Effect Of Al-substitution Research Articles

Atomistic Mechanism of Al Substitution Effects on the Ferroelastic Post-stishovite Transition by High-Pressure Single-Crystal X-Ray Diffraction

Atomistic Mechanism of Al Substitution Effects on the Ferroelastic Post-stishovite Transition by High-Pressure Single-Crystal X-Ray Diffraction

Surface Energies, Al-Substitution Effects, and Water Adsorption on Ferrihydrite: Insights from Density Functional Theory Calculations

Surface Energies, Al-Substitution Effects, and Water Adsorption on Ferrihydrite: Insights from Density Functional Theory Calculations

Effect of Al substitution on the electron-phonon interaction for β-Ga2O3

The relevant parameters of electron–phonon (e-ph) interaction, like mean phonon temperature and e-ph interaction strength for Al-substituted β-Ga2O3, i.e., β-(AlxGa1–x)2O3 alloys, have been determined from the fitting of the temperature dependence of the band gap using Bose–Einstein empirical model. Both e-ph interaction strength and mean phonon temperature decrease sharply for initial Al compositions; then, they increase slightly and become more or less constant. This is explained by using the already existed concepts of propagon and diffuson for the phonon modes that interact with the electrons. Presence of two sublattices at the local level is found to be the origin of diffuson-like behaviour of phonon modes in β-(AlxGa1–x)2O3 alloyed system, which vibrate independently like a non-propagating oscillator and diffuse through the β-(AlxGa1–x)2O3 lattice. The diffuson-like behaviour of phonon modes in the β-(AlxGa1–x)2O3 alloy is found to be responsible for the reduction in e-ph interaction. The reduction of e-ph interaction strength of β-Ga2O3 with Al substitution may lead to the better performance of power devices working at higher temperatures.

Stability and transformation of jarosite and Al-substituted jarosite in an acid sulfate paddy soil under laboratory and field conditions

Jarosite, a prominent mineral in oxidised acid sulfate soil, is known to sorb and incorporate a variety of elements, including Al. However, to understand the role that jarosite plays in regulating element cycles, it is crucial to understand the stability and transformation pathways of jarosite in an acid sulfate soil under dynamic biogeochemical conditions. In this study, we observed the transformation of unsubstituted jarosite and Al-substituted jarosite, collectively referred to as ‘jarosite’, in an acid-sulfate rice paddy topsoil and subsoil from Thailand. Jarosite was incubated in flooded paddy topsoils and subsoils for up to sixteen weeks, both in laboratory mesocosms and in the field, using bags made of polyethylene terephthalate mesh. One set of mesh bags contained jarosite that was not mixed with any other minerals, and referred to as ‘pure mineral’ incubations. Mineral transformations occurred under the influence of the soil porewater only and were primarily followed by X-ray diffraction analysis. A parallel set of mesh bags contained soil with 57Fe-labelled jarosite enrichment (Fe enriched in soil by a factor of 1.3 but 57Fe enrichment factor of 12.5–13.6), which allowed jarosite transformation to occur in close association with the soil matrix. Mineral transformations in 57Fe-jarosite-enriched soil were followed using 57Fe Mössbauer spectroscopy. In laboratory mesocosms and in the field, jarosite transformed most quickly in topsoil, whereas jarosite underwent limited transformation in subsoils, especially in laboratory mesocosms where Fe reduction was slow. The chemical environment around the jarosite affected the outcome of the transformation processes. Crystalline Fe oxyhydroxides, such as goethite, dominated the products in mesh bags where jarosite was not mixed with soil, whereas short-range-ordered or non-mineral Fe phases, such as Fe(II) sorbed to mineral surfaces or complexed with organic ligands, were dominant transformation products of jarosite when mixed in soil. Furthermore, Al substitution in jarosite caused contrasting effects in mesh bags containing pure minerals or mineral-enriched soil. Aluminium substitution slowed the transformation of jarosite in pure mineral mesh bags, but Al-substituted and unsubstituted jarosite showed similar transformation rates and pathways when incubated as a mixture with soil. The contrasting rate of transformation in topsoil and subsoil, the contrasting products of transformation in pure mineral mesh bags and 57Fe-jarosite-enriched soil, and the contrasting effect of Al substitution in pure mesh bags or jarosite-enriched soil, all demonstrate that the rate and products of jarosite transformation are defined by a balance between competitive transformation pathways that affect the transforming minerals.

