Electronic Distortion Research Articles

The origin of broadband blue emission in zero-dimensional organic lead iodine perovskites: A first-principles study.

Broadband blue emission in zero-dimensional perovskites has received considerable attention, which is very important for the realization of stable blue-light emitters; however, the underlying formation mechanism remains unclear. Based on first-principles calculations, we have systematically studied the self-trapped excitons (STEs) behavior and luminescence properties in 0D-(DMA)4PbI6 perovskite. Our calculations show that there is a significant difference between the intrinsic STE luminescence mechanism (∼2.51eV) and experimental observations (∼2.70eV). In contrast, we found that the iodine vacancy (VI) is energetically accessible and exhibits a shallow charge transition level at ∼2.69eV (0/+1) above the valence band maximum, which provides the initial local well for the STEs formation. Moreover, the low electronic dimension synergistic Jahn-Teller distortion facilitates the formation of extrinsic excitons self-trapping. Further excited state electronic structure analysis and configuration coordinate diagram calculations confirmed that the broadband blue emission in 0D-(DMA)4PbI6 is the origin of VI-induced extrinsic STEs instead of intrinsic STEs. Therefore, our simulation results rationalize the experimental phenomena and provide important insights into the formation mechanism of STEs in low-dimensional perovskite systems.

Crack propagation effects on the critical temperature degradation of superconducting Nb3Sn single crystal

The irreversible degradation of Nb3Sn critical performance caused by the crack propagation brings challenges to the reliability of Nb3Sn service equipment. In this paper, the crack propagation behavior of Nb3Sn single crystal was studied by molecular dynamics method. The results show that amorphous transformation occur in Nb3Sn samples with cracks under the applied loading conditions. On the basis of these results, the electronic structures of different regions in the cracked sample are studied by first principles method. The critical temperature response in this process is analyzed in combination with our proposed trans-scale electromechanical coupling model. The physical mechanism behind the critical temperature degradation caused by the transition between the cracked surface and the amorphous zone at the crack tip is discussed. Amorphous states and the crack surface destroy the special kind of bonding in the atom chain direction, inducing the electronic band structure distortions. The density of states curve of Nb3Sn no longer exhibits the characteristic peaks near the Fermi surface observed in cubic crystalline Nb3Sn. The intrinsic relationship between the crack propagation, the electronic structure evolution driven by the local atomic rearrangements, and the irreversible critical temperature degradation of cracked Nb3Sn is revealed by the given model. The results deepen the understanding of the electromechanical coupling behavior of Nb3Sn under complex deformation.

Cross section sensitivity to perturbation strengths in distorted waves for double electron capture by alpha particles from helium targets

Computer experiments are performed on total cross sections for capture of both electrons from helium targets at 100-10000 keV. Employed are four quantum-mechanical perturbative four-body distorted wave methods (one of the first and three of the second order). The goal is to determine the cross section sensitivity to the perturbation strengths in distorted waves from the second-order methods. The perturbation strength is parametrized by the Sommerfeld factor (the quotient of the nuclear charge and the relative velocity of the colliding particles). At each fixed impact energy, the sought sensitivity is monitored by gradually modifying the nuclear charges in the Sommerfeld factors. These factors reside in the Coulomb distortions of the unperturbed channels states. The focus is on the electronic distortions through the eikonal Coulomb logarithmic phases and the full Coulomb waves. The logarithmic phases are the constituents of the compound phases for the net charges of the two heavy scattering aggregates in relative motions. A striking perturbation strength sensitivity of the obtained total cross sections is recorded.

First-principles calculation of self-interstitial atom-impurity atom interactions in ferritic steel

In this study, the interactions between self-interstitial atoms (SIA) and impurity atoms (Cu and P) in the body-centered cubic (bcc)-Fe matrix have been investigated using the first principles approach. The results show that Cu and P atoms are more prone to segregation on perpendicular and parallel surfaces containing dumbbell atoms, respectively. Next, by combining the charge density difference and considering the electronic structure and lattice distortion, the origin of the binding energy of complexes formed between SIA and impurity atoms was discussed. The results show that as the number of impurity atoms increases, the atomic bonds formed by the interactions between the impurity atoms decrease the binding energy between single impurity atoms and the matrix and reduce the strain field around them, resulting in an increase in the stability of the complexes. Comparison with previous experimental results revealed the reasons for the changes in atomic occupancy during the segregation of Cu and P atoms. The results provide insights into the behavior of impurity atoms in irradiated materials and provide a deeper understanding of the electron level of impurity atomization.

