Effect Of Ga Content Research Articles

Effects of Ga Content on Microstructure Evolution and Mechanical Response of Heterostructured Dual-Phase Ag-49Cu Alloys

Effects of Ga Content on Microstructure Evolution and Mechanical Response of Heterostructured Dual-Phase Ag-49Cu Alloys

Investigation on Preparation and Performance of High Ga CIGS Absorbers and Their Solar Cells.

Tandem solar cells usually use a wide band gap absorber for top cell. The band gap of CuIn(1-x)GaxSe2 can be changed from 1.04 eV to 1.68 eV with the ratio of Ga/(In+Ga) from 0 to 1. When the ratio of Ga/(In+Ga) is over 0.7, the band gap of CIGS absorber is over 1.48 eV. CIGS absorber with a high Ga content is a possible candidate one for the top cell. In this work, CuInGa precursors were prepared by magnetron sputtering with CuIn and CuGa targets, and CIGS absorbers were prepared by selenization annealing. The Ga/(In+Ga) is changed by changing the thickness of CuIn and CuGa layers. Additionally, CIGS solar cells were prepared using CdS buffer layer. The effects of Ga content on CIGS thin film and CIGS solar cell were studied. The band gap was measured by PL and EQE. The results show that using structure of CuIn/CuGa precursors can make the band gap of CIGS present a gradient band gap, which can obtain a high open circuit voltage and high short circuit current of the device. With the decrease in Ga content, the efficiency of the solar cell increases gradually. Additionally, the highest efficiency of the CIGS solar cells is 11.58% when the ratio of Ga/(In+Ga) is 0.72. The value of Voc is 702 mV. CIGS with high Ga content shows a great potential for the top cell of the tandem solar cell.

Microstructure and mechanical properties of hot-extruded Mg–2Zn-xGa (x=1, 3, 5 and 7 wt.%) alloys

The effects of Ga content on the microstructure and mechanical properties of the hot-extruded Mg–2Zn-xGa alloys (x = 1, 3, 5 and 7 wt%) were investigated. The microstructure was characterized using X-ray diffraction spectroscopy (XRD), optical microscope (OM), scanning electron microscope (SEM), transmission electron microscope (TEM) and electron back-scattered diffractometer (EBSD). The results showed that the Mg–2Zn-xGa alloys were mainly composed of α-Mg matrix phase and Mg5Ga2 precipitates. The grains were continuously refined from 28.6 μm to 16.4 μm with increasing Ga content from 1 wt% to 7 wt%. The amount of micron-scale and nano-scale Mg5Ga2 precipitates increased with increasing Ga content and they were distributed both at the grain boundaries and inside the grain interiors. The tensile tests revealed that the addition of Ga element significantly enhanced the yield strength (YS) and ultimate tensile strength (UTS) due to the synergistic effects of refinement strengthening and precipitation strengthening. This strengthening effect was positively correlated with Ga content. The elongation (EL) firstly increased as Ga content increased from 1 wt% to 5 wt% and then decreased as Ga content further increased to 7 wt% because of the formation of excessive Mg5Ga2 precipitates.

A novel energy-resolved radiation detector based on the optimized CIGS photoelectric absorption layer

In this paper, we develop a novel energy-resolved X-ray detector based on the CuIn1-xGaxSe2 (CIGS) photoelectric conversion layer. The effect of Ga content on the crystal phase and the dark current of the photoelectric conversion layer has been studied. Furthermore, the photoelectric conversion capability of the CIGS thin film layer is optimized by the surface passivation process including the sulfurization treatment and Al2O3 treatment, achieving a low dark current of 90 nA/cm2 and high specific detectivity of 2.3 × 1014 Jones. The optimized CIGS photoelectric conversion layer and the Gd2O2S scintillator are used in the X-ray detector. The directions of the incident X-ray propagation and the induced fluorescence signal propagation are mutually perpendicular, thus the effective thickness of the scintillator is substantially increased without sacrificing the resolution of the sensor. In addition, the X-ray response of the detector is evaluated, the pixels at different X-ray penetration depths show obvious differences in absorption, contributing its ability of energy-resolution. The sensitivity of the prepared indirect X-ray detector is ∼8 μCGyair−1cm2 at an irradiation intensity of ∼6.5 mGyair/s. This work offers a new strategy to fabricate high performance energy-resolved X-ray detectors.

