Hybridization Of 3d Orbitals Research Articles

Construction of medium-entropy alloys coupled Z-Scheme heterojunction and its enhanced photocatalytic performance by regulating mechanism of LSPR effect

Optimizing the local surface plasmon resonance (LSPR) effect of non-noble metals through alloying has been crucial for improving its practical application in the field of photocatalysis. Rare studies capture the detail that the change in the electronic structure of metal elements caused by alloying affects plasma carrier concentration and the local surface plasmon resonance effect. Herein, NiCuCoFe medium-entropy alloys (MEAs) nanoclusters were designed and used to modify the Bi3O4Br/CNNs Z-scheme heterojunction. The cocktail effect of MEAs causes the 3d-orbital hybridization of various metal elements, which promotes the release of charge carriers. The higher the carrier concentration, the stronger the LSPR effect of MEAs. In addition, the mechanism of three typical working pathways of the LSPR effect to improve the photocatalytic performance of heterojunction is discussed. And compared with those of Bi3O4Br, CNNs, and Bi3O4Br/CNNs, the rate constant of MEAs-Bi3O4Br/CNNs was 3.26, 11.16, and 3.17 times higher during the degradation of norfloxacin, respectively. This study provides a new strategy for understanding the mechanism of LSPR and the rational design of plasmonic coupling architectures for enhanced photocatalysis.

Novel yellowish-green single-phased spinel Mg1-xBaxAl2O4:Mn2+ phosphor(s) for color rendering white-light-emitting diodes.

For white light-rendering research activities, interpretation by using colored emitting materials is an alternative approach. But there are issues in designing the white color emitting materials. Particularly, differences in thermal and decay properties of discrete red, green, and blue emitting materials led to the quest for the search of a single-phased material, able to emit primary colors for white light generation. The current study is an effort to design a simple, single-phase, and cost-effective material with the tunable emission of primary colors by a series of Mg1-xBaxAl2O4:Mn2+ nanopowders. Doping of manganese ion (Mn2+) in the presence of the larger barium cation (Ba2+) at tetrahedral-sites of the spinel magnesium aluminate (MgAl2O4) structure led to the creation of antisite defects. Doped samples were found to have lower bandgaps compared with MgAl2O4, and hybridization of 3d-orbitals of Mn2+ with O(2p), Mg(2s)/Al(2s3p) was found to be responsible for narrowing the bandgap. The distribution of cations at various sites at random results in a variety of electronic transitions between the valance band and oxygen vacancies as well as electron traps produced the antisite defects. The suggested compositions might be used in white light applications since they have three emission bands with centers at 516 nm (green), 464 nm (blue) and 622 nm (red) at an excitation wavelength of 380 nm. A detailed discussion to analyze the effects of the larger cationic radius of Ba2+ on the lattice strain, unit cell parameters, and cell volumes using X-ray diffraction analysis is presented.

The 5d-5p-3d orbital hybridization induced by light incorporation of Cu into surface-uneven Pt3Sn intermetallic nanocubes customizes dual-intermediates adsorptions for CO-resilient methanol oxidation

Catalysts with excellent performances for methanol oxidation reaction (MOR) are supposed to equip with a weaker *CO adsorption but a stronger *OH adsorption. Herein, light incorporation of Cu is implemented into surface-uneven Pt3Sn intermetallic nanocubes to manipulate crucial CO*/OH* intermediates adsorptions for boosting MOR electrocatalysis. The generated ternary Cu0.2Pt3Sn/CNTs intermetallic preserves the uneven cubic shape of non-doped Pt3Sn/CNTs, providing a defect-rich surface structure for affording abundant available active sites. More importantly, the incorporated Cu induces a strong Pt 5d-Sn 5p-Cu 3d orbital hybridization, which upgrades the electron density of Pt but reversely downgrades that of Sn. Such delicately tailored local coordination environments of Pt and Sn result in an intrinsically attenuated CO* adsorption on Pt sites but a promoted OH* adsorption on Sn sites, remarkably diminishing the energy barrier of CO* oxidation. The elaborately customized dual-intermediates adsorptions combined with the defect-rich cubic architecture superiorities consequently contribute to highly elevated MOR performance.