Information Placement in Notarial Registries: Issues with Evaluating the Actions of Participants

Within the framework of improving legislation, the Federal Notary Chamber has been entrusted with the responsibility of maintaining a registry of notifications regarding the pledge of movable property and the cancellation of powers of attorney executed in simple written form. It should be noted that these changes have a positive impact on civil transactions. However, there are specific questions regarding the procedure for their implementation. The main issue is that neither the notary nor the person posting the relevant information about the pledge or cancellation of powers of attorney is held responsible for the accuracy of the information, which allows for the possibility of abuse. In defining the purpose of this research, attention should be paid to the evaluation and analysis of the procedural and legal aspects of maintaining the aforementioned registries, identifying specific cases of abuse of rights by individuals posting information in the respective registries. This necessitates finding a solution to the stated problem, namely: clarifying the procedure and limits of actions for the parties involved in the relevant legal relationships in order to prevent the possibility of their misconduct. The research is based on general scientific methods of cognition and legal hermeneutics. During the analysis of current legislation and legal practices, it has been determined that in the existing reality, there is a possibility of abuse by individuals posting information in notarial registries regarding the cancellation of powers of attorney and the registry of notifications about pledges. The legislation does not provide indications of sanctions against individuals who violate the prescribed registry procedure. The presumption of notification from the moment the information is posted in the registry by an interested party, despite possible errors that compromise the accuracy of electronic search or distortions in the information, which prevent proper identification of the sought-after object, leads to violations of property rights of participants in civil transactions.

A-site heterovalency induced cationic disorder effects on the structural, electronic, and magnetic properties of double perovskite: Sr2FeMnO6

The 5 s/6 s (A-site)-3d (B-site) based double perovskites enounce multiple aspects to study the interactive effects on structural (global and local), electronic, and other physical properties of synthesized compounds. The characteristic feature of this family is the B-site cations, which have comparative ionic radii and multivalency. Here, we report a detailed analysis of the structural, electronic, and magnetic properties of Sr2FeMnO6 (SFMO) and La-substituted SrLaFeMnO6 (SLFMO). The relatively smaller radii but large valance La3+ (1.36 Å) substitution at Sr2+ (1.44 Å) sites led to adequate changes in the structural and physical properties. SLFMO crystallized in a lower crystal symmetry than SFMO, further confirmed by Raman analysis. Spectroscopic analyses showed that the Mn-valency compensates for the cationic disorder introduced by the La-substitution. These analyses also revealed that Mn and Fe preserve high spin states of their 3+ and 4+ valence states, and thus, the studied compounds also have Jahn-Teller (JT) distortion. These structural and electronic distortions affect the magnetic properties of SFMO and SLFMO. SFMO showed antiferromagnetic behavior, while SLFMO showed spin-glass-type characteristics.

First-principles calculation of lattice distortion, electronic structure, and bonding properties of GeTe-based and PbSe-based high-entropy chalcogenides