Effect of Al substitution on the magnetic, optical and electronic properties of KBiFe2O5 brownmillerite

We reveal the influence of non-magnetic Al3+ ion on magnetic, optical and electronic properties of KBiFe2O5. Al doped KBiFe2-xAlxO5 (x = 0, 0.2, 0.4) are synthesized by citrate combustion method. All the samples are found to be crystalized in monoclinic structure with P2/c space group. With Al doping, the grain size of the samples is reduced however, Fe ions maintain its +3 state. A mere difference in the low temperature zero field cooling and field cooling curve discards the multiple magnetic phases at low temperature, however, with Al, an improved magnetic moment is detected in the magnetic isotherms. A schematic model is adopted to explain the enhanced magnetization. Furthermore, the magnetic anomaly around the dielectric transition (760–780 K) depicts an existence of magnetoelectric coupling in all the samples. The optical band gap is reduced from 1.73 eV to 1.69 eV with Al doping. Extensive dielectric and electric modulus analysis is carried out to explore the conduction as well as relaxation process in the parent and Al doped system. The activation energy estimated from the electric modulus is (0.412 ± 0.021) eV for x = 0 and (0.370 ± 0.025) eV for x = 0.2 respectively but surprisingly, Al doping with x = 0.4 shows a completely different relaxation mechanism. Moreover, the frequency dependent ac conductivity is also explained and agrees well with the electric modulus data.

Scientific and simulation study of the manufacturing technology of the ancient Chinese rare Hare’s Fur glazed bowl

The red Hare’s Fur glazed bowls of the Jin and Yuan periods(1115–1368 A.D.) were analysed by optical microscopy, EDXRF, XRD, SEM-EDS, Micro-Raman spectroscopy and thermal expansion instrument. We also conduct simulation experiments at different temperatures and atmospheres. The results revealed that the Fe2O3 content of the Hare’s Fur glaze was about 5%. ε-Fe2O3 was found in the crystals on the glaze surface. The ε-Fe2O3 was all found on the rim of the bowl and it can exceed 10 µm in size. They were fired at about 1250 °C in a reducing atmosphere. The simulation experiments showed that ε-Fe2O3 was formed in the cooling stage and needed to be held for a period of time at about 1160–1190 °C. The presence of mullite will promote the formation of ε-Fe2O3. This is because the Al-substitution effect changes the crystal structure of ε-Fe2O3 and makes it more stable.

Effect of Al substitution at the Ga site on the structural and magnetic properties of GaFeO3

GaFeO3 compound figures among those orthoferrites that are potential candidates for multiferroics. However, GaFeO3 suffers from a relatively low Nèel temperature, TN ≈ 200 K, and magnetic moment. Based on the results of a detailed investigation of Raman-active modes, structural and magnetic properties of the Ga1-xAlxFeO3 (x = 0.0, 0.05, 0.10, 0.20, 0.30) samples, we show that Al substitution at the Ga sites remedies these shortcomings to a large extent. This work brings out clearly that Al preferentially occupies the tetrahedral (Ga1) sites rather than the octahedral (Ga2, Fe1 and Fe2) sites. The effect of Al substitution in Ga1-xAlxFeO3 is to (i) decrease the lattice parameters and cation-O bond lengths which results in a shift in the positions of Raman peaks towards higher wavenumbers, and (ii) increase (decrease) the cation-O-cation bond-angles such that the antiferromagnetic (ferromagnetic) superexchange interactions grow in strength. An enhancement in these interactions accounts for the observed increase in the Nèel temperature, TN, as well as in the saturation magnetization. The radically different temperature variations of the ‘zero-field-cooled’ and ‘field-cooled’ magnetizations below the irreversibility temperature can be qualitatively understood in terms of the Nèel molecular-field theory for ferrimagnetism. The temperature dependence of inverse susceptibility in the paramagnetic state provides evidence for the non-linear behavior at temperatures well above TN and hence for the persistence of short-range magnetic order to temperatures as high as 1.75 TN.