Effects of Ga content on the microstructure and mechanical properties of as-extruded Mg-xGa alloys

Microstructures and mechanical properties of the as-extruded Mg-xGa (x = 1, 3, 5, 7 wt%) alloys were investigated in the present work. Examination of as-extruded microstructures revealed that the grains were gradually refined from an average size of 45 µm (Mg-1Ga) to 15.7 µm (Mg-7Ga). Meanwhile, the volume fractions of Mg5Ga2 precipitates and dynamic recrystallization grains were significantly increased with increasing Ga content, and the texture was continuously weakened. The grain refinement and texture weakening were mainly ascribed to the increasing dynamic recrystallization stimulated by increasing Mg5Ga2 precipitates. The tensile test showed the as-extruded Mg-xGa alloys possessed both high strength and ductility that can meet the mechanical properties required by orthopedic implants. The tensile properties of as-extruded Mg-xGa alloys were gradually increased with increasing Ga content, reaching the highest yield strength of 166 MPa, ultimate tensile strength of 268 MPa, and elongation of 22.2% (Mg-7Ga). The enhanced tensile properties were benefited from a combination of grain refinement strengthening, solid solution strengthening and precipitation strengthening.

Effects of Ga content on the structure and electrical performances of 0.69BiFe1-xGaxO3-0.31BaTiO3 lead-free ceramics

Lead-free 0.69BiFe1-xGaxO3-0.31BaTiO3 (x, 0–0.06) piezoceramics were synthesized via traditional sintering techniques. The phase structure, dielectric, piezoelectric and ferroelectric performances of the ceramics were studied systematically. The results revealed that all the samples locate near MPB of rhombohedral (R)-pseudocubic (pC) phase coexistence, and that Ga doping has distinct influences on the R/pC phase content ratio. An appropriate content of Ga doping favors densification and grains growth of the ceramics during sintering. With the increment of Ga content, the Curie temperature of the samples shifts towards lower temperature owing to increased tolerance factor t of the perovskites, and enhanced diffuse phase transition behavior was observed. In addition, both the piezoelectric and ferroelectric property are sensitive to the concentration of Ga doping. Significantly, the excellent piezoelectric coefficient d33 up to 206 pC/N along with strong remanent polarization Pr of 25 μC/cm2 are obtained in 0.69BiFe0.985Ga0.015O3-0.31BaTiO3 materials which would be a promising substitute for the conventional lead zirconate titanate system ceramics.

Effect of the Ga Content on the Magnetic Properties and Microstructure of the Nanocrystalline Ce-Fe-B Alloys

In this work, the Ce17Fe78-xB6Gax (x = 0~3) nanocrystalline alloys are prepared by the direct melt spinning method with the wheel speed of 18 m/s. The effect of Ga content on the hard magnetic properties and the crystal structure of Ce17Fe78-xB6Gax (x = 0~3) nanocrystalline alloys has been investigated. The results show that the Curie temperature (Tc) and the phase content hard magnetic Ce2Fe14B phase can be increased by adding appropriate amount of low melting point Ga element. The results of magnetic properties show that the enhanced magnetic properties are obtained for the alloy with x = 1: Hcj = 5.61 kOe, Br = 5.4 kG, Hk/Hcj = 0.49, and (BH)max = 5.1 MGOe. The magnetization reversal characteristics of the alloys are analyzed by the recoil loops and the δM-H curves; the sample with the Ga-doped shows a single hard magnetic behavior. The positive peak of δM-H curve of the sample (x = 1) is obviously sharper and the peak value is higher, indicating the strongest magnetic interaction between grains. The reasons of the enhanced magnetic properties for the Ce-Fe-B alloy by the Ga addition are analyzed depending on the microstructure.

Effect of Ga content on magnetic properties of BaFe12−xGaxO19/epoxy composites

The article reports about the effect of Ga content on magnetic properties of 30 wt% BaFe12−xGaxO19/epoxy(x = 0.1, 0.3, 0.6, 0.9 and 1.2) composites with uniform and aligned (due to the action of external magnetic field under preparation) distribution of hexaferrite filler in epoxy matrix. The XRD investigations of BaFe12−xGaxO19/epoxy (x = 0.1, 0.3, 0.6, 0.9 and 1.2) composites have revealed that the alignment degree of a crystalline hexaferrite phase with a hexagonal unit cell of crystal structure and P63/mmc space group in composites with uniform filler distribution is near 0.5 and for the composites with aligned filler distribution it is 1 for the direction along the applied magnetic field and it is 0 for the direction across the applied magnetic field, respectively. The investigation of the hysteresis loops of BaFe12−xGaxO19/epoxy (x = 0.1–1.2) composites with the aligned distribution of filler for both directions to the applied magnetic field has shown that magnetic properties across the alignment direction are superior in comparison with similar measurements taken on composites with uniform filler distribution. It was shown that anisotropy of magnetic properties of BaFe12−xGaxO19/epoxy (x = 0.1–1.2) composites is observed for all the investigated composites with the aligned distribution of the filler. Squareness ratio Ms along/Ms across decreases with Ga content increase, while the value Hc along/Hc across approaches to 1. Such behavior of magnetic characteristics of the investigated composites indicates clearly the decrease in magnetocrystalline anisotropy of Ga-substituted hexaferrite under Ga content increase.

