrogenation properties of ZnO nanowires and Mg doped ZnO (MgxZn1−xO, x = 0, 5, 10 and 20 at. %) nanowires were studied. The hydrogenated samples were further investigated through XRD and Fourier transform infrared spectroscopy (FTIR). The hydrogen storage capacity of as grown ZnO nanowires has been estimated to be 0.57 wt. % H2 at room temperature. However, the hydrogen storage capacity gets increased to ∼1 wt. % upon doping ZnO with 10 at. % Mg. Further increase in Mg concentration decreases the hydrogen storage capacity of ZnO nanowires. Thus for 20 at. % Mg doped ZnO; the hydrogen absorption capacity gets decreased from ∼1 wt. % to 0.74 wt. %. The mechanism of hydrogen storage in ZnO nanowires and Mg doped samples of ZnO has been discussed.

Influence of Si and Mg Contents on the Mechanical Behavior of Al-Mg-Si Alloys in the Semi-Solid State under Isothermal and Non-Isothermal Conditions

The shear behavior of aluminum alloys containing increased amounts of Si or Mg compared with the 6061 alloy has been investigated by carrying out isothermal and non-isothermal tests in the mushy state during solidification. In isothermal conditions, it is shown that (i) an increase in Mg content leads to a more resistant semi-solid alloy compared with the 6061 alloy for the same solid fraction and (ii) an increase in Si content leads to a more brittle mushy alloy. In non-isothermal conditions, stress increases continuously with decreasing temperature with the formation of cracks for some compositions. This study shows that an increase in Mg content seems to be the most appropriate solution to reduce the formation of cracks in a solidifying 6061 alloy.

Modelling of the Precipitated Phases and Properties of Al-Zn-Mg-Cu Alloys

The effects of Zn and Mg variations on the precipitated phases and the properties of Al-Zn-Mg-Cu alloys are investigated in this study. The quantities of stable and metastable phases have been calculated under various Zn and Mg contents by using software package JmatPro. The results show that the amount of the main hardening η (MgZn2) phase and η′ phase increase with higher Zn and Mg contents. T (AlCuMgZn) phase and metastable counterpart significantly increase with the reduction of Zn contents or the increase of Mg contents. S (Al2CuMg) phase reduces gradually with the increase of Mg content, while S phase varies only slightly with the Zn content. The precipitation of GP zones is promoted by the increase of Zn or Mg content. The physical and mechanical properties of the alloys have been modelled in such way that increasing Zn or Mg content could reduce electrical conductivity and thermal conductivity, while the mechanical properties improve with increasing Zn content and varies markedly as Mg content changes from 2.7 to 2.9 wt.%.

Dielectric relaxation behavior of acceptor (Mg)-doped BaTiO3

Dielectric relaxation behavior of acceptor (Mg)-doped BaTiO3 ceramics was investigated with the increase of Mg concentration up to 0.6 mol. % in the temperature rang of 120 ∼ 540 °C. In the high temperature range above 320 °C, the activation energies of dielectric relaxation (Eτ) showed nearly similar values of ∼ 1.2 eV irrespective of Mg concentration. However, in the low temperature range below 320 °C, they continuously decreased from ∼ 1.2 eV and then saturated to ∼ 0.4 eV with the increase of Mg concentration. The activation energies of electrical conduction (Eσ) of the bulk grain evaluated by impedance analysis also showed almost the same behavior. Such coincidence demonstrates that the observed dielectric behaviors are caused by the space charge polarization at grain boundaries by conducting charge carriers. The disappearance of the dielectric relaxation in submicrometer fine-grain specimen also supports this mechanism. The variation of Eτ and Eσ with the increase of Mg concentration in the low temperature range was supposed to be caused by the dominant hopping conduction between ionized acceptor (MgTi″) and neutral or hole-trapped acceptor (MgTi×).

Linear and nonlinear optical response of MgxZn1−xO: A density functional study

Total and partial density of states, frequency dependent complex refractive index including extinction coefficient, optical conductivity and transmission of MgxZn1−xO (0≤x≤1) in rocksalt and wurtzite phases are calculated using full potential linearized augmented plane wave (FP-LAPW) method. The real part of refractive index decreases while the extinction coefficient, optical conductivity and transmission for rocksalt phase increases with the increase in Mg concentration. In wurtzite phase, ordinary and extraordinary indices decrease while extinction coefficient, optical conductivity and transmission increase in parallel as well as perpendicular to c-axis with the increase in the Mg concentration.