Surface-strain-dependent room-temperature ferromagnetism in hexagonal MIn2S4 monolayers

The electronic occupation at 3d transition metal and crystal symmetry play a critical role in realizing spin polarization, but the weak spin exchange interaction makes it difficult to obtain room-temperature ferromagnetism, especially in two-dimensional (2D) materials. Different from traditional bulk phase with semiconducting feature, the free-standing hexagonal MIn2S4 (M = Fe, Co, Ni, Mn) monolayers are proposed to discuss the strain-dependent magnetic behavior, in which the 3d-orbital hybridization and charge transfer can be regulated by structural deformation to enforce their spin exchange interaction, finally leading to a room-temperature 2D magnetic characteristic. The calculations disclose that the structural deformation not only regulates the spin polarization feature but also leads to an electronic reconfiguration. Our findings provide a new insight into designing 2D spintronic devices by strain engineering in hexagonal MIn2S4 monolayers.

Boosted N2 Activation through 4f–2p–3d Orbital Hybridization for Efficient Nitrate Electrosynthesis

AbstractThe electrochemical N2 oxidation reaction (NOR) has emerged as a promising approach for achieving high selectivity in nitric acid (HNO3) production. However, the sluggish N2 activation process in NOR due to the high cleavage energy barrier of the N≡N bond remains a challenge. Herein, a novel orbital hybridization strategy for tuning the NOR performance through the construction of cerium (Ce) 4f–O 2p–Co 3d network in Ce‐doped Co3O4 (Ce–Co3O4) is proposed. The Ce–Co3O4 catalyst exhibits an enhanced HNO3 yield of 24.76 µg h−1 mgcat−1 and a promoted Faradaic efficiency of 31.93% in 0.1 m Na2SO4 electrolyte under ambient conditions compared to those of the pure Co3O4 (13.75 µg h−1 mgcat−1 and 23.43%). Density functional theory caculations demonstrate the strong 4f–2p–3d orbital hybridization and electron transfer in Ce–Co3O4. Moreover, a series of in situ techniques provide direct evidence of stronger adsorption peaks for Co─N bond and the key intermediate *NO formed after N2 activation on the surface of Ce–Co3O4. This work provides a promising route for the preparation of efficient NOR catalysts and sheds light on the mechanism of N2 activation through orbital hybridization.

Critical role of hydrogen for superconductivity in nickelates.

The newly discovered nickelate superconductors so far only exist in epitaxial thin films synthesized by a topotactic reaction with metal hydrides1. This method changes the nickelates from the perovskite to an infinite-layer structure by deintercalation of apical oxygens1-3. Such a chemical reaction may introduce hydrogen (H), influencing the physical properties of the end materials4-9. Unfortunately, H is insensitive to most characterization techniques and is difficult to detect because of its light weight. Here, in optimally Sr doped Nd0.8Sr0.2NiO2H epitaxial films, secondary-ion mass spectroscopy shows abundant H existing in the form of Nd0.8Sr0.2NiO2Hx (x ≅ 0.2-0.5). Zero resistivity is found within a very narrow H-doping window of 0.22 ≤ x ≤ 0.28, showing unequivocally the critical role of H in superconductivity. Resonant inelastic X-ray scattering demonstrates the existence of itinerant interstitial s (IIS) orbitals originating from apical oxygen deintercalation. Density functional theory calculations show that electronegative H- occupies the apical oxygen sites annihilating IIS orbitals, reducing the IIS-Ni 3d orbital hybridization. This leads the electronic structure of H-doped Nd0.8Sr0.2NiO2Hx to be more two-dimensional-like, which might be relevant for the observed superconductivity. We highlight that H is an important ingredient for superconductivity in epitaxial infinite-layer nickelates.