Effects of Ga Content on Dynamic Recrystallization and Mechanical Properties of High Strain Rate Rolled Mg–Ga Alloys

The Mg–xGa (x = 1, 2, 3 and 5 in mass%) alloys are subjected to high strain rate rolling (HSRR) at 275 °C with the rolling strain rate of 9.1 s−1 to develop high performance Mg alloy sheets with high plasticity. Effects of Ga content on microstructure and mechanical properties of the Mg–Ga alloys are investigated by SEM, XRD, tensile testing and etc. The Ga addition can reduce the critical strain of DRX in Mg alloys, which is associated with the reduced stacking fault energy, the increased twinning density during deformation and the more DRX nucleation sites during HSRR. With the Ga content increasing from 2 to 3%, the reduced DRX degree is attributable to the hindrance of dynamic precipitates. With the Ga content increasing from 3 to 5%, the slightly increased DRX degree can be ascribed to the relatively coarse precipitates. The Mg–2 Ga alloy sheet, featured with complete DRX, exhibits an ultra-high plasticity (with the elongation to rupture of 36.6%) and a relatively low anisotropy of yield strength and plasticity. The Mg–5 Ga alloy sheet has the best comprehensive mechanical properties, with the ultimate tensile strength of 292 MPa, yield strength of 230 MPa and elongation to rupture of 30.3%, which can be ascribed to the combination of grain refinement strengthening and precipitation strengthening. Effects of Ga content on microstructure, dynamic recrystallization (DRX) and mechanical properties of the Mg-Ga alloys prepared by high strain rate rolling (HSRR) are systematically studied. Among all the alloys, the HSRRed Mg-2Ga alloy exhibits the smallest DRX critical strain, an ultrahigh plasticity (δ up to 36.6%) and a low anisotropy of yield strength and plasticity, due to the complete DRX. The HSRRed Mg-5Ga alloy shows the optimal mechanical properties, with σb of 292 MPa, σ0.2 of 230 MPa and δ of 30.3%. The high strength is mainly attributed to precipitation strengthening and grain refinement strengthening.

Effect of Ga content on luminescence and defects formation processes in Gd3(Ga,Al)5O12:Ce single crystals

Luminescence characteristics of Ce3+ - doped Gd3GaxAl5-xO12 single crystals with different Ga contents (x = 1, 2, 3, 4, 5) are studied in the 9–500 K temperature range. The spectra of the afterglow, photoluminescence, radioluminescence, and thermally stimulated luminescence (TSL) of each crystal coincide. The increase of the Ga content results in the high-energy shift of the spectra while the radioluminescence intensity at 9 K remains practically constant up to x = 4. No Ce3+ emission is observed in case of x = 5. The total TSL intensity drastically increases, reaches the maximum value around x = 2–3, and then decreases due to the thermal quenching of the Ce3+ emission. The TSL glow curve maxima are gradually shifting to lower temperatures, and the dependence of the maxima positions and the corresponding trap depths on the Ga content is close to linear. However, the activation energy of the TSL peaks creation under irradiation of the crystals in the 4f – 5d1 absorption band of Ce3+ decreases drastically with the increasing Ga content (especially in the range of x = 1–2), and this dependence is found to be strongly nonlinear. Possible reasons of the nonlinearity are discussed.

Effect of Ga content on the properties of CuGaS precursor thin films produced by electrochemical Co-deposition

Cu–Ga–S ternary thin films were produced by one-step co-electrochemical deposition from an aqueous deposition bath consisting CuCl2, GaCl3 and Na2S2O3 as precursor, and LiCl. The pH of the deposition solution was adjusted to 2.0 adding HCl. Cyclic voltammogram studies were performed in detail prior to the film growth. The best deposition potential was determined to be −0.4 V from the standpoint of the film homogeneity, doping all elements in the bath and avoidance of the immediate atomic aggregation. The chronoamperometry technique was applied to the deposition solution at −0.4 V for 30 min. The effect of Ga content on the film characteristics was investigated. Optical band gap of the films was found to be in 1.6–2.2 eV range. It was concluded that energy band gap of the thin films decreased, as Ga content increased. All deposited films exhibited p-type semiconductor behavior.

