Increasing Gallium Content Research Articles

Microstructure and hydrogen storage properties of magnesium–gallium binary alloys

In this paper, gallium was used as alloying element to improve hydrogen storage properties of magnesium. Therefore, Mg–x wt% Ga (x = 5, 10, 25, 50) binary alloys were prepared by induction melting method. The microstructure and phase composition of Mg–Ga alloy were analyzed using X-ray diffractometer and scanning electron microscope. The results show that Mg–Ga binary alloys consist of Mg and Mg5Ga2 phases. The Mg and Mg5Ga2 react with H2 to form Mg2Ga and MgH2 during hydrogenation process. The hydrogen storage kinetics and thermodynamic properties of the alloys were tested using a Sieverts-type apparatus. It is found that the dehydrogenation rates of the samples increase with increasing gallium content, and they are all better than pure magnesium. Thermal analysis results indicate that increasing gallium content decreases dehydrogenation temperature of Mg–Ga alloy. The beneficial effects of adding gallium in magnesium is that interfaces and secondary phase resulted from alloying can promote the hydrogen desorption process of the alloy. The Mg–50 wt% Ga alloy has the lowest dehydrogenation activation energy. However, increasing gallium content inevitably reduces the hydrogen storage capacity of the Mg–Ga alloys. Furthermore, alloying with gallium does not change the thermomechanical properties of magnesium.

Phase formation during crystallization of melts and glasses of the GaxGe40-xS60 system

The purpose of this work is to study phase formation during quenching of glass-forming melts and crystallization of GaxGe40-xS60 glasses (x = 0–15 at.%), which are promising materials for optical IR glass-ceramics. The stability against crystallization of the glasses is determined to decrease with increasing gallium content. In the case of the glass-forming melts, the stability against crystallization increases in the range x = 0–8 at.% and then decreases. It is established that, during crystallization, not pure phases of binary sulfides are formed, but their solid solutions. When quenching the melts with a gallium content of 10–15 at.%, Ga2-xGexS3 solid solutions, which are isostructural to one of the polymorphic modifications of gallium sesquisulfide, are crystallized. Solid solutions form skeletal crystals, the growth of which leads to the formation of a dendritic crystal structure. Micro-liquation in the GaxGe40-xS60 glasses is observed.

Structural and Thermomagnetic Properties of Gallium Nanoferrites and Their Influence on Cells In Vitro.

Magnetite and gallium substituted cuboferrites with a composition of GaxFe3-xO4 (0 ≤ x ≤ 1.4) were fabricated by thermal decomposition from acetylacetonate salts. The effect of Ga3+ cation substitution on the structural and thermomagnetic behavior of 4-12 nm sized core-shell particles was explored by X-ray and neutron diffraction, small angle neutron scattering, transmission electron microscopy, Mössbauer spectroscopy, and calorimetric measurements. Superparamagnetic (SPM) behavior and thermal capacity against increasing gallium concentration in nanoferrites were revealed. The highest heat capacity typical for Fe3O4@Ga0.6Fe2.4O4 and Ga0.6Fe2.4O4@Fe3O4 is accompanied by a slight stimulation of fibroblast culture growth and inhibition of HeLa cell growth. The observed effect is concentration dependent in the range of 0.01-0.1 mg/mL and particles of Ga0.6Fe2.4O4@Fe3O4 design have a greater effect on cells. Observed magnetic heat properties, as well as interactions with tumor and healthy cells, provide a basis for further biomedical research to use the proposed nanoparticle systems in cancer thermotherapy (magnetic hyperthermia).

Using neutron diffraction to explore lithium displacement within cubic phase stabilised Ga-doped Li6.75La3Zr1.75Ta0.25O12 lithium garnet oxides

Typical Li6.75La3Zr1.75Ta0.25O12 exists as a mixture of tetragonal and cubic arrangements, but adding small amounts of Ga3+ (Li6.75–3xGaxLa3Zr1.75Ta0.25O12 x ≥ 0.1) resulted in a single cubic (I a-3d) phase lithium garnet oxide. Following the stabilisation of the cubic phase, the effects on lithium distributions were explored with neutron powder diffraction concerning Ga3+ content and temperature. Increasing the amount of Ga3+ reduced the amount of lithium within the structure, directly decreasing the Li 96h site occupancy and showing a minimal effect on the Li 24d site occupancy. High-temperature neutron diffraction studies revealed the migration of lithium from the Li 24d site to the Li 96h with increasing temperature. The inclusion of Ga3+ improved the total ionic conductivity over the gallium-free system. However, with increasing gallium content (x > 0.1), a negative correlation between the garnet's gallium content and total lithium ionic conductivity is observed, showing how the total amount of free lithium ions impact the system's total ionic conductivity. Though the electrolytes explored here show some limitations, the lithium-ion displacement trends with doping and temperature give us further insight into how these lithium garnet systems respond to chemical and physical change.

