Doped Alloys Research Articles

Influence of rare earth doping on hydrogen absorption properties of Zr7V5Fe alloy

As a representative of non-evaporative getter, Zr–V–Fe has gained widespread attention due to its advantages including low activation temperatures and rapid hydrogen absorption rates. In this study, we investigated the impact of La and Ce doping on the thermodynamic, kinetic, and activation properties of Zr7V5Fe alloy. X-ray diffraction analysis shows that rare earth doping causes a decrease in the cell volume of both the ZrV2 and α-Zr phases of Zr7V5Fe alloy, which results in an increase in the plateau pressure of the alloys. The kinetic curves illustrate that rare earth doping leads to a coarse α-Zr phases and a larger particle size after activation, resulting in a decrease in the hydrogen absorption kinetic properties. As for the activation process, the rare earth doped alloys exhibit excellent activation with shorter incubation periods. X-ray photoelectron spectroscopy investigations reveal that Zr and V are initially in a highly oxidized state. As the heating temperature increases, they undergo a transition from oxidation state to metal state. The content of metal Zr in rare earth doped alloys is higher than that in undoped alloys at 250 °C, primarily due to rare earth elements' affinity for oxygen.

Achieving high quality factor and enhanced thermoelectric performance in polycrystalline SnS by Ag doping and Se alloying

The polycrystalline SnS with a similar layered crystal structure and band structure to SnSe exhibits enormous commercial thermoelectric potential due to its lower cost and environmentally friendly characteristics. However, the wider bandgap of SnS leads to low carrier concentration and inferior electrical transport performance. The two-dimensional interlayer hinders carrier transport, leading to interesting and mysterious anisotropic thermoelectric properties. Herein, we reported the optimized electron–phonon transport in anisotropic polycrystalline SnS by Ag doping and Se alloying, realizing a high quality factor B by multiple strategies of optimizing carrier concentration, modifying band structure, and introducing various defects; further potential performance is predicted by the single parabolic band model. Specifically, Ag-doped SnS not only significantly increases the carrier concentration and weighted mobility μw in both directions but also induces multi-scale precipitates proven by the Debye–Callaway model to suppress phonon transport. Moreover, additional Se alloying optimizes the electronic band structure and increases the Seebeck coefficient, further improving μW and boosting the maximum power factor to ∼3.72 μW cm−1 K−2 at 873 K in the out-of-plane direction. Consequently, the synergistic optimization of carrier and phonon transport achieved a high B of 0.7 and a maximum zTmax of ∼0.8 at 873 K in Ag0.02Sn0.98S0.99Se0.01. Additionally, the high B predicted a high zTmax∼1.5 based on optimized carrier transport characteristics, demonstrating the potential great-performance polycrystalline SnS. This work provides a promising avenue for optimizing the zT of polycrystalline SnS by transport engineering.

First-Principles Study on Si Atom Diffusion Behavior in Ni-Based Superalloys.

The Si atom diffusion behavior in Ni-based superalloys was evaluated based on first-principles calculations. Also, the site occupation of Si atoms as the melting point depressant elements in Cr, Mo, and W atom doped γ-Ni and γ'-Ni3Fe supercells was discussed and Si atom diffusion behaviors between both adjacent octahedral interstices were analyzed. Calculation results indicated that formation enthalpy (∆Hf) was decreased, stability was improved by doping alloying elements Cr, Mo, and W in γ-Ni and γ'-Ni3Fe supercells, Si atoms were more inclined to occupy octahedral interstices and the diffusion energy barrier was increased by increasing the radius of the doped alloy element. Especially, two diffusion paths were available for Si atoms in the γ'-Ni3Fe and Si diffusion energy barrier around the shared Fe atoms between adjacent octahedral interstices and was significantly lower than that around the shared Ni atoms. The increase of interaction strength between the doped M atom/octahedron constituent atom and Si atom increased Si atom diffusion and decreased the diffusion energy barrier. The Si atom diffusion behavior provides a theoretical basis for the phase structure evolution in wide-gap brazed joints.

