Function Of Mg Content Research Articles

Growth and Investigation of Annealing Effects on Ternary Cd1−xMgxO Nanocomposit Thin Films

Thin films of Cd1−xMgxO (CdMgO) (0 ≤ x ≤ 1) were investigated by depositing the films on glass substrates using the co-evaporation technique. The structural, surface morphological, optical, and electrical characteristics of these films were studied as a function of Mg content after annealing at 350 °C. The XRD analysis showed that the deposited films had an amorphous nature. The grain size of the films reduced as the Mg concentration increased, as evidenced by the surface morphology, and EDAX supported the existence of Mg content. It was observed that as the films were annealed, the transmittance of the CdMgO films saw an increase of up to 85%. The blue shift of the absorption edge was observed by the increase of Mg content, which was useful for enhancing the efficiency of solar cells. The optical band gap increased from 2.45 to 6.02 eV as the Mg content increased. With increased Mg content, the refractive index reduced from 2.49 to 1.735, and electrical resistivity increased from 535 Ω cm to 1.57 × 106 Ω cm.

Synchrotron high-resolution XRD and thermal expansion of synthetic Mg calcites

The structural parameters and the thermal behavior of a complete series of Ca–Mg carbonates synthesized at high pressure and temperature (1–1.5 GPa, 1273–1373 K) in the range 0–50 mol% MgCO3 have been investigated by in situ powder synchrotron high-resolution X-ray diffraction at ambient and up to 1073 K under self-controlled CO2 partial pressure. The crystal structures are disordered Mg calcite in the range 1–41 mol% MgCO3, and Ca dolomite at 49 mol% MgCO3. New calibration curves of the cell parameters for the Mg content and thermal expansion from ambient to 1073 K are given. Short-range structural effects of cation substitution and ordering and their thermal behavior as a function of Mg content were identified from three sets of data: the peak broadening, the cell parameter strains and the Raman band enlargements. Both intra- and inter-crystalline levels of compositional heterogeneity are identified and allow splitting the Mg calcites into two groups: low- and high-Mg calcites. The low-Mg calcites (up to 22 mol% MgCO3) are homogeneous in Mg content with short-range ordering. High-Mg calcite (up to 41 mol% MgCO3) displays domains with different local ordering configurations and similar or slightly different Mg contents, and to which is added a compositional variation between crystals, as determined by EMP, of the order of ± 0.8 mol% MgCO3. The cation ordering in Ca-rich dolomites similarly occurs in high-Mg synthetic calcites. The role of (CO3)2− group ordering is shown to be an important factor in the formation of Ca–Mg carbonates.

Electrochemical impedance spectroscopy analysis of ZnO films: the effect of Mg doping

ABSTRACTPure and Mg-doped ZnO films have been successfully grown on indium-doped tin oxide (ITO) substrates by simple chemical spray pyrolysis and their crystallographic properties characterised using X-ray diffraction (XRD) measurements in the range . The XRD measurements revealed that all samples have a hexagonal wurtzite crystal structure and a polycrystalline nature. The structural parameters of the samples were evaluated as a function of Mg content. The electrical properties of the films were evaluated using electrochemical impedance spectroscopy measurements. The circuit parameters were obtained by an equivalent circuit model presuming certain corrosion features of the synthesised films. Additionally, open-circuit potentials and the Bode approximation were used to create a correlation between structural changes resulting from Mg content addition and the variation in the corrosion behaviour of the films.

Structural, optical and NO2 gas sensing properties of ZnMgO thin films prepared by the sol gel method

In this present work, ZnO and ZnMgO thin films prepared by a sol-gel process were deposited on glass substrates via spin coating technique. The structural, morphological and optical properties of the obtained films were investigated. X-ray diffraction study revealed that all layers exhibit a hexagonal wurtzite structure without any secondary phase segregation. The atomic force microscopy (AFM) depicts that the grains size of ours samples decreases as magnesium content increases. The absorption spectra obtained on ZnMgO thin films show a band gap tuning from 3.19 to 3.36eV, which is also consistent with blue shifting of near-band edge PL emission, measured at low temperature. The incorporated amount of magnesium was calculated and confirmed by EDX. The gas sensing performances were tested in air containing NO2 for different operating temperatures. The experimental result exhibited that ZnMgO sensors shows a faster response and recovery time than the ZnO thin films. The resistivity and the sensor response as function of Mg content were also investigated.

Growth and characterization of epitaxial magnesium ferrite thin films

Epitaxial magnesium ferrite thin films have been grown by molecular beam epitaxy (MBE) on MgO(100). Growth conditions such as substrate temperature and growth rates were optimized. By using different characterization techniques, structural, electrical and optical properties of the films were studied as a function of Mg content. In particular, we highlight the importance of the growth rate on the actual Mg/Fe ratio in the film.

