Solubility Limit Of Mg Research Articles

Atomic resolution analysis of extended defects and Mg agglomeration in Mg-ion-implanted GaN and their impacts on acceptor formation

We carried out atomic-scale observations of Mg-ion-implanted GaN by transmission electron microscopy (TEM) and atom probe tomography (APT) to clarify the crystallographic structures of extended defects and Mg agglomerations that form during post-implantation annealing. The complementary TEM and APT analyses have shown that Mg atoms agglomerate at dislocations that bound extended defects. The concentration of Mg is higher at the dislocations with a larger Burgers vector. This indicates that Mg agglomeration is caused by the pressure at the dislocations. Mg concentration in highly Mg-rich regions is 1 at. %, which exceeds the solubility limit of Mg in GaN. We investigated isothermal and isochronal evolution of the defects by TEM, cathodoluminescence analysis, and positron annihilation spectroscopy. The results indicated that the intensity of donor–acceptor pair emission increases with the annealing temperature and duration and reaches a maximum after elimination of the extended defects with highly Mg-rich regions. These results strongly suggest that such extended defects reduce the acceptor formation and that they as well as the previously reported compensating centers, such as N-related vacancies, can inhibit the formation of p-type GaN. The mechanism by which the extended defects reduce acceptor formation is discussed.

Nano-treating promoted solute dissolution for novel high strength Al-Cu-Mg alloys

High-strength Al-Cu-Mg alloys are normally designed with a low Mg content because of their tendency towards solidification cracking and a limited solubility of Cu when the Mg content exceeds 2 wt.%. Nano-treating is an emerging metallurgical method to improve the manufacturability and properties of alloys by adding a small volume fraction of ceramic nanoparticles. In this study, approximately 1.0 vol.% of TiC nanoparticles was added to cast Al-4.6Cu-xMg-0.3Mn alloys with a high Mg content ranging from 1.5 wt.% to 4.0 wt.%. Nanoparticles not only eliminated shrinkage porosities during casting but also significantly improved the dissolution of secondary phases during solution treatment of the alloys. Moreover, it was discovered that TiC nanoparticles promoted an unusual solute dissolution behavior to break the thermodynamic solubility limit of Mg in the Al-4.6Cu-xMg-0.3Mn system to achieve high mechanical performance. Theoretical analysis and TEM suggest that the promoted solute dissolution was driven by an overall reduction in interfacial energy between nanoparticles and the S phase during solutionization. The density of primary S’ precipitates was significantly increased by nano-treating, as an unusually high supersaturation was achieved in the nano-treated samples.

The combined influence of Mg and Ca on microstructural evolution of alumina

AbstractThe solubility limits of Ca and Mg co‐doped in alumina at 1600°C were determined by equilibrating alumina saturated with Ca and Mg. This resulted in the formation of MgAl2O4 (Mg spinel), CaO·6Al2O3 (CA6), Ca2Mg2Al28O46 (CAM‐II), and alumina grains saturated with Mg and Ca. Under these conditions, the amount of Ca and Mg in the alumina grains represents the solubility limits. The solubility limits were measured using a fully standardized wavelength dispersive spectrometer mounted on a scanning electron microscope. In the co‐doped state, the solubility limit of Ca in alumina was 32 ± 13 ppm, and the solubility limit of Mg in alumina was 210 ± 43 ppm. The presence of Ca results in an increase of the solubility limit of Mg in alumina from 132 to 210 ppm, suggesting that the increased Mg in solution results in more Mg excess at the alumina grain boundaries, thus contributing to a decreased grain‐boundary mobility by solute‐drag.

Influence of A-site magnesium doping on structural and electrical properties of BaZr0.1Ti0.9O3 ceramics

The effects of the replacement of Ba2+ by off-center Mg2+ ions on the structural and electrical properties of BaZr0.1Ti0.9O3 ceramics were investigated. We show that the use of magnesium as A-site dopant favors the formation of the perovskite phase at a lower temperature and improves the densification of the ceramics. Combining XRD, SEM and electrical measurements, we determined that the solubility limit of Mg is ~ 2%. We show that Mg doping leads to a decrease in both the Curie temperature and remnant polarization of the ceramics. A 1% Mg content, however, enhances the room-temperature d33 piezoelectric coefficient due to the composition proximity to an impurity induced morphotropic phase boundary.

