Ga Atoms Research Articles

Integration of ML methods with CR model-based optical diagnostic for the estimation of electron temperature in Ga laser produced plasma

Accelerated diagnostic of plasma plays a significant role in controlling and optimizing plasma-mediated processing, particularly for plasma with higher temporal and spatial gradients, such as laser produced plasma (LPP). In the present work, two advanced machine learning (ML) algorithms, random forest regression, and gradient boosting regression are integrated with noninvasive collisional radiative (CR) model-based optical diagnostics to facilitate accurate diagnostics. A comprehensive fine-structure resolved CR model framework is developed by incorporating our consistent cross section data obtained from the Relativistic Distorted Wave method [Suresh et al., “Fully relativistic distorted wave calculations of electron impact excitation of gallium atom: Cross sections relevant for plasma kinetic modelling,” Spectrochim. Acta B: At. Spectrosc. 213, 106860 (2024)]. An extensive dataset of CR model simulated intensities is created to train and test the ML methods. The present CR model is applied to characterize the Gallium LPP coupling with the optical emission spectroscopic measurements of Guo et al. [“Time-resolved spectroscopy analysis of Ga atom in laser induced plasma,” Laser Phys. 19, 1832–1837 (2009)] at different delay times. Further, a detailed correlation study of the line intensity ratios is performed to observe the qualitative behavior of the plasma parameters. The electron temperature results obtained from the CR model, ML, and line ratio methods were compared and found to be in excellent agreement. Overall, the present study demonstrates diagnostic approaches that can benefit the LPP community significantly by providing a rapid understanding of the plasma behavior across various operating conditions.

P-type doped AlxGa1-xAs nanowire photocathode: A theoretical perspective on structural and optoelectronic properties

In this work, the effect of p-type doping on the structural, electronic, and optical properties of AlxGa1-xAs nanowires are investigated by first-principles calculations. Different doping elements (Be, Mg, Zn), doping methods (interstitial and substitution doping) and doping concentration are considered. The calculations of formation energy suggest that the structural stability of p-type AlxGa1-xAs nanowires is gradually weaken as the rise of doping concentration and Al composition. Besides, the difficulty of forming substitution doping for different doping elements obeys the following order: Be<Mg<Zn. In addition, the substitution doping atom tends to replace Ga atom rather than Al atom to form substitution doping structure. After substitution doping, all energy bands shift to higher energy region due to the orbital hybridization of electronic states induced by impurity atom and nanowire atoms. Moreover, the substitution doping leads to the Fermi level entering into the valence band, resulting in obviously p-type conductivity. The p-type modulation doping is indeed effective in the axial type AlxGa1-xAs nanowires with p-type carrier concentration varying between 1.85×1020 cm-3 and 4.42×1020 cm-3, and the conductivity will be further enhanced with increasing substitution doping concentration or Al composition. Finally, the optical absorption of AlxGa1-xAs nanowire photocathodes can be effectively enhanced through BeGa doping. Our findings not only present a comprehensive understanding of p-type doping mechanism of AlxGa1-xAs nanowires, but also provide a theoretical basis for preparing AlxGa1-xAs nanowire based photoelectric devices with p-type properties.

The crystal structure of R3Fe0.1Ga1.6S7 chalcogenides (R – La, Ce, Pr and Tb)