The massive amount of wasted heat energy from industry has pushed the development of thermoelectric (TE) materials that directly convert heat into electricity to a new level of concern. Recently, multicomponent alloys such as GeTe-based and PbSe-based high-entropy (HE) chalcogenides have attracted a great deal of attention due to their potential application as TE materials. The nature of the interatomic bonding, lattice distortion (LD), and the electronic structure in this class of materials is not fully understood. Herein, we report a comprehensive computational investigation of nine GeTe-based HE alloys with eight metallic elements (Ag, Pb, Sb, Bi, Cu, Cd, Mn, and Sn) with large supercells of 1080 atoms each; seven PbSe-based HE solid solutions: Pb0.99−ySb0.012SnySe1−2xTexSx (x = 0.1, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, with y = 0) with supercells of 1000 atoms each; and five Pb0.99−ySb0.012SnySe1−2xTexSx (y = 0.05, 0.1, 0.15, 0.2, 0.25 with x = 0.25) solid solutions with supercells of 1000 atoms each. All these HE models are theoretically investigated for the first time. The electronic structure, interatomic bonding, charge transfer, and lattice distortion (LD) are investigated by first-principles calculations based on density functional theory. Multicomponent HE alloys can cause a significant LD, which affects their mechanical, thermal, and TE properties. The calculations for the GeTe-based HE chalcogenides showed that they are semiconductors with a narrow bandgap, except for m8, which has a semi-metallic characteristic, and this makes them good candidates for TE applications. For most of these models, the Fermi level shifts upward and locates deeply in the conduction bands, resulting in the enhancement of the electrical conductivity (σ). The bonding properties showed that most bonds in m5 are more dispersed, indicating highest LD and lower lattice thermal conductivity. For PbSe-based HE solid solutions, the LD calculations showed that the models Pb0.99Sb0.012Se0.5Te0.25S0.25 and Pb0.89Sb0.012Sn0.1Se0.5Te0.25S0.25 have the higher LD, and thus a lower lattice thermal conductivity. Such investigations are in high demand since it enables us to design new HE chalcogenides for TE applications. We use the novel concept of total bond order density as a single quantum mechanical metric to characterize the internal cohesion of these HE alloys and correlate with calculated properties, especially the mechanical properties. This work provides a solid database for HE chalcogenides and a road map for many potential applications. Moreover, the computational procedure we developed can be used to design new HE chalcogenides for specific TE applications.

Modulating electronic confinement and structural distortion of multiple resonance emitters enables high-performance ultrapure blue OLED

Developing deep-blue emitters with high color purity is crucial for the advancement of ultrahigh-definition display technology based on organic light-emitting diodes (OLEDs). Since most emitters are empirically designed, establishing a feasible design strategy for developing ultrapure blue emitters with narrowband characteristics remains an urgent and challenging goal. Here, we subtly construct four blue emitters with multiple resonance (MR) effect and provide an in-depth understanding for the nature of narrowband emission from the perspective of electronic confinement and structural distortion combined with actual molecular structures. A novel and feasible molecular design strategy is proposed based on the “flexible locking-ring” concept, enabling effective narrowing main peak while retaining bluer emission. More impressively, a simple sensitizer-free OLED based on SAC2MN2B with the “flexible locking-ring” design achieves one of state-of-the-art device performance with a maximum external quantum efficiency of 19.80 %, and a pure deep-blue emission peaking at 448 nm with small full-width at half-maximum (FWHM) of 25 nm and CIE coordinates of (0.147, 0.061). This work successfully achieves high-performance OLED with high color purity and provides a feasible and promising design strategy for developing organic emitters with ultrapure blue emission.

Investigation of nonlinear optical properties in α-A2BB'O6 (A = Li, Na, K; B = Ti, Zr, Hf; B' = Se, Te) by first-principles calculations.

Nonlinear optical (NLO) crystals based on oxides typically have wide bandgaps and large laser damage thresholds (LDTs), which are important for generating high-power and continuous terahertz radiation. Recently, a new family of NLO materials α-A2BB'O6 including Li2TiTeO6 (LTTO) with a strong second harmonic generation (SHG) efficiency of 26 × KH2PO4 (KDP) and a large LDT of 550 MW cm-2 were reported. Herein, we systematically study the electronic structures and NLO properties of α-A2BB'O6 (A = Li, Na, K; B = Ti, Zr, Hf; B' = Se, Te) to explore the relationship between the structure and SHG coefficient. First, 15 members of the A2BB'O6 family are demonstrated to be highly stable and NLO materials, excluding K2TiTeO6, K2TiSeO6 and K2ZrSeO6. Then, the electronic band structure, dipole moment and distortion of BO6/B'O6 octahedrons, SHG coefficient and terahertz absorption spectrum are calculated comprehensively with the element variation of A-site, B-site and B'-site. Finally, the magnitude of the SHG coefficient is found to be directly proportional to the value of total dipole moment and distortion, and inversely proportional to the bandgap value. Most importantly, among the A2BB'O6 materials, K2HfSeO6 shows the smallest direct bandgap of 2.99 eV, the largest SHG coefficient d33 of about 5 × LTTO and low terahertz absorbance from 0.1 to 9 THz. Our results provide new NLO crystals that may have potential application in terahertz radiation sources and other nonlinear electronics.

