Ga Substitution Research Articles

Unusual Yb magnetic properties in YbMn6Ge1.8−xSn4.2Gax and YbMn6Ge1.8Sn4.2−yGay

We investigate the magnetic properties of the new HfFe6Ge6-type (P6/mmm) YbMn6Ge1.8−xSn4.2Gax (x=0.05, 0.4 and 0.9) and YbMn6Ge1.8Sn4.2−yGay (y=0.05, 0.5 and 1.0) alloys from DC magnetization and powder neutron diffraction experiments. The electronic structure modifications induced by the Ga substitution are found to promote the ferromagnetic order of the Mn sublattice, to enhance the Yb ordering temperature (up to TYb∼170K) and to strongly increase the low-temperature coercive field (up to µ0Hc∼1T). By contrast, the changes in the Yb magnetic moment magnitude upon Ga substitution are analyzed to be mainly driven by chemical pressure effects. The reduced Yb magnetic moment (1.0µB<mYb<1.8µB) compared with the free ion value (4µB) is interpreted as resulting from Kondo screening. There are strong indirect indications that the high temperature Yb magnetic ordering likely involves intermediate valent Yb.

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.

Microwave dielectric properties of Ga3+ and Ta5+ co-doped CaTiO3

Compositions in the (1 − x)CaTiO3–xCa(Ta1/2Ga1/2)O3 (x = 0.4, 0.45, 0.50, 0.55) series were processed through a solid-state mixed-oxide route. X-ray diffraction (XRD) of x = 0.5 and 0.55 compositions revealed the formation of single-phase ceramics with orthorhombic (Pbnm) symmetry. At x ≤ 0.45, a couple of low intensity XRD peaks matching PDF# 04-002-5066 for Ca3TiTaGa3O12 were also observed which indicated second-phase formation. The microstructure of the sintered pellets for x = 0.5 and 0.55 compositions comprised densely packed irregular-shaped large grains with uniform contrast. The unit cell volume increased with increasing Ta5+ and Ga3+ contents at the B-site, which caused a decrease in both the relative permittivity (er) and temperature coefficient of resonance frequency (τf) but an increase in quality factor (Q × fo). The optimum microwave dielectric properties (i.e., er ~ 47, Q × fo ~ 26,630 GHz and τf ~ −2.64 ppm/ °C) were achieved for the x = 0.5 composition (i.e., CaTi0.5Ta0.25Ga0.25O3) which can be a potential candidate material for microwave dielectric applications. Thus, the substitution of Ta and Ga at the B-site of CaTiO3 was useful in tuning the larger positive τf through zero and increasing Q × fo without too much compromise on er.

Investigations on the origin of ferromagnetism in Ga1−xCrxN and Si-doped Ga1−xCrxN films: Experiments and theory

In this paper, we combined experiments and first-principles calculations to investigate the physical properties especially the magnetic properties of Ga1−xCrxN and Si-doped Ga1−xCrxN thin films grown by molecular beam epitaxy. The results of experiments indicate that Si doping improved the crystallinity by improving the substitution of Ga in Si-doped Ga1−xCrxN. And the size and/or the number of vacancy defects are reduced in the Si-doped Ga1−xCrxN thin films. All the samples show room-temperature ferromagnetism, and the measured saturation magnetizations are 15 emu/cm3 (2.26 μB per Cr atom) and 10 emu/cm3 (1.31 μB per Cr atom) respectively for Ga1−xCrxN and Si-doped Ga1−xCrxN thin films. First-principles calculations based density-functional theory show that there is a strong magnetic coupling between the Ga vacancies and the impurities of Cr and Si ions. And Si doping reduced the saturation magnetization in Si-doped Ga1−xCrxN thin films which is in agreement with the experiment results. This intrinsic defect derived magnetic interaction plays an important role on improving the ferromagnetism in Ga1−xCrxN and Si-doped Ga1−xCrxN, and the ferromagnetism of the system is the result of long-range mediation between VGa, Cr and Si ions.