Tailoring of composition, band-gap, and structural phase in ZnMgO films by simply controlling growth temperature and oxygen partial pressure during sputter deposition

Abstract It has been suggested in this study that the Mg content, band-gap energy, and structural phase in the sputter deposited ZnMgO films could be tailored in a wide range by simply controlling the growth temperature and sputtering ambient. The Mg content in film and the band-gap energy showed a strong dependence on the growth temperature and sputtering ambient, increasing with the growth temperature or decreasing by an oxygen addition into the plasma ambient. In this work, the wurtzite ZnMgO film with a wide band gap of 4.53 eV and a high Mg content of XMg = 0.53 could be realized for the first time by sputtering the Zn0.7Mg0.3O alloy targets with Mg contents of 0.3–0.35 below 200 °C and under pure Ar ambient. From the dependence of the structural phase on the growth temperature, the solubility limit of Mg in the wurtzite ZnMgO single phase without phase segregation was estimated to be about 0.53–0.56 and confirmed to reduce with the growth temperature, possibly due to the lower formation Gibbs free energy of MgO than ZnO and the difference in growth condition.

Effect of magnesium addition on the structural, microstructural and electrical properties of YVO4

The synthesis of Y1-x/2MgxV1-x/2O4-δ (MgxYV) (x = 0.0–0.5) by solid state reaction technique is reported. This preparation method is compared with chemical synthesis method such as nitrate-citrate auto-combustion route. The crystal structure and the surface morphology of the samples were determined by X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) techniques, respectively. Substantial decrease in phase formation temperature was observed for combustion method. The solubility limit of Mg in YVO4 lattice was found to be low i.e., x ≤ 0.1. The temperature dependence of conductivity of MgxYV samples indicated an increase in ionic conductivity values compared to the parent YVO4 due the formation of oxygen ion vacancies produced by the incorporation of acceptor Mg cations. Combustion-synthesized MgxYV samples showed higher conductivity compared to the samples prepared by conventional solid state reaction.

Phase structure and the dielectric properties of the (Zn, Mg)2(Ti, Sn)O4 ceramics

(1−x)ZnO–xMgO–0.88TiO2–0.12SnO2 (x=0.05, 0.10, 0.15 and 0.20) ceramics were prepared by conventional mixed-oxide method. The phase structure, morphology and dielectric properties of the ceramics were investigated. The results show that Mg was incorporated into the phase of Zn2(Ti,Sn)O4 and the spinel-type solid solution (Zn(1−x),Mgx)2(Ti0.88,Sn0.12)O4 formed, the solid solubility limit of Mg was situated at x=0.05–0.10. The 0.95ZnO–0.05MgO–0.88TiO2–0.12SnO2 ceramics sintered at 1080°C exhibit dielectric properties εr=18.9, tanδ=5.5×10−4 and near zero temperature coefficient of dielectric constant (τε=2.89ppm/°C). Due to their stable dielectric property, the 0.95ZnO–0.05MgO–0.88TiO2–0.12SnO2 ceramics can serve as the promising high-frequency dielectric capacitor after further modification.

Structural and photoluminescence properties of Mg substituted ZnO nanoparticles

This paper reports on structural and optical properties of Mg doped ZnO nanoparticles prepared through sol–gel method using polyvinyl alcohol as chelating agent. X-ray diffractometer (XRD), Field Emission Scanning Electron Microscope (FE-SEM), UV–Vis (UV–Vis), Fourier Transform Infrared (FTIR) and Photoluminescence (PL) spectrophotometers were employed to study the structural and optical properties. XRD and FE-SEM results demonstrated that particle size of ZnO decreased with increase in Mg concentrations. It was observed that the absorption spectrum of ZnO blue shifted as the Mg concentration enhanced from 1mol.% to 5mol.%, presumably due to reduction in particle size. It was found that MgO secondary phase was not formed even above the solid solubility limit of Mg in ZnO. ZnO nanoparticles exhibited an intense and strong UV emission peak at 396nm and this peak is attributed to the electron transition from the localized level slightly below conduction band to the valence band. The position of this emission peak remained same for all concentrations of Mg in ZnO.