The paper reports the study of the crystal structure of chalcogenides of the composition R3Fe0.1Ga1.6S7 (R = La, Ce, Pr and Tb) as promising materials predicted to possess interesting nonlinear optical and electrical properties. Samples of stoichiometric composition were synthesized by co-melting the elements in quartz containers evacuated to a residual pressure of 10–2 Pa at the maximum synthesis temperature of 1100 °C. The crystal structure of the chalcogenides La3Fe0.1Ga1.6S7 {a = 10.1884(6) Å, c = 6.0515(4) Å}, Ce3Fe0.1Ga1.6S7 {a = 10.0864(4) Å, c = 6.0440(3) Å}, Pr3Fe0.1Ga1.6S7 {a = 9.9853(3) Å, c = 6.0648(2) Å} and Tb3Fe0.1Ga1.6S7 {a = 9.6692(7) Å, c = 6.0799(5) Å} was studied by X-ray powder method. It was determined that the structure of the synthesized phases belongs to the hexagonal symmetry (La3CuSiS7 structure type; space group P63). The structure of the complex chalcogenides (A), (B), (C) and (D) is based on the R3Ga1.67S7 sulfides (R = La, Ce, Pr, and Tb) by substituting gallium atoms in the 2a sites with atoms of statistical mixture M1{0.57(2) Ga + 0.10(2) Fe}, M2{0.56(1) Ga + 0.10(2) Fe}, M3 {0.61(8) Ga + 0.09(1) Fe} and M4 {0.57(2) Ga + 0.10(2) Fe}, respectively. Rare earth atoms are localized in the 6c sites and center sulfur atoms to form trigonal prisms with an additional atom [R 3S13S21S3]. Atoms of statistical mixtures M1, M2, M3, M4 are localized in the 2a sites forming [M 6S2] octahedra. Ga atoms in the 2b sites are surrounded by four sulfur atoms [Ga 3S11S3].

Embedding Single Pd Atoms on NiGa Intermetallic Surfaces for Efficient and Selective Alkyne Hydrogenation.

Catalytic removal of alkynes is essential in industry for producing polymer-grade alkenes from steam cracking processes. Non-noble Ni-based catalysts hold promise as effective alternatives to industrial Pd-based catalysts but suffer from low activity. Here we report embedding of single-atom Pd onto the NiGa intermetallic surface with replacing Ga atoms via a well-defined synthesis strategy to design Pd1-NiGa catalyst for alkyne semi-hydrogenation. The fabricated Pd1Ni2Ga1 ensemble sites deliver remarkably higher specific mass activity under superb alkene selectivity of >96 % than the state-of-the-art catalysts under industry-relevant conditions. Integrated experimental and computational studies reveal that the single-atom Pd synergizes with the neighbouring Ni sites to facilitate the σ-adsorption of alkyne and dissociation of hydrogen while suppress the alkene adsorption. Such synergistic effects confer the single-atom Pd on the NiGa intermetallic with a Midas touch for alkyne semi-hydrogenation, providing an effective strategy for stimulating low active Ni-based catalysts for other selective hydrogenations in industry.

Structural Stability of Vacancy and Substitutional Defects in g-GaN: A First-Principles Study

Herein, the first-principles calculations of defected monolayer graphene-like gallium nitride (g-GaN) were elucidated. The optimized geometric revealed that the nearest-neighbor distances of N-N (between N atoms) and Ga-Ga (between Ga atoms) were narrowing in most configurations. Interestingly, the VGa has a similar atomic symmetry as the pure g-GaN, which is D3h. Most defected configurations are degraded into C2V symmetries, while the Stone-Wales configuration has the lowest symmetry of CS. The formation energies of V­­Na systems are lower, which implies better energetic stability. For the divacancies, the VGa system is more stable than the V­­Na system. Moreover, the Stone-Wales configuration is energetically more stable than the interchange configuration. Furthermore, the reaction coordinates represent the geometric evolution of each defected system. The result revealed that the N-atoms are consistent with moving outward while the Ga-atoms move inward only for monovacancies and divacancies configurations. In contrast, the N-atoms move inward while the Ga-atoms move outward for substitutions, interchanges, and Stone-Wales configurations. We believe that this finding will be beneficial as the groundwork for future 2D g-GaN-based semiconductor devices. HIGHLIGHTS The V­­Na defective system is more stable than the VGa system in monovacancies and substitutions. The VGaGa defective system is more stable than the V­­Na system in divacancies. The Stone-Wales system is a stable configuration with a Cs symmetry. GRAPHICAL ABSTRACT

Detection of an unintentional Si doping gradient in site-controlled GaN nanowires grown using a Si3N4 mask by spatially resolved cathodoluminescence and Raman spectroscopy

