Increasing Ga Content Research Articles

Effect of Al/Ga substitution on photoluminescence and chromatic properties of Y3Al5−xGaxO12:Ce3+ phosphor

Y3Al5−xGaxO12:0.05Ce3+ (x = 0–2) phosphors have been prepared by using the high temperature solid state reaction in a reducing H2 atmosphere. The phase structures, photoluminescence (PL) properties, and chromaticity properties of the phosphors have been investigated in detail. SEM image shows the phosphors exhibits well-developed crystal faces with the crystal size is about 50 μm. The two PLE excitation bands attributed to the 4f–5d 1 and 4f–5d 2 transitions showed shift in opposite directions as x increasing. PL emission bands of Y3Al5−xGaxO12:0.05Ce3+ showed a blue-shift tendency gradually from 560 to 520 nm with increasing Ga content (x value). The PL measurement combined with blue light and CIE chromaticity diagram show that ideal white light with high CRI can be obtained by mixing the Y2.95Al3.5Ga1.5O12:0.05Ce (or Y2.95Al3Ga2O12:0.05Ce) phosphors and commercial red phosphors with appropriate proportion of the components.

Structural evolution and magnetic properties of L10-type Mn54.5Al45.5-xGax (x = 0.0, 15.0, 25.0, 35.0, 45.5) phase

The intermetallic compounds Mn54.5Al45.5-xGax (x = 0.0, 15.0, 25.0, 35.0, 45.5) with L10 structure were prepared by melt-spinning and annealing. The structural and magnetic properties were investigated by means of X-ray diffraction, neutron powder diffraction and magnetic measurement. Al and Ga atoms are found to occupy both the 1a (0, 0, 0) and 1d (1/2, 1/2, 1/2) sites and show a preference occupation for the 1d site. It was found that the lattice parameter a slightly decreases, while c abnormally increases with the increase of Ga content x, which can be attributed to the fact that the Ga atom located at the 1d sites is larger than that of Al. The mass magnetization decreases from 134 emu/g to 91 emu/g at 5 K as x increases from 0.0 to 45.5 due to higher density of the alloys with Ga in comparison to the alloys with Al. A coercivity (iHc) value of 3.67 kOe and the maximum energy product (BH)max of 2.05 MGOe were obtained for Mn54.5Al30.5Ga15 sample. All the L10 samples show a Curie temperature (Tc) well above room temperature and the value of Tc decreases almost linearly from 644 K for Mn54.5Al45.5 to 578 K for Mn54.5Ga45.5 due to the decrease of ferromagnetic Mn-Mn interaction in the a-b plane. The observed magnetic properties are in accordance with the competing ferromagnetic interactions between Mn moments at the regular 1a site and antiferromagnetic coupling with the excess Mn atoms occupying the Ga (1d) site.

Nd0.5Bi2.5Fe5−yGayO12 thin films on Gd3Ga5O12 substrates prepared by metal–organic decomposition

Highly Bi-substituted neodymium iron gallium garnet thin films with a Bi content of 2.5, Nd0.5Bi2.5Fe5−yGayO12 (NBIGG) with y = 0–1, on gadolinium gallium garnet (111) and (100) substrates have been prepared by metal–organic decomposition. Magnetic properties and magnetic anisotropy energies were measured using an alternating field gradient magnetometer and by magnetic torque measurement, respectively. Faraday rotation spectra and hysteresis loops were measured using a Faraday rotation spectrometer. The magnetization of NBIGG thin films exhibiting a large Faraday rotation of 10–15°/µm decreased with increasing Ga content, resulting in increased effective magnetic anisotropy energy Keff. The dependence of the magnetic anisotropies on the Ga content is discussed in terms of the reverse magnetostrictive effect caused by thermal stress as well as the magnetocrystalline and shape anisotropies.

Structural and Electrochemical Consequences of Al and Ga Cosubstitution in Li7La3Zr2O12 Solid Electrolytes.