Experimental study of the crystal structure of the Mg15−xZnxSr3 ternary solid solution in the Mg–Zn–Sr system at 300°C

Abstract A new ternary compound, Mg 15 − x Zn x Sr 3 with extensive solid solubility in the Mg–Zn–Sr system was observed and studied using electron probe microanalysis (EPMA), scanning electron microscopy SEM, and X-ray techniques. The solid solubility limits of this compound were found to be Mg 15 − x Zn x Sr 3 (0.24 ≤ x ≤ 10.58, at.%) at 300 °C using a diffusion couple and several equilibrated alloys. Analysis of the X-ray diffraction (XRD) patterns was carried out by Rietveld method. XRD data has shown that this solid solution crystallizes in the hexagonal P6 3 /mmc (194) space group with the Ni 11 Si 4 Sc 3 prototype. The lattice parameters decrease linearly with decreasing Mg content indicating substitutional solid solubility. The fractional atomic occupancy of the 6h, 6g, 4f, 2b and 12k sites of this compound are function of Mg content.

Optical and electrical properties of Mg-doped zinc tin oxide films prepared by radio frequency magnetron sputtering

In this study, magnesium (Mg)-doped zinc tin oxide (ZTO) films were deposited by radio frequency (RF) magnetron sputtering. The Mg was selected as an electron suppressor for the ZTO films. X-ray diffraction (XRD) was carried out to observe the crystallinity of the films. The Mg-doping effects on the elemental properties of the films were investigated by X-ray photoelectron spectroscopy (XPS). The optical properties, such as transmittance, optical band gap, Urbach energy, and refractive index, were compared as a function of Mg content. Bottom-gate transparent thin-film transistors (TTFTs) were fabricated on N+ Si wafers. The turn-off voltage, threshold voltage, and mobility variation as a function of Mg content were studied.

Effects of Mg incorporation by co-sputtering into the ZnO channel layer of thin-film transistors

We fabricated a series of ZnO-based thin-film transistors (TFTs) in which the Mg composition ratio in the active layer was varied by controlling the RF power applied to the ZnO and the Mg0.3Zn0.7O targets. Mg x Zn1−x O alloy films were deposited by RF co-sputtering onto a SiO2/n+-Si substrate at 300 °C. The Mg content in each ZnO film was measured and the band gaps were found to increase from 3.27 to 3.93 eV with increasing Mg content. The field effect mobility and the on/off ratio were decreased from 9.12 cm2V−1s−1 and 109 to 3.11 cm2V−1s−1 and 108, respectively, as Mg incorporation was increased. We report the feasibility of Mg incorporation by using a cosputtering technique, and the electrical and the structural properties of the TFT ZnO active layer as a function of Mg content are discussed.

Mechanical characteristics of Mg–Cu–Zr thin film metallic glasses

For improving the ductility of metallic glasses, nanocrystals within the amorphous matrix are frequently intentionally added. In this study, the MgCuZr thin film metallic glasses (TFMGs) with a positive mixing heat between Mg and Zr are fabricated via co-sputtering in an attempt to separate the pure Mg nano-particles. The microstructure and mechanical properties of the sputtered MgCuZr thin films and their FIB-machined micropillars are examined as a function of Mg content from 39 to 100at.%. From the nanoindentation and micropillar load–displacement curves, the Mg-rich metallic glass composites exhibit smoother nature and more ductile behavior. Meanwhile, due to strong (0002) basal texture, the Mg-rich thin films and micropillars possess strong modulus (~80GPa), hardness (~3.5GPa), and yield stress (~1.5GPa), coupled with more ductile behavior. All of these would allow promising applications in micro-electro-mechanical systems.

Mg-substituted hydroxyapatite nanopowders: Synthesis, thermal stability and sintering behaviour

This paper reports a systematic investigation on Mg-substituted hydroxyapatite (Ca 10− x Mg x (PO 4) 6(OH) 2) nanopowders produced by precipitation of Ca(NO 3) 2·4H 2O and Mg(NO 3) 2. The Mg content ranged between 0.6 and 2.4 wt%. Semicrystalline Mg-substituted hydroxyapatite powders made up of needle-like nanoparticles were obtained, the specific surface area ranged between 87 and 142 m 2/g. Pure hydroxyapatite nanopowder decomposed around 1000 °C. Mg-substituted hydroxyapatites were thermally stable up to 660 °C ( x = 1.0), 760 °C ( x = 0.5) and 840 °C ( x = 0.25) showing a distinct decreased thermal stability with respect to the pure sample. A relevant displacement of the sintering curve at lower temperature as a function of Mg content was observed, comparing to the behaviour of a pure HAp material, synthesized following the same procedure, and ascribed to the β-TCP formation.