Highly uniform arrays of site-controlled GaN nanowires are synthesized by selective area growth using a Si3N4 mask and molecular beam epitaxy. Systematic modulation of the emission along the nanowire axis is observed in spectrally resolved cathodoluminescence linescans. We show that this intensity change is an indicator of unintentional Si incorporation during growth resulting from the interaction between the impinging Ga atoms and the mask material. The gradual reduction of the cathodoluminescence intensity along the nanowire highlights the important role of the growth geometry within the synthesis reactor, with shadowing from the elongating nanowires inhibiting the reaction with the mask. This gradient in Si doping is confirmed by the quenching of the longitudinal optical phonon line measured in Raman spectra along the nanowire axis. The corresponding carrier density is derived from the frequency of the coupled phonon–plasmon mode. The spectroscopic identification of inversion domain boundaries in the majority of the nanowires is also attributed to the Si incorporation. From temperature dependent cathodoluminescence experiments, we derive the activation energy for excitons bound to these defects.

Janus monolayers Fe2SSeX2(X = Ga, In, and Tl): Robust nontrivial topology with high Chern-number

Abstract High-performance quantum anomalous Hall (QAH) systems are the crucial materials to explore emerging quantum physics and magnetic topological phenomena. Inspired by layered FeSe materials with excellent superconducting properties, the Janus monolayers Fe2SSeX2 (X = Ga, In, and Tl) are built by the decoration of Ga, In, and Tl atoms in monolayer Fe2SSe. Using the first-principles calculations, the Fe2SSeX2 have stable structures and prefer ferromagnetic (FM) orders, which belong to the Weyl semimetal without spin-orbit coupling (SOC). For the out-of-plane (OOP) magnetic anisotropy, the large nontrivial gaps are opened, and the Fe2SSeX2 are predicted to be large-gap QAH insulators with high Chern-number C = 2, proved by two chiral edge states and Berry curvatures. When the magnetization is flipped, two chiral edge states can be simultaneously changed and C = -2 can be obtained, revealing one fascinating behavior of chiral spin-edge-state locking. It is found that the QAH properties of the Fe2SSeX2 are robust against the strain. Especially, the nontrivial topological quantum states can spontaneously appear for the Fe2SSeGa2 and Fe2SSeIn2, because the easy magnetic axis orientations are adjusted from in-plane to OOP by the biaxial strain. Our studies provide excellent candidate systems to realize the QAH properties with high Chern-number, and advocate more experimental explorations in the combination of superconductivity and topology.

Role of local structure in the optical and electronic properties of oxygen vacancies in different crystal phases of Ga2O3

We investigate the structural, electronic, and optical properties of oxygen vacancies (VO) in crystalline α, β, and ε−Ga2O3 using density functional theory (DFT) calculations with the PBE0-TC-LRC functional. Our results reveal that the charge transition levels (CTLs) associated with VO exhibit significant variations depending on the crystal phase and the coordination environment of surrounding atoms. In particular, VOs surrounded by tetrahedral Ga atoms (T-Ga) exhibit deeper CTLs compared to those surrounded by octahedral Ga atoms (O-Ga). We also observe distinct atomic relaxations, with larger displacements of T-Ga atoms compared to O-Ga atoms in the vicinity of VOs. Using linear-response time-dependent DFT, we investigate the optical transitions of VO and identify two distinct types of transitions: defect state to conduction band state and valence band to defect state. These results can be used to better understand the optical properties of VO defects in Ga2O3 films. Published by the American Physical Society 2024

Investigation on Be, Mg, Ca, B, Ga, C, Si, and Ge atoms doped on Al (111) surface and their effect on oxygen adsorption: A first-principle calculation