Growth and structural characterization of intrinsic, acceptor, and donor doped (Mg,Zn)O epilayers via metalorganic vapor phase epitaxy on (1 0 1¯ 0) ZnO substrates

We report on the epitaxial growth of ZnO and Mg x Zn 1− x O films grown epitaxially on (1 0 1¯ 0) ZnO substrates for 0≤ x≤0.50 via a metal organic vapor phase epitaxy (MOVPE) process. Morphological properties of these epilayers investigated using scanning electron microscopy (SEM) and atomic force microscopy (AFM) indicate step-flow growth mode. Structural analysis conducted by high resolution X-ray diffraction (HRXRD) and transmission electron microscopy (TEM) indicates monocrystalline deposition and increasing biaxial strain with increase in Mg concentration. In particular, TEM indicates the prevalence of stacking faults as the main strain defects in Mg x Zn 1− x O epilayers. Temperature-dependent photoluminescence studies identify neutral donor–acceptor pair transitions occurring in Mg 0.20Zn 0.80O at 3.45 eV corresponding to an acceptor energy of 211 meV. Acceptor profiles measured by secondary ion mass spectrometry (SIMS) reveal the presence of dopant diffusion.

Influence of Mg content on quench sensitivity of Al–Zn–Mg–Cu aluminum alloys

The influence of Mg content on quench sensitivity of Al–8.0Zn– x(=1.0–2.0)Mg–1.6Cu alloys was investigated by an end-quenching test method. The depths of age hardening layer referenced to hardness retention values (e.g., 90%) of the end-quenched samples were used to describe the quench sensitivity. The results showed that the depths of age hardening layer decreased with increase of Mg content. The amount of the equilibrium-state MgZn 2 ( η) particles was the primary factor that determined the depths of age hardening layer. The η particles underwent two precipitation processes successively with decrease of cooling rate during quenching: precipitation on grain boundaries and precipitation inside the grains. The precipitation temperature peaks rose, and the ranges of the temperatures are extended with the increase of Mg content. A preliminary prediction has been made for the initial precipitation temperatures and the temperature peaks satisfying linear relation with Mg content (wt.%).

Effect of magnesium on the crystal structure and thermodynamics of the La 3− xMg xNi 9 hydrides

The present work gives the data of systematic studies of the influence of magnesium on the crystal structure and hydrogenation behaviour of the PuNi 3 -type La 1− x Mg x Ni 3 ( x = 0–0.67) intermetallic alloys. Synchrotron X-ray diffraction studies revealed that substitution of La in LaNi 3 by Mg proceeds in an ordered way, only within the Laves type layers of the hybrid crystal structures build from the MgZn 2 - and CaCu 5 -type slabs. When completed, it leads to the formation of LaMg 2Ni 9 (2MgNi 2 + LaNi 5). Gradual increase of Mg content is accompanied by a linear decrease of the volumes of the unit cells. Interestingly, a substantial contraction takes place also for the Mg-free CaCu 5 -type slabs. Hydrogen interaction with the La 1− x Mg x Ni 3 alloys was investigated by in situ synchrotron X-ray, neutron powder diffraction and pressure–composition–temperature studies. In the whole substitution range, La 1− x Mg x Ni 3 alloys form intermetallic hydrides with H/ M ratio ranging from 0.77 to 1.16. Magnesium influences structural features of the hydrogenation process and determines various aspects of the hydrogen interaction with the La 1− x Mg x Ni 3 intermetallics causing: (a) more than 1000 times increase in equilibrium pressures of hydrogen absorption and desorption for the Mg-rich LaMg 2Ni 9 as compared to the Mg-poor La 2.3Mg 0.7Ni 9 and a substantial modification of the thermodynamics of the formation–decomposition of the hydrides; (b) an increase of the reversible hydrogen storage capacities following increase of Mg content in the La 1− x Mg x Ni 3 to ∼1.5 wt.% H for La 2MgNi 9; (c) improvement of the resistance against hydrogen-induced amorphisation and disproportionation; (d) change of the mechanism of the hydrogenation from the anisotropic to isotropic one. Thus, optimisation of the magnesium content provides different possibilities in improving properties of the studies alloys as hydrogen storage and battery electrode materials.

