Substitution Of Al For Ga Research Articles

Структурa і властивості матеріалів Fe—Al—Ga в області концентрацій, збагачених залізом

The structure and mechanical properties of materials of the Fe—Al—Ga system (in the concentration range of 78—82% (wt.) Fe), obtained by sintering at 1150 oC in Ar medium for 1 hour, were studied. The starting materials were mixtures of Fe, Al powders and crushed Fe—Ga ligature alloy of equiatomic composition. Seven mixtures were produced, of which two mixtures had a binare compo¬sition (% (wt.)): Fe—17,5Al and Fe—21,4Ga; and all the others were three-component, with gradual substitution of Al for Ga. The phase composition of the samples was studied by the methods of X-ray diffraction and local X-ray microspectral analyses. To determine the mechanical characteristics, the Brinell method was used, microdurometric studies were carried out, and mechanical tests of the samples were carried out under conditions of uniaxial compression. The effect of Al on the change in the porosity of Fe—Al—Ga ternary alloys and the maximum manifestation of the “swelling” effect for Fe—Al composition samples was established. It is shown that the main phase of the obtained materials is a solid solution based on Fe, in which Al and Ga are dissolved in the appropriate proportions. In the Fe—Al samples and in the samples of the ternary composition, there are local separations of phases containing, in addition to the main metals, carbon and oxygen in significant quantities. In the structure of Fe—Ga samples, carbon is not detected, and oxygen is present in a small amount. The results of the mechanical compression tests showed that the Fe—21,4Ga composition samples, like the pure Fe samples, are quite plastic and do not break up to a degree of compression of 75—82%. For materials with binary composition with Ga, an increase in the elastic range was recorded compared to pure Fe, and the replacement of a small proportion of Ga with Al (up to 2% by weight) in the material composition contributes to its strengthening. Keywords: Fe, Al, Ga, microstructure, phase formation, microhardness, mechanical compression characteristics.

Novel intermetallics RE5Ru3Ga2 (RE = La, Ce, Pr, Nd): Synthesis and crystal structures; thermodynamic and electrical transport properties of Ce5Ru3Ga2

Novel ternary gallides RE5Ru3Ga2 (RE = La, Ce, Pr, and Nd) crystallize with a cubic structure of the La5Ru3Al2 type (space group I213) with the lattice parameters: a = 9.9082(3), 9.6926(4), 9.7509(5), and 9.7222(4) Å, respectively. Upon small substitution of Al for Ga (≤1 at% Al), the compound Ce5Ru3Ga2−xAlx can be stabilized as a low-temperature trigonal variant (space group R3). The latter phase, bearing the unit cell parameters a = 13.7892(3) Å and c = 8.3095(2) Å, is closely related to the Ce5Ru3Al2 structure type. Its characteristic structural feature is the presence of very short interatomic Ce-Ru distances of 2.40(4) Å. The cubic Ce5Ru3Ga2 exhibits Curie-Weiss paramagnetism with notably reduced effective magnetic moment. At TC = 1.7 K, the compound orders magnetically, probably with a ferrimagnetic magnetic structure. The metallic-like electrical conductivity of this material bears a Kondo lattice character.

Effect of Al substitution for Ga on magnetostriction enhancement by annealing of as-cast Fe–Ga–Al alloys under low magnetic fields

Abstract Samples of Fe82Ga18-xAlx (1.5 £ x £ 15) alloys were prepared using a high vacuum arc melting system and homogenized at 1100 8C for 3 h, 1 000 8C for 120 h, and 730 8C for 168 h. The Fe82Ga18-xAlx(3 £ x £ 13.5) alloys were annealed at 550 8C for 15 min, while being exposed to a low magnetic field. The structure of the alloys was analysed by X-ray diffraction and optical microscopy. The magnetostriction coefficient of each of the samples was measured. It was found that the magnetostriction values of Fe82Ga18-xAlx(3 £ x £ 13.5) alloys were enhanced by magnetic field annealing. The magnetostrictive growth rate of the Fe82Ga15Al3sample was particularly large at 165%, and the Fe82Ga9Al9sample showed the highest magnetostrictive coefficient (up to 114 · 10-6) without compressive stress.