Temperature and Pressure Dependences of the Electronic and Crystal Structures of Yb4TGe8 (T = Cr, Mn, Fe, Co, and Ni) Studied by High-resolution X-ray Absorption Spectroscopy, X-ray Diffraction, and Photoelectron Spectroscopy

Temperature and pressure dependences of the electronic structure of the Kondo lattice systems of Yb4CrGe8 and Yb4MnGe8 have been investigated in detail using high-resolution x-ray absorption spectroscopy. Temperature-induced valence changes of Yb are on the order of 0.08 for Yb4MnGe8 and 0.1 for Yb4CrGe8 at the temperature range between 12 and 300 K. The c–f hybridization remains at the low temperatures where the crossover from Fermi liquid to non-Fermi liquid like behavior occurs. We also measured the x-ray absorption spectra of Yb4CrGe8 at the Cr-K and Ge-K absorption edges and found the hybridization of 3d orbitals of Cr with the Yb band at low temperatures. Photoelectron spectroscopy of Yb4TGe8 (T = Cr, Mn, Fe, Co, and Ni) showed an anomaly of the energy shift of the Yb3+ component in the valence band spectra. The Yb valence increased rapidly with pressure up to 6–7 GPa, and further increase in the pressure did not change the Yb valence significantly. The compressibility along the b axis is larger than those along the a and c axes.

Polarization-enhanced photovoltaic response and mechanisms in Ni-doped (Bi0.93Gd0.07)FeO3 ceramics for self-powered photodetector

Multiferroic toxicity-free perovskite BiFeO3-based materials reveal potentials in photoelectrical conversion, energy harvesting and photodetector. This work highlights polarization-enhanced photovoltaic (PV) effects and mechanisms in B-site Ni-doped (Bi0.93Gd0.07)FeO3 ceramics with indium tin oxide (top electrode) and Au (bottom electrode) thin films. The enhanced PV effects are attributed to the reduced bandgap, polarization-modulated Schottky barrier, increased O 2p-Fe 3d orbital hybridization, and nucleation of domain walls to improve transportation of charge carriers. Improved PV parameters of responsivity (R) ∼1.71 × 10−2 A/W, detectivity (D*) ∼9.56 × 1011 Hz1/2/W (Jones), open-circuit voltage (Voc) ∼0.65 V, and short-circuit current density (Jsc) ∼80 μA/cm2 were obtained from the ITO/ (Bi0.93Gd0.07)(Fe0.97Ni0.03)O3/ Au heterostructure after 2 kV/cm poling under 405 nm irradiation at 103 W/m2 intensity. This work demonstrates that Ni-doped (Bi0.93Gd0.07)FeO3 ceramics can be potential candidates for self-powered UV photodetector.

Enhanced Photovoltaic and Photosensing Performances in Gadolinium-Doped Bismuth Ferrite

Recent emerging developments have demonstrated that bismuth ferrite is one of the promising lead-free perovskite materials for solar-energy harvesting, photoelectrochemical conversion, and photodetector. This work reports high short-circuit photocurrent densities ~1.2×1033 µA/cm2 in p-type gadolinium (Gd)-doped BiFeO3 ceramic with n-type indium-tin-oxide under 405 nm irradiation and sunlight at 102 mW/cm2 intensity, respectively. A polarization-enhanced photosensing responsivity (R) of ~5.4×10-2 A/W and detectivity (D*) of ~1.5×1011 Jones were achieved at low 405 nm irradiation. Enhanced photovoltaic conversion via a prior electric-field poling can be attributed to the p-n junction and field-modulated Schottky barrier in conjunction with domain nucleation, ordered polar nano-regions (PNRs), and increased O 2p-Fe 3d orbital hybridization. The network of domain walls and grain boundaries serves as conduction pathways for the photo-generated charge carriers. The remarkable improvement of photocurrent in polycrystalline Gd-doped BiFeO3 opens a window for using bismuth ferrite materials in self-powered UV-visible photodetector.