Effect of Al substitution on phase evolution in synthesized Mg2Cu nanoparticles

Effect of Al substitution on phase evolution in synthesized Mg2Cu nanoparticles

Atomic positions and displacements in piezoelectric materials Ca3TaGa3Si2O14 and Ca3TaGa1.5Al1.5Si2O14 investigated by Ta-Lα X-ray fluorescence holography

The atomic positions and displacements of atoms around the Ta atom in piezoelectric materials Ca3TaGa3Si2O7 (CTGS) and Ca3TaGa1.5Al1.5Si2O7 (CTGAS) were investigated at 100 K by Ta-Lα X-ray fluorescence holography (XFH). The experimental atomic images were compared with the simulated ones using the crystal structures of CTGS and CTGAS, which were determined by single crystal X-ray diffractometry (SC-XRD). The atomic positions agreed between XFH and SC-XRD experiments. With the help of XFH simulation, the displacements of Ta, Ca, Si, and Ga atoms relative to the Ta atom were qualitatively analyzed using experimental atomic image intensities. The relative displacement of the Ca atom was increased by Al substitution, while those of the Ta and Ga atoms were decreased. The first principles calculation based on density-functional theory (DFT) was performed to understand bonding character between constituents. The evaluation of the crystal orbital Hamilton population (COHP) clarified that the Ca-O bond has strong ionic character different with the other bonds, suggesting that the positional shift of the Ca atom is responsible for the piezoelectricity in CTGS. The effect of Al substitution on piezoelectricity was also considered based on the change in the Ca-O bond.

Complexation mechanism of Pb2+ at the ferrihydrite-water interface: The role of Al-substitution

Ferrihydrite is a poorly crystalline iron (hydr)oxide and highly efficient adsorbent for heavy metals. Al-substitution in ferrihydrite is ubiquitous in nature. However, the effect of Al-substitution on the surface reactivity of ferrihydrite remains unclear due to its low crystallinity. The present study aims to clarify the microstructure and interfacial reaction of Al-substituted ferrihydrite. Al-substitution had little effect on the morphology and surface site density of ferrihydrite, while the presence of ≡AlOH−0.5 sites resulted in higher proton affinity and surface positive charge of ferrihydrite. Besides, the affinity constant of Pb2+ adsorption on the surface of ferrihydrite decreased at higher Al content, which further decreased the adsorption performance of ferrihydrite for Pb2+. The modeling results revealed that bidentate complex was the dominant Pb complexation species on the surface of ferrihydrite, which was less affected by Al-substitution. The present study provides important insights into the effect of Al-substitution on the interfacial reaction at the ferrihydrite-water interface. The obtained parameters may facilitate the future advance of surface complexation model.

Effect of aluminum substitution on structural, electronic and dielectric properties of cubic CaCu3Ti4O12 ceramics: A first-principles study