Effect of Mg substitution on the magnetic properties of NiCuZn ferrite nanoparticles prepared through a novel method using egg white

Nanocrystalline Mg-substituted NiCuZn ferrites were successfully synthesized, for the first time, by using metal nitrates and freshly extracted egg white. The thermal decomposition process of the nitrate–egg white precursors was investigated by thermogravimetric (TG) technique. X-ray diffraction (XRD) revealed that, single-phase cubic ferrites with average particle size of 23.9–35.1 nm were directly formed after ignition at 500 °C. No noticeable variation of lattice parameters with increasing magnesium content was observed, while X-ray densities were found to decrease. This can be explained on the basis of ionic radii and atomic masses of the substituted cation. Transmission electron microscope (TEM) shows that, particles are permanently magnetized and get agglomerated. The saturation magnetization ( M s ) and coercivity ( H c ) as a function of Mg content were investigated using vibrating sample magnetometer (VSM). It has been found that the M s increases firstly up to x=0.2 and then decreases, while H c continuously decreases. Magnetic susceptibility measurements give results which agree well with those obtained by VSM. The obvious decrease in the Curie temperature ( T C ) with increasing Mg indicates that the ferrimagnetic grains are widely separated and enclosed by non-magnetic magnesium ions.

Correlation of microstructure and magnetic properties for exchange-biased Co ferromagnets grown above and below the diluted antiferromagnet Co(Mg)O

The microstructure of ferromagnetic/antiferromagnetic (FM/AFM) coupled bilayers consisting of 6 nm Co films, grown above and below 20 nm CoO layers diluted with nonmagnetic Mg, is correlated with measurements of exchange-bias field and coercivity as a function of Mg content. Increased Mg dilution is found to slightly decrease the grain width of the columnar oxide layers but no suggestion of Mg segregation at grain boundaries is detected using small-probe microanalysis. The order of growth and the amount of Mg dilution both play an important role in determining the size of the exchange bias field. The large increase in exchange coupling that is measured for Co-below bilayers is attributed to partial oxidation of the upper Co surface during initiation of the AFM deposition. The large decrease in coercivity measured for Co-above bilayers with high Mg dilution is closely correlated with the falloff in exchange-bias field. Overall, these results provide strong support for the uncompensated spin model of exchange bias.

Initial responses of carbonate-rich shelf sediments to rising atmospheric pCO 2 and “ocean acidification”: Role of high Mg-calcites

Carbonate-rich sediments at shoal to shelf depths (<200 m) represent a major CaCO 3 reservoir that can rapidly react to the decreasing saturation state of seawater with respect to carbonate minerals, produced by the increasing partial pressure of atmospheric carbon dioxide ( pCO 2) and “acidification” of ocean waters. Aragonite is usually the most abundant carbonate mineral in these sediments. However, the second most abundant (typically ∼24 wt%) carbonate mineral is high Mg-calcite (Mg-calcite) whose solubility can exceed that of aragonite making it the “first responder” to the decreasing saturation state of seawater. For the naturally occurring biogenic Mg-calcites, dissolution experiments have been used to predict their “stoichiometric solubilities” as a function of mol% MgCO 3. The only valid relationship that one can provisionally use for the metastable stabilities for Mg-calcite based on composition is that for the synthetically produced phases where metastable equilibrium has been achieved from both under- and over-saturation. Biogenic Mg-calcites exhibit a large offset in solubility from that of abiotic Mg-calcite and can also exhibit a wide range of solubilities for biogenic Mg-calcites of similar Mg content. This indicates that factors other than the Mg content can influence the solubility of these mineral phases. Thus, it is necessary to turn to observations of natural sediments where changes in the saturation state of surrounding waters occur in order to determine their likely responses to the changing saturation state in upper oceanic waters brought on by increasing pCO 2. In the present study, we investigate the responses of Mg-calcites to rising pCO 2 and “ocean acidification” by means of a simple numerical model based on the experimental range of biogenic Mg-calcite solubilities as a function of Mg content in order to bracket the behavior of the most abundant Mg-calcite phases in the natural environment. In addition, observational data from Bermuda and the Great Bahama Bank are also presented in order to project future responses of these minerals. The numerical simulations suggest that Mg-calcite minerals will respond to rising pCO 2 by sequential dissolution according to mineral stability, progressively leading to removal of the more soluble phases until the least soluble phases remain. These results are confirmed by laboratory experiments and observations from Bermuda. As a consequence of continuous increases in atmospheric CO 2 from burning of fossil fuels, the average composition of contemporary carbonate sediments could change, i.e., the average Mg content in the sediments may slowly decrease. Furthermore, evidence from the Great Bahama Bank indicates that the amount of abiotic carbonate production is likely to decline as pCO 2 continues to rise.