Improved near-infrared up-conversion emission of YAG:Yb,Tm phosphor substituted by Gallium and Indium

Gallium–Indium co-substituted yttrium aluminum garnet (YAG:Yb,Tm) phosphors were synthesized by co-precipitation method. It can be seen that gallium and indium ions co-substitution didn’t change the phase of YAG. The upconversion luminescence (UCL) properties of the Gallium–Indium co-substituted (YAG:Yb,Tm) samples were measured under 980 nm excitation. The effects of different In3+concentration on the luminescence properties of Gallium–Indium co-substituted (YAG:Yb,Tm) were also investigated. The fluorescence-lifetime investigation shows that the substitution of Ga3+ and In3+ has a significant influence on energy transfer between Yb3+ and Tm3+ in the YAG samples.

Effect of Ga substitution on magnetocaloric effect in La0.7(Ba, Sr)0.3Mn1−xGaxO3 (0.0≤x ≤0.20) polycrystalline at room temperature

In this paper, we have investigated the effect of the non-magnetic (d10) Ga3+ doping on structural, magnetic and magnetocaloric properties of La0.7(Ba, Sr)0.3Mn1−xGaxO3 (x=0.0, 0.1 and 0.2) manganites prepared by solid state reaction method. The XRD study has revealed that all samples crystallized in the orthorhombic symmetry with Pnma space group. Magnetization measurements have confirmed that when the temperature increases, all the compositions exhibit a ferromagnetic to paramagnetic transition. The substitution of Mn by gallium Ga leads to a tune of the magnetic transition temperature (TC) to room temperature and the Curie temperature decreases from 314K for x=0.0 to 299K for x=0.2. Moreover, the obtained results of the magnetocaloric effect are in accordance with the reported values of other doped manganites, leading to the conclusion that our sample can be used as a magnetic refrigerant at room temperature.Finally, using Arrott plots, the phase transition from ferromagnetic to paramagnetic was found to be of a second order. The second order magnetic phase transition has been confirmed by the construction of the universal curve of the magnetic entropy change.

Magnetic and magnetocaloric properties of Gd2In0.8X0.2 compounds (X=Al, Ga, Sn, Pb)

We show that it is possible to replace in Gd2In some amount of In by X=Al, Ga, Sn and Pb to obtain Gd2In1−xXx samples after melting. The magnetic and magnetocaloric properties of the Gd2In0.8X0.2 intermetallic compounds have been investigated through dc magnetization measurements. We evidence that the substitution of Al and Ga for In barely changes the Curie temperature TC but decreases the second magnetic transition temperature T′ which corresponds to the transition from a ferromagnetic to an antiferromagnetic state. On the other hand, the substitution of Sn and Pb for In strongly increases TC and changes the nature or even suppresses the transition at lower temperature. This magnetic behavior gives rise to an interesting way to tune the Curie temperature near room temperature without diluting the Gd network and thus to modify the magnetocaloric effect in Gd2In1−xXx compounds.

Phase Formation in the Rapidly Solidified Al70−xGaxPd13Mn17 Alloys

In the present investigation, the effect of Ga substitution at Al site on the phase formation and stabilization of decagonal quasicrystalline phase in the rapidly solidified Al70−xGaxPd13Mn17 alloys have been studied by employing X-ray diffraction, scanning electron microscopy, transmission electron microscopy and energy dispersive x-ray analysis. The as-cast and rapidly solidified alloys with x = 0, 2.5 and 5 have been investigated. The melt-spinning technique has been used for rapid solidification of the as-cast alloys. The alloys up to 5 at.% Ga exhibit the formation of small amount of icosahedral quasicrystalline phases along with major amount of decagonal phase in the rapidly solidied ribbons. The energy dispersive X-ray analysis investigations suggest the homogeneous presence of Ga in the quasicrystalline alloys.

