Lattice Positions Research Articles

Investigation of the effect of scandium concentration in the oxide composition Y<sub>2</sub>O<sub>3</sub>–Sc<sub>2</sub>O<sub>3</sub>–Al<sub>2</sub>O<sub>3</sub>–Er<sub>2</sub>O<sub>3</sub> on the thermophysical properties of optical ceramics

The influence of the concentration and position of scandium cations on the thermophysical characteristics of optical ceramics based on a solid solution of Y2O3–Er2O3–Sc2O3–Al2O3 oxides with a garnet structure has been studied. It is established that an increase in the total concentration of scandium leads to a decrease in the thermal conductivity coefficient in ceramics. The dependences of the thermal conductivity coefficient on the concentration and position of scandium cations in the garnet lattice are obtained. As a result the decrease in thermal conductivity of ceramics based on yttrium-erbium-scandium-aluminum garnet is due to structural disordering associated with partial substitution of cations in six- and eight-coordinate positions in the garnet lattice.

Preparation of Y–TiO2@MIL-53(Fe) and performance study of photocatalytic degradation of tetracycline

Y–TiO2@MIL-53(Fe) photocatalyst composites were synthesized by a facile solvothermal method and their photocatalytic activity were assessed by photodegradation of tetracycline (TC) under visible light irradiation. Comprehensive material characterization, including XRD, XPS, BET, UV–Vis, SEM, and PL techniques, were employed to analyze the properties of the composites. Experimental results revealed that the removal rates of TC from a 20 mg/L TC solution using Y–TiO2, MIL-53(Fe), and Y–TiO2@MIL-53(Fe) were 61.0%, 75.1%, and 93.2% respectively, under specific conditions of 500 W UV-Hg lamp irradiation, a 30 min dark reaction, a 60 min light reaction, a Ti:Fe molar ratio of 1:1, and a catalyst concentration of 0.6 g/L. The Y–TiO2 component in Y–TiO2@MIL-53(Fe) primarily existed in the form of anatase, while Fe3+ ions entered the lattice gap or replaced Ti4+ ions at certain lattice positions, effectively inhibiting the recombination of photoelectrons and holes and broadening the light absorption band. This modification positively influenced the photocatalytic ability of the composites. Quenching experiments and ESR characterization confirmed that •O2−, •OH, and h+ were the active species involved in the photocatalytic process, with •O2− being the main active species. This investigation of the photocatalytic properties of the composites provides valuable insights into the photocatalytic reaction mechanism, supporting the application and further development of photocatalytic technology.

Transmission and control of band gap vortex solitons in fractional-order diffraction honeycomb lattices