Oxygen corrosion of the aluminum alloy has a substantial impact on the durability of engineering materials and equipment. To better understand how various alloy elements affect oxygen corrosion, we used first-principle DFT method to study the role of each given dopant atom (Be, Mg, Ca, B, Ga, C, Si, and Ge) in the formation of surface oxide film on the Al (111) surface, in the case replacing a surface Al atom. Our calculations show that the electron gain or loss abilities of these alloy elements differ from that of Al metal, with Be, B, C, and Si atoms tending to penetrate into the surface, Mg, Ca, and Ga atoms protruding, and Ge atom just embedded into the Al (111) surfaces. Additionally, the type of doping element at the Al (111) surface can greatly affect the O2 absorption, predicting that Ca-doped surface absorb the least amount of oxygen, followed by Si-doped surface, with Be-, Mg-, B-, Ga-, C-, and Ge-doped surfaces showing higher O2 absorption. Based on adsorption energy (Eads) and partial density of states (PDOS) analysis, we conclude that the doped Al (111) surfaces can make O2 adsorption different owing to the difference in electronic properties of the doping atoms. These insights draw a greater knowledge of the role of alloy elements in the oxygen corrosion of Al alloys, enabling guidance for designing more corrosion-resistant materials.

Embedding Single Pd Atoms on NiGa Intermetallic Surfaces for Efficient and Selective Alkyne Hydrogenation

AbstractCatalytic removal of alkynes is essential in industry for producing polymer‐grade alkenes from steam cracking processes. Non‐noble Ni‐based catalysts hold promise as effective alternatives to industrial Pd‐based catalysts but suffer from low activity. Here we report embedding of single‐atom Pd onto the NiGa intermetallic surface with replacing Ga atoms via a well‐defined synthesis strategy to design Pd1−NiGa catalyst for alkyne semi‐hydrogenation. The fabricated Pd1Ni2Ga1 ensemble sites deliver remarkably higher specific mass activity under superb alkene selectivity of &gt;96 % than the state‐of‐the‐art catalysts under industry‐relevant conditions. Integrated experimental and computational studies reveal that the single‐atom Pd synergizes with the neighbouring Ni sites to facilitate the σ‐adsorption of alkyne and dissociation of hydrogen while suppress the alkene adsorption. Such synergistic effects confer the single‐atom Pd on the NiGa intermetallic with a Midas touch for alkyne semi‐hydrogenation, providing an effective strategy for stimulating low active Ni‐based catalysts for other selective hydrogenations in industry.

The Relation between Nature and Stability of H2‐Dissociating Sites and Propene Selectivity in Silica‐Supported (Ga,Al)2O3 Mixed Oxide Propane Dehydrogenation Catalysts

AbstractColloidal solutions of gallia‐alumina (Ga,Al)2O3(x:y) solid‐solution nanoparticles with nominal atomic Ga : Al (x:y) ratios of 1 : 6, 1 : 3, 3 : 1, and 1:0 were used to prepare silica‐supported catalysts for propane dehydrogenation (PDH). A comparison of the unsupported and silica‐supported catalysts reveals that the dispersion on silica increases the Ga‐normalized PDH rates for all catalysts, albeit with a notably lower propene selectivity for (Ga,Al)2O3(1:6)/SiO2. Fourier transform infrared (FTIR) spectroscopy allows contrasting the H2 dissociation sites in the calcined and H2‐treated (Ga,Al)2O3(x:y)/SiO2, indicating a transformation of Ga3+ surface sites with Al (mainly) and Ga atoms in the second coordination sphere (Ga(Al/Ga) sites) in the calcined (Ga,Al)2O3(1:6)/SiO2 to predominantly Ga(Ga/Si) surface sites in the H2‐treated material. The resulting sites are similarly unselective as in amorphous gallia on silica. H2 produced during the PDH reaction can cause a similar transformation as H2 pretreatment in (Ga,Al)2O3(1:6)/SiO2, rapidly resulting in a notably lowered selectivity. The stable and selective Ga(Al/Ga) surface sites in (Ga,Al)2O3(1:3)/SiO2 yield a Ga−H band at ca. 1990 cm−1 under H2 dissociation conditions while the less selective surface sites, observed for the other Ga : Al ratios, give Ga−H bands at ca. 2040 and 2060 cm−1.

