Doping Sites Research Articles

Analysis of the magnetic and optical properties of (Fe, V)-co-doped 3C–SiC using first-principles calculations

The electronic structure and the magnetic and optical properties of a 3C–SiC system co-doped with Fe and V were systematically investigated by first-principles calculations. The origin and formation mechanism of the system's magnetism were elucidated by our analyzing the density of states of each electron orbital and calculating the magnetic moments contributed by each element. The most stable doped structure was determined by our calculating the formation energy of the system at ten different doping sites. The (5, 7) doping configuration demonstrated the greatest system stability and was used to calculate the electron spin density and optical properties. Our results showed that the co-doped 3C–SiC system exhibits better optical absorption throughout the infrared and visible regions, indicating that co-doping with Fe and V is an effective approach to improve the properties of 3C–SiC materials. We found that doping introduces magnetism to the system, generates spin polarization, and increases electrical conductivity. Furthermore, the co-doped system combines the electrical properties of semiconductors and the magnetic properties of magnets, providing a promising avenue for developing new semiconductor technology and electronic devices.

X-ray Absorption Fine Structural Study of Atomic Structures and Chemical States of Dopants in 4H-SiC(0001)

The atomic structures and chemical states of active and inactive dopant sites in n-type and p-type 4H-SiC(0001) substrates have been investigated by X-ray absorption near edge structure (XANES) and photoelectron spectroscopy (PES). In N atom-doped n-type 4H-SiC(0001), the PES results indicated that a N–C species was formed near the surface. XANES simulations showed that SiNx and N–C species were attributed to active and inactive dopant states, respectively. Angle-resolved XANES measurements showed that the N–C species acted as an inactive dopant site in N-doped 4H-SiC(0001). In Al-doped p-type 4H-SiC, PES analysis revealed that a single chemical state was present at the Al-doped 4H-SiC. The simulated XANES spectra showed that the Si site in 4H-SiC(0001) was replaced by an Al dopant atom, which was the active dopant site. Furthermore, relaxation of the local structure around the Al dopant in Al-doped 4H-SiC(0001) was observed due to bond stretching.

The mechanism of B, N co-doping for enhancing graphene catalytic performance: CO oxidation and O2 dissociation as model reactions

Carbon-based metal-free catalysts are becoming increasingly attractive for the low cost and environmental friendliness. With one more valence electron than C, N doping has been extensively studied for the preparation feasibility. While the main group element B is comparable to transition metals in many reactions for co-existence of lone pair electrons and vacant orbitals. The synergistic effect of co-doping B and N has been explored both experimentally and theoretically. However, the in-depth understanding of the structure–property relationships of B, N co-doping in carbon materials remains to be uncovered. Herein, through extensive density functional theory (DFT) calculations, the doping sites (meta vs ortho) and number of N atoms around B on the synergetic promotion for O2 activation was investigated. Our results reveal that ortho-N captured more electrons from B compared with meta-N. Moreover, O2 activation effect is directly related to the energy level of empty sp3 orbital of B. Subsequently, O2 dissociation and CO oxidation were used as probe reactions to evaluate the catalytic performance of all B, N co-doped graphene structures. It is found that the introduced N atoms, especially meta-N creates another electrophilic center to accommodate the dissociated O atom, thus O2 dissociation process was promoted kinetically. Besides, CO oxidation proceeds easily on meta- and meta, ortho-N co-doped structures, while the strong interaction between O2 and ortho-N doped substrates hampers the reaction, which perfectly obeys the Sabatier Principle. This work not only uncovers the synergetic effect of BN co-doping in carbon-based materials, but also shed new light on developing metal-free catalysts.

