Changes In Electronic Structure Research Articles

How Nature Makes O2: an Electronic Level Mechanism for Water Oxidation in Photosynthesis.

In this paper, we combine broken symmetry density functional calculations and electron paramagnetic resonance analysis to obtain the electronic structure of the penultimate S3 state of nature’s water-oxidizing complex and determine the electronic pathway of O–O bond formation. Analysis of the electronic structure changes along the reaction path shows that two spin crossovers, facilitated by the geometry and magnetism of the water-oxidizing complex, are used to provide a unique low-energy pathway. The pathway is facilitated via the formation and stabilization of the [O2]3– ion. This ion is formed between ligated deprotonated substrate waters, O5 and O6, and is stabilized by antiferromagnetic interaction with the Mn ions of the complex. Combining the computational, crystallographic, and spectroscopic data, we show that an equilibrium exists between the O5 oxo and O6 hydroxo forms with an S = 3 spin state and a deprotonated O6 form containing a two-center one-electron bond in [O5O6]3– which we identify as the form detected using crystallography. This form corresponds to an S = 6 spin state which we demonstrate gives rise to a low-intensity EPR spectrum compared with the accompanying S = 3 state, making its detection via EPR difficult and overshadowed by the S = 3 form. Simulations using 70% of the S = 6 component give rise to a superior fit to the experimental W-band EPR spectral envelope compared with an S = 3 only form. Analyses of the most recent X-ray emission spectroscopy first moment changes for solution and time-resolved crystal data are also shown to support the model. The computational, crystallographic, and spectroscopic data are shown to coalesce to the same picture of a predominant S = 6 species containing the first one-electron oxidation product of two water molecules, that is, [O5O6]3–. Progression of this form to the two-electron-oxidized peroxo and three-electron-oxidized superoxo forms, leading eventually to the evolution of triplet O2, is proposed to be the pathway nature adopts to oxidize water. The study reveals the key electronic, magnetic, and structural design features of nature’s catalyst which facilitates water oxidation to O2 under ambient conditions.

Identifying silicides via plasmon loss satellites in photoemission of the Ru-Si system

The phase and composition of several transition metal silicides are challenging to identify with common surface analysis techniques such as X-ray photoelectron spectroscopy (XPS). While silicide formation is concomitant with a distinct change in electronic structure, only minute changes in the main spectral features are observed for example for the family of Ru silicides. Here, the authors combine XPS, grazing-incidence X-ray diffraction, and density functional theory calculations to demonstrate that the characteristic excitation energies of plasmons in Ru and its silicides are a sensitive and easily accessible descriptor that reflects the change in electronic structure upon the formation of specific silicides in the XPS spectra. Electron energy loss satellites are reported to shift by more than 4 eV upon the formation of Ru silicide, by 1.1 eV between RuSi and Ru2Si3 and by 1.9 eV across the measured range of silicide layers, making these changes accessible even for basic experimental equipment. In the context of literature on metal silicides and electron energy loss spectroscopy, this approach is considered promising as a general pathway to enhance the chemical sensitivity of surface spectroscopy methods.

Stress-Tuned Optical Transitions in Layered 1T-MX2 (M=Hf, Zr, Sn; X=S, Se) Crystals.

Optical measurements under externally applied stresses allow us to study the materials’ electronic structure by comparing the pressure evolution of optical peaks obtained from experiments and theoretical calculations. We examine the stress-induced changes in electronic structure for the thermodynamically stable 1T polytype of selected MX compounds (M=Hf, Zr, Sn; X=S, Se), using the density functional theory. We demonstrate that considered 1T-MX materials are semiconducting with indirect character of the band gap, irrespective to the employed pressure as predicted using modified Becke–Johnson potential. We determine energies of direct interband transitions between bands extrema and in band-nesting regions close to Fermi level. Generally, the studied transitions are optically active, exhibiting in-plane polarization of light. Finally, we quantify their energy trends under external hydrostatic, uniaxial, and biaxial stresses by determining the linear pressure coefficients. Generally, negative pressure coefficients are obtained implying the narrowing of the band gap. The semiconducting-to-metal transition are predicted under hydrostatic pressure. We discuss these trends in terms of orbital composition of involved electronic bands. In addition, we demonstrate that the measured pressure coefficients of HfS and HfSe absorption edges are in perfect agreement with our predictions. Comprehensive and easy-to-interpret tables containing the optical features are provided to form the basis for assignation of optical peaks in future measurements.