Variations of structure and composition in magnesium incorporated hydroxyapatite/β-tricalcium phosphate

The phase evolution of magnesium incorporated hydroxyapatite/β-tricalcium phosphate (HA/β-TCP) ceramics of high purity prepared by solid-state reaction was investigated with the aid of x-ray diffraction and infrared spectroscopy (IR) in transmittance mode analysis. The dependence of the microstructure on the phase evolution of biphasic ceramics during natural sintering was also investigated as a function of Mg content. When sintered at 1100 °C, Mg is preferentially incorporated into the β-TCP phase rather than the HA phase. This Mg incorporation into the β-TCP effectively suppresses the phase transition from β- to α-TCP. With increasing sintering temperature, the solubility limit of the Mg in the β-TCP decreases and Mg starts to be either incorporated into the HA phase or segregated as free MgO. The decreased Mg content in the β-TCP facilitates the phase transition from β- into α-TCP, at 1300 °C or higher. Different processing methods on Mg addition show that the retarded phase transition from β- to α-TCP is the inherent property of Mg-doped HA/TCP. The variations in processing parameters mainly affect the microstructure instead of the phase evolution, leading to highly densified HA/β-TCP ceramics.

Electrical Properties of Mg Doped (Ba0.5Sr0.5)TiO3 Thin Films

The microstructures and electrical characteristics of Mg doped (Ba0.5Sr0.5)TiO3 (BSTM) thin films were investigated as a function of Mg content. Also the multi-layered structure, BSTM/BST/BSTM was proposed to improve both of the leakage current and dielectric constant. With increasing Mg content, the perovskite peak intensity slightly decreased and grains became smaller. For the films above 15 mol% Mg, the secondary phase (MgTi2O5) was observed in X-ray diffraction (XRD) patterns. The dielectric constant decreased with increasing Mg content, while leakage current decreased up to 10 mol% Mg and then increased with further addition, which were explained by the effect of grain size and charge compensation. For the BSTM/BST/BSTM multi-layered films, the leakage current dramatically decreased without reduction of the dielectric constant when the thicknesses of BSTM and BST were 70 nm and 210 nm, respectively. These results confirm that a promising BST thin film capacitor can be obtained by introduction of Mg modified multi-layer structure.

First principles study of the solute atom induced lattice distortion effects on bulk modulus and band structure in Li-alloys

Electronic and mechanical properties of Li-X (X = Na,, Mg, Al) alloys are studied here using the first principles structural optimization method. The lattice distortion induced by solute atoms is shown to have effects on the volume and bulk modulus of Li-alloys. The pressure dependence of this distortion differs from solute to solute, but the general trends can be accounted for with a model based on the properties of pure solute and solvent elements only. It is shown that the change in the volume of an alloy does not depend only on the magnitude of the lattice distortion, but the actual pressure dependence of this distortion is important, too. The volume of an alloy is decreased or increased due to lattice distortion depending on the type of the solute atom in question. However, contrary to volume, bulk modulus is decreased in all cases investigated. Optimization of the crystal structure is also essential in obtaining the correct trend for the initial slope of the volume of Li 1− x Mg x as a function of Mg content. The band structure and Fermi surface topology depend also on the type of solute atom. In Li 15Na there exist only small splitting effects of various bands, whereas in Li 15Mg and Li 15Al this splitting is quite pronounced. According to our results the effect of lattice distortion on the energy bands of LiMg is small.

Ignition and combustion of [formula omitted] alloy particles in O 2 at high pressures

The ignition and combustion of Al, Mg, and Al Mg alloy particles in 99% O 2 1% N 2 mixtures is investigated at high temperatures and pressures for rocket engine applications. The 20-μm particles contain 0, 5, 10, 20, 40, 60, 80, and 100 wt.% Mg alloyed with Al, and are ignited in oxygen using the reflected shock in a single-pulse shock tube near the endwall. Using this technique, the ignition delay and combustion times of the particles are measured at temperatures up to 3250 K as a function of Mg content for oxygen pressures of 8.5, 17, and 34 atm. An ignition model is developed that employs a simple lumped capacitance energy equation and temperature and pressure dependent particle and gas properties. Good agreement is achieved between the measured and predicted trends in the ignition delay times. For the particles investigated, the contribution of heterogeneous reaction to the heating of the particle is found to be significant at lower temperatures, but may be neglected at gas temperatures above 3000 K. As little as 10% Mg reduces the ignition delay time substantially at all pressures tested. The particle ignition delay times decrease with increasing Mg content, and this reduction becomes less pronounced as oxidizer temperature and pressure are increased.