Comparative analysis of the substitutional and interstitial Li-, Na-doped, and Li∖Na-Codoped Cu2O via density functional calculations

A comprehensive comparative study utilizing HSE06 and GGA density functional calculations was conducted to investigate the impact of Li and Na doping, as well as their co-doping, on the physical properties of cuprous oxide (Cu2O). This study examined three possible structures, including substitution of Li, Na, and Li/Na for Cu, and interstitial Li, Na, and Li/Na in both tetrahedral and octahedral sites. The results of the study revealed that the introduction of alkaline atoms leads to structural changes in Cu2O, and the degree of lattice parameter extension or compression varies across different doping sites. Additionally, the study provided an estimation of the enthalpies of formation for pure and doped-Cu2O, which is useful in understanding the stability of the systems. Notably, the study found that Li, Na, and Li/Na-doped-Cu2O were more readily formed in substitutional sites rather than in interstitial sites. The findings also indicate that substitutional doping and co-doping exhibit a large band gap while maintaining the properties of a p-type semiconductor, while interstitial doping and co-doping of Cu2O led to significant absorption enhancement and n-type conductivity characteristics. These results provide new insights into the structural and electronic properties of Cu2O, with the findings suggesting that interstitial doping of Li and Na could be a promising approach for improving the absorption of visible light in Cu2O-based solar cells, thus contributing to the development of more efficient and cost-effective photovoltaic devices.

Tailoring Curie temperature and dielectric properties by changing the doping sites of Y ions in (Ba, Ca)(Zr, Ti)O3 ceramics

Tailoring Curie temperature and dielectric properties by changing the doping sites of Y ions in (Ba, Ca)(Zr, Ti)O3 ceramics

First-principles calculations of electronic and optical properties of Ce3+-activated phosphors toward evaluating valence stability of Eu ions

The valence stability of activator ions with multiple stable valence states has always been a major concern in the field of luminescent materials. Here we present a computational protocol that is able to predict the valence stability of the europium (Eu) ion in its activated phosphors, in terms of the energy difference between the ground-state level of Eu2+ and the Fermi level of the host. The protocol is based on hybrid density functional theory (DFT) and wavefunction-based multiconfigurational ab initio calculations of the dopant Ce3+, in conjunction with the established relationship between energy levels of Ce3+ and Eu2+. The predictions are in good agreements with experimental findings. It is demonstrated that across the study set consisting of five borate-containing phosphors, the valence stability of the dopant Eu2+ is positively correlated with the host band gap, and this positive correlation is more significant than the negative correlation with the energy level of Eu2+ within the host band gap. Microscopic analysis reveals that a strong bonding of electrons within the anion groups together with a large dopant site is beneficial for the reduction of Eu3+ into Eu2+. The influence of hybrid DFT functional on the predicted valence stability of a given compound was found be negligible due to cancellation of changes in the host band gap and the Eu2+ ground level. This study clarifies the reasons for the stabilization of Eu2+ in phosphors synthesized in air at high temperature and is expected to help to screen out the host compounds that could stabilize Eu2+ activators for diverse optical applications.

Stabilizing sulfur doped manganese oxide active sites with phosphorus doped hierarchical nested square carbon for efficient asymmetric supercapacitor

The introduction of heteroatom species into hollow carbon lattice networks (HCLN) and metallic oxides have been exploited as an effective approach to enhance the performance of the electrochemical electrodes. Herein, square hierarchical P-doped porous carbon/S-doped manganese oxide (S-Mn5O8@PPC) is designed via a solvothermal, chemical vapor deposition and wet chemical growth method from the solid-state gas-steaming operation of zinc of square acids, offering a unique nested hierarchical and stable integrated structure. As a result, the as-fabricated S-Mn5O8@PPC and PPC demonstrated impressive electrochemical capacitance of 1819.8F g−1 and 325.1F g−1 at 1 A g−1, respectively, which both superior than the Mn5O8@PPC and porous carbon (PC, 1604.0F g−1 and 193.2F g−1). Especially, the specific capacitance of the PPC is preferred to that of most non-metallic heteroatom-doped MOFs-derived carbons. More importantly, two supercapacitor (SC) electrodes - square hierarchical P-doped porous carbon (PPC) and S-doped manganese oxide coated PPC - are further self-assembled a hybrid SC device, which possesses a wide voltage of 0–1.6 V, outstanding electrochemical capacitance of 154.8F g−1, impressive energy storage performance and a reliable capacitive stability (87.24% after 5000 cycles), apart from the ideal energy density and power density (55.1 W h kg−1 at 800.0 W kg−1). Such excellent features originate from the large specific surface area of the porous hierarchical hollow structure, the doping of heterogeneous P and S, the dispersive loading of manganese oxide, and harmonious matching of positive and negative electrodes.