The Ga20Ge20Se60 glass-ceramics as a promising long-wave IR optical material

The Ga20Ge20Se60 chalcogenide glass-ceramics with a crystalline phase volume fraction of 50–55%, an average crystal size of 2–5 μm, and a transparency of 50–65% in the spectral range of 7–16 μm (at 2 mm sample thickness) are prepared. The features of phase formation during glass-forming melt quenching and subsequent annealing are studied. In samples quenched in water from 750 to 850 °C, Ga40-xGexSe60 (x = 20–30) solid solutions with a cubic unit cell are formed. Upon quenching from 700 °C, solid solutions isostructural to monoclinic Ga2Se3 are formed. Annealing of glass-ceramics at 480 °C leads to the decomposition of the cubic phase and the appearance of mixed GaGeSe3. Fracture toughness, elastic modulus, and abrasive resistance increase with increasing gallium content in GaxGe40-xSe60 (x = 5–20) samples. The reasons for the high transparency of Ga20Se20Se60 glass-ceramics in the long-wave infrared range and its dependence on the production conditions are established and discussed.

Structural, magnetic, optical, and photoresponse studies of hydrothermally prepared nanocrystalline GaxFe2-xO3 (x=0.7, 1 & 1.3)

Effect of gallium content on the structural, magnetic, optical and optoelectronic properties of nanocrystalline gallium ferrite GaxFe2-xO3 (x = 0.7, 1 & 1.3) prepared via hydrothermal synthesis is reported herein. X-ray diffraction, FTIR, Raman spectroscopy, and scanning electron microscopy techniques are used to study the structural and morphological properties of the samples. The crystal structure for all of the samples is single-phase orthorhombic with a P212121 space group. The structural investigation via Rietveld refinement of XRD shows a decrease in lattice parameters and volume with increasing gallium content. The structural modifications with Ga content are also confirmed from the Raman analysis and FTIR analysis. The scanning electron microscopy indicates that the size of nanoparticles is < 150 nm for all the samples, and particle size increases with Ga content. The optical and magnetic properties of GaxFe2-xO3 is not varying monotonically with x and are distinctly different from most studied Pc21n structures of GFO samples, which indicate the influence of pressure-induced cation site disorder during hydrothermal synthesis. The composition with x = 1 shows relatively less cation disorder. UV absorption analysis proves that the band gap decreases with increasing Ga concentration. The photoluminescence lifetime and quantum yield results also demonstrate the significant variation with Ga concentrations. A relatively high fluorescence value is observed for GFO with x = 1. The thin films with x < 1 show a negative photoconductive gain, whereas those with x > 1 show a positive gain. This study suggests that hydrothermally prepared nanocrystalline gallium ferrite's structural, magnetic, optical, and photosensitivity properties can be largely tailored with Ga content. The cation site disorder also plays a significant role in modulating the magneto-optical properties of this system. The photosensitivity exhibited by the multiferroic GFO systems opens an avenue into optoelectronic applications of this material.

Peculiarities of GaxGe100-x-ySey glasses crystallization as potential materials for optical IR glass-ceramics

A comprehensive study of the crystallization of GaxGe100-x-ySey (x = 0–30; y = 60–75) glasses by means of differential scanning calorimetry, X-ray diffraction analysis, optical microscopy and scanning electron microscopy as carried out. Glass transition temperature and stability against crystallization decrease with increasing gallium content in the glasses. During the glass crystallization, phases of variable composition, isostructural to the polymorphic modifications of Ga2Se3, are formed. Samples with ≤10 at.% gallium content contain germanium mono- and diselenide phases. A distinctive feature of the crystallization of GaxGe100-x-ySey glasses is the formation of globules – localized 10–60 µm sized regions with an increased crystalline phase content. The formation of globules at the stage of melt quenching determines the microscopic structure of glasses. Among the studied compositions, glasses with a selenium content of 60 at.% and gallium content up to 15 at.% are recommended as optimum for the preparation of IR glass-ceramic materials.