Several “Beyond Li-Ion Battery” concepts such as all solid-state batteries and hybrid liquid/solid systems envision the use of a solid electrolyte to protect Li-metal anodes. These configurations are very attractive due to the possibility of exceptionally high energy densities and high (dis)charge rates, but they are far from being realized practically due to a number of issues including high interfacial resistance and difficulties associated with fabrication. One of the most promising solid electrolyte systems for these applications is Al or Ga stabilized Li7La3Zr2O12 (LLZO) based on high ionic conductivities and apparent stability against reduction by Li metal. Nevertheless, the fabrication of dense LLZO membranes with high ionic conductivity and low interfacial resistances remains challenging; it definitely requires a better understanding of the structural and electrochemical properties. In this study, the phase transition from garnet (Ia3̅d, No. 230) to “non-garnet” (I4̅3d, No. 220) space group as a function of composition and the different sintering behavior of Ga and Al stabilized LLZO are identified as important factors in determining the electrochemical properties. The phase transition was located at an Al:Ga substitution ratio of 0.05:0.15 and is accompanied by a significant lowering of the activation energy for Li-ion transport to 0.26 eV. The phase transition combined with microstructural changes concomitant with an increase of the Ga/Al ratio continuously improves the Li-ion conductivity from 2.6 × 10–4 S cm–1 to 1.2 × 10–3 S cm–1, which is close to the calculated maximum for garnet-type materials. The increase in Ga content is also associated with better densification and smaller grains and is accompanied by a change in the area specific resistance (ASR) from 78 to 24 Ω cm2, the lowest reported value for LLZO so far. These results illustrate that understanding the structure–properties relationships in this class of materials allows practical obstacles to its utilization to be readily overcome.

Electrical transport properties of CoMn0.2−xGaxFe1.8O4 ferrites using complex impedance spectroscopy

In this study, we report the influence of Ga content on the microstructural, magnetic, and AC impedance properties of Co-based ferrites with compositions of CoMn0.2−xGaxFe1.8O4 (x=0, 0.1, and 0.2) prepared by the solid-state reaction method. Experimental results showed that the as-prepared Co-based ferrites had a single-phase spinel structure; the Curie temperature of Co-based ferrites decreased with increasing Ga content. All ferrite samples exhibited a typical hysteresis behavior with good values of saturation magnetization at room temperature. The electrical properties of Co-based ferrites were investigated using complex impedance spectroscopy analysis in the frequency range of 100 kHz-50 MHz at temperatures of 150 to 250 oC. The impedance analysis revealed that the magnitudes of the real part (Z’) and the imaginary part (Z”) of complex impedance decreased with increasing temperature. Only one semicircle was observed in each complex impedance plane plot, which revealed that the contribution to conductivity was from the grain boundaries. It was found that the relaxation time for the grain boundary (τgb) also decreased with increasing temperature. The values of resistance for the grain boundary (Rgb) significantly increased with increasing Ga content, which indicated that the incorporation of Ga into Co-based ferrites enhanced the electrical resistivity.

Characterization of carrier concentration in ZnO nanowires by scanning capacitance microscopy

AbstractScanning capacitance microscopy (SCM) has been investigated on Ga doped ZnO staircase multi‐layers grown by molecular beam epitaxy (MBE) and ZnO NWs grown by chemical bath deposition (CBD). It is found that SCM data amplitude experiences a monotonic decrease with increasing Ga concentration from 2×1017 cm‐3 to 3×1020 cm‐3, indicating SCM being an appropriate technique for two dimensional dopant/carrier profiling in ZnO at nanoscale. For ZnO nanowires (NWs), a planariz‐ation process was developed based on dip‐coating of silica sol‐gel and chemical‐mechanical polishing. Then ZnO NWs were well detected from the silica matrix by SCM and the residual carrier concentration inside them was estimated through calibration method to be between 5×1017 cm‐3 and 2×1018 cm‐3. Finally, the result was compared with that obtained from conventional capacitance‐voltage (C‐V) measrement and their difference was discussed. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Effect of Ga3+ substitution on the microwave dielectric properties of 0.67CaTiO3–0.33LaAlO3 ceramics