How Atomic Bonding Plays the Hardness Behavior in the Al–Co–Cr–Cu–Fe–Ni High Entropy Family

A systematic study on a face‐centered cubic‐based compositionally complex alloy system Al–Co–Cr–Cu–Fe–Ni in its single‐phase state is carried out, where a mother senary compound Al8Co17Cr17Cu8Fe17Ni33 and five of its suballoys, obtained by removing one element at a time, are investigated and exhaustively analyzed determining the contribution of each alloying element in the solid solution. The senary and the quinaries are compared using experimental techniques including X‐ray absorption spectroscopy, X‐ray diffraction, transmission electron microscopy, and first principles hybrid Monte Carlo/molecular dynamics simulations. Chemical short‐range order and bond length distances have been determined both at the experimental and computational level. Electronic structure and local atomic distortions up to 5.2 Å have been correlated to the microhardness values. A linear regression model connecting hardness with local lattice distortions is presented.

Higher harmonics and supercontinuum generated from the Kerr response time in different states of matter from a universal electromagnetic model

There is a need for a universal model to describe higher harmonic generation (HHG) in different states of matter. Based on an electromagnetic model (EM), the generation of odd higher harmonic (HHG) and supercontinuum (SC) from intense fs and ps pulses for visible, NIR, and MIR lasers is simulated based on the parameters from experimental observation. HHG and SC depend critically on the different Kerr material response times τ from the ultrafast on the order of 100 as for electronic cloud distortion to fast ~ 10 fs from plasma and molecular redistribution and to the slower picoseconds rotational and vibrational molecular processes. The number of odd HHG generated is shown to depend critically on the fastest Kerr response time on the order of ~ 1 fs from electronic self-phase modulation (ESPM). In this study, different states of matter from noble gas Argon to condensed matter ZnO and LBG are simulated showing the dependence on the Kerr response time to produce HHG for various applications in Physics, Chemistry, Biology, and Engineering. The EM model is universal to produce HHG and SC in different states of matter.

Electronic and Lattice Distortions Induce Elastic Softening in Refractory Multicomponent Borides.

Borides are extensively employed in applications demanding exceptionally high hardness, which arises from the unique and strong crystallographic arrangement of boron atoms therein. Addition of multiprincipal elements in borides is expected to enhance their structural properties due to lattice distortion and high configurational entropy. In contrast, we unravel a phenomenon of elastic softening in refractory multicomponent borides from first-principle predictions, which concur with experimentally determined metrics in their single-phase multiprincipal element counterparts. The reductions in the bulk and Young's modulus of these compounds are attributed to the lengthening and distortion of the boron-boron bonds and angles, but more critically to the perturbation in the charge densities arising from the different cations and the consequential increase in statistical weights of the d5 configuration states of the transition metals present in the boride..

Improving the Five-Photon Absorption from Core-Shell Perovskite Nanocrystals.

It is necessary to improve the action cross section (η × σn) of high-order multiphoton absorption (MPA) for fundamental research and practical applications. Herein, the core-shell FAPbBr3/CsPbBr3 nanocrystals (NCs) were constructed, and fluorescence induced by up to five-photon absorption was observed. The value of η × σ5 reaches 8.64 × 10-139 cm10 s4 photon-4 nm-3 at 2300 nm, which is nearly an order of magnitude bigger than that of the core-only NCs. It is found that the increased dielectric constant promotes modulation of MPA effects, addressing the electronic distortion in high-order nonlinear behaviors through the local field effect. Meanwhile, the quasi-type-II band alignment suppresses the biexciton Auger recombination, ensuring the stronger MPA induced fluorescence. In addition, the core-shell structure can not only reduce the defect density but also promote the nonradiative energy transfer though the antenna-like effect. This work provides a new avenue for the exploitation of high-performance multiphoton excited nanomaterials for future photonic integration.