Effect of Magnetic Field Annealing on Magnetic Properties of Iron–Gallium Alloys

The concentration dependence of magnetic properties of iron alloys with 3–25% of gallium is studied. It was shown that the saturation induction monotonically decreases with increasing gallium content, while the coercivity exhibits a step increase with a step from 85 to 135 A/m between 12 and 15 at % Ga. The effect of magnetic field annealing (MFA) on the behavior of the residual induction and coercive force in alloy samples containing from 3 to 18 at % Ga is studied. As a result of MFA, magnetic anisotropy is induced in the alloy: magnetic hysteresis loops become narrower, the residual induction increases, and the coercivity decreases. The MFA efficiency reaches a maximum at a Ga content of 15–18 at %. The features of the structure state of iron–gallium alloys and their role in the formation of magnetic properties during annealing in a dc magnetic field are discussed.

Влияние отжига в постоянном магнитном поле на магнитные свойства сплавов железо--галлий

The concentration dependence of the magnetic properties of iron alloys with 3 – 25 at.% gallium has been studied. It is shown that with increasing gallium content, saturation induction decreases monotonically, but coercive force shows a stepped increase with a jump from 85 to 135 A/m between 12 and 15 at.% Ga. The effect of annealing in a dc magnetic field (magnetic field annealing (MFA)) on the behavior of residual induction and coercive force in samples containing from 3 to 18 at.% of gallium was investigated. After the MFA, in the alloy a magnetic anisotropy is induced: magnetic hysteresis loops become narrower, the residual induction increases and the coercive force decreases. The MFA efficiency reaches a maximum when the gallium content is at 15 – 18 at.%. The features of the structural state in iron-gallium alloys and their role in the formation of the magnetic properties during annealing in the dc magnetic field are discussed.

The hunt for the third acceptor in CuInSe2 and Cu(In,Ga)Se2 absorber layers

The model for intrinsic defects in Cu(In,Ga)Se2 semiconductor layers is still under debate for the full range between CuInSe2 and CuGaSe2. It is commonly agreed by theory and experiment, that there are at least one shallow donor and two shallow acceptors. Spatially resolved photoluminescence on CuGaSe2 previously revealed a third acceptor. In this study we show with the same method that the photoluminescence peak at 0.94 eV in CuInSe2, previously attributed to a third acceptor, is a phonon replica. However another pronounced peak at 0.9 eV is detected on polycrystalline CuInSe2 samples grown with high copper and selenium excess. Intensity and temperature dependent photoluminescence measurements reveal that this peak originates from a DA-transition from a shallow donor (<8 meV) into a shallow acceptor A3 (135 10) meV. The DA3 transition has three distinct phonon replicas with 28 meV spectral spacing and a Huang Rhys factor of 0.75. Complementary admittance measurements are dominated by one main step with an activation energy of 125 meV which corresponds well with the found A3 defect. The same defect is also observed in Cu(In,Ga)Se2 samples with low gallium content. For [Ga]/([Ga] + [In])-ratios of up to 0.15 both methods show a concordant increase of the activation energy with increasing gallium content shifting the defect deeper into the bandgap. The indium vacancy is discussed as a possible origin of the third acceptor level in CuInSe2 and in Cu(In,Ga)Se2.

Composition-tuned optical absorption and luminescence of TlGaxIn1-xS2 layered mixed crystals at T = 10 K

Transmittance on TlGaxIn1-xS2 mixed crystals (0 ≤ x ≤ 1) was carried out in the 2.35–2.75 eV photon energy range at T = 10 K. Band gap energies of crystals were obtained utilizing the derivative spectra of transmittance and photon energy dependence of absorption coefficient. The dependence of direct band gap energy on composition at T = 10 K revealed that as gallium composition is elevated in the mixed crystals, the direct band gap energy increases from 2.56 to 2.67 eV.Photoluminescence spectra of TlGaxIn1-xS2 crystals were studied in the photon energy region of 2.30–2.95 eV at T = 10 K. The observed bands were attributed to transitions of electrons from shallow donor levels to valence band. The shift of PL bands to higher energies with increasing gallium content was revealed. Furthermore, composition ratio of crystals was determined from energy dispersive spectroscopy experiments.

Thermomigration Kinetics in the Si–Al–Ga and Si–Al–Sn Systems

The thermodynamics and kinetics of the thermomigration of molten zones based on Al–Ga and Al–Ga melts in the preparation of silicon epilayers have been studied in detail. We have determined the threshold thermomigration temperature for zones of various compositions. The migration onset temperature has been shown to increase monotonically with increasing Ga or Sn concentration in the liquid phase. The thermomigration rate of Si–Al–Ga zones decreases with increasing gallium concentration at temperatures below 1473 K and increases at higher temperatures. The thermomigration rate of Si–Al–Sn zones decreases with increasing Sn concentration over the entire temperature range studied. No chemical compounds have been detected in the Si–Al–Ga or Si–Al–Sn system, which simplifies the use of the thermomigration method in these systems.