Cerium-Doped CoMn2O4 Spinels as Highly Efficient Bifunctional Electrocatalysts for ORR/OER Reactions

Low-cost and highly efficient electrocatalysts for oxygen reactions are highly important for oxygen-related energy storage/conversion devices (e.g., solar fuels, fuel cells, and rechargeable metal-air batteries). In this work, a range of compositionally-tuned cerium-doped CoMn2O4 (Ce-CMO-X) spinels were prepared via oxidizing precipitation and subsequent crystallization method and evaluated as electrocatalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). The Ce modification into the CMO spinels lead to the changes of surface electronic structure. And Ce-CMO-X catalysts display better electrochemical performance than that of pristine CMO spinel. Among them, Ce-CMO-18% shows the best activity. The Ce-CMO-18% processes a higher ratio of Co3+/Co2+, Mn4+/Mn3+, which is beneficial to ORR performance, while the higher content of oxygen vacancies in Ce-CMO-18% make for better OER performance. Thus, the Ce-doped CMO spinels are potential candidates as bifunctional electrocatalysts for both ORR and OER in alkaline environments. Then, the hybrid Ce-CMO-18%/MWCNTs catalyst was also synthesized, which shows further enhanced ORR and OER activities. It displays an ORR onset potential of 0.93 V and potential of 0.84 V at density of 3 mA cm−2 (at 1600 rpm), which is comparable to commercial Pt/C. The OER onset potential and potential at a current density 10 mA cm-2 are 183 mV and 341 mV. The superior electrical conductivity and oxygen functional groups at the surface of MWCNTs can facilitate the interaction between metal oxides and carbon, which promoted the OER and ORR performances significantly.

Theoretical investigation on defect induced changes in electronic structure and magnetism of Eu-doped In2S3

Using density functional theory calculations, the effects of various point defects, including indium vacancy (VIn) and europium doping (EuIn), on the crystal structure, electronic structure and magnetic properties of Eu-doped In2S3 have been investigated. The magnetic origin of the system, especially the contribution of each atomic orbit, is analyzed through the state density of spin polarization. The total magnetic moment of EuIn, VIn and EuIn + VIn systems are 0.267, 1.900 and 2.063 μB, respectively. Our results show that the introduction of Eu doping and In vacancy defects induce impurity energy levels. This impurity band is mainly formed by Eu-4f orbitals, which are also spin polarised and hybridised with S-3p orbitals. The calculated defect formation energies of EuIn, VIn and EuIn + VIn systems are −12.30, 1.67 and −4.05 eV, respectively. This work provides theoretical guidance for designing unique spintronic materials, which can promote the development of spintronic applications.

The effect of vanadium substitution on the structural and magnetic properties of (Fe[formula omitted]V[formula omitted])[formula omitted]Ga[formula omitted

Fe3Ga4 displays a complex magnetic phase diagram that is sensitive and tunable with both electronic and crystallographic structure changes. In order to explore this tunability, vanadium-doped (Fe1−xVx)3Ga4 has been synthesized and characterized. High-resolution synchrotron X-ray diffraction and Rietveld refinement show that samples up to 20% V-doping remain isostructural to Fe3Ga4 and display a linear increase in unit cell volume as doping is increased. Magnetic measurements reveal a suppression of the antiferromagnetic helical spin-density wave (SDW) with V-doping, revealed by changes in both the low-temperature ferromagnetic–antiferromagnetic (FM–AFM) transition (T1) and high-temperature AFM–FM transition (T2). At 7.5% V-doping, the metamagnetic behavior of the helical AFM SDW phase is no longer observed. These results offer an avenue to effective tuning of the magnetic order in Fe3Ga4 for devices, as well as increased understanding of the magnetism in this system.