Influencing the surface quality of free-standing wurtzite gallium nitride in ultra-high vacuum: Stoichiometry control by ammonia and bromine adsorption

Gallium nitride (GaN), a wide bandgap semiconductor with absorption and emission in the ultraviolet/visible range, is proposed as an alternative to metallic surfaces for assembling organic molecular structures aiming at optoelectronic applications. However, the formation of a persistent surface oxide layer in air considerably limits the use of GaN for well-defined interfaces. In this work, we have investigated, characterized and processed n-type free-standing c-plane hexagonal wurtzite GaN crystals grown by hydride vapor phase epitaxy and ammonothermal growth methods. Surface cleaning and full removal of the oxide layer on GaN surfaces could be reproducibly achieved via sputtering and annealing cycles, as evidenced by X-ray photoelectron spectroscopy and low-energy electron diffraction. Scanning tunneling microscopy, however, indicated substantial roughening of the GaN surface and the formation of unwanted Ga-rich islands and clusters. Although ammonia (NH3) and bromine (Br) treatments compensated the N/Ga atoms ratio reduced by sputtering, the surface morphology remained rough, exhibiting randomly shaped and distributed hillocks. In addition, we studied the effect of electron bombardment on the surface quality of GaN during NH3 annealing, on-surface debromination and polymerization of 1,3,5-tris(4-bromophenyl) benzene on GaN, and the removal of Ga atoms by Br atoms during the desorption.

Amorphous Ru-based metallene with monometallic atomic interfaces for electrocatalytic hydrogen evolution in anion exchange membrane electrolyzer

Amorphous metallene is a prospective catalyst due to disordered atomic arrangement and abundant defects/edges. However, challenges persist in preparing amorphous metallene with atomic interface, primarily due to thermodynamic impediment of unconventional phase and difficulty in precise controlling of atomic interface. Here, we synthesized a new class of amorphous RuGa metallene (A-RuGa metallene) with abundant atomic interface by introducing trace atomic-dispersed Ga. The atomic interface between Ga-coordinated Ru and Ru0 achieves monometallic synergism during alkaline hydrogen evolution reaction. The turnover frequency value of A-RuGa0.06 metallene reaches 67 s−1 at −0.1 V vs. RHE. Meanwhile, the mass activity of A-RuGa0.06 metallene in anion exchange membrane electrolyzer reaches 5.2 A mgRu−1 at 2.0 V, firstly surpassing commercial Pt/C (1.0 A mgPt−1). The trace atomic dispersed Ga could change the local valence state of monometallic Ru, thus promoting water adsorption and dissociation, optimizing H* adsorption and accelerating H* transport at the atomic level.

[formula omitted] magnetism engineering in the low-buckled hexagonal SiS monolayer: A first-principles study

In this work, vacancy- and doped-induced magnetism engineering is investigated to functionalize the non-magnetic low-buckled hexagonal silicon sulfide (SiS) monolayer. This monolayer is an indirect gap semiconductor two-dimensional (2D) material with an energy gap of 2.20(3.02) eV obtained from the PBE(HSE06)-based calculations. Creating a single Si vacancy leads to a significant magnetization of SiS monolayer with the feature-rich half-metallic nature. Herein, a total magnetic moment of 1.89 μB is obtained and magnetic properties are produced mainly by S and Si atoms closest to the defect site. In contrast, single S vacancy preserves the non-magnetic nature inducing a band gap reduction of the order of 26.36%. n-type doping with P atom metalizes the monolayer, meanwhile As impurity leads to the emergence of the half-metallicity with a total magnetic moment of 1.00 μB. Similarly, this value is also obtained by p-doping using P and As atoms as dopants, where the diluted magnetic semiconductor nature is obtained. Moreover, doping with IA- (Na and K) and IIIA-group (Al and Ga) atoms is also proposed to engineer the magnetism in SiS monolayer. It is found that these impurities induce either half-metallic or diluted magnetic semiconductor behaviors with total magnetic moment between 0.99 and 1.00 μB. The electronic and magnetic properties are regulated mainly by the interactions between impurities and their neighbor S atoms, which modify the charge distribution in their outermost orbitals. In addition, the Bader charge analysis asserts that dopant atoms gain charge from the host monolayer when substituting S atom, meanwhile they act as charge loser — transferring charge to the host monolayer when doping at Si sublattice. The presented results may suggest efficient approaches to properly engineer SiS monolayer electronic and magnetic properties, making new 2D candidates for spintronic applications.