In this paper, the existence and transmission characteristics of gap vortex optical solitons in a honeycomb lattice are investigated based on the fractional nonlinear Schrödinger equation. Firstly, the band-gap structure of honeycomb lattice is obtained by the plane wave expansion method. Then the gap vortex soliton modes and their transmission properties in the fractional nonlinear Schrödinger equation with the honeycomb lattice potential are investigated by the modified squared-operator method, the split-step Fourier method and the Fourier collocation method, respectively. The results show that the transmission of gap vortex solitons is influenced by the <inline-formula><tex-math id="M3">\begin{document}$ {\mathrm{L}}\acute{{\mathrm{e}}}{\mathrm{v}}{\mathrm{y}} $\end{document}</tex-math><alternatives><graphic specific-use="online" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="9-20232005_M3.jpg"/><graphic specific-use="print" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="9-20232005_M3.png"/></alternatives></inline-formula> index and the propagation constant. The stable transmission region of gap vortex soliton can be obtained through power graphs. In the stable region, the gap vortex soliton can transmit stably without being disturbed. However, in the unstable region, the gap vortex soliton will gradually lose ring structure and evolves into a fundamental soliton with the transmission distance increasing. And the larger the <inline-formula><tex-math id="M4">\begin{document}$ {\mathrm{L}}\acute{{\mathrm{e}}}{\mathrm{v}}{\mathrm{y}} $\end{document}</tex-math><alternatives><graphic specific-use="online" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="9-20232005_M4.jpg"/><graphic specific-use="print" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="9-20232005_M4.png"/></alternatives></inline-formula> index, the longer the stable transmission distance and the lower the power of the bandgap vortex soliton. When multiple vortex solitons transmit in the lattice, the interaction between them is influenced by the lattice position and phase. Two vortex solitons that are in phase and located at adjacent lattices, are superimposed with sidelobe energy, while two vortex solitonsthat are out of phase are cancelled with sidelobe energy. These vortex solitons will gradually lose ring structure and evolve into dipole modes in the transmission process. And they are periodic rotation under the azimuth angle modulating. When two vortex solitons located at non-adjacent lattice, vortex solitons can maintain a ring-shaped structure due to the small influence of sidelobes. When three gap vortex solitons are located at non-adjacent lattices, the solitons can also maintain their ring-like structures. However, when there are more than three gap vortex solitons, the intensity distribution of vortex solitons are uneven due to the sidelobe energy superimposed. These vortex solitons will form dipole modes and rotate under the azimuthal angle modulating in the transmission process. These results can offer theoretical guidance for transmitting and controlling the gap vortex solitons in the lattice.

Advances and challenges in designing active site environments in zeolites for Brønsted acid catalysis.

Zeolites contain proton active sites in diverse void environments that stabilize the reactive intermediates and transition states formed in converting hydrocarbons and oxygenates to chemicals and energy carriers. The catalytic diversity that exists among active sites in voids of varying sizes and shapes, even within a given zeolite topology, has motivated research efforts to position and quantify active sites within distinct voids (synthesis-structure) and to link active site environment to catalytic behavior (structure-reactivity). This Feature Article describes advances and challenges in controlling the position of framework Al centers and associated protons within distinct voids during zeolite synthesis or post-synthetic modification, in identifying and quantifying distinct active site environments using characterization techniques, and in determining the influence of active site environments on catalysis. During zeolite synthesis, organic structure directing agents (SDAs) influence Al substitution at distinct lattice positions via intermolecular interactions (e.g., electrostatics, hydrogen bonding) that depend on the size, structure, and charge distribution of organic SDAs and their mobility when confined within zeolitic voids. Complementary post-synthetic strategies to alter intrapore active site distributions include the selective removal of protons by differently-sized titrants or unreactive organic residues and the selective exchange of framework heteroatoms of different reactivities, but remain limited to certain zeolite frameworks. The ability to identify and quantify active sites within distinct intrapore environments depends on the resolution with which a given characterization technique can distinguish Al T-site positions or proton environments in a given zeolite framework. For proton sites in external unconfined environments, various (post-)synthetic strategies exist to control their amounts, with quantitative methods to distinguish them from internal sites that largely depend on using stoichiometric or catalytic probes that only interact with external sites. Protons in different environments influence reactivity by preferentially stabilizing larger transition states over smaller precursor states and influence selectivity by preferentially stabilizing or destabilizing competing transition states of varying sizes that share a common precursor state. We highlight opportunities to address challenges encountered in the design of active site environments in zeolites by closely integrating precise (post-)synthetic methods, validated characterization techniques, well-defined kinetic probes, and properly calibrated theoretical models. Further advances in understanding the molecular details that underlie synthesis-structure-reactivity relationships for active site environments in zeolite catalysis can accelerate the predictive design of tailored zeolites for desired catalytic transformations.