The paper sheds light on the effect of Al substitution on structural, electronic and dielectric properties of cubic CaCu3Ti4O12 ceramics based on first principles method. The CaCu3Ti4-xAlxO12 (x = 0, 0.5, 1, 1.5 and 2) ceramics still keeps a cubic lattice, and the lattice constant decreases with Al concentration enhanced. Phonon dispersion curves show that the structures of CaCu3Ti4-xAlxO12 ceramics are thermodynamically stable at x ≤ 1. The CaCu3Ti4-xAlxO12 ceramics have magnetic semiconductor properties and the band gaps corresponding to the high symmetry point G increases with increasing Al concentration. It can be concluded that doping Al can increase the dielectric constant and electronic transition intensity of cubic CaCu3Ti4O12 ceramics, and reduce its energy loss. In the low energy region, the dielectric constant of CaCu3Ti3.5Al0.5O12 ceramics is about ten times that of cubic CaCu3Ti4O12 ceramics. The ratio of aluminum atoms to titanium atoms of 1:7 May be the best ratio. It can also be concluded that when A13+ replaces Ti4+ ions, A1 also acts as an electron acceptor to reduce the electron concentration of Ti4+ ions, leading to the generation of oxygen vacancies. These results will provide a theoretical basis for the design of high dielectric constant materials.

Effect of Al substitution and secondary CuO phase on dielectric response in microwave-processed CaCu3Ti4−xAlxO12 ceramics

Effect of Al substitution and secondary CuO phase on dielectric response in microwave-processed CaCu3Ti4−xAlxO12 ceramics

Nano-scale investigation of organic C sequestration and distribution on Fe oxides during ferrihydrite transformation: effect of Al-substitution

Al-substitution in Fe oxides increased the sorption of aromatic C, which was dominantly bound to the outer layer of the organo–mineral interfaces as the carboxyl C was preferentially sorbed onto the surfaces of Fe oxides.

Al substitution effect on magnetic properties of magnetocaloric material HoB2

We investigate the Al substitution effect for HoB2 to tune the Curie temperature (TC). The HoB2−xAlx samples with nominal x (xnom) of 0, 0.1, 0.3, and 0.5 are characterized by powder X-ray diffraction measurements, EDS analysis and magnetization measurements. The HoB2−xAlx samples with xnom of 0.1, 0.3, and 0.5 show two ferromagnetic transitions at TC1 of ∼15 K and TC2 of >32 K. The TC1 is identical to the TC of HoB2 and does not change with Al substitution. The TC2 is similar to the TC of HoAl2 and varies with Al content. In an EDS analysis, the inhomogeneous elemental distribution is observed in Al-substituted HoB2, where the Al-rich regions exist. Our results suggest that the Al added to HoB2 does not form a solid solution, but rather leads to the phase segregation into stoichiometric HoB2 and B-substituted HoAl2. The xnom = 0.5 sample exhibits the maximum |ΔSM(μ0H:5 T→0 T)| of 32.1 J kg K−1 at TC1 and a small kink of |ΔSM| at TC2. Because the |ΔSM| exhibits a maximum at TC1, stoichiometric HoB2 mainly contributes to the maximum of |ΔSM|.

Structural, cation distribution, thermal properties, and electrical resistivity of nano NiAlxFe2-xO4 synthesized by flash auto combustion method

This work reports the effect of Al substitution in Ni ferrite on the structural and electrical resistivity of NiAlxFe2-xO4 (where, x= 0.00, 0.20, 0.40, 0.60, 0.80, and 1.00) nanoparticles synthesized by the flash auto combustion method. The XRD results show the presence of single-phase spinel structure. The average particle size estimated using Debye–Scherer׳s equation and was found to be in the range of 14 – 23.9 nm. Lattice parameter a (Å), cell volume and density the studied ferrite NiAlxFe2-xO4 were decreased with increasing Al+3 content. Fe, Al and Ni ions dominantly occupy both tetrahedral (A) and octahedral (B) sites. Occupancy from x=0 to x=1, are changed in A site, from 25%, 8% and 0% to 16% 13% and 6% for Fe, Ni, and Al ions, respectively, and in B site, from 42%, 25% and 0%, to 17% Fe, 22% Ni, 26% for Fe, Ni, and Al ions, respectively. The formation of spinel ferrite confirmed by the two types of stretching vibrations of metal oxide (M-O) bonds. The lower absorption band ʋocta lies in the range of 399-462 cm−1 and the higher absorption band ʋtetra lies in the range of 590-624 cm−1. Mössbauer measurement showed three broad hyperfine magnetic sextets in addition to superparamagnetic doublet were observed in most the measured samples. the component with the higher field value is associated with Fe3+ ions at B- site, while that with smaller field is associated with Fe3+ ions at A-site. The third collapse sextet which have smallest field and very broad width represents an intermediate phase between magnetic and superparamagnetic states. From TGA results, the activation energy of two weight losses are 20.7, 40.6 KJ/mol for Ni-Al ferrite and 14.12, 26.08 KJ/mol for Ni ferrite. The increase of Al content lead to increase in the resistivity from 7.4 to 412 MΩ at room temperature. With increasing temperature, the resistivity of all samples decreased which is a typical semiconductor behavior of ferrites consistent with Verwey hopping model. Curie temperature also increase as Al content increased in range of 353-634 K and in range of 474-577 K for DC and AC respectively. The high electrical resistivity of Ni-Al ferrites makes it preferable to be used in data storage devices