Formation of nano-amorphous domains in Ce75Al25 − xGax alloys with delocalization of cerium 4f electrons

The formation of nano-amorphous domains in melt spun ribbons of Ce75Al25 − xGax alloys with x = 0, 0.01, 0.1, 0.5 and 1 is reported. For x = 0, a homogenous metallic glass feature is observed. Ga substitution has led to phase separation giving rise to nano-amorphous domains in a glassy matrix. The rationale of phase separation could not be explained in terms of enthalpy of mixing of the three possible binaries in this system. The Ce L3-edge XAS spectra of melt-spun ribbons for x = 0, 0.5 and 4 have shown appearance of 4f0 delocalized states in Ga substituted alloy. Such a substitution has led to shortening of Ce–Ce distance in the alloys owing to chemical pressure. This work, therefore, opens up new direction of research for delineating issues pertaining to phase separation in amorphous systems.

ZnO:Ga nanowires with low turn-on field for field-emission lighting

ZnO:Ga nanowires were synthesized using a ZnO seed layer as a pseudo-catalyst by a vapor-phase transport method. Nanowire growth was facilitated along the longitudinal axis, and the aspect ratio was increased from 27.3 to 54.1 by doping with Ga3+, which also slightly enhanced growths of the (100) and (101) planes. The luminescent spectrum was narrower, more red-shifted, and less intense when the Ga3+ doping concentration was increased. However, the substitution of Ga for Zn enhanced the tunneling capability of electrons at the ZnO–vacuum interface. ZnO:Ga nanowires doped with 0.5mol% of Ga3+ achieved a low turn-on electric field of 0.57V/μm. A stable emission current of 0.85mA/cm2 with fluctuations within ±12.9% was observed over 5h of operation.

Defusing Complexity in Intermetallics: How Covalently Shared Electron Pairs Stabilize the FCC Variant Mo2Cu(x)Ga(6-x) (x ≈ 0.9).

Simple sphere packings of metallic atoms are generally assumed to exhibit highly delocalized bonding, often visualized in terms of a lattice of metal cations immersed in an electron gas. In this Article, we present a compound that demonstrates how covalently shared electron pairs can, in fact, play a key role in the stability of such structures: Mo2Cu(x)Ga(6-x) (x ≈ 0.9). Mo2Cu(x)Ga(6-x) adopts a variant of the common TiAl3 structure type, which itself is a binary coloring of the fcc lattice. Electronic structure calculations trace the formation of this compound to a magic electron count of 14 electrons/T atom (T = transition metal) for the TiAl3 type, for which the Fermi energy coincides with an electronic pseudogap. This count is one electron/T atom lower than the electron concentration for a hypothetical MoGa3 phase, making this structure less competitive relative to more complex alternatives. The favorable 14 electron count can be reached, however, through the partial substitution of Ga with Cu. Using DFT-calibrated Hückel calculations and the reversed approximation Molecular Orbital (raMO) method, we show that the favorability of the 14 electron count has a simple structural origin in terms of the 18 - n rule of T-E intermetallics (E = main group element): the T atoms of the TiAl3 type are arranged into square nets whose edges are bridged by E atoms. The presence of shared electron pairs along these T-T contacts allows for 18 electron configurations to be achieved on the T atoms despite possessing only 18 - 4 = 14 electrons/T atom. This bonding scheme provides a rationale for the observed stability range of TiAl3 type TE3 phases of ca. 13-14 electrons/T atom, and demonstrates how the concept of the covalent bond can extend even to the most metallic of structure types.

Glass forming ability, thermal stability and indentation characteristics of Ce60Cu25Al15 − xGax (0 ≤ x ≤ 4) metallic glasses

Glass forming ability, thermal stability and indentation characteristics of Ce60Cu25Al15−xGax (0≤x≤4) metallic glasses have been investigated. Amorphous phase has been confirmed in all these samples with the help of X-ray diffraction (XRD), differential scanning calorimetry (DSC) and transmission electron microscopy (TEM) studies. The compositional dependence of the glass forming ability (GFA) and its correlation with related parameters as well as thermal stability have also been discussed. The load dependent hardness behavior of metallic glasses is reported in detail. It has been observed that substitution of 1at.% Ga improved micro-hardness property of Ce–Cu–Al–Ga alloy. The value of yield strength of the materials is estimated with the help of hardness data and Meyer exponent. It has been found that this exponent decreases with respect to Ga substitution.