Automatic knowledge acquisition from superconductivity information in literature

In this study, we developed a natural language processing model for extracting information solely from the abstracts of literature on superconducting materials, with the aim of making predictions for materials science. Using a dataset of tagged documents (annotations) on superconductivity, the DyGIE++ framework was employed for the simultaneous extraction of the named entities, relations, and events. Additionally, a model was developed for classifying the subject material in the abstracts. After training with 1,000 annotated abstracts, the model extracted information, such as the material composition, superconducting transition temperature, doping information, and process information, automatically from 48,565 abstracts registered in the Scopus database since 1937. The numbers of extracted entries concerning superconducting materials and transition temperatures were 43,944 and 24,075, respectively, i.e. equivalent to the number of entries in the existing databases. Machine learning models were constructed to predict physical and chemical properties. For example, the superconducting transition temperatures were predicted for compositions, with a mean absolute error of 15 K. In addition, the doping information indicated that the superconducting transition temperature was correlated with the choice of dopant and doping site.

Structural effects of nitrogen-doped titanium oxide supports on stabilization of ruthenium active species in carbon dioxide hydrogenation to formate

A single atom Ru catalyst supported on a N-doped TiO2 was investigated for the conversion of CO2 to formate by hydrogenation. N-dopant sites induced a strong binding environment to Ru single-atom catalysts (SACs), resulting in a stable and atomically isolated dispersion state of Ru SACs upon metalation. Consequently, Ru/MN-TiO2 exhibited enhanced catalytic stability, which incorporated both substitutional (Ns) and interstitial (Ni) dopant sites, retaining 42 % of its original relative activity after the fifth recycle test. In contrast, Ru/N-TiO2, which contained only Ni-dopants, showed a lower stability, retaining only 19 % of its initial activity after the fifth run, and Ru/TiO2 was fully deactivated after the third run. Density functional theory calculations revealed that the stronger binding ability of the Ns sites to the Ru species compared with that of the Ni sites and the bare surface of the TiO2 structure improved the catalytic stability during hydrogenation.

Constructing sulfur and oxygen co-doped carbon nanosheets by tailoring poly tannic acid for fast and stable potassium storage

Carbonaceous material with excellent structural stability and low cost has always been deemed focus of pursuer, nevertheless it showed the sluggish dynamics and large volume expansion as the anode materials for potassium-ion batteries (PIBs). Herein, S, O co-doped ultra-thin carbon nanosheets (S/O-CNS) with enlarged interlayer spacing was synthesized through pyrolysis poly tannic acid with a sulfur-assisted carbonization strategy. Under the unique synthesis process, sulfur acts as a dopant and intercalating agent to acquire few-layer carbon nanosheets with large interlayer spacing (0.42 nm), while oxygen was in-situ doped into the carbon lattice and provides sites for sulfur doping. With the synergistic effects of the co-doping effect and heterostructure, S/O-CNS delivers an excellent reversible capacity of 375.6 mA h g−1 at 0.1 A g−1, an impressive rate performance of 159.9 mA h g−1 even at 10 A g−1 as well as outstanding cycle stability of 198.9 mA h g−1 after 700 cycles at 1.0 A g−1. Kinetics analysis indicates that the capacitance-controlled process plays a dominant role in K+ storage. The results prove that the enlarged interlayer spacing and abundant edge defects accelerate the ion diffusion kinetics. This dual-doping strategy provides a way to design high-performance carbonaceous materials for PIBs.