On the structural evolutionary behavior of the CdTe/HgCdTe interface during the annealing process

In this study, secondary ion mass spectrometry and a semiconductor parameter analyzer were used to study and analyze the component interdiffusion at the CdTe/HgCdTe interface before and after annealing, as well as the effect of the formation of a gradient bandgap layer from annealing on the electrical properties of the metal–insulator-semiconductor (MIS) structure. The site-direction relationship of the contracted crystals at the CdTe/HgCdTe interface was revealed by transmission electron microscopy, and it was found that the stacking dislocations in the CdTe layer were significantly reduced after annealing and that the Hg atoms diffused into the CdTe layer through the high-temperature annealing and occupied the lattice positions of the Cd atoms, thus forming the HgCdTe structure, which formed a contracted-crystalline structure with the CdTe substrate. Molecular dynamics was applied to simulate the specific atomic diffusion behavior at different temperatures and different times during the high temperature annealing process, and the above experimental results were verified by a research note on the variation of the diffusion phenomena during the process.

Magnetic field modulation of polaron relaxation coherence effects in III-V semiconductor Gaussian quantum wells

We have theoretically investigated the effects of the cyclotron frequency of magnetic field, the initial depth and the range of the asymmetrical Gaussian confinement potential on the vibrational frequency, ground state energy, excited state energy and coherence time of polaron in III-V semiconductors by using a linear combination operator and unitary transformations methods. Through numerical calculations, we find some interesting phenomena that the polaron decreases the energy level and releases the energy of a phonon to jump. From the point of view of the energy level of the polaron, which is αℏωLO energy lower than that of the electron, and the transition of the polaron to the ground state will have a change in lattice position, and the lattice relaxation phenomenon will appear. The theoretical study of the quantum coherence effect of polaron energy levels will provide guidance for the development of optoelectronic devices and the transmission of quantum information.

Electron irradiation modified point defects of SiC nanoparticles with tunable high electromagnetic wave absorption

Silicon carbide nanoparticles (SiC nps) were modified by changing the injection amount using 1 MeV high-energy electron as radiation source. When the injection volume reaches 5ⅹ1013 cm−2, the irradiated particles produce defect structures sufficient to optimize the electromagnetic wave absorption performance. With the increase of beam amount, the value of g detected by electron paramagnetic resonance (EPR) energy spectrum moves towards the silicon suspension bond, and the macroscopic electromagnetic wave absorption peak gradually moves towards the low frequency, accompanied by the enhancement of absorption intensity and the increase of absorption bandwidth. When the injection volume reaches 3ⅹ1014 cm−2, the loss value of −62.79 dB is achieved at the optimal thickness of 2.56 mm, and the absorption frequency band covers the entire Ku band. SiC presents point defects, and carbon atoms leave the original lattice position due to electron irradiation, forming carbon vacancies, resulting in uneven charge distribution inside the material, resulting in dipoles of orientation polarization, which further affects the electromagnetic wave absorption performance. As the irradiation dosage increases, the defects become denser and purer. This leads to higher electromagnetic wave absorption intensity and a correspondingly lower optimal absorption frequency. Thus, the modification of SiC nps through irradiation achieves tunable absorbers.

Unveiling the crystallization mechanism of cadmium selenide via molecular dynamics simulation with machine-learning-based deep potential

Cadmium selenide (CdSe) is an inorganic semiconductor with unique optical and electronic properties that make it useful in various applications, including solar cells, light-emitting diodes, and biofluorescent tagging. In order to synthesize high-quality crystals and subsequently integrate them into devices, it is crucial to understand the atomic scale crystallization mechanism of CdSe. Unfortunately, such studies are still absent in the literature. To overcome this limitation, we employed an enhanced sampling-accelerated active learning approach to construct a deep neural potential with ab initio accuracy for studying the crystallization of CdSe. Our brute-force molecular dynamics simulations revealed that a spherical-like nucleus formed spontaneously and stochastically, resulting in a stacking disordered structure where the competition between hexagonal wurtzite and cubic zinc blende polymorphs is temperature-dependent. We found that pure hexagonal crystal can only be obtained approximately above 1430 K, which is 35 K below its melting temperature. Furthermore, we observed that the solidification dynamics of Cd and Se atoms were distinct due to their different diffusion coefficients. The solidification process was initiated by lower mobile Se atoms forming tetrahedral frameworks, followed by Cd atoms occupying these tetrahedral centers and settling down until the third-shell neighbor of Se atoms sited on their lattice positions. Therefore, the medium-range ordering of Se atoms governs the crystallization process of CdSe. Our findings indicate that understanding the complex dynamical process is the key to comprehending the crystallization mechanism of compounds like CdSe, and can shed lights in the synthesis of high-quality crystals.