Synthesis and Characterization of Ultrasmall Nanocrystalline Zn-substituted Ni-Sm-Ga Ferrites

Ultrasmall nanocrystalline NiSm0.01Fe1.99O4 and Ni1−x Zn x Sm0.01Ga0.5Fe1.49O4 (x = 0.0, 0.3, 0.5) ferrites were synthesized by sol-gel method. The effect of Ga and Zn substitution on the particle size and structural and magnetic properties was investigated using X-ray diffraction patterns (XRD), transmission electron microscope (TEM), Mossbauer effect spectroscopy (ME), and vibrating sample magnetometer (VSM) techniques. XRD measurements suggest the formation of single-phase spinel ferrites with ultrasmall particles size ranging from 4 to 8 nm. Mossbauer effect measurements show a clear signature of superparamagnetism in the studied samples, where the reduced particle size causes the broadening of the Mossbauer spectra and the presence of a pronounced central doublet in all the measured samples. VSM measurements show a strong reduction of saturation magnetization due to size effects.

Effect of fluctuation in Al incorporation on the microstructure, bond lengths, and surface properties of an Al x Ga1−x N epitaxial layer

Al x Ga1−x N (0.15 ≤ x ≤ 0.87) epilayers were grown on sapphire substrates by metal-organic chemical vapor deposition (MOCVD). The lattice deformation, chemical bonding states, and local electronic structure were characterized by a series of techniques, including X-ray diffraction (XRD), Raman scattering, X-ray photoelectron (XPS), and extended Xray absorption fine structure (EXAFS) spectroscopy. The XRD and Raman spectra revealed that substitution of Ga with Al in Al x Ga1−x N epilayers induces a significant contraction in the crystal lattice and a slight expansion of internal parameter u. The XPS measurements indicated the absence of remarkable disorder of the chemical bonds in AlGaN with a high Al content. The EXAFS analysis also demonstrated that the Ga-N and Ga-Al bond lengths are independent of the Al content, whereas the Ga-Ga bond length varies with Al content.

Radioluminescence enhancement in Eu3+-doped Y3Al5O12 phosphors by Ga substitution

Effects of the Ga substitution on the radioluminescence properties of Eu3+-doped Y3Al5O12 nanopowders were investigated. These nanopowders weresynthesized by a sol–gel method. The nanopowders were characterized by X-ray powder diffraction, Raman spectroscopy and scanning electron microscopy. The samples obtained have good crystallinity and mean sizes between 40 and 100nm. The Ga substitution at low levels induces an enhancement on the radioluminescence due to the Y-site symmetry distortion, as probed by the asymmetric ratio of the magnetic and electric dipole transition.

Electronic and surface properties of Ga-doped In2O3 ceramics

The limit of solubility of Ga2O3 in the cubic bixbyite In2O3 phase was established by X-ray diffraction and Raman spectroscopy to correspond to replacement of around 6% of In cations by Ga for samples prepared at 1250°C. Density functional theory calculations suggest that Ga substitution should lead to widening of the bulk bandgap, as expected from the much larger gap of Ga2O3 as compared to In2O3. However both diffuse reflectance spectroscopy and valence band X-ray photoemission reveal an apparent narrowing of the gap with Ga doping. It is tentatively concluded that this anomaly arises from introduction of Ga+ surface lone pair states at the top of the valence band and structure at the top of the valence band in Ga-segregated samples is assigned to these lone pair states. In addition photoemission reveals a broadening of the valence band edge. Core X-ray photoemission spectra and low energy ion scattering spectroscopy both reveal pronounced segregation of Ga to the ceramic surface, which may be linked to both relief of strain in the bulk and the preferential occupation of surface sites by lone pair cations. Surprisingly Ga segregation is not accompanied by the development of chemically shifted structure in Ga 2p core XPS associated with Ga+. However experiments on ion bombarded Ga2O3, where a shoulder at the top edge of the valence band spectra provide a clear signature of Ga+ at the surface, show that the chemical shift between Ga+ and Ga3+ is too small to be resolved in Ga 2p core level spectra. Thus the failure to observe chemically shifted structure associated with Ga+ is not inconsistent with the proposal that band gap narrowing is associated with lone pair states at surfaces and interfaces.