Role of O 2p-Ti 3d orbital hybridization in dielectric and ferroelectric properties of barium zirconate titanate ceramics

Barium zirconate titanate (BaZryTi1-yO3) ceramics for y = 0.10, 0.15 and 0.20 were synthesized using conventional solid-state method to study the effect of O 2p-Ti 3d orbital hybridization on dielectric and ferroelectric properties. X-ray diffraction, transmission electron microscopy and Rietveld refinement show structural phase transition from tetragonal P4mm to cubic Pm3¯m with increasing Zr concentration. Dielectric permittivity and Raman spectra show enhanced relaxor behavior which is attributed to decreased O 2p-Ti 3d orbital hybridization as Zr doping increased. Lattice distortion due to decreased O 2p-Ti 3d orbital hybridization induced by Zr doping caused lattice strain mismatch contributing to enhancement of dielectric permittivity. Reduced ferroelectric instability due to decreased Ti-O covalency with increasing Zr significantly reduced Pr values. Temperature dependent P-E loops shows increased Wrec and η implying no energy dissipation and good thermal stability of BZT perovskites even at elevated temperatures which is beneficial for energy storage applications.

Origin of Energy States in the Bandgap of Zn1 –xMnxO

We report on the results of analysis of optical absorption, EPR signals under optical excitation and magnetic susceptibility of hydrothermal Zn1 –xMnxO single crystals. In the absorption spectra of polarized light at temperatures of 4.2 and 77.3 K, narrow intense a, b, c, and d lines are observed in the energy range 1.877–1.936 eV of light quanta. The spectrum of these lines differs significantly from the spectra of donor and acceptor excitons for ZnO:Co and ZnO:Ni. The intensity of allowed and forbidden EPR signals of the Mn2+(d5) ions does not change under the action of light in the impurity absorption band, while the EPR signals of uncontrollable Fe3+ (d5) ions under illumination practically disappear. New experimental results for Zn1 –xMnxO lead to the conclusion that the d5/d4 donor level of the Mn2+ ion falls into the valence band, while the bandgap of Zn1 –xMnxO contains several dangling bond hybrid (DBH) states due to hybridization of 3d orbitals of the Mn2+ ion with the p-bonds of the nearest O2– oxygen ions. Electron transitions from the DBH states to the conduction band form a broad impurity absorption band of Zn1 –xMnxO, below the edge of which the a, b, c, and d lines referred to as donor excitons [(hloc + d5)e] and emerging as a result of Coulomb interaction of a free s-electron and a hole localized on DBH states (p + d5) are observed. The detection of donor excitons [(hloc + d5)e] makes it possible to study in detail the DBH states in the bandgap, which is important for photocatalysis in the visible light range.

Composition and thermal structural evolution in Pr modified bismuth ferrite near the morphotropic phase boundary

Nanoscale domains and structural disorder are important phenomena in lead-free rare-earth-substituted bismuth ferrite in the vicinity of the morphotropic phase boundary (MPB). This work highlights substitution-driven transitions in (Bi1-xPrx)FeO3 (x = 0.05–0.25) polycrystalline ceramics from ferroelectric (FE) rhombohedral R3c to antiferroelectric (AFE) orthorhombic Pbam, then nonpolar orthorhombic Pnma phases as the system crosses over the MPB, identified by the 12{ooo}, 12(011), 14{111}, and 12{100} electron superlattice diffraction patterns. Enhanced ferromagnetic (FM) magnetizations near the MPB may result from a minor Fe4+ valence state and structural disorder. Sequential temperature-dependent phase transitions were observed and the orthorhombic Pnma phase becomes a dominant phase upon heating. The decreased O 2p–Fe 3d orbital hybridization plays a critical role for substitution-driven and thermally-activated structural transitions in the vicinity of the MPB.

Electronic Structure and Optical Absorption Spectra of C–Cr Co‐Doped Anatase TiO2 Based on First Principles

The geometrical structure, defect formation energies, electrical and optical properties of C and/or Cr doped anatase TiO2 are calculated by GGA + U method under the framework of density functional theory. The relationship between band structure and light absorption is revealed. The results show that the lattice is obviously distorted after doping, and the stability of C and Cr co‐doping is higher than just Cr doping, second only to Cr doped TiO2. The contribution of C is forming impurity energy levels, and the contribution of Cr is to reduce the band gap in the single doped system. In the co‐doped system, Cr atoms are used as donor impurities and C atoms act as acceptor impurities. The impurity energy is composed of C 2p and Cr 3d orbital hybridization, which reduces the band gap and promotes the separation of the impurity levels. C and Cr co‐doping expands the light absorption of TiO2 to the entire visible region, thereby increasing the absorption coefficient and effectively enhancing the photocatalytic efficiency.