Single step electrosynthesis of NiMnGa alloys

An electrochemical synthesis route for NiMnGa alloys is presented. Thin films of NiMnGa were fabricated by single step electrodeposition from aqueous electrolytes using direct current over a range of current densities. By electrolyte tuning, homogeneous films with high Ga and Mn content could be achieved at current densities as high as −400mAcm−2. Detailed compositional analysis of the alloys showed that growth was homogeneous and oxygen content was minimized. Films plated at very low current densities were found to be nanocrystalline/amorphous. In order to obtain fully crystalline samples, thermal annealing was carried out. Mechanical characterization was assessed by nanoindentation, and the effect of Ga content on mechanical properties was investigated.

Effects of Ga Contents on Structural and Electrical Properties in Cu(In,Ga)Se<SUB>2</SUB> Thin Film Solar Cell

Effects of Ga Contents on Structural and Electrical Properties in Cu(In,Ga)Se<SUB>2</SUB> Thin Film Solar Cell

Effect of Ga content in Cu(Ga) on the growth of V3Ga following bronze technique

Diffusion–controlled growth rate of V3Ga in the Cu(Ga)/V system changes dramatically because of a small change in Ga content in Cu(Ga). One atomic percent increase from 15 to 16 leads to more than double the product phase layer thickness and a decrease in activation energy from 255 to 142 kJ/mol. Kirkendall marker experiment indicates that V3Ga grows because of diffusion of Ga. Role of different factors influencing the diffusion rate of Ga and high growth rate of V3Ga are discussed.

The Effect of Ga Content on the Recombination Behavior of Grain Boundaries in Cu(In,Ga)Se2 Solar Cells

ABSTRACTThe highest efficiency CuIn1-xGaxSe2 (CIGS) based solar cells have been produced from films with x∼0.3 which gives a value of Eg around 1.1-1.2eV. Increasing the Ga content of the CIGS absorber provides an increase in Voc, allows tuning of the band gap that can enhance performance under actual operating conditions, and potentially makes it possible to use CIGS films in multi-junction devices. However, champion cells have not yet been produced for values of x significantly greater than 0.3. This work focuses on how increased Ga content in CIGS films affects the recombination behavior of grain boundaries. Cathodoluminescence spectral imaging (CLSI) measurements on fully processed devices allow us to compare device properties with recombination behavior and optical properties of grain boundaries in films with different Ga content. Our data suggests that grain boundaries in high efficiency films with x∼0.3 exhibit a significant red shift in the CL spectra whereas grain boundaries in films with higher Ga content typically show either a small shift or none at all. This shift indicates band bending near the boundaries which could enhance charge separation and subsequent collection of carriers generated near grain boundaries. This is investigated statistically to identify trends in different regions of the films.

Solid state phase transformation study on a series of Pu–Ga alloys containing 0.18–0.63wt.% Ga

• Solid state phase transformation behaviours of Pu–Ga alloys were investigated. • Effects of Ga content and starting condition on Pu–Ga alloy were found significant. • The nature of as cast α-phase is independent of the nominal Ga content. • The ε → δ transformation happens through two mechanisms when Ga < 0.63 wt.%. • Increase of thermal expansion coefficient of δ-phase with increasing Ga confirmed. The effects of Ga concentration and starting condition of Pu–Ga alloys on their solid-state phase transformation behaviours in a set of Pu–Ga alloys containing 0.18–0.63 wt.% Ga were studied under non-equilibrium conditions with a heating/cooling rate of 10 °C/min in the temperature range of 25–560 °C by a dilatometry method. The characteristic abrupt slope changes shown in the dilatometry tracks during heating and cooling are ascribed to the known phase transformations in the Pu–Ga alloys. The rationale for such an ascription is discussed. The study showed that, as expected, Ga concentration and the starting condition of the Pu–Ga alloy have significant effects, demonstrated by the variety of the onset and completion temperatures of a phase transformation. We find that the nature of as cast α-phase is independent of the nominal Ga content. The ε → δ transformation happens through two mechanisms when Ga < 0.63 wt.%. Furthermore, the increase of thermal expansion coefficient of δ-phase with increasing Ga is also confirmed.