Spin-Dependent Destructive and Constructive Quantum Interference Associated with Chirality-Induced Spin Selectivity in Single Circular Helix Molecules.

Chirality-induced spin selectivity (CISS) effect in straight helical molecules has received intense studies in past decade; however, the CISS effect in circular helical molecules (CHMs) has still rarely been explored. Here, we have constructed single CHMs having chirality-induced spin-orbit coupling (SOC) and connected by two nonmagnetic leads and successfully gained the required conditions for CISS effect occurring in CHMs for the first time. Our results uncover that only when the CHMs form a closed loop and when the lattice positions are coupled asymmetrically with both leads does the CISS effect occur. More importantly, the CISS-associated spin-dependent destructive and constructive quantum interference (QI) together with their phase transition appears in CHMs. The combination of CISS effect and spin-dependent QI phenomena opens up a new door to understand the underlying physics of the CISS effect in helical molecules.

Synthesis and study of luminescence properties of a deep red-emitting phosphor K2 LiAlF6 :Mn4+ for plant cultivation.

Light is the most important component in plant growth and development. This study synthesised a novel Mn4+ -doped K2 LiAlF6 red-emitting phosphor using the coprecipitation method. We observed that on addition of dopant Mn4+ ions to the host K2 LiAlF6 , its phase changed from rhombohedral to cubic due to the change in the lattice position of the atoms. When the atoms are excited at 468 nm, the K2 LiAlF6 :Mn4+ phosphor exhibited a red emission band ranging from 630 to 700 nm, centred at 638 nm, which matched well with the absorption spectra of phytochrome PR. The critical quenching content of Mn4+ ions was ~3mol%. The critical distance between Mn4+ ions was determined to be 19.724 Å, and non-radiative energy transfer among the nearest-neighbour Mn4+ ions was the mechanism used for the concentration quenching effect. The Commission International de l'Eclairage (CIE) chromaticity coordinates of the K2 LiAlF6 :0.03 Mn4+ sample were (x = 0.7162, y = 0.2837). The luminescence mean decay time was calculated to be 8.29 ms. These results demonstrated the promising prospect of K2 LiAlF6 :Mn4+ as a red-emitting phosphor for application in red light-emitting diodes for plant cultivation.

Preparation and chemical stability evaluation of Ln2Zr2O7‐SrZrO3 novel composite ceramics cured simultaneously with An and 90Sr

AbstractIn response to the low separation efficiency of actinide nuclide (An) and fission product (FP) in the separation process of high‐level radioactive waste, as well as the large amount of secondary waste. A novel Ln(1‐x)SrxZrO(3.5‐0.5x) (0 ≤ x ≤1) multiphase ceramic waste form (Nd3+ simulating An3+), which can cure both An and Sr simultaneously, was in‐situ synthesized by sol‐gel spray pyrolysis method. The series of multiphase ceramics are composed of cubic pyrochlore phase Nd2Zr2O7 (NZO) and orthorhombic perovskite phase SrZrO3 (SZO), without any accompanying impurities. The two phases exhibit excellent compatibility, and their content can change regularly with the change of x. Nd and Sr occupy their most stable crystal lattice positions, with low transposition doping levels. The density of the composite ceramics is high, and the measured density is as high as 88 % of the theoretical density. The above experimental results confirm that the new multiphase ceramics can cure An and Sr simultaneously and separately, showing strong adaptability to waste components and high chemical stability.