Electrical tuning of robust layered antiferromagnetism in MXene monolayer

A-type antiferromagnetism, with an in-plane ferromagnetic order and the interlayer antiferromagnetic coupling, owns inborn advantages for electrical manipulations but is naturally rare in real materials except in those artificial antiferromagnetic heterostructures. Here, a robust layered antiferromagnetism with a high Néel temperature is predicted in a MXene Cr2CCl2 monolayer, which provides an ideal platform as a magnetoelectric field effect transistor. Based on first-principles calculations, we demonstrate that an electric field can induce the band splitting between spin-up and spin-down channels. Although no net magnetization is generated, the inversion symmetry between the lower Cr layer and the upper Cr layer is broken via electronic cloud distortions. Moreover, this electric field can be replaced by a proximate ferroelectric layer for non-volatility. The magneto-optic Kerr effect can be used to detect this magnetoelectricity, even if it is a collinear antiferromagnet with zero magnetization.

Electronic Origin of Laser-Induced Ferroelectricity in SrTiO3.

Although ultrafast control of the nonthermally driven ferroelectric transition of paraelectric SrTiO3 was achieved under laser excitation, the underlying mechanism and dynamics of the photoinduced phase transition remain ambiguous. Here, the determinant formation mechanism of ultrafast ferroelectricity in SrTiO3 is traced by nonadiabatic dynamics simulations. That is, the selective excitation of multiple phonons, induced by photoexcited electrons through the strong correlation between electronic excitation and lattice distortion, results in the breaking of the crystal central symmetry and the onset of ferroelectricity. The accompanying population transition between 3dz2 and 3dx2-y2 orbitals excites multiple phonon branches, including the two high-energy longitudinal optical modes, so as to drive the titanium ion away from the center of the oxygen octahedron and generate a metastable ferroelectric phase. Our findings reveal a cooperative electronic and ionic driving mechanism for the laser-induced ferroelectricity that provides new schemes for the optical control of ultrafast quantum states.

Understanding the migration mechanism of hydrogen atom from the α-Fe matrix into nano-precipitates via DFT calculations.

The service of high-strength steel suffers from the threat of hydrogen embrittlement and introducing nano-precipitates is an effective avenue to mitigate it. How hydrogen atoms migrate into nano-precipitates is an important question that needs to be clarified. In this study, NEB-based DFT calculations have clearly constructed the energy evolution profiles of the whole process for hydrogen atoms diffusing from α-Fe through the α-Fe/MC (M = V, Ti, Nb) coherent interfaces and finally into the nano-precipitates. The calculation results indicate that a hydrogen atom migrates with difficulty through the α-Fe/MC coherent interfaces and the diffusions in nano-precipitates follow two-step pathways. The C atom vacancy is easier to form in MC nano-precipitates. When introducing a C atom or metallic atom vacancy into the α-Fe/MC interface, the C atom vacancy is the hydrogen trapping site, while the metallic atom vacancy reduces the migration barrier. In addition, once a C atom or metallic atom vacancy is formed in the nano-precipitate, the vacancy will behave as an irreversible trapping site. Finally, electronic structure analyses and distortion energy calculations clearly reveal the effects of the local atomic environment on hydrogen diffusion from α-Fe into nano-precipitates.