Effects of carbon doping on annealing behavior of a CoCrFeNiMn high-entropy alloy

A 1 at% carbon non-equiatomic doped Co19Cr5Fe38Ni19Mn19 high-entropy alloy was synthesized by vacuum arc-melting in a high-purity argon atmosphere, followed by homogenization, cold rolling, and annealing under various conditions. The evolutions of microstructure and mechanical properties during annealing were systematically studied and compared with the carbon free alloy. Results showed that nano-sized fibrous deformation grains were formed in the 90% cold rolled alloys, resulting in high strength but low plasticity. Recovery sub-structures and recrystallized grains gradually formed with increasing annealing temperature, leading to a significant decrease in defect density, thereby softening the materials and increasing their plasticity. The early stage of recovery was mainly related to the migration of vacancy and interstitial carbon atoms, while dislocation climb became the main recovery mechanism in the late recovery stage. The carbon-doped alloy exhibited a higher recovery activation energy compared with the carbon free alloy. Therefore, 1 at% interstitial carbon effectively increased the recovery and recrystallization resistance of the Co19Cr5Fe38Ni19Mn19 alloy.

Microstructural evolution and duplex structure-enhanced high-temperature mechanical properties of Al-doped VCoNi medium entropy alloy

The microstructures and mechanical properties of 7 at% Al-added VCoNi medium entropy alloy are studied and compared with those of the undoped alloy at various temperatures. Doping Al promotes the formation of a microstructure composed of the FCC matrix and the BCC-L21 phase, which remains stable until the matrix gradually transforms into the HCP-к and tetragonal-σ phases after 600 °C. Compared with the VCoNi alloy, the differences involve that the Al addition suppresses the strain-induced FCC-HCP transformation at 25 °C, and delays the eutectoid reaction at 700 °C. Corresponding to the microstructure evolution, the doped alloy preserves higher strength and strain hardening capacity until 600 °C due to the high-content harder BCC phase but comparable values at 700 and 800 °C with the relatively less HCP phase. Besides, the added Al can also reduce the susceptibility to the serration flow. The results reveal that the (VCoNi)93Al7 alloy has high potentials for intermediate-temperature applications.

Mn-doped NiCoP nanopin arrays as high-performance bifunctional electrocatalysts for sustainable hydrogen production via overall water splitting

Active bifunctional electrocatalysts that can catalyze both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are highly desirable for overall water splitting. One such catalyst, NiCoP, demonstrates potential due to its unique electronic and structural properties that allow for efficient charge transfer between the catalyst and reactants. However, its OER performance is often unsatisfactory compared to its high HER performance. To address this problem, we prepared Mn-doped nickel cobalt phosphide (Mn-NiCoP) with nanopins arrays by in situ growth on nickel foam (NF), which only requires the overpotentials of 148 mV for HER and 266 mV for OER at a high current density of 100 mA cm−2. Consequently, the achieved water splitting performance with Mn-NiCoP as both anode and cathode at a high current density of 100 mA cm−2 were as low as 1.69 V, and its maintenance was 94% after 240 h. Furthermore, we demonstrate that the simultaneous improvement of both the OER and HER performances on Mn-NiCoP is due to the synergistic effect of the preferred moderate amount of Mn doping and Co alloying, through first-principles calculations of electronic structures, electrochemical stabilities, and reaction chemical potentials for different surface adsorption states. Overall, this work provides inspiration for optimizing the OER performance of traditional HER catalysts, thereby promoting overall water splitting using only one catalyst in the same solution.

Research Progress and Development Prospects of Enhanced GaN HEMTs

With the development of energy efficiency technologies such as 5G communication and electric vehicles, Si-based GaN microelectronics has entered a stage of rapid industrialization. As a new generation of microwave and millimeter wave devices, High Electron Mobility Transistors (HEMTs) show great advantages in frequency, gain, and noise performance. With the continuous advancement of material growth technology, the epitaxial growth of semiconductor heterojunction can accurately control doping level, material thickness, and alloy composition. Consequently, HEMTs have been greatly improved from material structure to device structure. Device performance has also been significantly improved. In this paper, we briefly describe MOCVD growth technology and research progress of GaN HEMT epitaxial films, examine and compare the “state of the art” of enhanced HEMT devices, analyze the reliability and CMOS compatibility of GaN devices, and look to the future directions of possible development.