Synthesis of Quaternary Cu(InxGa1 − x) Se2 Nanoparticles for Photovoltaic Applications Using Heating-up Method

Nowadays, thin-film solar cells based on nanoparticles have attracted much attention from photovoltaic cell researchers and industries due to their fairly high efficiency and economic costs. In this paper, tetragonal chalcopyrite, Cu(InxGa1 − x)Se2, with x = 0, 0.5, 0.8, 1 is produced by heating-up method. The structure of nanoparticles differ in terms of morphology and absorption properties based on synthesis temperatures 250, 255, 260, 265, 270 and 280 °C and gallium molar ratio over total gallium and indium content. These features are characterized using scanning electron microscope, X-ray diffraction, and absorption spectroscopy in visual, ultra-violate and close-infrared wavelengths. Results indicated that by decreasing x, or in other word increasing gallium content, absorption edge rises toward visible light. Any difference in absorption edge changes band gap and as a result energy gap and cell absorption increase considerably. Furthermore, in heating-up method, increasing reaction temperature improves nanoparticle crystallites and as a result absorption and cells efficiency increase. Produced nanoparticles are spherical in shape which vary around 30–80 nm in size.

Development of a novel bioactive glass suitable for osteosarcoma-related bone grafts.

In this study, zinc borate-based glasses with increasing gallium content (0, 2.5, 5, 10, and 15 wt % Ga) were synthesized and their effect on the viability and proliferation of preosteoblasts and osteosarcoma cancer cells were investigated. Methyl thiazolyl tetrazolium (MTT) cell viability assays using glass degradation extracts revealed that the extracts from glasses with lower Ga contents could enhance the viability of preosteoblasts, while extracts from the glass composition with 15 wt% Ga caused statistically significant reduction of their viability. MTT cell viability assays using the extracts and osteosarcoma cells showed that only extracts from the glass composition with 5 wt% Ga (G3) did not cause a statistically significant increase in the viability of cancer cells for all degradation periods (1 day, 7 days, and 28 days). G3 was selected as the most suitable composition for the osteosarcoma-related graft operations as it could improve the viability of preosteoblasts without increasing the viability of cancer cells. The viability of preosteoblasts and osteosarcoma cells in contact with the glass powders were also investigated using MTT assays. The results showed that the G3 powders could enhance the viability of preosteoblasts while decreasing the viability of osteosarcoma cells. Finally, live/dead assays revealed that suppression of proliferation appeared to be the mechanism causing the observed reductions in the viability of osteosarcoma cells exposed to G3 powders. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 1186-1193, 2018.

The impact of gallium content on degradation, bioactivity, and antibacterial potency of zinc borate bioactive glass.

Zinc borate glasses with increasing gallium content (0, 2.5, 5, 10, and 15 Wt % Ga) were synthesized and their degradation, bioactivity in simulated body fluid (SBF), and antibacterial properties were investigated. ICP measurements showed that increased gallium content in the glass resulted in increased gallium ion release and decreased release of other ions. Degradability declined with the addition of gallium, indicating the formation of more symmetric BO3 units with three bridging oxygens and asymmetric BO3 units with two bridging oxygens in the glass network as the gallium content in the series increased. The formation of amorphous CaP on the glass surface after 24 h of incubation in SBF was confirmed by SEM, XRD, and FTIR analyses. Finally, antibacterial evaluation of the glasses using the agar disc-diffusion method demonstrated that the addition of gallium increased the antibacterial potency of the glasses against P. aeruginosa (Gram-negative) while decreasing it against S. epidermidis (Gram-positive); considering the ion release trends, this indicates that the gallium ion is responsible for the glasses' antibacterial behavior against P. aeruginosa while the zinc ion controls the antibacterial activity against S. epidermidis. The statistical significance of the observed trends in the measurements were confirmed by applying the Kruskal-Wallis H Test. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 367-376, 2018.

Effect of the chemical composition of Cu–In–Ga–Se layers on the photoconductivity and conversion efficiency of CdS/CIGSe solar cells

The effect of the [Ga]/[In+Ga] ratio of gallium and indium on the microwave photoconductivity of Cu–In–Ga–Se (CIGSe) films and on the efficiency of solar cells fabricated in accordance with the same technology is investigated. According to the observations of a field-emission scanning electron microscopy (FESEM), the grain size decreases with increasing Ga content. With increasing gallium content in the samples, the photogenerated-electron lifetime and the activation energy of the microwave photoconductivity also decrease. The changes in the activation energy of the through conduction in darkness are less than 20%. Analysis of the obtained data shows that the known effect of the gallium gradient on the efficiency should be associated with modification of the internal structure of grains instead of with their boundaries.