Topological acoustic waveguide with high-precision internal-mode-induced multiband

In this paper, we propose a topological acoustic waveguide which can transmit high-precision and multiband sound energy with backscattering suppression and no energy loss. It is a kind of acoustic waveguide with spatial lattice uniformity without destroying lattice position. This acoustic structure is obtained by integrating two kinds of multi-stage resonators arranged in a triangular lattice pattern in the air environment. On one hand, the introduction of internal modes greatly improves the transmission accuracy of topological acoustic waveguide compared with the Bragg scattering alone under the same overall structure size. On the other hand, it greatly improves the utilization rate of the internal space of the structure and makes full use of the multi-modal in structure to construct more sound transmission bands. After introducing the rotational scattering mechanism, the numerical and experimental results show that up to seven high-precision acoustic transmission channels with backscattering suppression and no energy loss below 14 kHz are obtained along the sonic crystal interface with different topological states in this topological acoustic waveguide. This research paves the way for engineering applications of high-precision acoustic transmission, multi-band acoustic antennas, acoustic logic control, covert sound transmission and other multifunctional acoustic devices.

Ultraviolet and visible persistent luminescence from Sr3MgSi2O8:Pr3+

In this paper, a low dose X-ray induced long afterglow luminescent phosphor Sr3MgSi2O8:Pr3+ has been reported. The structure analysis shows the as-prepared samples possess good crystallinity and the emitting center Pr3+ is more likely to occupy the lattice position of Sr2+ due to their similar ionic radius. And under 471.1 nm excitation, Sr3MgSi2O8:Pr3+ shows bright visible lights peaked at 545.5, 617.1 and 648.6 nm, respectively, corresponding to the transitions of 3P0→3H5, 3P0→3H6 and 3P0→3F2 of Pr3+. After the X-ray irradiation, this phosphor shows strong ultraviolet C (291.7 nm), blue (493.2 nm) and red lights (617.1 nm). More important, only 5 s X-ray irradiation X-ray irradiation can easily charge Sr3MgSi2O8:Pr3+ to produce 5400 s afterglow emission. Even after 5400 s, its afterglow emissions still remain strong, which is about 20 times of the background intensity. The thermoluminescent results indicate that Sr3MgSi2O8 possesses a high absorption rate for X-rays and thus X-ray irradiation can excite the host to produce large number of electrons, Secondary electron, which would rapidly fill up the traps and thus produce excellent long afterglow luminescence. In addition, the existing suitable traps with 0.76 eV trap depth are also favorable for persistent luminescence at room temperature. Thus, Sr3MgSi2O8:Pr3+ is confirmed to be a very efficient low dose X-ray induced long afterglow luminescent phosphor.

Phase transformations in WC-Cr3C2-Ni thermal spray coatings under low, medium and high thermal input: Part 2 – DSC analysis and heat-treated coating characterisation

Conventionally, bulk WC and Cr3C2-based carbide compositions have been used independently of each other. However, recent investigations have begun to explore combining these carbides together within the same composite/hard metal coating system. This work explored the diversity of phases produced in the coatings from a 42 wt% WC-42 wt% Cr3C2–16 wt% Ni powder sprayed under “low”, “medium” and “high” thermal input conditions using high velocity oxygen-fuel (HVOF), an argon‑helium (ArHe) plasma and an argon‑hydrogen (ArH2) plasma respectively. The thermally driven solid-state transformations in the coatings were investigated as a function of carbide dissolution/decomposition, using differential scanning calorimetry (DSC). All coatings exhibited a well defined exothermic peak attributed to the transformation of the metastable supersaturated Ni-alloy and WC1-X phases in the as-sprayed coatings, into the equilibrium Ni alloy and a mix of the intermediate metastable carbide phases β-W2C and Cr3C2-Y. At higher temperatures the metastable compounds transformed to the equilibrium phases of ε-W2C and Cr3C2. A defining feature of the XRD analysis was the significant shift in lattice positions of all phases, indicating substitutional alloying. The mechanisms of phase formation are discussed.