Effect of magnesium substitution on dielectric and magnetic properties of Ni–Zn ferrite

The dielectric and magnetic properties of Mg incorporated Ni–Zn spinel ferrites have been investigated. Ni 0.5− x Zn 0.5Mg x Fe 2O 4 ferrites have been prepared by sol–gel auto-combustion technique. The as prepared ferrites were annealed at 673, 873 and 1073 K. The X-ray diffraction studies reveal the spinel structure of annealed ferrites. The TEM results are in agreement with XRD results. FTIR study has also been carried out to get insight into the structure of these ferrites. The dielectric measurements show that the dielectric constant ( ε′), dielectric loss (tan δ) and conductivity ( σ ac) increase on incorporation of Mg in the Ni–Zn ferrite. ε′, tan δ and σ ac also show dependence on temperature, frequency of external applied electric field and microstructure of the samples. The magnetic moment measurements reveal that the saturation magnetization ( M s) increases and coercivity ( H c) decreases with the increase in concentration of Mg 2+ ions. M s and H c also show dependence on the annealing temperature.

The magnesium doping effect of the vanadate spinel MnV2O4

We investigate the structural, transport, and magnetic properties of Mn1−xMgxV2O4(0≤x≤0.8) to study the role of the A-site magnetism in vanadate spinels. With increasing Mg2+ concentration, the lattice parameters shrink and the hopping energy for electrons increases, whereas both the magnetic transition temperature and the structural transition temperature decrease gradually. The two temperatures become closer and eventually equal to each other at x=0.2. For x>0.2 the first order transition disappears and the magnetic ground state switches from a long range ordered ferrimagnetic state to a glassy state. The transition temperature of the glassy state continues to decrease with further increase of Mg content, which is attributed to the dilution in the magnetism on A sites.

Characterization of MgxZn1 − xO thin films grown on sapphire substrates by metalorganic chemical vapor deposition

Wurtzite-structure MgxZn1−xO materials with five different compositions of x from 0 to 0.14 were grown on sapphire substrates by metalorganic chemical vapor deposition. It was found that increasing Mg content in the MgxZn1−xO not only increased the band gap energy of the film but was also beneficial to the epitaxial growth of p-type MgxZn1−xO without using any doping sources. In addition, the combined ultraviolet photoluminescence (PL) and Raman scattering spectra were measured with PL–Raman signals obtained together, showing a blue-shift of PL band and variation of resonant Raman multi-order longitudinal optical phonon modes with an increase of Mg content.

Temperature dependence of electrical properties for P-doped ZnMgTe bulk crystals of high quality grown by Bridgman method

Electrical properties of P-doped Zn1−xMgxTe have been clarified as a function of measurement temperature. The activation energy of P-acceptor, and donor and acceptor concentrations of P-doped Zn1−xMgxTe crystals were derived from a carrier concentration analysis. The activation energy becomes higher with increasing Mg content, in agreement with the photoluminescence properties. The mobility at low temperature tends to decrease with an increase in Mg content. A strong emission band originating from interband transition appears clearly at room temperature in P-doped Zn1−xMgxTe with any Mg content, though broad luminescence is found for x=0.11 in the wavelength region from 650 to 720nm.

Statistical Optimization of Anaerobic Biological Processes for Dye Treatment

In the present study both the synthetic media composition as well as some process parameters in the anaerobic decolorization of Reactive Black 5 (RB5) by activated sludge were studied and optimized using statistical design of experiments (DOEs). Statistical analysis of the results of Plackett–Burman DOE showed that the addition of Mn or Fe, or increase in concentration of Mg, had a positive effect on the anaerobic decolorization efficiency whereas the effect of increase in concentration of glucose, ammonium chloride, and calcium chloride was negative. The effect of change in the concentration of glucose, mixed liquor suspended solid (MLSS), and RB5 on the anaerobic decolorization efficiency and rate and chemical oxygen demand (COD) removal was studied using central composite design methodology. Statistical analysis of the data showed that all the factors had significant effect on both the dye decolorization efficiency and rate. The interaction of glucose with MLSS and with dye and the interaction of MLSS with glucose and with dye were significant when the response was decolorization efficiency and rate, respectively. When COD removal was the response, the effect of change in glucose and MLSS concentration and the interaction between these two factors had statistically significant effect on the response.