Cu Catalysts Doped with a Heteroatom into the Subsurface: Unraveling the Role of Subsurface Chemistry in Tuning the Catalytic Performance of C2H2 Selective Hydrogenation.

Heteroatoms doped into the subsurface of transition metals play a vital role in heterogeneous catalysis via either expressing surface structures or even directly participating in the reaction. Herein, DFT calculations and microkinetic modeling are implemented to examine C2H2 selective hydrogenation over heteroatom (H, B, C, N, or P)-doped Cu(111) and Cu(211) subsurfaces, which are compared with pure Cu(111) and Cu(211) to unravel the role of subsurface chemistry in tuning the surface structure and further regulating catalytic performance. Our results indicate that the catalytic performance toward C2H2 selective hydrogenation is closely related to the type of doped subsurface heteroatom and the Cu surface coordination environment, which can be attributed to the simultaneous change of Cu surface geometric and electronic structures. Catalytic performance improvement over the heteroatom-doped Cu(111) is generally better than that over the doped Cu(211); especially, B- or N-doped Cu(111) has excellent C2H4 activity and selectivity and greatly inhibits green oil. For the heteroatom-doped Cu(211), better performance is only obtained on P-Cu(211), which is still lower than the B- and N-doped Cu(111). The subsurface heteroatom doping should focus on high-coordination Cu(111) instead of low-coordination Cu(211). AIMD simulations verified the thermal stability of B-Cu(111) and N-Cu(111); both were screened out to be the most suitable catalysts toward C2H2 hydrogenation. This work clearly unravels the role of subsurface chemistry in heterogeneous catalysis and contributes to the rational design of high-performance metal catalysts by tuning surface structures with the heteroatom into the subsurface.

Carrier Multiplication in Transition Metal Dichalcogenides Beyond Threshold Limit.

Carrier multiplication (CM), multiexciton generation by absorbing a single photon, enables disruptive improvements in photovoltaic conversion efficiency. However, energy conservation constrains the threshold energy to at least twice bandgap (2 ). Here, a below threshold limit CM in monolayer transition metal dichalcogenides (TMDCs) is reported. Surprisingly, CM is observed with excitation energy of only 1.75 due to lattice vibrations. Electron-phonon coupling (EPC) results in significant changes in electronic structures, which favors CM. Indeed, the strongest EPC in monolayer MoS2 leads to the most efficient CM among the studied TMDCs. For practical applications, chalcogen vacancies can further lower the threshold by introducing defect states within bandgap. In particular, for monolayer WS2 , CM occurs with excitation energy as low as 1.51 . The results identify TMDCs as attractive candidate materials for efficient optoelectronic devices with the advantages of high photoconductivity and efficientCM.

Protonation and Non-Innocent Ligand Behavior in Pyranopterin Dithiolene Molybdenum Complexes.