Real-space renormalization-group treatment of quadratic chains

We have recently proposed a one-dimensional nonperiodic chain with lattice positions at 02 d, 12 d, 22 d, ... with length d a constant. The spectrum is singular-continuous, and for weak potential, the states are all extended apart from a trivial set of localized states. In this study, we obtain the exact extended-state spectrum of the quadratic chain in a nearest-neighbor tight-binding model where the quadratic modulation is in the onsite matrix elements. Then, a real-space renormalization-group method (RSRG) is used by decimation to reduce the transfer matrix for the chain into self-similar matrix products. The RSRG decimation scheme is used here to organize the calculation and facilitate numerical computation. The extended-state spectrum appears as minibands broken by numerous gaps. Previous work on quadratic chains shows that the structure factor is singular-continuous and given by a dense set of states with wavevectors with scaling exponent γ(k) = 2 as in periodic and quasi-periodic chains. The origin of extended states in this nonperiodic lattice appears to arise from a type of mechanism not yet identified in deterministic nonperiodic lattices, and is based on a hidden symmetry giving rise to an energy-dependent translational invariance of the transfer matrix.

The Effect of Exchange Interaction on Phase Transition Behavior of Magnetic Nanotubes

In this paper, the phase diagram of the Blume-Capel model under exchange interaction between lattice points in different positions in magnetic nanotube lattice is studied with effective field theory. The research shows that the interaction between nearest neighbors and the lattice field strength strongly influences the system’s three critical points and phase transition temperature. Under certain conditions, there are three critical points in the system. That is, the relationship between the crucial points is linear from the second-order phase transition to the first-order phase transition. First-order phase transition replaces second-order phase transition in the system’s phase transition. The findings demonstrate that exchange interaction significantly affects the system’s phase transition, and they offer a theoretical framework for both industrial production and experimental study.

Vertex Position Optimization for LATTICE Therapy

LATTICE radiation therapy (RT) aims to deliver 3D heterogenous dose of high peak-to-valley dose ratio (PVDR) to the tumor target, with peak dose at lattice vertices inside the target and valley dose for the rest of the target. In current clinical practice the lattice vertex positions are constant during treatment planning. This work proposes a new LATTICE plan optimization method that can optimize lattice vertex positions as plan variables, which is the first lattice vertex position optimization study to the best of our knowledge. The new LATTICE treatment planning method optimizes lattice vertex positions as well as other plan variables (e.g., photon fluences or proton spot weights), with optimization objectives for target PVDR and organs-at-risk (OAR) sparing. To satisfy mathematical differentiability, the lattice vertices are approximated in sigmoid functions. For geometric feasibility, proper geometry constraints are enforced onto the lattice vertex positions. The lattice vertex position optimization problem is solved by iterative convex relaxation method, where lattice vertex positions and photon/proton plan variables are jointly updated via the Quasi-Newton method. Both photon and proton LATTICE RT were considered, and the optimal lattice vertex positions in terms of plan objectives were found by solving all possible combinations on given discrete positions via heuristic searching based on standard IMRT/IMPT, which served as the ground truth for validating the new LATTICE method ("NEW"). That is, the plan with the smallest optimization objective ("BEST"), the plan with the median optimization objective ("MID"), and the plan with the largest optimization objective ("WORST") were selected as the reference plans to be compared with NEW. The table was for an abdomen case with the large bowel as the OAR, where the parameters are total optimization objective f, the mean valley dose of target Dvalley, the mean peak dose of target Dpeak, PVDR = Dpeak/Dvalley, and the mean dose of large bowel Dbowel. The unit of doses is Gy. The results in the table show that the new method indeed provided the optimal lattice vertex positions with the smallest optimization objective, the largest target PVDR, and the best OAR sparing. A new LATTICE treatment planning method is proposed and validated that can optimize lattice vertex positions as well as other photon or proton plan variables for improving target PVDR and OAR sparing.