0.67CaTiO3–0.33La(Al1−xGax)O3 (0≤x≤0.4) (CTLAG) ceramics with pure perovskite structure were prepared by a conventional two-step solid-state reaction process. The effect of Ga3+ substitution for Al3+ on the microwave dielectric properties of the ceramics was subsequently investigated. As Ga content increased, the ionic polarizability increased and led to an increase of the dielectric constant (εr). Meanwhile, both the tolerance factor (t) of CTLAG ceramics and A-site bond valence were considered to have effect on the temperature coefficient of the resonant frequency (τf) with the increase of Ga content. Results also showed that the quality factor (Q×f ) varied with increasing Ga3+ content because of not only intrinsic factor but also extrinsic factors such as the bimodal grain size distribution, the variation of relative density, and the packing fraction. Excellent microwave dielectric properties with εr≈45.81, Q×f≈34,152GHz, and τf≈3.09ppm/°C were achieved for 0.67CaTiO3–0.33La(Al0.9Ga0.1)O3 ceramics sintered at 1420°C for 4h.

Structure and magnetism in Ga-rich MnGa/GaN thin films and unexpected giant perpendicular anisotropy in the ultra-thin film limit

We report structural, surface, and magnetic investigations of ferromagnetic Ga-rich MnGa thin and ultra-thin films grown on semiconducting GaN(0001) using molecular beam epitaxy. The Mn:Ga composition ratio is varied from ≈1 (stoichiometric) to ≈0.42 (very Ga-rich) for different samples. We find that the L10 MnGa phase is preserved down to a Mn:Ga ratio of ≈0.81. As the Ga concentration increases, we observe the coexistence of more Ga-rich phases, namely Mn3Ga5 and Mn2Ga5. Room temperature scanning tunneling microscopy imaging reveals highly epitaxial films, with atomically smooth and highly reconstructed surfaces. Magnetic characterizations show how the magnetic properties evolve with changing composition and that giant perpendicular magnetic anisotropy is induced by reducing the size of our films.

Effects of Ga Content on Optical and Scintillation Properties in Ce<sup>3+</sup>-Doped YGd<sub>2</sub>(Al,Ga)<sub>5</sub>O<sub>12</sub> Scintillators

The optical and scintillation properties of Ce3+-doped YGd2(Al,Ga)5O12 single crystal scintillators were investigated. The Ce3+ 5d-4f emission was blue-shifted with increasing Ga content due to the decrease of the crystal field strength. Temperature dependence of the photoluminescence decay times was measured and the thermal activation energy for the luminescence quenching was calculated. Light yield (LY) and its dependence on an integration time were measured under γ-ray excitation. The fast component content in the scintillation response increases with increasing Ga content. The YGd2Al2Ga3O12:Ce sample showed a high LY of 38,000 photons/MeV. The decrease of LY value observed for a YGd2Al1Ga4O12:Ce sample is mainly due to the thermal ionization of the 5d1 excited state of the Ce3+ emission center to the conduction band.

Influences of Ga content on the structure and magnetic properties of Mn2 -xNiGa1+x alloys

The structure magnetism and ordering transition of the ferromagnetic shape memory alloy Mn2 -xNiGa1+xhave been systematically studied in this paper. With increasing Ga content, the structure of the parent phase Mn2 -xNiGa1+x is transformed from Hg2CuTi-type to Cu2MnAl-type Heusler alloy gradually. Its lattice constant increases first and then decreases, reaching its maximum at x=0.3. The sample displays both the primary phase of Heusler and the Ni2In-type hexagonal phase in precipitate form when x lies in the range of 0.3-0.8. The Curie temperature of the primary phase of Heusler alloy Mn2 -xNiGa1+x reduces gradually from 590 K for Mn2NiGa to about 220 K for Ga2MnNi with the decrease of the exchange interaction between 3d electrons in the transition metals. However, the variation of Curie temperature of Ni2In-type hexagonal phase is gentle. The separation of Curie temperatures between the Ni2In-type hexagonal phase and the primary phase of Heusler occurs when x lies in the range from 0.6 to 0.8. Substitution of Mn by Ga has a significant influence on the coupling interaction among various atoms, leading to first increasing and then decreasing of the saturated magnetization of Mn2 -xNiGa1+x at low temperatures. That is, the saturated magnetization will rise for x0.4 and drops sharply for x0.4. Results of differential scanning calorimeter show that the melting temperature decreases gradually as x increases. Meanwhile, the transition temperature from parent phase (B2) to Heusler phase decreases first and increases later.