The complex [TEA][Tp*MoIV(O)(S2BMOPP)] (1) [TEA = tetraethylammonium, Tp* = tris(3,5-dimethylpyrazolyl)hydroborate, and BMOPP = 6-(3-butynyl-2-methyl-2-ol)-2-pivaloyl pterin] is a structural analogue of the molybdenum cofactor common to all pyranopterin molybdenum enzymes because it possesses a pyranopterin-ene-1,2-dithiolate ligand (S2BMOPP) that exists primarily in the ring-closed pyrano structure as a resonance hybrid of ene-dithiolate and thione-thiolate forms. Compound 1, the protonated [Tp*MoIV(O)(S2BMOPP-H)] (1-H) and one-electron-oxidized [Tp*MoV(O)(S2BMOPP)] [1-Mo(5+)] species have been studied using a combination of electrochemistry, electronic absorption, and electron paramagnetic resonance (EPR) spectroscopy. Additional insight into the nature of these molecules has been derived from electronic structure computations. Differences in dithiolene C-S bond lengths correlate with relative contributions from both ene-dithiolate and thione-thiolate resonance structures. Upon protonation of 1 to form 1-H, large spectroscopic changes are observed with transitions assigned as Mo(xy) → pyranopterin metal-to-ligand charge transfer and dithiolene → pyranopterin intraligand charge transfer, respectively, and this underscores a dramatic change in electronic structure between 1 and 1-H. The changes in electronic structure that occur upon protonation of 1 are also reflected in a large >300 mV increase in the Mo(V/IV) redox potential for 1-H, resulting from the greater thione-thiolate resonance contribution and decreased charge donation that stabilize the Mo(IV) state in 1-H with respect to one-electron oxidation. EPR spin Hamiltonian parameters for one-electron-oxidized 1-Mo(5+) and uncyclized [Tp*MoV(O)(S2BDMPP)] [3-Mo(5+)] [BDMPP = 6-(3-butynyl-2,2-dimethyl)-2-pivaloyl pterin] are very similar to each other and to those of [Tp*MoVO(bdt)] (bdt = 1,2-ene-dithiolate). This indicates that the dithiolate form of the ligand dominates at the Mo(V) level, consistent with the demand for greater S → Mo charge donation and a corresponding increase in Mo-S covalency as the oxidation state of the metal is increased. Protonation of 1 represents a simple reaction that models how the transfer of a proton from neighboring acidic amino acid residues to the Mo cofactor at a nitrogen atom within the pyranopterin dithiolene (PDT) ligand in pyranopterin molybdenum enzymes can impact the electronic structure of the Mo-PDT unit. This work also illustrates how pyran ring-chain tautomerization drives changes in resonance contributions to the dithiolene chelate and may adjust the reduction potential of the Mo ion.

Revisiting Formal Copper(III) Complexes: Bridging Perspectives with Quasi-d 10 Configurations.

The formal Cu(III) complex [Cu(CF3)4]1- has often served as a paradigmatic example of challenging oxidation state assignment - with many reports proposing conflicting descriptions. Here we report a computational analysis of this compound, employing Energy Decomposition Analysis and Intrinsic Bond Orbital Analysis. We present a quasi-d 10 perspective of the metal centre, resulting from ambiguities in d-electron counting. The implications for describing reactions which undergo oxidation state changes, such as the formal reductive elimination from the analogous [Cu(CF3)3(CH2Ph)]1- complex (Paeth et al. J. Am. Chem. Soc. 2019, 141, 3153), are probed. Electron flow analysis finds that the changes in electronic structure may be understood as a quasi-d 10 to d 10 transition at the metal centre, rendering this process essentially redox neutral. This is reminiscent of a previously studied formal Ni(IV) complex (Steen et al., Angew. Chem. Int. Ed. 2019, 58, 13133-13139), and indicates that our description of electronic structure has implications for the understanding of elementary organometallic reaction steps.

Electronic structure analysis of copper photoredox catalysts using the quasi-restricted orbital approach.