Difference between resistance degradation of fixed valence acceptor (Mg) and variable valence acceptor (Mn)-doped BaTiO3 ceramics

The difference in the resistance degradation behavior was investigated between fixed valence acceptor (Mg) and the variable valence acceptor (Mn)-doped BaTiO3 ceramics with an increase of each acceptor concentration. Coarse-grained specimens with uniform grain sizes and different acceptor concentrations were prepared. In the case of Mg-doped BaTiO3, the time to degradation systematically decreased with the increase in Mg concentration. In contrast, there is a systematically increased time to degradation with the increase in Mn concentration in Mn-doped BaTiO3. The fast degradation by the increase in Mg concentration directly corresponded to an increase in the Warburg impedance and ionic transference number (tion) associated with an increase in oxygen vacancy concentration ([VO••]). On the other hand, no distinct Warburg impedance or ionic conduction contribution could be observed with the increase in Mn concentration. It is supposed that the increase in [VO••] is negligible in spite of the increase in acceptor Mn concentration, when it is compared to Mg-doped BaTiO3. The much lower [VO••] and more dominant electron/hole trapping effect due to multivalence nature of Mn are supposed to cause such a contrary degradation behavior between Mg and Mn-doped BaTiO3. Reoxidation in a slightly reducing atmosphere (N2) showed better resistance to degradation behavior than in a oxidizing air atmosphere in both Mg and Mn-doped BaTiO3, which is anticipated to be an increase in the electron/hole trapping sites. All these behaviors could be explained by the low temperature defect chemical model that shows difference in the defect structure between Mg and Mn-doped BaTiO3, and its dependence on the oxygen partial pressure (pO2) during reoxidation and cooling. Not only the [VO••], but also the density of electron/hole trap sites, are believed to be crucial in controlling resistance degradation.

Effect of acceptor concentration on the bulk electrical conduction in acceptor (Mg)-doped BaTiO3

Bulk electrical conductivity of acceptor (Mg)-doped BaTiO3 ceramics were evaluated via an impedance spectroscopy analysis for materials with Mg concentrations up to 0.6 mol % and over a temperature range of 120–540 °C. At high temperatures beyond 320 °C, the activation energies of the bulk electrical conduction (Eσ) slightly decreased from 1.2 to ∼1.0 eV with an increase in the Mg concentration. However, in the low temperature range below 320 °C, there is a continuous decreased from 1.2 eV and then this saturated to ∼0.4 eV with the increase in Mg concentration. The calculated bulk conductivities based on a defect chemistry model explains conductivity for temperatures above 320 °C. The model demonstrates a predominant electronic conduction in the low concentration range below 0.1 mol % Mg and mixed conduction with ionic and electronic carriers in the intermediate and in high acceptor concentration range of 0.2–0.6 mol % Mg. However, the decrease in Eσ with the increase in Mg concentration in the low temperature range could not be explained by the defect chemical model. Such deviation however could be explained by a transition to hopping conduction between ionized acceptor (MgTi″) and neutral or hole-trapped acceptor (MgTi×) with the increase in Mg concentration in the low temperature range.

P‐86: Effect of Mg on Properties of ZnS: Cu, Mn Phosphors

AbstractInfluence of the different concentration of Mg in ZnS powder precursor on properties of derived phosphors has been investigated. for this were synthesized ZnS: Cu, Mn phosphors co‐doped with different amount of Mg, introduced with MgCl2×6H2O. Comparison of properties shows that a small amount of Mg increases the brightness of the photo and electroluminescence. However, further increase in Mg content leads to a sharp decrease in brightness of the electroluminescence and a small shift of the spectrum to the shorter wavelengths.

Effects of Sc, Zr and Ti on the microstructure and properties of Al alloys with high Mg content

The effects of trace Sc, Zr, and Ti on the microstructure and hardness of Al alloys with high Mg content (Al-6Mg, Al-8Mg, and Al-10Mg) were studied by optical microscope, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Brinell hardness. The grain size of the as-cast alloys was refined by the addition of Sc and Zr, and it was further refined by the addition of Ti. With the same contents of Sc, Zr, and Ti, an increase in Mg content was beneficial to the refinement due to the solution of Mg into α-Al. The refined microstructures of the as-cast alloys were favorable for Brinell hardness. Addition of Sc, Zr, and Ti to the Al-10Mg alloy results in the improvement of peak hardness and it is about 45% higher than that of the Al-10Mg alloy, which is due to fine precipitations of Al3(Sc1−xZrx), Al3(Sc1−xTix), and Al3(Sc1−x−yZrxTiy).