Optical and reliability properties studies of green YAG phosphors by Ga substitution

In this paper, green Y2.94(Al1−xGax)5O12:0.06Ce phosphors were prepared by conventional solid-state reaction. The crystal structures, the influence of Ga concentration on the photoluminescence, thermal stability and reliability properties of the phosphors were studied. The PL emission bands of Y2.94(Al1−xGax)5O12:0.06Ce showed blue shift from 545 nm to 525 nm with increasing Ga content (x value) under excited at 460 nm. The thermal stability of Y2.94(Al1−xGax)5O12:0.06Ce phosphor is hindered by adding Ga. As the temperature increases from 300 to 500 K, the PL intensity of Y2.94(Al0.8Ga0.2)5O12:0.06Ce and Y2.94(Al0.65Ga0.35)5O12: 0.06Ce phosphor decreases by 11.11 and 16.57 %, respectively. Reliability test results show that the relative PL intensity of Y2.94(Al1−xGax)5O12:0.06Ce phosphor decrease to from 99.76 to 95.37 % with x value increased from 0.15 to 0.35 after the ambient condition of 85 °C/RH 85 % for the exposure time of 168 h. And the relative PL intensity of Y2.94(Al1−xGax)5O12:0.06Ce phosphor decrease to from 99.53 to 91.78 % after soaking into boiled water for 4 h. It can be summarized that the addition of Ga deteriorates the thermal stability as well as the reliability of the phosphors slightly.

Synthesis of CuIn<I><SUB>1-x</SUB></I>Ga<I><SUB>x</SUB></I>Se<SUB>2</SUB> Nanoparticles by Thermal Decomposition Method with Tunable Ga Content

Chalcopyrite Culn(1-x)Ga(x)Se2 (CIGS) nanoparticles were synthesized by mixing copper (I) chloride (CuCl), Indium (III) chloride (InCl3), gallium (III) chloride (GaCl3) and selenium (Se) in oleylamine (OLA) at 260 degrees C for 4 h under nitrogen atmosphere. The Ga/(In+ Ga) ratio was tuned across the entire stoichiometric range from 0 to 1. X-ray diffraction analysis (XRD) revealed chalcopyrite crystal structure for samples prepared with x = 0, 0.3, 0.5, 0.7 and 1. The lattice parameters a and c decreased linearly with increasing Ga concentration which is consistent with Vegard's law. Raman spectra exhibited A, optical phonon vibrational mode for synthesized nanoparticles which gradually shifted to higher wavenumber with increasing Ga content. Field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM) images showed irregular as well as hexagonal plate like morphologies in the size range of 100 to 400 nm. High-resolution transmission electron microscopy (HR-TEM) images showed well-defined lattice fringes and d-spacing correspond to (112) plane which gradually decreases with increasing Ga content. The material compositions of synthesized CIGS nanoparticles with x = 0, 0.3, 0.5, 0.7 and 1 were very close to the desired stoichiometry which was confirmed by energy dispersive X-ray analysis (EDAX). Ultraviolet visible near infrared (UV-VIS-NIR) absorption spectra of the synthesized CIGS nanoparticles revealed that the bandgap could be tuned over the range 1 to 1.7 eV by varying the Ga/(In+Ga) ratio.