Effect of Al substitution for Ga on magnetostriction enhancement by annealing of as-cast Fe–Ga–Al alloys under low magnetic fields

Abstract Samples of Fe82Ga18-xAlx (1.5 £ x £ 15) alloys were prepared using a high vacuum arc melting system and homogenized at 1100 8C for 3 h, 1 000 8C for 120 h, and 730 8C for 168 h. The Fe82Ga18-xAlx(3 £ x £ 13.5) alloys were annealed at 550 8C for 15 min, while being exposed to a low magnetic field. The structure of the alloys was analysed by X-ray diffraction and optical microscopy. The magnetostriction coefficient of each of the samples was measured. It was found that the magnetostriction values of Fe82Ga18-xAlx(3 £ x £ 13.5) alloys were enhanced by magnetic field annealing. The magnetostrictive growth rate of the Fe82Ga15Al3sample was particularly large at 165%, and the Fe82Ga9Al9sample showed the highest magnetostrictive coefficient (up to 114 · 10-6) without compressive stress.

Study of lattice deformation and atomic bond length for AlxGa1−xN epi-layers with synchrotron radiation X-ray absorption spectroscopy

The lattice deformation in wurtzite AlxGa1−xN epi-layers (0.19 ≤ x ≤ 0.58) grown on sapphire substrates by metal organic chemical vapor deposition has been studied with synchrotron radiation X-ray absorption spectroscopy and X-ray diffraction. The result reveals that Al substitution for Ga in AlGaN epi-layers induces a significant contraction in crystal lattice and c/a ratio (c and a are the lattice constants for AlGaN epi-layer, respectively), while the substitution only results in a slight expansion in internal parameter u, which is used to describe the lattice deformation of wurtzite structure. This fact suggests that u is not sensitive to Al substitution for Ga. A detailed analysis of extended X-ray absorption fine structure of Ga K-edge spectra show that the Ga–N bond length has only a weak composition dependence, while the Ga–Ga (Al) bond lengths are strongly dependent on the Al composition.

Piezoelectric La3Ga5.3Ta0.5Al0.2O14 crystal: growth, crystal structure perfection, piezoelectric, and acoustic properties

A five-component crystal of lanthanum–gallium silicate group La3Ga5.3Ta0.5Al0.2O14 (LGTA) was grown by the Czochralski method. The LGTA crystal possesses unique thermal properties and substitution of Al for Ga in the unit cell leads to a substantial increase of electrical resistance at high temperatures. The unit cell parameters of LGTA were determined by powder diffraction. X-ray topography was used to study the crystal structure perfection: the growth banding normal to the growth axis were visualized. The independent piezoelectric constants d 11 and d 14 were measured by X-ray diffraction in the Bragg and Laue geometries. Excitation and propagation of surface acoustic waves were studied by the double-crystal X-ray diffraction at the BESSY II synchrotron radiation source. The analysis of the diffraction spectra of acoustically modulated crystals permitted the determination of the velocity of acoustic wave propagation and the power flow angles in different acoustic cuts of the LGTA crystal.

Tunable room-temperature zero temperature coefficient of resistivity in antiperovskite compounds Ga1−xCFe3 and Ga1−yAlyCFe3

The effects of the Ga content and the substitution of Al for Ga on the temperature coefficient of resistivity (TCR) of antiperovskite GaCFe3 have been investigated systematically. Our results indicate the value of TCR and its temperature range can be tuned by altering chemical compositions. With decreasing the Ga content in Ga1−xCFe3 or increasing Al dopant in Ga1−yAlyCFe3, the sign of TCR changes from positive to negative and room-temperature zero TCR material can be achieved. Typically, the optimized TCR values are about −5.72 ppm/K(265–315 K) and −14.68 ppm/K(280–320 K) for Ga0.95CFe3 and Ga0.85Al0.15CFe3, respectively. The possible mechanisms for the observed low TCR are discussed.