Investigation of structural and magnetic properties of polycrystalline Ni 0.50Zn 0.50− xMg xFe 2O 4 spinel ferrites

The structural and magnetic properties of Mg substituted Ni 0.50Zn 0.50− x Mg x Fe 2O 4 (where x = 0.0, 0.10, 0.20, 0.30, 0.40 and 0.50) sintered at various temperatures have been studied thoroughly. X-ray diffraction patterns of the samples showed single-phase cubic spinel structure without any detectable impurity phases. The lattice parameter decreases linearly with increase of Mg contents obeying Vegard's law. The bulk density, average grain size and initial permeability, μ i ′ , decrease with increasing Mg substitution but increase with increasing sintering temperature for a particular composition. The highest initial permeability and quality factor, Q, are obtained for the Ni 0.50Zn 0.50Fe 2O 4 sintered at 1350 and 1250 °C, respectively. Domain wall relaxation frequency, f r, and Néel temperature, T N, are found to increase with Mg substitution. It is observed that when Zn is completely substituted by Mg in Ni 0.50Zn 0.50− x Mg x Fe 2O 4, the T N is increased by 106% and f r by 178%. On the other hand, μ i ′ decreases by 86%. It is observed that all samples are in ferrimagnetic state at room temperature. The number of Bohr magneton, n( μ B), decreases with increasing Mg substitution which is explained by probable cation distribution in the spinel crystal structure. Possible explanation for the observed features of microstructure, initial permeability, DC magnetization and Néel temperature of the studied samples are discussed.

Structural, electrical and optical properties of transparent Zn1 − xMgxO nanocomposite thin films

Zn1−xMgxO thin films of various Mg compositions were deposited on quartz substrates using inexpensive ultrasonic spray pyrolysis technique. The influence of varying Mg composition and substrate temperature on structural, electrical and optical properties of Zn1−xMgxO films were systematically investigated. The structural transition from hexagonal to cubic phase has been observed for Mg content greater than 70mol%. AFM images of the Zn1−xMgxO films (x=0.3) deposited at optimized substrate temperature clearly reveals the formation of nanorods of hexagonal Zn1−xMgxO. The variation of the cation–anion bond length to Mg content shows that the lattice constant of the hexagonal Zn1−xMgxO decreases with corresponding increase in Mg content, which result in structure gradually deviating from wurtzite structure. The tuning of the band gap was obtained from 3.58 to 6.16eV with corresponding increase in Mg content. The photoluminescence results also revealed the shift in ultraviolet peak position towards the higher energy side.

Using Mg as a Proxy for Crystal Structure and Sr as an Indicator of Marine Growth in Vaterite and Aragonite Otoliths of Aquaculture Rainbow Trout

AbstractOtoliths of rainbow trout Oncorhynchus mykiss reared in marine cages were analyzed by laser ablation‐inductively coupled plasma mass spectrometry to determine their Sr and Mg concentrations and by micro‐Raman spectrometry to assess mineralogy. Analyses of transects from the core of the otolith to the growing edge (incorporating otolith material produced during freshwater hatchery and marine cage growth) revealed that these transects were composed of aragonite, vaterite, or both. The concentration of Sr varied significantly between mineral polymorphs and environments (hatchery or marine). In vaterite transects, Sr concentrations increased an average of 130 μg/g between freshwater hatchery growth and marine growth. This increase represents a near doubling of the Sr concentration in vaterite and made Sr a suitable indicator of a change in the environment as reflected in vaterite transects. In aragonite transects, Sr concentrations increased an average of 1,330 μg/g between hatchery and marine growth, which simplified the identification of the timing of marine transfer. The concentrations of Mg also varied significantly between mineral polymorphs, the difference in the average concentration between aragonite and vaterite being 1,179 μg/g. This allowed for the use of Mg as a proxy for mineralogy. While there was an increase in Mg concentration between hatchery and marine growth in some vaterite otoliths, the change was small compared with the change as a result of mineralogy. The average aragonite‐vaterite partition coefficients were 5.238 and 8.096 for Sr and 0.057 and 0.128 for Mg for hatchery and marine growth, respectively.