First principles investigation of the substitutional doping of rare-earth elements and Co in La4MgNi19 phase

RE-Mg-Ni alloys, including AB3, A2B7, A5B19 and AB4 types, have received extensive attention due to their excellent hydrogen storage properties. La4MgNi19 is the one of the outstanding candidate for hydrogen storage. In this work, the structure, phase stability and electronic structure of the different La-site partial substituted by Pr, Sm, Gd, Nd and NI-site substituted by Co have been investigated by means of the density functional theory.The calculation results show that La4MgNi19 alloy shows the negative enthalpy of formation, indicating the more stable in the thermodynamic. When the substitution of La occurs, among the two sites La(2c) and La(4f), Pr, Nd, Sm and Gd preferentially occupy the La(4f) site. And the addition of the four doping elements will reduce the stability of the phase. Among them, Pr substituted La4MgNi19 has the highest structural stability. When Co substituting Ni, a single Co atom occupies the Ni(12k) preferentially among the seven different Ni positions. During this process, the crystal structure will be destabilized. The DOS results show that the system still puts up the metallic character after substitution. Sm(La(4f)) has the maximum valence band width. The stability of four doped alloys from high to low is: Pr, Nd, Sm, Gd, which is consistent with the enthalpy of formation results. The enthalpy of formation of hydrides shows that, the bounding hydrogen capacity of the system can be obtained as Nb > Sm > Pr > Gd.

EIS Study of Doped High-Entropy Alloy

The promising results obtained in the research of high-entropy alloys are increasingly encouraging new configurations of these alloys. Our research was conducted on the high-entropy CoCrFeMoNi alloy and the Ti-doped CoCrFeMoNi alloy. Electrochemical impedance spectroscopy (EIS) measurements were performed on samples with and without Ti-doped CoCrFeMoNi high-entropy alloys in order to evaluate the influence of voltage on their behavior in a simulated aggressive environment. The impedance spectra were measured between −1.0 and +0.8 V vs. SCE at various potential levels. Using an electrical equivalent circuit to match the experimental data, the impedance spectra were analyzed. The corresponding circuit that successfully fits the spectra has two time constants: the first one is for the attributes of the compact passive layer and the second one is for the features of the porous passive layer. The results show that doping CoCrFeMoNi alloy with 0.36 at.% Ti reduces the alloy’s ability to resist corrosion, as the alloy can react more quickly to the surrounding environment and cause a decrease in the corrosion resistance of the alloy.

Enhanced optical and thermoelectric properties of Ti doped half - Heusler alloy NbRuP: A first principles study

The effect of Titanium (Ti) doping on structural, electronic, optical and thermoelectric properties of NbRuP half - Heusler alloy was investigated. These properties were investigated by using density functional theory (DFT) with GGA, GGA + U, modified Becke –Johnson (mBJ) exchange, and spin orbit coupling (SOC) methods. The full Potential (FP) linearized augmented plane wave (LAPW) approach as implemented in WIEN2k code is used. The optimized lattice parameters for pure and doped alloys are 5.85 Å and 5.84 Å. The density of states (DOS) and band structure were also investigated. Results revealed that NbRuP alloy exhibit the semiconducting nature whereas the doped Nb0·75Ti0·25RuP compound shows the metallic behaviour. The DOS results revealed that the alloys show non magnetic behaviour. The optical conductivity, absorption coefficient, electron e-loss, refractive index and extinction coefficient are calculated using real and imaginary sections of dielectric function. The refractive index of doped alloy is 5.8 which is substantially higher than GaAs (3.2–3.8) and quite close to that of Ge (5.9). These optical properties make the doped material as an appropriate candidate for optoelectronic and solar cell applications. The effect of temperature on the electrical conductivity, Seebeck coefficient and Power factor were also investigated. Results showed that the doping of Ti in pure NbRuP increases the electric conductivity and power factor under TB-mBJ and SOC approaches which makes the alloy as potential candidate for thermoelectric energy applications.

Effects of alloying elements on the interfacial segregation of bismuth in tin-based solders

Sn-Bi solders are potential candidates for replacing traditional lead-based solders in electronic packaging due to their low melting points, superior wettability, and mechanical properties. The grain coarsening due to the interfacial Bi segregation is a vital issue that affects the reliability of Sn-Bi solder joints. Through first-principles calculations, this study systematically revealed the effects of different alloying elements on the interfacial segregation of Bi towards Sn(100) surface. Bi tends to segregate to the top-surface of Sn due to the formation of vacancies on Sn surface. However, doping alloying elements into the Sn-Bi solders could effectively suppress the interfacial Bi segregation. The presence of elements such as Pd, Pt, and Au located at the adjacent surface layer of Bi could inhibit the Bi precipitation, by apparently increasing the segregation energies of Bi to the Sn surface. The results can be interpreted by the enhanced bond orders and charge transfer between Bi, alloying elements, and their neighboring Sn atoms. This study could provide valuable insights into the design of multi-component Sn-Bi solders with minor alloying elements doping in the future.