Electronic, magnetic and transport properties of transition metal-doped holely C2N-h2D nanoribbons

A novel layered two-dimensional graphene-like material C2N-h2D with evenly distributed holes and nitrogen atoms has been synthesized via a bottom-up wet-chemical reaction [Nat. Commun. 6, 6486 (2015)]. The presence of holes provides a ground for further functionalization by doping. By performing a first-principles study, we have doped transition metals at the center of the holes of C2N-h2D nanoribbons and explored their doping effects on electronic, magnetic and transport properties. It is found that the doping can essentially regulate the electronic properties of C2N-h2D nanoribbons. The metallic zigzag ribbon is tuned into a semiconductor for Mn, Fe and Co-doped cases, but half-metal for Ni-doping. This transition is derived from the peculiar band morphology which has a big band gap between the edge state and the higher band, so when the energy of the edge state is reduced by the impurity state, the band gap falls too and crosses the Fermi level. In contrast, the pristine semiconducting armchair C2N-h2D nanoribbon is changed into metallic. Different from the zigzag case, its physical mechanism originates from the hybridization of 3d orbitals of transition metal atoms and the p orbitals of carbon and nitrogen atoms which introduces several resonant peaks at the Fermi level in the density of states. Furthermore, the magnetic moments of all doped materials are enhanced compared to the pristine structures but decrease as the atomic number of the transition metal atom increases. And the spin polarization of armchair C2N-h2D nanoribbon is increased, while that of the zigzag structure is decreased except the Ni-doped one which is completely spin-polarized suggesting great prospects in the future of spintronics and nanoelectronics.

First-principles study on half-metallic ferromagnetic properties of Zn1−x V x Se ternary alloys

The spin-polarised density functional theory along with self-consistent plane-wave pseudopotential is used to investigate the half-metallic ferromagnetic properties of ternary alloys Zn1−x V x Se. The generalized gradient approximation is used for exchange–correlation potential. The equilibrium lattice constants, bulk modulus, and its derivatives are calculated. The calculated spin-polarised energy-band structures reveal that these alloys are half-metallic for x = 0.375 and 0.50 and nearly half-metallic for other values of x. The estimated direct and indirect bandgaps may be useful for the magneto-optical absorption experiments. It is found that there is strong Zn 4s, Se 4p, and V 3d orbital hybridization in the conduction bands of both the spins, while Se 4p and V 3d orbital hybridization predominates in the valence bands of both the spins. The s, p–d, and p–d orbital hybridization reduces the local magnetic moment of V atoms and small local magnetic moments are produced on Zn and Se atoms which get coupled with V atoms in ferromagnetic and antiferromagnetic phases, respectively. The conduction and valence-band-edge splittings and exchange constants predict the ferromagnetism in these alloys. The conduction band–impurity (s and p–d) exchange interaction is more significant for ferromagnetism in these alloys than the valence band–impurity (p–d) exchange interaction.

Effect of Microwave Radiation on the Band Structure and Electronic Parameters of the Heterosystems with Fullerenes

The results of a complex study of C60/Si heterosystems are presented in this work: the crystal structure and composition of the films, internal mechanical stresses, electronic parameters of the film and the film-substrate interface, and the effect of external influences (ultraviolet irradiation, thermal annealing, gamma and microwave irradiation). The advantage of microwave treatment over others is established: the absence of fullerene decomposition, the removal of internal mechanical stresses in the heterosystem, and the improvement of its electronic parameters. Methods for remove the decomposition of C60 molecules under the influence of other treatments have been developed. To eliminate the interaction of fullerenes with oxygen, it was proposed to perform thermal annealing and UV irradiation in vacuum, and in the case of g-irradiation, apply a protective coating on the surface of the film (GeOx or SiOx). In solar cells with C6 films in the polymer matrix on Si, a significant advantage of titanium contacts in comparison with gold is established, especially after microwave treatment. Contact resistance decreased as a result of hybridization of 3d-orbitals of titanium and 2p-orbitals of fullerenes with the formation of ТіхС60 carbides and radiation-stimulated diffusion of metals, which increases the contact area.