Giant magnetocaloric effect in MnCoGe with minimal Ga substitution

The effects of Ga-doping on the phase transition behaviors and magnetocaloric properties of MnCoGe alloys are systematically investigated through calorimetry and magnetic measurements. The magneto-structural coupling between the structural and magnetic transitions is achieved in the MnCoGe1–xGax alloys by decreasing the structural transition temperature via Ga substitution. An 80K Curie-temperature window is established between Curie temperatures of austenite and martensite phases. Within the window, a magnetic entropy change of 34Jkg−1K−1 can be obtained near room temperature under the application of a 5T magnetic field.

Effects of Zn additions to highly magnetoelastic FeGa alloys

Fe1−xMx (M = Ga, Ge, Si, Al, Mo and x ∼ 0.18) alloys offer an extraordinary combination of magnetoelasticity and mechanical properties. They are rare-earth-free, can be processed using conventional deformation techniques, have high magnetic permeability, low hysteresis, and low magnetic saturation fields, making them attractive for device applications such as actuators and energy harvesters. Starting with Fe-Ga as a reference and using a rigid-band-filling argument, Zhang et al. predicted that lowering the Fermi level by reducing the total number of electrons could enhance magnetoelasticity. To provide a direct experimental validation for Zhang's hypothesis, elemental additions with lower-than-Ga valence are needed. Of the possible candidates, only Be and Zn have sufficient solubility. Single crystals of bcc Fe-Ga-Zn have been grown with up to 4.6 at. % Zn in a Bridgman furnace under elevated pressure (15 bars) in order to overcome the high vapor pressure of Zn and obtain homogeneous crystals. Single-crystal measurements of magnetostriction and elastic constants allow for the direct comparison of the magnetoelastic coupling constants of Fe-Ga-Zn with those of other magnetoelastic alloys in its class. The partial substitution of Ga with Zn yields values for the magnetoelastic coupling factor, −b1, comparable to those of the binary Fe-Ga alloy.

Influence of Ga-doping on the thermoelectric properties of Bi(2−x)GaxTe2.7Se0.3 alloy

Bi(2−x)GaxTe2.7Se0.3 (x=0, 0.04, 0.08, 0.12) alloys were fabricated by vacuum melting and hot pressing technique. The structure of the samples was evaluated by means of X-ray diffraction. The peak shift toward higher angle can be observed by Ga-doping. The effects of Ga substitution for Bi on the electrical and thermal transport properties were investigated in the temperature range of 300–500K. The power factor values of the Ga-doped samples are obviously improved in the temperature range of 300–440K. Among all the samples, the Bi(2−x)GaxTe2.7Se0.3 (x=0.04) sample showed the lowest thermal conductivity near room temperature and the maximum ZT value reached 0.82 at 400K.

Syntheses, structures, and ionic conductivities of perovskite-structured lithium–strontium–aluminum/gallium–tantalum-oxides

The ionic conductivities of new perovskite-structured lithium–strontium–aluminum/gallium–tantalum oxides were investigated. Solid solutions of the new perovskite oxides, (LixSr1−x)(Al(1−x)/2Ta(1+x)/2)O3 and (LixSr1−x)(Ga(1−x)/2Ta(1+x)/2)O3, were synthesized using a ball-milled-assisted solid-state method. The partial substitution of the smaller Ga+3 for Ta+5 resulted in new compositions, the structures of which were determined by neutron diffraction measurements using a cubic perovskite structural model with the Pm−3m space group. Vacancies were introduced into the Sr(Li) sites by the formation of solid solutions with compositions (LixSr1−x−y☐y)(Ga[(1−x)/2]−yTa[(1+x)/2]+y)O3, where the composition range of 0≤y≤0.20 was examined for x=0.2 and 0.25. The highest conductivity, 1.85×10−3Scm−1 at 250°C, was obtained for (Li0.25Sr0.625☐0.125)(Ga0.25Ta0.75)O3 (x=0.25, y=0.125). Enhanced ionic conductivities were achieved by the introduction of vacancies at the A-sites.