Sharp MIR plasmonic modes in gratings made of heavily doped pulsed laser-melted Ge1-xSnx

Plasmonic structures made out of highly doped group-IV semiconductor materials are of large interest for the realization of fully integrated mid-infrared (MIR) devices. Utilizing highly doped Ge1-xSnx alloys grown on Si substrates is one promising route to enable device operation at near-infrared (NIR) wavelengths. Due to the lower effective mass of electrons in Sn compared to Ge, the incorporation of Sn can potentially lower the plasma wavelength of Ge1-xSnx alloys compared to that of pure Ge. However, defects introduced by the large lattice mismatch to Si substrates as well as the introduction of alloy scattering limit device applications in practice. Here, we investigate pulsed laser melting as one strategy to increase material quality in highly doped Ge1-xSnx alloys. We show that a pulsed laser melting treatment of our Ge1-xSnx films not only serves to lower the material’s plasma frequency but also leads to an increase in active dopant concentration. We demonstrate the application of this material in plasmonic gratings with sharp optical extinction peaks at MIR wavelengths.

High thermoelectric and mechanical performance achieved by a hyperconverged electronic structure and low lattice thermal conductivity in GeTe through CuInTe2 alloying

The thermoelectric figure of merit ZT of GeTe is increased by about 77% through the optimized carrier concentration and hyperconverged electronic structure by Bi doping and CuInTe2 alloying.

Structure, thermal and physic-chemical properties of some chalcogenide alloys

Bulk products of crystalline Bi2Se3-xTex alloys (x =0.0, 0.1, 0.3, 0.5) were prepared using simple melting synthesis. Crystalline features, microstructure, and surface morphologies of the synthesized samples were examined via X-ray diffraction, scanning electron microscope, and energy dispersive X-ray spectrometer. Elemental distribution was studied by energy dispersive analysis of X-ray spectroscopy. Polycrystalline of rhombohedral crystal structure was observed for the concerned samples. Perfect crystallinity and micro-scalability of the prepared were also reflected by the physic-chemical properties of each sample. Thermal behavior was studied throughout differential scanning calorimetry and thermo-gravimetric analysis showing that the samples are of high stability over high temperature range. Physic-chemical properties were determined in terms of experimental density. These properties were compactness value, molar volume and the percentage of free volume. Density of Bi2Se3 alloy was obtained at 7.37 gm/cm3. The Te doping enhanced the density of the Bi2Se3-xTex system. The most Te doped alloy showed density of 9.018 gm/cm3. All other physic-chemical properties showed strong dependence on the Tea amounts in the system.

Influence of the Electrolytic Dy-Cu alloy on the Coercivity of Sintered Nd-Fe-B Magnet

The fluorine salt oxide molten-salt electrolytic Dy-Cu alloy was used as a grain boundary diffusion source instead of the doped Dy-Cu alloy. The microstructure and coercivity of the GBDPed magnets with the different diffusion times were studied. The results show that the coercivity increased with the increase in the GBDP time. The ability of the electrolytic Dy-Cu alloy to improve the coercivity of Nd-Fe-B is more advantageous than that of the doped Dy-Cu alloy. Microstructure analysis shows that the segregation and metal inclusion, a small amount of Dy₂O₃, and the poor synergy diffusion between Dy and Cu lead to the unsatisfactory performance of the doped Dy-Cu alloy to improve the coercivity. The diffusion rate and depth of the GBD source improved by replacing the doped alloy with an electrolytic alloy.

Large magnetostriction of heavy-metal-element doped Fe-based alloys

Using density functional theory calculation and rigid band model, we investigate the electronic structure and magnetostrictive properties of transition heavy-metal doped Fe-based (Fe–Al, Fe–Si, Fe–B, and Fe–Be) alloys. It is found that a small amount of addition of 4d/5d heavy-metal atoms greatly enhances the coefficient of tetragonal magnetostriction of Fe-based alloys, reaching up to about 1000 ppm in Fe87.5Al6.25Pt6.25 and Fe75Al18.75Rh6.25 alloys. The underlying mechanism is mainly ascribed to combined factors of band narrowing induced by non-bonded states in pure Fe layer, strong spin–orbit coupling effect by heavy metals, and improved mechanical properties, through analysis of the electronic density of states near Fermi level and k-mesh resolved magnetocrystalline anisotropy energy in momentum space. These results provide useful guidance for optimizing the magnetostrictive performance of Fe-based alloys for practical application.