Electronic and Thermal Properties of the Cation Substitution-Derived Quaternary Chalcogenide CuInSnSe4.

Quaternary chalcogenides continue to be of interest for a variety of technological applications, with physical properties stemming from their structural complexity and stoichiometric variation. In certain structure types, partial vacancies on specific lattice positions present an opportunity to investigate electrical and thermal properties in light of these lattice defects. In this work, we investigated the structural, thermal, and electronic properties of CuInSnSe4, a material that belongs to a relatively unexplored class of quaternary chalcogenides with a defect adamantine crystal structure. First-principles calculations together with experimental measurements revealed a chalcopyrite-like structure with inherent vacancies and characteristic s-p and p-d orbital hybridizations in the electronic structure of the material. Cation disorder and lattice anharmonicity result in very low thermal conductivity with values significantly lower than those for related compositions. This work reveals the fundamental physical properties of a previously uninvestigated quaternary chalcogenide and may aid investigations of similar as well as other quaternary chalcogenide compositions.

Electrochemical phase evolution of NiCo2S4 nanoparticles in aqueous alkaline electrolyte

Evaluating structural stability of electrode materials under electrochemical operation in the alkaline electrolyte needs to further clarify, which is closely related with the electrochemical mechanism. Herein, NiCo2S4 nanoparticles@CNT sponge was prepared as the working electrode in three-electrode test system. From the first 20th CV test procedure, specific capacitances with the range of 1034 ∼ 1344F/g show electrochemical reversibility. Intriguingly, NiCo2S4 nanoparticles have not only stacked into nanosheets, and but also separated from the surface of the CNT sponge. Spinel NiCo2S4 nanoparticles have first partially cracked into the metastable derivative phases of Ni(Co)OOH, Ni(OH)2, and then quickly converted into the mixed hexagonal NiOOH and cubic Co3S4. S atoms disengage from the lattice positions of spinel NiCo2S4 nanoparticles, which depicts the irreversible electrochemical reaction occurring during electrochemical operation process.

Tailoring doping locations and types for high‐performance CuFeO2‐based photocatalysts

AbstractDoping engineering has been recognized as an effective strategy for improving the solar‐to‐hydrogen conversion efficiency of delafossite CuFeO2‐based photocatalysts. However, a comprehensive and systematic study on the doping effect in CuFeO2 is still needed to establish a universal law. To address this, we utilized density functional theory calculations to scrutinize the doping effects of various dopants at different lattice positions. Our findings revealed that Mn replacing Fe and N replacing O are the most readily achievable doping methods under oxygen‐rich and oxygen‐poor conditions, respectively, with a maximum doping concentration of 1020 cm−3 achievable at 900 K. Interestingly, we found that doping with N for O, F for O, and Ni for Cu generates impurity levels capable of capturing photogenerated holes at the top of the valence band, while Zn for Cu and Co for Fe engender impurity levels capable of capturing photogenerated electrons at the bottom of the conduction band, thereby facilitating the separation of photogenerated electron–hole pairs. However, it is worth highlighting that Mn replacing Fe results in impurity levels forming in the middle of the bandgap, acting as a recombination center for photogenerated electron–hole pairs. Furthermore, we discovered that Mg replacing Cu or Fe serves as an example of heterovalent doping capable of promoting the solar‐to‐hydrogen conversion efficiency of CuFeO2. In isovalent doping, dopants with more valence electrons than Cu, dopants with the same valence electron as Fe, and dopants with less valence electron than O can enhance the solar‐to‐hydrogen conversion efficiency of CuFeO2. Overall, this study provides a systematic analysis of the doping effects on CuFeO2‐based photocatalysts and can be applied to doping engineering of ABO2‐type delafossite photocatalytic materials.