Electronic structure engineering on NiSe2 micro-octahedra via nitrogen doping enabling long cycle life magnesium ion batteries

Multivalent ion batteries have attracted great attention because of their abundant reserves, low cost and high safety. Among them, magnesium ion batteries (MIBs) have been regarded as a promising alternative for large-scale energy storage device owing to its high volumetric capacities and unfavorable dendrite formation. However, the strong interaction between Mg2+ and electrolyte as well as cathode material results in very slow insertion and diffusion kinetics. Therefore, it is highly necessary to develop high-performance cathode materials compatible with electrolyte for MIBs. Herein, the electronic structure of NiSe2 micro-octahedra was modulated by nitrogen doping (N-NiSe2) through hydrothermal method followed by a pyrolysis process and this N-NiSe2 micro-octahedra was used as cathode materials for MIBs. It is worth noting that N-NiSe2 micro-octahedra shows more redox active sites and faster Mg2+ diffusion kinetics compared with NiSe2 micro-octahedra without nitrogen doping. Moreover, the density functional theory (DFT) calculations indicated that the doping of nitrogen could improve the conductivity of active materials on the one hand, facilitating Mg2+ ion diffusion kinetics, and on the other hand, nitrogen dopant sites could provide more Mg2+ adsorption sites. As a result, the N-NiSe2 micro-octahedra cathode exhibits a high reversible discharge capacity of 169 mAh g−1 at the current density of 50 mA g−1, and a good cycling stability over 500 cycles with a maintained discharge capacity of 158.5 mAh g−1. This work provides a new idea to improve the electrochemical performance of cathode materials for MIBs by the introduction of heteroatom dopant.

Circular dichroism in hard X-ray photoelectron diffraction observed by time-of-flight momentum microscopy

X-ray photoelectron diffraction (XPD) is a powerful technique that yields detailed structural information of solids and thin films that complements electronic structure measurements. Among the strongholds of XPD we can identify dopant sites, track structural phase transitions, and perform holographic reconstruction. High-resolution imaging of kll-distributions (momentum microscopy) presents a new approach to core-level photoemission. It yields full-field kx-ky XPD patterns with unprecedented acquisition speed and richness in details. Here, we show that beyond the pure diffraction information, XPD patterns exhibit pronounced circular dichroism in the angular distribution (CDAD) with asymmetries up to 80%, alongside with rapid variations on a small kll-scale (0.1 Å−1). Measurements with circularly-polarized hard X-rays (hν = 6 keV) for a number of core levels, including Si, Ge, Mo and W, prove that core-level CDAD is a general phenomenon that is independent of atomic number. The fine structure in CDAD is more pronounced compared to the corresponding intensity patterns. Additionally, they obey the same symmetry rules as found for atomic and molecular species, and valence bands. The CD is antisymmetric with respect to the mirror planes of the crystal, whose signatures are sharp zero lines. Calculations using both the Bloch-wave approach and one-step photoemission reveal the origin of the fine structure that represents the signature of Kikuchi diffraction. To disentangle the roles of photoexcitation and diffraction, XPD has been implemented into the Munich SPRKKR package to unify the one-step model of photoemission and multiple scattering theory.

Engineering 2D MoS2 for Enhanced Selectivity and Sensitivity of Selected Green House Gases (CO2, CH4 and N2O): An ab initio Study

2D MoS2 has been identified as a potential material for greenhouse gas (CO2, N2O, and CH4) sensing, however, the underlying principles are not well understood yet such knowledge may offer optimization opportunities for the development of superior devices. Using ab initio Density Functional Theory approach, selected dopants X (X= Cl, O, P, and Se) were judiciously introduced on 2D MoS2 and the response of the modified monolayer to the various greenhouse gases analyzed. The results showed that when the gas molecules are introduced within the periphery of the dopant site, the gases become adsorbed on the dopant with interactions that are characteristic of physisorption due to moderate adsorption energies. Based on the magnitude of adsorption energies, Cl, P, and O doped 2D MoS2 were found to be sensitive and selective to CO2, N2O and CH4 gas molecules respectively. Further, charge transfer analysis of CO2, and N2O adsorbed on Cl and P doped 2D MoS2 monolayer respectively, showed that these gas molecules gain electrons from the doped 2D MoS2 monolayer during adsorption, while CH4 molecule loses electrons to O doped 2D MoS2 surface. In addition, CO2, N2O, and CH4 gas molecules are desorbed from the surfaces of Cl, P, and O doped 2D MoS2 at 432 K, 438 K and 298 K respectively, thus rendering the modified monolayer re-usable detection of greenhouse gases. Cl doped 2D MoS2 monolayer showed superior performance in CO2 detection due to its fast recovery time and moderate thermal treatment temperature.Our results reveal that the competitive adsorption at the X doped 2D MoS2 surfaces between the analyte and the greenhouse gas present in the atmosphere induces a switching in surface conductance that can be related to the greenhouse gases concentration and can be detected electronically, thus disclosing the sensing mechanism and optimization route that can guide future experimental studies.