Formation of Icosahedral Quasicrystals and 1/1 Crystal Approximants in Al-Pd-RE (RE: Rare Earth Metals) Systems

We have investigated the formation of an icosahedral quasicrystal (i-phase) and its 1/1-crystal approximant (1/1-phase) in the (Al, Ga)-Pd-RE (Rare earth metals) systems. Consequently, the Ga-Pd-Sc 1/1-phase, the Al-Pd-RE (RE = Yb, Tm and Er) 1/1-phase and the Al-Pd-Yb i-phase have been newly found by the substitution of Al for Ga, or Sc for other RE in the constituent elements of the Al54Pd30Sc16 i-phase previously reported. For the i- and the 1/1-phases studied in this work, the number of valence electrons per atom (e⁄a) ratio is 2.10 and the atomic radius ratio of the rare earth element to that of the other base elements is in the range 1.15–1.24, which fulfilled the formation conditions previously reported for other Tsai-type i-phases. On the other hand, the stability of the i-phases becomes lower with increasing the atomic radii of the RE elements, which indicates that the atomic radius ratio plays important role in the formation of the Al-Pd-RE i- and 1/1-phases.

Enhancement of thermoelectric efficiency in type-VIII clathrate Ba8Ga16Sn30 by Al substitution for Ga

Single-crystalline samples of type-VIII clathrate Ba8Ga16−xAlxSn30 (0≤x≤12) were grown from Sn flux to characterize the structural and thermoelectric properties from 300 to 600 K. The lattice parameter increases by 0.5% as x is increased to 10.5 whose value is the solubility limit of Al. The Seebeck coefficients of all samples are largely negative and the absolute values increase to approximately 300 μV/K on heating to 600 K. This large thermopower coexists with the metallic behavior in the electrical resistivity. The values of resistivity for 1≤x≤6 at 300 K are in the range 3.3–3.8 mΩ cm which is 70% of that for x=0. As a result, the power factor for x=4 and 6 has a rather large maximum of 1.83×10−3 W/m K2 at 480 K. The thermal conductivity stays at a low level of 0.72 W/mK up to 480 K, and the sample with x=6 reaches a ZT value of 1.2 at 500 K.

Influence of Al addition on martensitic transformation and magnetic properties of Ni–Fe–Ga ferromagnetic shape memory alloys

The effect of the fourth element Al on the martensitic transformation and magnetic properties of polycrystalline Ni–Fe–Ga alloys is investigated. A complete thermoelastic martensitic transformation in Ni–Fe–Ga–Al alloys was observed in a range of 309–394 K. Martensitic transformation temperatures of Ni–Fe–Ga alloys are obviously decreased by the substitution of Al for Ga element: the addition of 1% Al can decrease the martensitic transformation temperature by about 68 K. On the other hand, the substitution of Al for Ga increases the saturation magnetization and decreases the saturation magnetic field.

Microstructure and electrical properties of aluminium-substituted La(Sr)Ga(Mg)O3–δ-based solid electrolytes

A study of the influence of the substitution of Al for Ga in the ceramic processing and electrical properties of La0.95Sr0.05Ga0.90–x Al x Mg0.10O3–δ (0 ≤ x ≤ 0.3) solid electrolytes is presented. The materials retained orthorhombic symmetry over the entire substitution range, whereas a deviation from Vegard’s law for x > 0.20 suggested a maximum Al solubility of x = 0.20. Scanning electron microscopy analysis of ceramic samples revealed that grain growth was inhibited for x ≥ 0.2. This microstructural change was related to an apparent deterioration of mechanical properties, as suggested by room-temperature Vickers hardness measurements. Impedance spectroscopy revealed a significant degradation of the grain-boundary electrical properties for x ≥ 0.20, whereas the bulk conductivity was enhanced for 0.10 ≤ x ≤ 0.15. Oxygen-permeability measurements confirmed that the studied materials remain essentially pure ionic conductors. An ionic conductivity maximum of 0.047 S/cm at 700 °C was obtained for x = 0.10. The effect of aluminium in the grain-bulk ionic conductivity is discussed in terms of defect cluster models and assuming fast oxygen diffusion along domain walls.