Effect of Ga content and growth temperature on Cu(In,Ga)Se2 thin film deposited on heat‐resistant glass substrates

AbstractCu(In,Ga)Se2 (CIGS) thin films were deposited on the Mo/heat‐resistant glasses (SS‐8, Nippon Electric Glass) by the three‐stage evaporation process. The coefficient of thermal expansion (CTE) of SS‐8 is 8.4×10–6/K, strain point of SS‐8 is 582 °C. SS‐8 has the CTE similar to that of SLG but higher thermal tolerance. Substrate temperature (Tsub) during deposition and Ga/(In+Ga) atomic ratio of CIGS thin films were controlled to 550∼600 °C and 0∼0.7, respectively. The effect of Tsub and Ga/(In+Ga) atomic ratios of CIGS films have been characterized by electron backscatter diffraction (EBSD) measurements. Grain size and ∑3 grain boundary ratio increased at higher Tsub. ∑3 grain boundary ratio was calculated from the fraction of the length of ∑3 grain boundary by the length of the total grain boundaries on EBSD image. There was the correlation among Ga contents, Tsub, grain size and efficiency. It is difficult to distinguish between effect of grain size and effect of grain boundary to efficiency. However, it is found that high Ga content up to 0.7 results in both high efficiency and ∑3 grain boundary ratio. (© 2013 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

The phase evolution, magnetic and exchange bias properties in Fe50Mn24+xGa26−x (x = 0–3) melt-spun ribbons

Effect of Ga content on the phase constitution, magnetic phase transition temperatures (TC), and exchange bias (EB) behaviors of Fe50Mn24+xGa26−x (x=0, 0.5, 1, 3) as-spun ribbons have been investigated. Fe50Mn24Ga26 ribbon exhibits a magnetic phase transition of B2-type structure from FM to PM state at TC1=190K. Another magnetic phase transition of face-center-cubic structure from AFM to FM takes place at TC2=240K for Fe50Mn25Ga25 sample. The values of exchange bias field (HE) at 10K after field-cooling (FC) at 30kOe from 300K are 14, 41, 1886, 1740Oe, respectively, as x is increased from 0 to 3. The phenomena are attributed to the change of exchange interactions at FM/AFM interfaces due to the change of proportion of FM and AFM phases in low temperature magnetic states. The maximum exchange bias field HE=2.4kOe at 10K after field-cooling at 40kOe is observed for Fe50Mn25Ga25.

Effects of Ga content and reaction pressure upon the aromatization of propane over H–Ga–Al-bimetallosilicate catalysts

Aromatization of propane has been investigated at 540 °C in a reaction pressure range up to 0.686 MPaG over MFI-type H–Ga–Al-bimetallosilicates having various Ga/(Ga + Al) atomic ratios but a constant Si/(Ga + Al) ratio of 15. Both the propane conversion and the aromatic selectivity increased with increasing the Ga/(Ga + Al) ratio up to 0.25. Further increase in the Ga content decreased the propane conversion, although the aromatic selectivity increased. Of the catalysts examined, the H–Ga–Al-bimetallosilicate sample having the Ga/(Ga + Al) ratio of 0.25 showed the highest performance for propane aromatization. The effect of reaction pressure was investigated using this catalyst. With increasing the reaction pressure, the propane conversion increased, but the aromatic selectivity decreased. The reaction pressure was also found to strongly influence the cracking activity and the deactivation rate of the catalyst. From the analysis of the gaseous products, it was concluded that the aromatization reaction was suppressed under high reaction pressure conditions because of the formation of methane and ethane by protolytic cracking and hydrogen transfer from aromatic precursors to olefinic intermediates.

Investigation of switching phenomenon of Se 75Te 25− xGa x amorphous system

Thin film samples of different thicknesses ranging from 185 to 630 nm, were prepared from the synthesized amorphous Se 75Te 25− x Ga x (0 ≤ x ≤ 15 at.%) chalcogenide glass compositions by thermal evaporation technique. X-ray analysis showed that the amorphous nature of the obtained films. Investigations of the current–voltage ( I– V) characteristics of amorphous films are typical for a memory type switch. The conduction activation energy (Δ E σ ) was calculated from the temperature dependence of the sample resistance of the studied films in the temperature range (293–333 K) below the glass transition temperature. The mean value of the threshold switching voltage V ¯ t h increases linearly with increasing film thickness and decreases exponentially with temperature (below T g ) for all investigated compositions. The threshold voltage activation energy ɛ th was calculated from the temperature dependence of V ¯ t h of the studied films. The switching phenomenon observed in these films is explained in accordance with the electrothermal model for the switching process. The effect of Ga content on the studied parameters was also investigated.