Decomposition of Ethane as a Hydrogen Rich Molecule on the Aluminum-Doped Boron Nitride Nanotube: A DFT Approach

It is predictable that hydrogen gas will be used as the common main energy supply instead of fossil fuels in the near future. Studying hydrogen-production by using hydrogen-rich materials as a source of hydrogen on metal-free catalysts may be worthwhile. We studied the adsorption of ethane, as a hydrogen-rich molecule, on the one, two and three aluminum-doped boron nitride nanotubes using density functional theory. The interactions between any possible sides of ethane and any possible sites on Al[Formula: see text]-doped BNNT were studied. The only adsorption has occurred from the carbon atom side of the ethane molecule on the doped aluminum atom site of the BNNT. After the adsorption process, the possible configurations of the intermediates and transition states to receive the decomposition reaction pathway of the ethane molecule were surveyed. The results showed that the ethane molecule was decomposed only on the two aluminum-doped BNNT to four hydrogen atoms.

First-principles calculations and Yb3+ doping effects study of garnet-type solid state electrolytes

Garnet-type solid state electrolyte Li7La3Zr2O12 (LLZO) plays a critical role in enhancing the safety of all solid-state lithium batteries, but its practical applications have been seriously limited by its poor ionic conductivity at room temperature. Elemental doping is an effective strategy to address this issue and the influence of Yb3+ doping on LLZO performance was investigated in this study. The doping site of Yb3+ in LLZO was determined by first-principles calculations based on DFT for the first time, and the results revealed that the Yb3+ doping position was La3+ site. A series of Li7La3-xYbxZr2O12 (x = 0.02, 0.04, 0.06, 0.15,0.30, LLYZO) were successfully produced by solid-state reaction route. It was found that the Yb3+ doping strategy not only enhanced the ion conductivity, but also was beneficial to inhibit the abnormal grain growth by forming LiYbO2 second phase and accelerate the sintering process. The LLYZO (x = 0.15) ceramic sintered at 1200 °C for 15 h shows a highest conductivity of 2.53× 10−4 S·cm−1, the lowest activation energy of 0.294 eV and a relative density of 90.2%.

Electronic structure alteration in MgO monolayer through alkali metal doping

We have studied the structural and electronic properties of MgO monolayer (ML) by substituting one of its Mg sites with alkali metal atoms (Li, Na, K) using DFT calculations in Quantum ESPRESSO. All the planar-doped monolayers are structurally stable shown by the computed binding energy per atom values. Formation energies suggest that Li exhibits the strongest binding with MgO ML. Doping turns the non-magnetic semiconducting MgO MLs into half-metallic magnets with magnetic moment of ∼ 1μB. The corresponding magnetic states are contributed by the valence orbitals of O atoms near the doping sites. Thus, Li, Na, K substitution introduces huge changes in electronic structure and properties of MgO ML.

Carbon nanofibers enabling manganese oxide cathode superior low temperature performance for aqueous zinc-ion batteries

Mn-based aqueous zinc-ion batteries are potential candidates for energy storage owing to the low cost, high efficiency, and safety. Nevertheless, the Jahn–Teller effect induces Mn2+ dissolution and irreversible phase changes, seriously deteriorating the cycling life. Herein, the facile construction and low temperature performance of the core–shell composites of polyimide derived nitrogen-doped carbon nanofibers and δ-MnO2 (δ-MnO2-CNFs) are reported, where ultrafine MnO2 arrays are tightly anchored on carbon nanofibers. The hybrid effect of nitrogen doping, porous structure, and abundant active sites effectively inhibits the structural damage of MnO2. The as-prepared δ-MnO2-CNFs cathode achieves a high specific capacity of 232.9 mAh g−1 and energy density of 450.7 Wh kg−1 at a current density of 100 mA g−1, and could be stably cycled for 500 cycles at a high current rate of 1 A g−1. The density functional theory calculation results show that the synergistic effect in δ-MnO2-CNFs is more conducive to the transfer of zinc ions. Furthermore, a salty ice electrolyte Zn(ClO4)2 has been used for the Zn//δ-MnO2-CNFs cell, which can work at a low temperature of −20 °C, and a stable low temperature (0 °C) cycle of 500 cycles is achieved at 1 A g−1.