All-scale hierarchical thermoelectrics: MgTe in PbTe facilitates valence band convergence and suppresses bipolar thermal transport for high performance

We report a high ZT of ∼2.0 at 823 K for 2% Na-doped PbTe with 6% MgTe with excellent thermal stability. We attribute the high thermoelectric performance to a synergistic combination of enhanced power factor, reduction of the lattice thermal conductivity and simultaneous suppression of bipolar thermal conductivity. MgTe inclusion in PbTe owns triple functions: the Mg alloying within the solubility limit in PbTe modifies the valence band structure by pushing the two valence bands (L and Σ bands) closer in energy, thereby facilitating charge carrier injection. When the solubility limit of Mg is exceeded, ubiquitous endotaxial nanostructures form, which when coupled with mesoscale microstructuring results in a very low (lattice) thermal conductivity through all-scaled length phonon scattering. Meanwhile, most significantly, the Mg alloying enlarges the energy gap of conduction band (C band) and light valence band (L band), thereby suppresses the bipolar thermal conductivity through an increase in band gap.

Mg substitution in CuCrO 2 delafossite compounds

A detailed investigation of the series CuCr 1− x Mg x O 2 ( x = 0.0 – 0.05 ) has been performed by making high-temperature resistivity and thermopower measurements, and by performing a theoretical analysis of the latter. Microstructure characterization has been carried out as well. Upon Mg 2+ for Cr 3+ substitution, a concomitant decrease in the electrical resistivity and thermopower values is found, up to x ∼ 0.02 – 0.03 , indicating a low solubility limit of Mg in the structure. This result is corroborated by scanning electron microscopy observations, showing the presence of MgCr 2O 4 spinels as soon as x = 0.005 . The thermopower is discussed in the temperature-independent correlation function ratio approximation as based on the Kubo formalism, and the dependence of the effective charge carrier density on the nominal Mg substitution rate is addressed. This leads to a solubility limit of 1.1% Mg in the delafossite, confirmed by energy dispersive X-ray spectroscopy analysis.

Effects of Magnesium Doping on Phase Transitions and Dielectric Figure of Merit of Barium Strontium Titanate Ceramics

Ba0.6Sr0.4(Ti1−xMgx)O3 (BSTM) ceramics were prepared by using a solid‐state reaction process. X‐ray diffraction results indicated that the solubility limit of Mg in Ba0.6Sr0.4TiO3 was about 3 mol%. Doping of Mg into BST led to diffused cubic–tetragonal (C–T) phase transition and reduced Curie temperature. The diffused parameter γ obtained by fitting the modified Curie–Weiss laws increased with increasing Mg content. Dielectric properties of the BSTM ceramics were measured. Figure of merit of BSTM3 was up to 127.8 at 17.5 kV/cm. Its dielectric loss was as low as 0.00133 at 1 kHz and room temperature.

Solubility Limits of La and Y in Aluminum Oxynitride at 1870°C

The solubility limits of important dopants (La and Y) in aluminum oxynitride (AlON) were measured using wavelength‐dispersive spectroscopy (WDS) mounted on a scanning electron microscope, from samples quickly cooled from 1870°C. To provide saturated AlON, samples were prepared with dopant concentrations well above the solubility limit, which was confirmed by the appearance of secondary phases using X‐ray diffraction, backscattered electron micrographs, and WDS. Measurements were conducted on polished samples without thermal or chemical etching. The results indicate solubility limits of 498±82 and 1775±128 ppm for La and Y in AlON at 1870°C, respectively. The solubility limit of Mg in AlON at 1870°C was found to be >4000 ppm. The relation between solubility limit and cation size is briefly discussed.

GaN: [formula omitted]-Mg grown by MOVPE: Structural properties and their effect on the electronic and optical behavior

The effect of Mg δ -doping on the structural, electrical and optical properties of GaN grown via metalorganic vapor phase epitaxy has been studied using transmission electron microscopy, secondary ion mass spectroscopy, atomic force microscopy, X-ray diffraction, Hall effect measurements and photoluminescence. For an average Mg concentration above 2.14 × 10 19 cm - 3 , phase segregation occurs, as indicated by the presence of Mg-rich pyramidal inversion domains in the layers. We show that δ -doping promotes, in comparison to Mg continuous doping, the suppression of extended defects on the sample surface and improves significantly the morphology of the epilayers. Conversely, we cannot confirm the reduction in the threading dislocation density—as a result of δ -doping—reported by other authors. In the phase separation regime, the hole concentration is reduced with increasing Mg concentration, due to self-compensation mechanisms. Below the solubility limit of Mg into GaN at our growth conditions, potential fluctuations result in a red-shift of the emission energy of the free-to-bound transition.