New p- and n-type ferromagnetic semiconductors: Cr-doped BaZn2As2

We find new ferromagnetic semiconductors, Cr-doped BaZn2As2, by employing a combined method of the density functional theory and the quantum Monte Carlo simulation. Due to a narrow band gap of 0.2 eV in host BaZn2As2 and the different hybridization of 3d orbitals of Cr impurity, the impurity bound states have been induced both below the top of valence band and above the bottom of conduction band. The long-range ferromagnetic coupling between Cr impurities is obtained with both p- and n-type carriers.

Modulation of electrical mobility in Au ion irradiated titanium oxide with crystal field splitting

Electrical modulation of radio frequency (RF) sputtered TiO2−x films were investigated as a function of Au swift heavy ion irradiation dose at room temperature. The prepared TiO2−x films were irradiated with 130 MeV Au swift heavy ion in the range from 1 × 1011 to 5 × 1012 ions/cm2. As the Au ion irradiation dose increased up to 1 × 1012 ions/cm2, the electrical mobility of TiO2−x films were dramatically increased 3.07 × 102 cm2 V−1 s−1 without the change of carrier concentration. These changes in electrical properties of Au irradiated TiO2−x film, are related to the modification of electronic structure such as crystal field splitting of Ti 3d orbital hybridization and sub-band edge states below the conduction band as a function of Au swift heavy ion irradiation dose.

Magnetic and electronic properties ofCaMn2Bi2: A possible hybridization gap semiconductor

We report the magnetic and electronic properties of ${\mathrm{CaMn}}_{2}{\mathrm{Bi}}_{2}$, which has a structure based on a triangular bilayer of Mn, rather than the ${\mathrm{ThCr}}_{2}{\mathrm{Si}}_{2}$ structure commonly encountered for 122 compounds in intermetallic systems. ${\mathrm{CaMn}}_{2}{\mathrm{Bi}}_{2}$ has an antiferromagnetic ground state, with a ${\mathrm{T}}_{N}$ of 150 K, and for a 250 K temperature range above ${\mathrm{T}}_{N}$ does not exhibit Curie-Weiss behavior, indicating the presence of strong magnetic correlations at high temperatures. Resistivity measurements show that ${\mathrm{CaMn}}_{2}{\mathrm{Bi}}_{2}$ exhibits semiconducting properties at low temperatures, with an energy gap of only 62 meV, indicating it to be a very narrow band gap semiconductor. The electronic structure of ${\mathrm{CaMn}}_{2}{\mathrm{Bi}}_{2}$, examined via ab-initio electronic structure calculations, indicates that Mn 3d orbital hybridization is essential for the formation of the band gap, suggesting that ${\mathrm{CaMn}}_{2}{\mathrm{Bi}}_{2}$ may be a hybridization-gap semiconductor.

Exchange interaction mediated ferroelectricity in multiferroic MnTiO3 with anisotropic orbital hybridization and hole delocalization

We present the orbital structure of MnTiO3 with polarization dependent x-ray absorption and resonant x-ray emission spectra accompanied with electronic structure calculations. The results clearly indicate a strongly anisotropic O 2p-Mn 3d orbital hybridization whereas the Mn 3d hole state shows a highly delocalized characteristic ascribed to the 3d-4p mixing. The extended Mn 4p orbital could enhance the exchange interaction between Mn (3d)-O (2p)-Mn (3d) leading to an asymmetric charge distribution in Mn-O bonds. The delocalized characteristic of Mn 3d holes is indispensable to the mechanism of spin-dependent-metal-ligand hybridization to explain magnetically induced ferroelectricity.