Impurity influence on the hydrogen diffusivity in B2–TiFe

The projector augmented-wave method within the electron density functional theory is used for calculations of the hydrogen absorption energy and its migration barriers in the doped B2–TiFe. An analytical expression for the temperature-dependent diffusion coefficients of the hydrogen in the doped alloy is derived using Landman's method. An approach for estimation of the average jump rates of hydrogen that are necessary for calculations of the diffusion coefficient in the doped alloys is developed. The activation energy of hydrogen diffusion and the pre-exponential factor are estimated. The effect of impurities on the hydrogen diffusion in the alloy is discussed.

Magnetization dependent spin orbit torques generated by ferrimagnetic FeCoTb alloys

Spin-orbit torques (SOTs) generated by magnetic materials have prompted a surge of interest in low-power spintronics. In this context, rare-earth doped magnetic alloys are the ideal candidate due to the low symmetry and large spin-orbit coupling. Here, we present a study on SOTs generated by ferrimagnetic FeCoTb alloys in permalloy (Ni80Fe20, Py)/Cu/FeCoTb spin valve structures, showing high-efficient damping-like and field-like torques. Crucially, the spin Hall conductivity of FeCoTb is up to 6.32 × 105 (ℏ/2e) Ω−1m−1, larger than that in conventional heavy metals. By controlling the magnetic configuration of the spin valve structure, the magnetization dependent behavior of the SOTs is achieved, which may origin from the anomalous Hall effect of FeCoTb dominated by Tb magnetization. Our results demonstrate great prospects of ferrimagnetic materials for low-power spintronic applications.

First-Principles Study of the Effect of Titanium Doping on Carbon Monoxide Poisoning Properties of Zirconium-Cobalt Alloys

It is very important to study impurity gas poisoning in ZrCo alloy because it is associated directly with the performance of ZrCo alloy as a hydrogen storage material. In this work, the effects of atomic replacement on the mechanism and properties of CO impurity gas poisoning in doped (Ti) ZrCo hydrogen storage alloys were investigated using the first principles method, based on the pseudopotential plane wave method. The adsorption energy, lattice constant, density of states, and charge density difference of the compounds before and after doping were calculated. Then, surface adsorption models of the ZrCo and Zr0.8Ti0.2Co alloys were established with the assistance of a conventional model. The resulting adsorption energy values of the clean surface and the surface adsorption energy values in the presence of CO impurity gases manifested that the Ti element-doped Zr0.8Ti0.2Co alloy was more susceptible to CO gas poisoning compared to ZrCo, which was consistent with the existing experimental results. In addition, by analyzing the conventional model, the electrons from the doped atoms overlapped with the surrounding electrons of C atoms, the phenomenon of orbital hybridization occurred, and the interactions increased. Consequently, Ti doping was not conducive to ZrCo to improve the ability to resist CO poisoning. The research results of this paper have laid a good foundation for the study of the effect of Ti doping on the antitoxicity performance.

Impurity Combination Effect on Oxygen Absorption in α2-Ti3Al

The effect of substitutional impurities of the transition metals of VB–VIIB groups on the oxygen absorption in the doped α2-Ti3Al alloy was studied by the projector-augmented wave method within the density functional theory. It is established that all considered impurities prefer to substitute for a Ti atom rather than an Al atom. Changes in the absorption energy due to impurities being in the first neighbors of the oxygen atom were estimated. It was demonstrated that the doping resulted in a decrease in the oxygen absorption energy, which is mainly caused by the chemical contribution to it. The interaction energy between impurity atoms was calculated in the dependence on the interatomic distance. It was shown that the configuration with the impurity atoms being in the second neighbors of each other was stable in comparison with other possible configurations. The influence of two impurity atoms being in the first neighbors of oxygen is additively enhanced. It was revealed that the effect of two impurity atoms on the oxygen absorption energy can be estimated as the sum of the effects of separate impurities with an accuracy of more than ~90%.