Effect of Al substitution on structure and cathode performance of MgMn2O4 spinel for magnesium rechargeable battery

Magnesium rechargeable batteries using Mg-metal anodes are promising post-lithium-ion batteries. MgMn2O4 is a strong candidate cathode material owing to its high energy density and relatively high Mg2+-ion diffusivity. However, while pristine MgMn2O4 forms a tetragonal spinel structure (I41/amd) owing to the Jahn–Teller effect of Mn3+, it adopts a cubic structure in the charged/discharged state. This results in a structural change from tetragonal to cubic during charge/discharge cycling, leading to poor battery performance and reversibility. To improve the cathode performance, we prepared Al-substituted MgMn2−xAlxO4 spinel (x = 0, 0.1, 0.2, 0.5) to suppress the Jahn–Teller distortion. The obtained MgMn2−xAlxO4 spinel is a two-phase crystal with coexisting tetragonal and cubic spinel structures, whereby the fraction of cubic phase tends to increase with the Al ratio. The Al-substituted spinels exhibit superior discharge capacities to that of MgMn2O4. The increase in cubic spinel phase fraction by Al-substitution and the reduced structural change during discharging will aid the development of superior cathodes for magnesium batteries.

Quaternary Fe‐Cu‐Cr‐Al HT‐WGS Catalysts – Effect of Al Substitution on the Efficiency at Steam‐Lean Process Gas

In the present work, we report on Fe–Cu–Cr–Al systems with various Cr/Al substitution as catalysts for high‐temperature water‐gas shift (HT‐WGS) to evaluate the possibility of Cr elimination and usability for carrying out the HT‐WGS process at steam‐lean process gas. The set of Fe–Cu–Cr–Al catalysts with the same Fe/Cu molar ratio and different Cr/Al molar ratio (0/∞) were prepared by the precursors' co‐precipitation and thermal treatment. The catalysts were investigated by XRF, DTG/MS, XRD, N2 sorption, H2‐TPR methods and activity tests. A relationship between Cr/Al ratio and physicochemical parameters and HT‐WGS activity, selectivity and stability of the catalysts have been estimated. Experimental results demonstrated that complete elimination of Cr from the Fe–Cu–Cr–Al catalyst is unfavorable, and it would lead to negative consequences as Cr enhances the catalyst activity and improve its durability.

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.

Heat flux sensing by anomalous Nernst effect in Fe–Al thin films on a flexible substrate

We performed a numerical analysis of the material parameters required for realizing a heat flux sensor exploiting the anomalous Nernst effect (ANE). The results showed the importance of high thermopower of ANE (SANE) and small saturation magnetization. This motivated us to investigate the effect of Al substitution of Fe on ANE and found SANE = 3.4 μV K−1 in Fe81Al19 because of the dominant intrinsic mechanism. Using this material, we made a prototype ANE-based heat flux sensor on a thin flexible polyimide sheet and demonstrated accurate sensing with it. This study gives important information for enhancing sensor sensitivity.