Microstructural studies and electrical properties of Mg-doped SrTiO 3 thin films

The structure–property relations of Mg-doped SrTiO 3 (ST) sol–gel thin films deposited on Pt/TiO 2/SiO 2/Si substrates have been investigated in order to determine the effect that Mg dopants have on the dielectric properties of SrTiO 3. It has been predicted that Mg-doped SrTiO 3 should exhibit a dielectric anomaly similar to that observed recently in Bi doped SrTiO 3 but, to date, no polar state has been reported. It has been suggested that this may relate to the low solubility of Mg on the A-site in bulk ceramics (<0.05 at.%). However, for Sr 1− x Mg x TiO 3 (SMT) ( x ⩽ 0.30) films annealed at 750 °C, all Mg ions were accommodated in the perovskite lattice and for SMT films annealed at 900 °C, the solubility limit of Mg was x = 0.10, above which a Mg-rich ilmenite second phase was observed. Irrespective of the higher solid solubility limit of Mg in the ST lattice for sol–gel ST films compared to equivalent ceramics, no ferroelectric or relaxor phase transition was observed, refuting previous predictions for this dopant.

Defect Structure in (Zn,Mg)O Films Prepared on YSZ Substrate

The defect structure of undoped ZnO and (Zn1-x,Mgx)O solid-solution films were deposited on YSZ substrate with pulsed laser deposition (PLD) to investigate defect equilibria in those films. In particular, the effects of thermal treatment on the structures and prosperities of (Zn1-x,Mgx)O solid-solution films were examined. The films with high MgO concentration (x&gt;0.12) decomposed to the wurtzite-type and rock-salt-type phase after thermal treatment, indicating that the solubility limit of Mg was about x=0.12 and the wurtzite-type (Zn,Mg)O films with x&gt;0.12 were indicated to be non-equilibrium ones. The subsequent analyses of oxygen diffusivity in those films revealed that the films under non-equilibrium state, i.e., wurtzite-type (Zn1-x,Mgx)O with x&gt;0.12, contained significantly high concentration of anion defects.

Solubility Limit of MgO in Al2O3 at 1600°C

The solubility of Mg in alumina was measured using wavelength‐dispersive spectroscopy mounted on a scanning electron microscope. Careful calibration of the microscope's working conditions was performed in order to optimize the detection limit and accuracy. Measurements were conducted on water‐quenched and furnace‐cooled samples, without any thermal or chemical etching to avoid alteration of the bulk concentration. The results indicate the solubility limit of Mg in alumina to be 132±11 ppm at 1600°C.

Microstructure and dielectric properties of Mg-doped barium strontium titanate ceramics

The dielectric properties of Ba0.8Sr0.2TiO3 ceramics doped with Mg from 0.5 to 10 mol % have been investigated systematically. Two effects of Mg doping on the dielectric properties of the Ba0.8Sr0.2TiO3 ceramics have been observed. At low Mg doping concentrations (&amp;lt;2 mol %), Mg mainly acts as an acceptor dopant to replace Ti in the B site of ABO3 perovskite structure, leading to a shift of Curie point (TC) to lower temperatures and a diffused phase transition. The permittivity and dielectric loss are suppressed gradually as the Mg content increases and the grain size decreases drastically. At higher Mg doping concentrations (⩾2 mol %), further suppression of permittivity and losses without further TC shift are observed, which indicates a “composite” mixing effect. The grain size remains almost constant. The solubility limit of Mg in the Ba0.8Sr0.2TiO3 appears to be ∼2 mol %.