Atomically precise inorganic helices with a programmable irrational twist.

Helicity in solids often arises from the precise ordering of cooperative intra- and intermolecular interactions unique to natural, organic or molecular systems. This exclusivity limited the realization of helicity and its ensuing properties in dense inorganic solids. Here we report that Ga atoms in GaSeI, a representative III-VI-VII one-dimensional (1D) van der Waals crystal, manifest the rare Boerdijk-Coxeter helix motif. This motif is a non-repeating geometric pattern characterized by 1D face-sharing tetrahedra whose adjacent vertices are rotated by an irrational angle. Using InSeI and GaSeI, we show that the modularity of 1D van der Waals lattices accommodates the systematic twisting of a periodic tetrahelix with a 41 screw axis in InSeI to an infinitely extending Boerdijk-Coxeter helix in GaSeI. GaSeI crystals are non-centrosymmetric, optically active and exfoliable to a single chain. These results present a materials platform towards understanding the origin and physical manifestation of aperiodic helicity in low-dimensional solids.

Electron Bridge Effect Induced by Oxygen‐Bridged Ga on PdMo Bimetallene Nanoribbons for Boosting Electrocatalytic Alkynol Semihydrogenation

AbstractThe utilization of green hydrogen sources in H2O for alkynols electrocatalytic semihydrogenation reaction (ESHR) at ambient temperature provides a promising pathway toward the sustainable conversion of alkynols. However, it is still a great challenge to construct specific interfacial structure to adjust the electronic structure of Pd for the purpose of altering the strong adsorption of Pd with active hydrogen to enhance the production of alkenols. Here, the atomically dispersed GaOx‐PdMo bimetallene nanoribbons (GaOx‐PdMo BNRs) via oxygen bridging Ga atoms is designed to the surface of PdMo BNRs for 2‐methyl‐3‐butyn‐2‐ol (MBY) ESHR to the synthesis of 2‐methyl‐3‐buten‐2‐ol (MBE). The GaOx‐PdMo BNRs achieve the excellent MBE selectivity (≈97.4%), Faraday efficiency (≈96.1%), and maintain long‐term stability. Density functional theory demonstrates that the top electron‐enriched Ga atoms and the bottom electron‐deficient Pd atoms construct a “pyramidal” interface via the oxygen bridge. The unique surface can effectively activate H2O and weaken interaction between catalyst and MBE, thus promoting MBE generation. Moreover, the electron bridge effect between Ga‐O‐PdMo can induce p‐d orbital hybridization to achieve lower the d‐band center of surface Pd thus modulating the reactants adsorption. This work provides a strategy to improve ESHR performance by electron bridge effect to modulate interfacial electron distribution.

Liquid Metal Alloys Enable Efficient Formate Electrosynthesis

AbstractLiquid metals are an interesting class of materials with the unique combination of metallic nature and liquid fluidity, and have recently been explored in many emerging fields. Their potential applications in catalysis, unfortunately, remain largely untapped. Herein, Ga‐mediated liquid metal alloying as an effective strategy is demonstrated to prepare functional alloys for catalysis. The alloying is carried out by dissolving indium or tin pellets in liquid gallium at room temperature or assisted by gentle heating, giving rise to binary Ga1−xInx and Ga1−xSnx liquid metal alloys with tunable chemical compositions. When further subjected to ultrasonication in water, they are ruptured into nanosized particles with liquid metal cores and thin surface oxide shells. Electrochemical measurements reveal that the liquid metal alloying significantly promotes electrocatalytic CO2 reduction to formate. Taking Ga0.75In0.25 as an example, its formate Faradaic efficiency is enhanced by 10%–20% compared to those of Ga and In, and its formate partial current density is 4–6 times larger than those of Ga and In. This enhancement is rationalized via computational simulations showing that the surrounding of In active sites with Ga atoms deactivates the undesirable reaction pathways to CO or H2, and facilitates selective formate electrosynthesis.