In this computational study, the electronic structure changes along the oxidative and reductive quenching cycles of a homoleptic and a heteroleptic prototype Cu(I) photoredox catalyst, namely, [Cu(dmp)2]+ (dmp = 2,9-dimethyl-1,10-phenanthroline) and [Cu(phen)(POP)]+ (POP = bis [2-(diphenylphosphino)phenyl]ether), are scrutinized and characterized using quasi-restricted orbitals (QROs), electron density differences, and spin densities. After validating our density functional theory-based computational protocol, the equilibrium geometries and wavefunctions (using QROs and atom/fragment compositions) of the four states involved in photoredox cycle (S0, T1, Dox, and Dred) are systematically and thoroughly described. The formal ground and excited state ligand- and metal-centered redox events are substantiated by the QRO description of the open-shell triplet metal-to-ligand charge-transfer (3MLCT) (d9L-1), Dox (d9L0), and Dred (d10L-1) species and the corresponding structural changes, e.g., flattening distortion, shortening/elongation of Cu-N/Cu-P bonds, are rationalized in terms of the underlying electronic structure transformations. Among others, we reveal the molecular-scale delocalization of the ligand-centered radical in the 3MLCT (d9L-1) and Dred (d9L-1) states of homoleptic [Cu(dmp)2]+ and its localization to the redox-active phenanthroline ligand in the case of heteroleptic [Cu(phen)(POP)]+.

Terminal N2 Dissociation in [(PNN)Fe(N2 )]2 (μ-N2 ) Leads to Local Spin-State Changes and Augmented Bridging N2 Activation.

Nitrogen fixation at iron centres is a fundamental catalytic step for N2 utilisation, relevant to biological (nitrogenase) and industrial (Haber-Bosch) processes. This step is coupled with important electronic structure changes which are currently poorly understood. We show here for the first time that terminal dinitrogen dissociation from iron complexes that coordinate N2 in a terminal and bridging fashion leaves the Fe-N2 -Fe unit intact but significantly enhances the degree of N2 activation (Δν≈180 cm-1 , Raman spectroscopy) through charge redistribution. The transformation proceeds with local spin state change at the iron centre (S= →S=3 /2 ). Further dissociation of the bridging N2 can be induced under thermolytic conditions, triggering a disproportionation reaction, from which the tetrahedral (PNN)2 Fe could be isolated. This work shows that dinitrogen activation can be induced in the absence of external chemical stimuli such as reducing agents or Lewis acids.

Hybridized Ag-CuCrO2 Nanostructured Composites for Enhanced Gas Sensing

Because of the special layered structure and catalytic properties, delafossite CuCrO2 has been extensively studied and can obtain outstanding performance by noble metal coupling. In this work, the Ag-decorated CuCrO2 hybridizations have been elaborated by a thermal evaporation method. Surface morphology characterization and chemical state analysis were combined to indicate that the isolated island distribution of Ag nanoclusters and the generation of a divalent copper ion may result in an improvement in the gas response toward 100 ppm volatile organic compounds, such as formaldehyde (38.7%), methanol (56.8%), and acetone (76.3%). First-principle calculations were carried out to demonstrate the sensing mechanism of the Ag-decorated CuCrO2, where the remarkable change in geometry and electronic structure provided the active interface and noble metal catalysis effect promoting the target gas adsorption and reaction process. Therefore, in this work, we propose that the thermal evaporation can be utilized to act as a controllable modification method to construct nanostructure gas sensors, and the fundamental enhancement mechanism is useful to guide the design of efficient delafossite-based composite catalysts.

Ternary cobalt–iron–manganese layered double hydroxides with 1D/2D hierarchical nanostructure for oxygen evolution reaction and urea oxidation reaction

Developing high-efficient and stable electrocatalysts for oxygen evolution reaction (OER) is crucial for water splitting and metal-air batteries. Herein, ternary CoFe1−XMnX (0 <X < 1) layered double hydroxides (LDHs) grown on nickel form (NF) with nanosheet-nanowires (1D/2D) hierarchical nanostructure are synthesized. The introduction of Mn causes the change of crystal phase, morphology, and electronic structure of CoFe-LDH through electron transfer from Co/Fe to Mn, which provides the whole merit structural features and synergistic effect. Further experimental results exhibit that CoFe0.75Mn0.25-LDH possesses superior OER performance, which only requires overpotentials of 243 and 298 mV to reach 20 and 100 mA cm−2. The remodeling of LDHs in the OER process is also discussed to further explore the OER catalytic mechanism. In addition, CoFe0.75Mn0.25-LDH can also be utilized to the urea oxidation reaction (UOR), which requests a low potential of 1.367 V to reach 10 mA cm−2. A solar driven water splitting system is assembled and acquires the current density of 10 mA cm−2 at the low cell voltage of 1.58 V. This work offers an effective approach to boost the OER and UOR performance of CoFe-LDH based bifunctional electrocatalysts.