Optical and scintillation properties of Ce3+-doped YGd2Al5−xGaxO12 (x=2,3,4) single crystal scintillators

The optical and scintillation properties of Ce3+-doped YGd2Al5−xGaxO12 (x=2,3,4) single crystals were investigated. With increasing Ga content in the garnet host, the 5d1 absorption and emission bands shift toward higher energy due to the decrease in the crystal field splitting of the 5d levels. Temperature dependences of absorption and emission spectra and of photoluminescence decays of both prompt and delayed components were measured. Light yield (LY) and its dependence on an amplifier shaping time were measured under excitation with γ-rays. High LY value of 38,000photons/MeV was obtained for a YGd2Al2Ga3O12:Ce sample. Scintillation decay was measured with an extended dynamical and temporal scale under the nanosecond-pulsed soft X-ray excitation. The relative content of the fastest component in the scintillation response increases with increasing Ga content.

Characteristics of 5M modulated martensite in Ni-Mn-Ga magnetic shape memory alloys

The applicability of the magnetic shape memory effect in Ni-Mn-based martensitic Heusler alloys is closely related to the nature of the crystallographically modulated martensite phase in these materials. We study the properties of modulated phases as a function of temperature and composition in three magnetic shape memory alloys Ni49.8Mn25.0Ga25.2, Ni49.8Mn27.1Ga23.1 and Ni49.5Mn28.6Ga21.9. The effect of substituting Ga for Mn leads to an anisotropic expansion of the lattice, where the b-parameter of the 5M modulated structure increases and the a and c-parameters decrease with increasing Ga concentration. The modulation vector is found to be both temperature and composition dependent. The size of the modulation vector corresponds to an incommensurate structure for Ni49.8Mn25.0Ga25.2 at all temperatures. For the other samples the modulation is incommensurate at low temperatures but reaches a commensurate value of q ≈ 0.400 close to room temperature. The results show that commensurateness of the 5M modulated structure is a special case of incommensurate 5M at a particular temperature.

Improved Blue‐Emitting AlN:Eu2+ Phosphors by Alloying with GaN

A method is designed to improve the luminescence of AlN‐based phosphors by tuning the band structure and crystal structure due to alloying with GaN. The pure (Al,Ga)N:Eu phosphors were initially prepared by gas‐phase reaction in an NH3 atmosphere. GaN alloying was used to expand the crystal lattice of AlN due to Ga3+ substituting for smaller Al3+ ions, making dissolution of Eu2+ easier. The dissolution of Ga in the AlN lattice was proven by the result of the Rietveld refinement and the increase in lattice parameters with increasing Ga content. To introduce other energy states mixing with the 5d states of Eu2+, Ga doping was also used to tune the band structure of AlN by acting on Eu2+ ions. The theoretical result was analyzed using the Cambridge Sequential Total Energy Package (CASTEP). According to the calculated total and atom resolved partial density of states, it was observed that the Ga 5p states contribute a large portion to the corresponding Eu2+ absorption band in (Al,Ga)N:Eu phosphors. As a consequence, an enhanced emission intensity at 470 nm and a high quantum efficiency for excitation at 330 nm was obtained despite of stronger thermal quenching of the (Al,Ga)N:Eu phosphors compared with AlN:Eu.

DC electrodeposition of NiGa alloy nanowires in AAO template

NiGa alloy nanowires were electrodeposited from an acidic sulfate bath into nanoporous anodized alumina oxide (AAO). This template was fabricated by two-step anodizing. The effects of bath composition and current density were explored on the Ga content of electrodeposited nanowires. The Ga content in the deposits was increased by increasing both Ga in the bath composition and electrodepositing current density. The NiGa alloy nanowires were synthesized for Ga content up to 2–4% without significant improving the magnetic properties. Above this threshold Ga clusters were formed and decreased the magnetic properties of the nanowires. For Ga content of the alloy above 30%, the wires were too short and incomplete. X-ray diffraction patterns reveal that the significant increase of Ga content in the nanowires, changes the FCC crystal structure of Ni to an amorphous phase. It also causes a sizeable increase in the Ga cluster size; these both lead to a significant reduction in the coercivity and the magnetization respectively.