Dilution of helical antiferromagnetic matrix of CaMn7O12 under nonmagnetic Ga[formula omitted] doping

The work reports dilution studies on antiferromagnetic CaMn7O12. Introduction of nonmagnetic ion in an antiferromagnetic matrix changes the magnetic properties in an interesting way. The study becomes significant due to the fact that remarkable increase in magnetization is observed as a result of substitution of a few of the magnetic Mn ions with the nonmagnetic Ga ion. For 5% doping of Ga, the magnetization value becomes nearly thrice of the un-doped CaMn7O12. A sequential decrease in antiferromagnetic ordering transition temperature is also observed with increasing Ga percentage in the parent compound. The solid solubility limit of Ga in the matrix is found to be nearly 5%, above which it start showing impurity peaks. Experimental results are well complemented with the Density functional theory (DFT) based calculations. Theoretical calculations are carried out on (CaMn7O12)3 unit cell with one Ga atom doped at different Mn sites resulting around 5% doping concentration. Besides identifying the most favourable doping site for Ga, results indicate a reduction of bulk band gap and significant increase in magnetization, both of which are in agreement with the experimental results.

Diffusion of Co and Ga in α-Ti

The diffusion of Co and Ga atoms in α-Ti has been studied using the projector augmented-wave method in combination with the transition state theory. The formation energies of the interstitial and substitutional defects and the corresponding migration and activation energies along two crystallographic directions within the interstitial and vacancy diffusion mechanisms have been calculated. It has been shown that the energetically preferred interstice for the incorporation of both impurities is crowdion. In the case of Co, the formation energy of this defect is only 0.7 eV higher than that of the substitutional defect, while for Ga this difference reaches 2.6 eV. Using the Landman method and the eight-frequency model, the diffusion coefficients of Co and Ga have been calculated within both interstitial and vacancy mechanisms. It has been shown that Co diffusion occurs faster through the interstitials, while Ga diffuses within the vacancy mechanism. The migration and activation energies as well as diffusion coefficients and their anisotropy obtained in these cases are consistent with experimental data.

Theoretical investigation of CO2 hydrogenation to methanol catalyzed on Pd-Ga bimetallic catalysts: Insights into the effects of Ga in different coordination environments

Methanol is easy to store compared to other gaseous hydrogenation products. Moreover, it can be further converted to other advanced hydrocarbons, so the conversion of CO2 to methanol (CTM) is a promising reaction. PdGa bimetallic catalysts are candidate catalysts for CTM conversion, which can promote H spillover to the active site and react with adsorbed CO2. However, the role of Ga atom in PdGa bimetallic catalysts and the underlying mechanism of CTM are still unclear at the molecular level. In this work, Ga atom with different coordination environments CN3, CN4 and CN5 were obtained on the Pd(111), and three reaction mechanisms of CTM on different catalysts are systematic investigated. Changes in the coordination environments of the Ga atom affected the adsorption configurations of HCOOH*, HCO*, and H2CO*, among others. Three catalysts have similar superior pathways, and the order of CO2 reactivity is CN4 > CN3 > CN5. The PdGa bimetallic catalysts containing 4-coordinated Ga atom are proposed to be the ideal catalysts. We hope that the conclusions obtained can help understand the reasons for the outstanding reactivity and selectivity of CTM on PdGa bimetallic catalysts at the molecular level, and can provide some guidance for the design and development of high-performance bimetallic catalysts.