Ferroelectric control of band alignments and magnetic properties in the two-dimensional multiferroic VSe2/In2Se3

Our first-principles evidence shows that the two-dimensional (2D) multiferroic VSe2/In2Se3 experiences continuous change of electronic structures, i.e. with the change of the ferroelectric (FE) polarization of In2Se3, the heterostructure can possess type-I, -II, and -III band alignments. When the FE polarization points from In2Se3 to VSe2, the heterostructure has a type-III band alignment, and the charge transfer from In2Se3 into VSe2 induces half-metallicity. With reversal of the FE polarization, the heterostructure enters the type-I band alignment, and the spin-polarized current is turned off. When the In2Se3 is depolarized, the heterostructure has a type-II band alignment. In addition, influence of the FE polarization on magnetism and magnetic anisotropy energy of VSe2 was also analyzed, through which we reveal the interfacial magnetoelectric coupling effects. Our investigation about VSe2/In2Se3 predicts its wide applications in the fields of both 2D spintronics and multiferroics.

Unveiling the effect of gas treatment on the electronic structure of carbon nanotube-supported Pd catalysts for electroreduction of H2O2 and Heck reaction

This study explored the impact of gas treatments on the structures of multi-walled carbon nanotubes supported Pd (CNT-Pd) catalysts used for electrocatalytic H2O2 reduction and the Heck cross-coupling reaction. The CNT-Pd catalyst was prepared by anchoring Pd nanoparticles on thiolated CNTs. XPS was conducted to examine the surface composition and electronic structure changes of the CNT-Pd catalyst before and after gas treatment. The XPS results revealed that as-prepared CNT-Pd contains at least two different oxidation states on the surface, whereon their proportions depend on the gas used for treatment. Treatment with H2 leads to Pd(0) enrichment near the surface, while O2 treatment causes Pd(Ⅱ) enrichment of CNT-Pd. All catalysts containing both Pd(0) and Pd(Ⅱ) were active toward H2O2 reduction, and the Heck cross-coupling reaction of n-butyl acrylate and 4-iodotoluene; increased proportion of metallic Pd(0) boosted the catalytic reaction. However, the catalyst stability increased as the amount of Pd(II) increased.

Anomalous pressure-responsive emission enhancement of FCO-CzS due to molecular configuration and electronic structure changes

Studying the stimuli-responsive properties of luminescent materials is important for their applications, while the luminescent materials studied up to now usually exhibit emission quenching and red shift in photoluminescence (PL) energy upon compression. Designing luminescent material with abnormal pressure responses remains challenging. Here, we report the discovery of abnormal luminescent properties of FCO-CzS upon compression. A theoretical study on the excited state decay process has been carried out for FCO-CzS at high pressure by hybrid quantum mechanics/molecular mechanics (QM/MM). A significant emission enhancement and blue shift are observed as pressure increases up to 20 GPa. This is opposite to the pressure response behaviours reported for other luminescent materials. It is further revealed that both the unique molecular configuration and the electronic structure change contribute to the anomalous pressure-responsive emission of FCO-CzS, which reduces the non-radiative rate and increases the radiative rate, respectively. Our study provides a strategy for the design of luminescent materials with desired pressure responses.