Investigation of characteristics of ZnO:Ga nanocrystalline thin films with varying dopant content

In this study, undoped and Ga doped ZnO thin films were synthesized by the sol–gel spin coating technique. The effect of Ga contribution on the structural, morphological and optical properties of the ZnO thin films was examined. XRD results showed that all films had a hexagonal wurtzite crystal structure with polycrystalline nature. The intensity of the (002) peak changed with the variable Ga content. The scanning electron microscopy (SEM) results revealed that the surface morphology of the ZnO thin films was affected by Ga content. Moreover, it consisted of nanorods as a result of the increased function of the Ga content. Additionally, the presence of Ga contributions was evaluated by energy dispersive x-ray (EDX) measurements. Although the transparency and the optical band gap of the ZnO thin films increased with Ga contribution, Urbach energy values decreased from 221meV to 98meV. In addition, these steepness parameters increased with the increased Ga content from 0% to 6%. The correlation between structural and optical properties was investigated and significant consistency was found.

Phase equilibria and magnetic properties of Heusler-type ordered phases in the Co–Mn–Ga ternary system

Phase equilibria at 800, 900 and 1000°C, as well as order–disorder and magnetic transitions of Heusler-type ordered phase were investigated in the Co–Mn–Ga ternary system. The β phase with bcc structure including the Heusler-type ordered phase exists in a wide composition range of the ternary system. It was confirmed by STEM–HAADF observation that the crystal structure of the Heusler-type ordered alloy Mn2CoGa is L21b-type Fm3¯m (i.e., (Mn,Co)2MnGa), but not inverse-Heusler (Hg2CuTi) type F4¯3m. The L21/B2 order–disorder transition temperature shows a maximum at the stoichiometric composition of Co2MnGa and the Curie temperature of the L21 phase decreases with increasing Ga content. Magnetic moments converted from magnetization curves at 4.2K for CoxMn(76−x)Ga24 alloys well follow the generalized Slater–Pauling rule in the composition of 25⩽x⩽50, and magnetization curves indicate very small high-field magnetic susceptibility.

Study on phase change properties of binary GaSb doped Sb–Se film

In this paper, phase change behaviors of GaSb doped Sb–Se films were investigated systematically for phase change memory. It is shown that the precipitation of Sb2Se3 phase from Ga–Sb–Se film was suppressed to some extent with the increasing Ga content. The crystallization temperature enhances from 245 to 320°C, and activation energy of crystallization increases from 3.49 to 5.52eV as Ga content increases from 8 to 34at.%. Correspondingly, the temperature for 10-year data retention of as-deposited amorphous state increases from 154 to 230°C. The minimum reset voltage and set resistance of Ga13Sb32Se55 are 0.7V lower and about one order of magnitude higher than those of Ge2Sb2Te5, respectively. The low power of Ga13Sb32Se55 results from both the low thermal conductivity (0.33W/mK) and low electrical conductivity (243.9Ω−1m−1) of crystalline state as well as low melting point (497°C).

Site Occupation of Ga and Al in Stabilized Cubic Li7–3(x+y)GaxAlyLa3Zr2O12 Garnets As Deduced from 27Al and 71Ga MAS NMR at Ultrahigh Magnetic Fields

Li-containing garnets, which are stabilized in their cubic modification by doping with Al or Ga, show very high Li-ion conductivities. This property qualifies them to be used as solid electrolytes in advanced all-solid-state batteries. The relation between local structures and dynamic properties, however, is still not fully understood. Here, cubic mixed-doped Li7–3(x+y)GaxAlyLa3Zr2O12 garnet solid solutions with different portions of Al and Ga were synthesized. It turned out that the solubility of Ga is higher than that of Al; the evaluation of 42 different doping compositions indicated an increase of the lattice parameter a0 with increasing Ga content. 71Ga MAS NMR spectra recorded at 21.1 T revealed two 71Ga NMR resonances, corresponding to Ga occupying both the 24d (243 ppm) and 96h sites (193 ppm). This behavior, which has been observed for the first time in this study, is very similar to that of Al. The 71Ga NMR line at 193 ppm observed here remained invisible in previous NMR studies that were carrie...