Electronic Structures of Iodine‐Doped Lithium Phthalocyanine Crystals

The electronic structures and stable doping sites of iodine‐doped lithium phthalocyanine (LiPc) are investigated using a first‐principles calculation based on the density functional theory. It is revealed that the metallic conductivity of highly doped LiPcIx is due to the band originating from the doped iodine, comparing the band structures of several x. It is also revealed that the doped iodines are energetically stable when they are arranged to make a line along the stacking direction that becomes a conducting path. The results well explain the experimental results of the strange dependence of the conductivity of LiPcIx on the doping rate x. These results indicate that there is a new mechanism for the electronic transport of doped organic materials in that the dopant plays the main role, which is completely different from the traditionally accepted partial oxidation theory.

Flexible Hierarchical Co‐Doped NiS2@CNF‐CNT Electron Deficient Interlayer with Grass‐Roots Structure for Li–S Batteries

AbstractThe key means to improve the performance of lithium–sulfur batteries (LSBs) is to reduce the internal resistance by building an electronic/ionic pathway and to accelerate the conversion kinetics of lithium polysulfides (LiPSs) through modulation of interface functions. Herein, inspired by a grass root system, a flexible hierarchical CNF‐CNT (carbon nanofiber‐carbon nanotube) membrane decorated with Co‐doped NiS2nanoparticles (Co‐NiS2@CNF‐CNT) is designed as an interlayer for LSBs, in which the in situ grown CNTs (root hairs) are wound on CNF (roots). Density functional theory (DFT) calculations show that Co doping introduces electron‐deficient regions at the doping sites in NiS2, thus improving chemical adsorption and catalytic activities toward LiPSs. The cell pairs with the Co‐NiS2@CNF‐CNT interlayer exhibit a high rate performance of 951.4 mAh g−1at 3 C, a reversible capacity of 944.1 mAh g−1after 500 cycles at 0.2 C, and a prolonged cycle life of 3000 cycles at 5 C. More importantly, an areal capacity of 7.96 mAh cm−2is achieved with a sulfur loading of 9.6 mg cm−2. This work provides a strategy for enhancing the electrochemical performance of LSBs by combining 3D hierarchical conductive skeletons and electron‐deficient functional adsorption and catalysis materials.

Correlation of Electrochemical Characteristics with Structural, Optical, and Electrical Properties in Tungsten-Doped Li4Ti5O12 Anodes

Tungsten (W) doping boosts electrochemical performance of the lithium titanate (LTO) anode accredited to varied fundamental features, i.e, crystalline and electronic structures and electronic/ionic conductivities. W6+ induces partial reduction of Ti4+ ions to Ti3+ owing to increased conduction electrons/energy levels, causing a reduced band gap of LTO and increased room-temperature electronic conductivity to a maximum of 1.3 × 10–6 S cm–1 for an optimal W concentration of x ∼0.15. An improved room-temperature Li-ion conductivity/diffusivity of 6.5 × 10–8 S cm–1/1.6 × 10–12 cm2s–1 for x ∼0.15 is owed to increased lattice spacing on the substitution of W6+ at Ti4+ octahedral sites. Temperature-dependent impedance over 25–300 °C depicts increases in ionic and electronic conductivities from 10–8 to 10–4 S cm–1 and 10–8 to 10–6 S cm–1, respectively. Activation energies Ea of 0.48–0.50 eV for both undoped and doped LTOs illustrate the same conduction mechanism of Li ions through 8a-16c-8a pathways. Electrochemical characteristics improve in correlation to the type of dopant, doping concentration, substitutional site of dopant, resulting structural variations, and varying electronic/ionic conductivities and conduction mechanisms.