The effect of the addition of gallium on the structure of zinc borate glass with controlled gallium ion release

Gallium ion released from bioactive glasses can perform therapeutic functions depending on its concentration. In this study, zinc borate based glasses with increasing gallium content (0, 2.5, 5, 10, and 15wt.% Ga) were synthesized and their structural properties and gallium ion release capabilities were investigated in order to understand how the substitution of gallium for boron affects the glass network. X-ray diffraction verified the amorphous state of the synthesized glasses. Thermal and spectroscopic analyses recorded a steady decline in both glass transition and crystallization temperatures of the glasses alongside small shifts in the position of borate triangles' peaks, indicating short-range order rearrangements, and a rise in the number of pentaborate and loose BO3 units by the addition of gallium. 11B Magic Angle Spinning Nuclear Magnetic Resonance (MAS NMR) analysis showed incremental addition of gallium reduces the BO4/BO3 ratio which indicates an increase in the non-bridging oxygens in the glasses with higher gallium content, and 31P MAS NMR analysis revealed the presence of orthophosphate units with one and two bridging oxygens and that the introduction of gallium overall lowers the fraction of units with two bridging oxygens. The released gallium ion was considerably more in glasses with higher gallium content.

Atomistic modeling of thermodynamic properties of Pu-Ga alloys based on the Invar mechanism

We present an atomistic model that accounts for a range of anomalous thermodynamic properties of the fcc $\ensuremath{\delta}$ phase of Pu-Ga alloys in terms of the Invar mechanism. Two modified embedded atom method potentials are employed to represent competing electronic states in $\ensuremath{\delta}$-Pu, each of which has an individual configuration dependence as well as distinct interactions with gallium. Using classical Monte Carlo simulations, we compute the temperature dependence of various thermodynamic properties for different dilute gallium concentrations. The model reproduces the observed effects of excessive volume reduction along with a rapid shift in thermal expansion from negative to positive values with increasing gallium concentration. It also predicts progressive stiffening upon dilute-gallium alloying, while the calculated thermal softening is nearly independent of the gallium concentration in agreement with resonant ultrasound spectroscopy measurements in the literature. Analysis of the local structure predicted by the model indicates that the distribution of the gallium atoms is not completely random in the $\ensuremath{\delta}$ phase due to the presence of short-range order associated with the Invar mechanism. This effect is consistent with the nanoscale heterogeneity in local gallium concentration which is observed in recent extended x-ray absorption fine structure spectroscopy experiments. Implications of the Invar effect for phase stability and physical interpretations of the two states are also discussed.

Magnetoelectric Polarization of Paramagnetic HoAl&lt;sub&gt;3-X&lt;/sub&gt;Ga&lt;sub&gt;X&lt;/sub&gt;(BO&lt;sub&gt;3&lt;/sub&gt;)&lt;sub&gt;4&lt;/sub&gt; Single Crystals

HoAl3-xGax(BO3)4 (0 ≤ х ≤ 3) single crystals were grown from Bi2Mo3O12Li2MoO4-based fluxes. Structural inversion twinning depending on crystal composition and heat treatment conditions is revealed. It is established that upon substitution of Ga3+ ions for Al3+ the magnetic characteristics of the crystals do not significantly change, while the magnetoelectric polarization decreases with increasing gallium content. The measured value and sign of polarization charges depend on a ratio between the left and right isomers.

CuIn&lt;sub&gt;1-x&lt;/sub&gt;Ga&lt;sub&gt;x&lt;/sub&gt;Se&lt;sub&gt;2&lt;/sub&gt; Thin Films Prepared by Co-Evaporation Technique

The optical properties of Cu-poor CuIn1-xGaxSe2 thin films with different gallium contents grown by co-evaporated technique were studied. Measurements of photoluminescence and photoreflectance were performed on the samples. The photoluminescence and photoreflectance emission peaks observed around 1.1 eV are attributed to donor-acceptor pair luminescence. These donor-acceptor pair emissions are considered to originate from relatively shallow acceptor and donor energy levels. With increasing gallium content, the emission peaks shift towards higher levels of photon energy, and the linewidths of the luminescence spectra for the samples become wider, which we attributes to the greater statistical disorder between indium and gallium. Moreover, the conversion efficiency of the CuIn1-xGaxSe2-based solar cells is obtained. The measured results coincide with the inference given by the photoluminescence spectra.