Neutron diffraction study of nitride perovskite LaReN3

AbstractNitride perovskites ABN3 are extremely rare with only two known instances of bulk‐phase materials, ThTaN3 and LaReN3. Here, we present a powder neutron diffraction study of the recently‐reported nitride perovskite LaReN3. A full structural model of LaReN3 at 300 K ( , a=5.58523(5), b=5.59297(5), c=7.90419(6) Å, α=89.9170(8), β=90.1729(7), γ=90.1709(7)°) has been refined simultaneously against powder neutron and previously‐collected synchrotron X‐ray diffraction data. This indicates that the triclinic distortion is due to cooperative electronic distortions of ReN6 octahedra, and also demonstrates that all nitrogen positions are fully occupied so the sample is stoichiometric LaReN3. Lattice strains derived from fits to variable temperature powder neutron data from 5 to 300 K indicate that LaReN3 undergoes structural transitions to higher symmetry perovskite tilt structures between 300 and 350 K.

Ultra-high intensity temporally oscillatory optical Kerr effect in Carbon Disulfide arising from electronic and molecular distortions

Temporal oscillatory structure of Kerr induced birefringence is revealed in Carbon Disulfide (CS2) using an intense femtosecond optical pump pulse. The optical Kerr effect using temporal gates were experimentally investigated using a 300 fs 600 nm probe and a 1200 nm pump pulses. Several input pump powers and focusing lenses were used to show how the oscillator nature of Kerr Gating scales with input pump intensity. Temporal curves were also simulated using the two primary Kerr (n2) mechanisms: the ultrafast electron cloud (n2(e)) and the slower molecular motion (n2(m)) distortions. Results reveal high level oscillatory structure in CS2 that had been previously unreported and show the influence of pulse duration on relaxation processes. The discrepancies between high intensity gates and corresponding simulated curves display the impactful role of plasma generation in Kerr processes at extreme intensities.

Mixed Co‐Mn Spinel Oxides Based Electrocatalysts for Amperometric Determination of Hydrogen Peroxide

AbstractHerein, we present an efficient non‐enzymatic electrochemical sensor for H2O2 detection based on the catalytic‐reduction of H2O2 on ZnMn0.5Co1.5O4. The ZnMn0.5Co1.5O4 derived from ZnCo2O4 by the partial substitution of Co with Mn was synthesized via sol‐gel combustion method. The catalytic performance of ZnMn0.5Co1.5O4 for the reduction of H2O2 is better than that of ZnCo2O4, attributing to the synergetic effects of electronic structure, lattice distortion, and multivalent state of Mn. Specifically, as‐fabricated ZnMn0.5Co1.5O4‐based electrochemical sensor shows an excellent quantitative detection capability toward H2O2 in a wide range of 5 to 7585 μM, with a theoretical detection limit of 0.12 μM (3S/N). Moreover, the excellent reproducibility and selectivity for H2O2 sensing was also verified. The excellent recoveries from 94.4 to 103.2 % were obtained for H2O2‐spiked orange juice and beer. More importantly, the sensor exhibits desirable performance in the real‐time monitoring of H2O2 released from living human colon cancer cell (HCT116 cells). The results indicate that the as‐presented sensor is a promising candidate for the H2O2 determination in food safety and clinical diagnose.

Theoretical insights into CO oxidation activities on CeO2(111) steps

Direct CO oxidation on four types of CeO2(111) surface steps were studied by using density functional theory (DFT) calculations. Our results showed that CO adsorption at step edges can be enhanced through the alignment of C-O and surface Ce-O bonds. Reactivities of various step edges on the CeO2(111) surface were found to be similar to those of the corresponding extended facets (i.e., {110} and {100}). In general, the oxygen sites at step edges with lower coordination numbers can give smaller vacancy formation energies and higher reactivities. In particular, nearly all the O species at the lower position of the step edges exhibit superior catalytic activities than those on the upper position. Moreover, it was found that the unusual decrease of the Ce 4f orbital energy level after CO adsorption on the Type II* step can contribute to its excellent catalytic activity towards CO oxidation, which is caused by the synergistic effect of structural and electronic distortions on the low-coordinated surface Ce5c at the step edge. Our results disclosed the unique role CeO2(111) steps play that influences the reactant adsorption, activation barriers, product desorption and thus the CO catalytic oxidation activities overall. These findings may inspire persistent research interests on the structure-reactivity relationships over surface defect sites on rare-earth oxide catalysts.