Carbon nanotubes decorated with Pt as a viable electrocatalyst system using electrochemical atomic layer deposition

Surface limited redox replacement (SLRR) is an electrochemical deposition method designed to deposit metal thin films, typically onto other metals, that are mere monolayers in thickness, where such low dimensions allows catalyst-support interactions to affect catalyst efficiency. Here we explore the growth of Pt, using iterative Cu-mediated SLRR cycles, directly onto carbon nanotubes (CNTs) which are potentially good candidates as electrocatalyst supports due to their electrical conductivity and chemical resistance. Scanning electron microscope images showed that Pt grew as nanoparticles, and hydrogen underpotential deposition from cyclic voltammetry showed that the active surface area approached an asymptotic value around eight iterations. Catalytic activity, measured using the oxygen reduction reaction, reached a maximum at ten iterations. Both are shown to be influenced by the growth mode, but electrochemical modeling indicates that the trend in activity is also due to a change in activation energy, possibly due to changes in Pt electronic structure due to interactions with the CNTs. Durability cycling showed a greater than 85% retention of surface area for the first 10,000 cycles of accelerated stress testing but decayed steadily to about 50% after 30,000 cycles. This performance may be related to the phenomenon that limits surface area growth.

Lix(C5H5N)yFe2-zSe2: A Defect-Resilient Expanded-Lattice High-Temperature Superconductor.

Two-dimensional iron chalcogenide intercalates display a remarkable correlation of the interlayer spacing with enhancement of the superconducting critical temperature (Tc). In this work, synchrotron X-ray absorption (XAS; at the Fe and Se K-edges) and emission (XES; at the Fe Κβ) spectroscopies allow one to discuss how the important rise of Tc (∼44 K) in the molecule-intercalated Lix(C5H5N)yFe2-zSe2 relates to the electronic and local structural changes felt by the inorganic host upon doping (x). XES shows that widely separated layers of edge-sharing FeSe4 tetrahedra carry low-spin moieties, with a local Fe magnetic moment slightly reduced compared to the parent β-Fe2-zSe2. Pre-edge XAS expresses the progressively reduced mixing of metal 3d-4p states upon lithiation. Doping-mediated local lattice modifications, probed by conventional Tc optimization measures (cf. the anion height and FeSe4 tetrahedra regularity), become less relevant when layers are spaced far away. On the basis of extended X-ray absorption fine structure, such distortions are compensated by a softer Fe network that relates to Fe-site vacancies, alleviating electron-lattice correlations and superconductivity. Density functional theory (DFT) guided modification of the isolated Fe2-zSe2 (z, vacant sites) planes, resembling the host layers, identify that Fe-site deficiency occurs at low energy cost, giving rise to stretched Fe sheets, in accordance with experiments. The robust high-Tc in Lix(C5H5N)yFe2-zSe2, arises from the interplay of electron-donating spacers and the iron selenide layer's tolerance to defect chemistry, a tool to favorably tune its Fermi surface properties.

Influence of Vacancy on Structural Stability, Mechanical Properties and Electronic Structures of a Ti5Sn3 Compound from First-Principles Calculations

Titanium alloy is widely used in biomedical materials. Ti-Sn alloy is a new type β titanium alloy with no toxicity. In this paper, the mechanical and electronic properties of Ti5Sn3 with vacancy defects have been studied by using first-principles method. The vacancy formation energy, vacancy formation enthalpy, elastic constant, elastic modulus, hardness and electronic structure of perfect Ti5Sn3 and Ti5Sn3 with different vacancies were also calculated and discussed. The results show that Ti5Sn3 is more likely to form vacancies at VTi2. In addition, the bulk deformation resistance of Ti5Sn3 is weakened by the vacancy, and the shear resistance, stiffness and hardness of Ti5Sn3 are increased by the Ti vacancy, but the brittleness of Ti5Sn3 is increased. On the contrary, the presence of Sn vacancy decreases the shear resistance, stiffness and hardness of Ti5Sn3, and increases the toughness of Ti5Sn3. By analyzing the change of electronic structure, it is found that removing the Ti atom at the VTi2 position can improve the interaction between atoms, while Sn vacancy can weaken the interaction.