A Mössbauer effect and X-ray diffraction study of Fe–Ga–Al thin films prepared by combinatorial sputtering

A combinatorial thin film library of the composition Fe 100− y Ga y − x Al x was prepared by magnetron sputtering. The composition was determined by electron microprobe and showed that the Fe content was reasonably constant across the library and the Al to Ga ratio varied linearly with position. The crystallographic structure was determined with X-ray diffraction and found to be bcc. 57Fe Mössbauer spectroscopy was used to investigate short-range order within the film. It was shown that non-magnetic atoms tend to cluster in these alloys, but that the substitution of Al for Ga reduced this tendency. This behavior may be, at least partially, responsible for the decrease in saturation magnetostriction between Fe–Ga and Fe–Al alloys.

The high-pressure C2/c–P21/c phase transition along the LiAlSi2O6–LiGaSi2O6 solid solution

Two synthetic single-crystals with composition Li(Al0.53Ga0.47)Si2O6 and LiGaSi2O6 and space group C2/c at room conditions have been studied under pressure by means of X-ray diffraction using a diamond anvil cell. The unit-cell parameters were determined at 12 and 10 different pressures up to P = 8.849 and P = 7.320 GPa for Li(Al0.53Ga0.47)Si2O6 and LiGaSi2O6, respectively. The sample with mixed composition shows a C2/c to P21/c phase transformation between 1.814 and 2.156 GPa, first-order in character. The transition is characterised by a large and discontinuous decrease in the unit-cell volume and by the appearance of the b-type reflections (h + k = odd) typical of the primitive symmetry. The Ga end-member shows the same C2/c to P21/c transformation at a pressure between 0.0001 and 0.39 GPa. The low-pressure value at which the transition occurred did not allow collecting any data in the C2/c pressure stability field except that on room pressure. Our results compared with those relative to spodumene (LiAlSi2O6, Arlt and Angel 2000a) indicate that the substitution of Al for Ga at the M1 site of Li-clinopyroxenes strongly affects the transition pressure causing a decrease from 3.17 GPa (spodumene) to less than 0.39 GPa (LiGaSi2O6) and decreases the volume discontinuity at the transition. As already found for other compounds, the C2/c low-pressure phases are more rigid than the P21 /c high-pressure ones. Moreover, the increase of the M1 cation radius causes a decrease in the bulk modulus K T0. The axial compressibility among the Li-bearing clinopyroxenes indicates that the c axis is the most rigid for the C2/c phases while it becomes the most compressible for the P21 /c phases.

Martensitic Transformations of Ni<sub>54</sub>Mn<sub>25</sub>Ga<sub>21-x</sub>Al<sub>x</sub> Shape Memory Alloys

The non-stoichiometric NiMnGa shape memory alloy with high Ni content has been developed as promising thermo-actuated materials applied at high temperature. A substitution of Al for Ga in the Ni54Mn25Ga21 alloys is performed. Differential scanning calorimetry (DSC) and X-ray diffraction (XRD) measurements have been carried out to study the effects of the phase transformations and microstructures of the Ni54Mn25Ga21-xAlx shape memory alloys. The results show that the martensitic transformation temperatures almost linearly decrease with the increase of Al substitution for Ga, which can be explained considering the effect of the size factor, i.e. the lattice parameter. A structural transition from a non-modulated tetragonal type to a seven-layered 14M one has been found during the increase of Al substitution for Ga.

The system Al 2O 3 and (Sr,Mg)-doped LaGaO 3: phase composition and electrical properties

Mixtures of α-Al 2O 3 and La 0.8Sr 0.2Ga 0.8Mg 0.2O 3− δ , with α-Al 2O 3 concentrations ranging from 1 to 20 wt.%, were uniaxially and isostatically pressed and finally sintered at 1500 °C for 4 h. The phase composition and microstructure were investigated by X-ray powder diffraction and scanning electron microscopy techniques. The electrical properties were studied by complex impedance spectroscopy in a wide range of temperatures (200–800 °C) in air. In the sintered bodies pure α-Al 2O 3 was not detected; the partial substitution of Al for Ga was suggested entailing the formation of the solid solutions of perovskite-type (La 0.8Sr 0.2)(Ga 1− x− y Al x Mg y )O 3− δ and La 0.8Sr 0.2Ga 1− x Al x O 3− δ . α-Al 2O 3 added to La 0.8Sr 0.2Ga 0.8Mg 0.2O 3− δ inhibited the grain growth of the majority phase. Under isothermal conditions, the electrical conductivity decreases with increasing alumina content, while the activation energies increase.