Electrical properties of MgO-doped BaTiO3

The defect chemistry of Mg-doped BaTiO3 has been quantitatively studied. BaTi1−xMgxO3−x samples (x = 0, 0.001, 0.005, 0.01, 0.012, 0.02) have been precisely synthesized by the Pechini method. The concentration of oxygen vacancies was estimated from the location of the oxygen partial pressure P°(O2) at which the minimum point of equilibrium electrical conductivities occurs. Below 1.0 mol% Mg substitution for Ti sites, the experimental result is in good agreement with the theoretical calculation if the concentration of oxygen vacancies is assumed to be 100 ppm for undoped BaTiO3, where the oxygen vacancies stem from the background acceptor impurities. The solubility limit of Mg on Ti sites was confirmed to close to 1.0 mol%.

Conduction properties of Mg-, Fe- or Co-substituted Sr2TiO4 at elevated temperatures

Electrochemical properties of Mg-, Fe- or Co-substituted K2NiF4-type Sr2TiO4-based oxide solid solutions were investigated and compared to those of indium substituted system, which had been confirmed to be a protonic conductor [1]. All samples were prepared using the conventional solid-state reaction method. The solubility limit of Mg for Sr2TiO4 was about 0.05, just the half of solubility limit of In, 0.1. The dependence of electrical conductivities of Sr2Ti1−xMgxO4−δ on x was very similar to that of conductivities of Sr2Ti1−xInxO4−δ on x/2. EMF’s of hydrogen or oxygen concentration cells using Sr2Ti0.97Mg0.03O4−δ as a solid electrolyte were the same as those using Sr2Ti0.93In0.07O4−δ. These results indicate that in the Sr2TiO4-based system the predominant factor governing the phase relation and protonic conduction properties is the concentration of introduced oxygen vacancies. Single phase samples of Fe- or Co-substituted solutions, Sr2Ti0.93Fe0.07O4−δ and Sr2Ti0.93Co0.07O4−δ were obtained. In Sr2Ti0.93Fe0.07O4−δ, the dependence of conductivity on oxygen partial pressure was qualitatively equal to that of Sr2Ti0.93In0.07O4−δ indicating that the valence state of Fe is settled at +3 (3d5) in Sr2Ti0.93Fe0.07O4−δ and five d-electrons of Fe3+ are localized. In Sr2Ti0.93Co0.07O4−δ, the dependence of conductivity on oxygen partial pressure was different from those of Sr2Ti1−xMxO4−δ (M=In, Mg and Fe). There were neither pure ionic conduction regions at intermediate PO2 nor n-type electronic contributions to conductivity in low PO2 in Sr2Ti0.93Co0.07O4−δ.

Etude de la substitution [formula omitted] dans l'orthophosphate tricalcique β

Samples of trimetallic phosphate containing various amounts of Ca 2+ and Mg 2+ ions (TCMP), isostructural with β-Ca 3(PO 4) 2, were prepared by a double decomposition method, then calcinated at 900°C for 2 hr. Unit cell parameters a h and c h, and molar volume V rh, decrease linearly for atomic ratios Mg (Ca + Mg) varying from 0 to 9.5%. Above this value, V rh remains constant, but a h and c h unit cell parameters still vary: a h continues to decrease linearly to Mg (Ca + Mg) = 14% , and, in contrast, c h increases dramatically near Mg (Ca + Mg) = 9.5% and remains constant until 14%. These variations indicate that Mg 2+ ions can substitute for Ca 2+ ions in the TCP lattice to that value. Moreover, the upper solubility limit of Mg 2+ ions in the β-tricalcium orthophosphate lattice is reached when Mg 2+ (Ca 2+ + Mg 2+) = 14% . Substitution mechanism occurs according to consecutive occupation of the Ca(5) and Ca(4) sites of the structure, which respectively represent 9.5 and 4.75% of the cations. For Mg 2+ (Ca 2+ + Mg 2+) values greater than 14%, solids are composed both of TCMP and stanfieldite Ca 7Mg 9(Ca, Mg) 2(PO 4) 12. In this case, measured unit cell parameters of the TCMP phase are close to those of a 10% TCMP: therefore, the Mg 2+ ion content in the TCMP phase of these diphasic solids is smaller than the observed upper solubility limit. Furthermore, the use of very slow cooling rates (10°C hr −1) shows that Mg 2+ ion content in the TCMP phase decreases with decreasing temperature between 900°C and room temperature. These changes indicate that equilibrium conditions still vary below 900°C.