Pressure dependence of the ferromagnetic to antiferromagnetic transition in Fe3(Ga1−xAlx)4 with x=0.0 and 0.1

The ferromagnetic to antiferromagnetic transition in Fe3Ga4 is studied by means of ac-susceptibility measurements under chemical and external hydrostatic pressure. Substitution of Al for Ga results in an increase of the ferromagnetic to antiferromagnetic transition temperature (T0) of 4.1(4) K/at. % Al. Application of hydrostatic pressures up to 7 kbar also yields a positive effect: dT0/dp=3.4(4) K/kbar. The external-pressure-induced increase of T0 in Fe3(Ga0.9Al0.1)4 is considerably weaker: dT0/dp=0.93(10) K/kbar. Thermal-expansion measurements reveal that the volume change at the ferromagnetic to antiferromagnetic transition ΔV/V amounts to only 0.02%. We believe that the volume effect in conjunction with a shift in the Fermi level drives the ferromagnetic to antiferromagnetic transition. The details of the band structure at the Fermi surface determine the magnetic properties and may give rise to the strong pressure dependence of T0.

Magnetic properties of the pseudo-binary GdGa 2− xAl x compounds

The effect of substitution of Al for Ga on the lattice parameters and the magnetic properties of the GdGa 2− x Al x compounds has been studied. It was found that there is an abrupt change in the lattice parameters at the Al concentration range x=0.6–0.75. With increasing Al concentration, the lattice parameter a increases whereas c decreases. From the magnetic measurements, it is likely that the compounds with low Al concentration (0⩽ x⩽0.3) have a complex magnetic structure, whereas for higher Al concentration (0.5⩽ x⩽1.2) the compounds can be described well as simple antiferromagnets. The change of the magnetic properties of GdGa 2− x Al x is attributed to the change in distance between the Gd atoms and to the conduction electron concentration with increasing Al concentration.

Magnetic and transport properties of Fe 3(Ga 1− xAl x) 4 compounds

The magnetic phase transitions of the itinerant-electron system Fe 3(Ga 1− x Al x ) 4, with x in the range 0.00⩽ x⩽0.10, are studied by means of magnetisation and (magneto)resistivity measurements. At 65.5 K, with increasing temperature a first-order magnetic phase transition from a ferromagnetic to an antiferromagnetic state is observed for Fe 3Ga 4. Substitution of Al for Ga results in an increase of the transition temperature of 4.1(4) K/at% Al; the low-temperature ferromagnetic state is stabilised with respect to the high-temperature antiferromagnetic state. This behaviour is different to the effect of Co substitution on the Fe sites, where the magnetism is suppressed, eventually leading to paramagnetism. The results are discussed in the framework of the theory on magnetic phase transitions in itinerant-electron systems of Moriya and Usami.

Magnetic behavior of Mn 3Ga 1− xAl xC under high magnetic field and high pressure

Mn 3GaC is antiferromagnetic (AF) below T t ∼ 160 K and ferromagnetic (F) above T t. The application of pressure enhances the Mn moment in the F state and produces an intermediate state between the AF and F states. Mn 3GaC shows a metamagnetic transition to the F state below T t. From the transition fields, the electronic specific heat coefficient in the F state is estimated to be γ = 43 mJ/K 2 mol, which is extremely large. The substitution of Al for Ga in Mn 3GaC produces the same effect as the application of high pressure.

Use of 19F nuclear magnetic resonance spectroscopy for probing substitution of Al for Ga in cloverite

The synthesis of gallophosphate cloverite in the presence of aluminum leads to a partial substitution of Ga by Al. 27Al and 19F magic-angle spinning nuclear magnetic resonance (MAS NMR) studies on this material confirm this substitution. 27Al MAS NMR shows a broad line at 30 ppm which can be attributed to tetrahedrally coordinated Al in the solid. The 19F MAS NMR results are more complex. The spectrum presents five lines between − 68 ppm and − 95 ppm which can be assigned to fluorine in D4Rs with variable composition in Ga and Al. Two other lines, at − 145.6 ppm and − 178.2 ppm, may correspond to impurities and to a fluorine atom in a pseudo-sodalite cage environment, respectively.