Boron-rich belt-like nanoclusters constitute a compelling frontier in low-dimensional materials science, combining intrinsic electron deficiency with highly delocalized multi-center bonding to afford exceptional tunability of optoelectronic properties. Here we present a comprehensive density functional theory (DFT) and time-dependent DFT (TD-DFT) investigation of a benzene-like boron-catenated (BC) belt and five exocyclic super-alkali(SA)-doped derivatives, BC@FLi2, BC@LiMg, BC@NLi4, BC@OLi3, and BC@Li3, with emphasis on frontier orbital engineering, global chemical reactivity indices, and the prerequisites for enhanced nonlinear optical (NLO) response. The SA doping introduces strong donor–acceptor asymmetry, compressing the HOMO–LUMO gap from 1.431 eV in boron-carbon nanobelt (BC) to as low as ∼0.19 eV in BC@OLi3. Koopmans' theorem-based reactivity descriptors reveal dramatic increases in electrophilicity (ω, 1.80 → 180.79 eV) and global softness (σ), quantitatively linking frontier orbital compression to enhanced charge-transfer susceptibility. TD-DFT analysis of BC identifies three near-infrared singlet excited states (0.84–0.96 eV) with negligible oscillator strengths, while doping systematically reduces exciton binding energies (0.140 → 0.124 eV), favoring free-carrier generation. These findings collectively establish exocyclic SA functionalization as a powerful and chemically tunable strategy for designing high-performance boron-belt NLO chromophores, with implications for photonic switching, frequency conversion, and two-photon absorption applications.
Yb:YAG crystal is an excellent laser material but is prone to color center defects when grown under oxygen-deficient atmosphere. Studying these color centers is essential for developing high-quality crystal growth techniques and understanding the origins of color centers. This study systematically analyzed the effects of Yb doping and oxygen vacancy(Vo) defects on atomic and bond populations, formation energy, lattice variations, defect electronic states, diffusion coefficients, and optical properties of YAG through density functional theory(DFT) calculations, annealing experiments, and characterization measurements(XRD/EPR/FTIR/UV-vis and transmission spectrum). Oxygen vacancies cause a decrease in the lattice parameter of Yb:YAG. The capture of electrons by oxygen vacancies, along with an increase in the number of trapped electrons, also leads to an expansion of the lattice parameter. Incorporating Yb3+ into YAG would affect Vo formation energy, which decreases with increasing dopant concentration, so controlling the doping concentration is crucial for balancing defects and optical properties. Annealing Yb:YAG reduces or eliminates vacancy defects, leading to an increase in the lattice parameter. Yb-doping into YAG increases the valence and bond population kind, as well as the system energy. The experimental changes of the EPR and absorption/transmission spectra after annealing are consistent with the calculated spin charge density difference and defect energy levels of the vacancy trapping one electron, indicating that the color center is the F+ center. After Yb doping, the diffusion coefficient of oxygen vacancies increases significantly and rises with temperature. Therefore, Yb:YAG should be grown in a weak oxygen atmosphere and annealed at 1000∼1400°C to produce high-quality crystals.
This paper presents results of experimental studies on the effect of thermomagnetic processes on the magnetic relaxation of the structure of a bulk amorphous Fe-based alloy. Thermomagnetic processes were conducted using a Faraday magnetic balance at an external magnetic field of approximately 0.7 T. They were conducted at temperatures above the Curie temperature but significantly below the crystallization temperature. The magnetization process was studied according to the ferromagnetic saturation approach. The obtained results indicate that the greatest effect in changing the magnetic structure is achieved after the first thermomagnetic step. However, the third step produces only minor changes in the range of external magnetic field strength at which structural defects affect the magnetization process. It was also shown that each subsequent relaxation process leads to a decrease in the coercive field value. No crystalline reflections were detected by X-ray diffraction (XRD) after the three thermomagnetic cycles.
We investigate a mixed-spin (3/2, 5/2, 7/2) Blume–Capel ferrimagnet on an ABA-stacked trilayer graphene-like lattice, in which the outer spin-3/2 and spin-7/2 planes are coupled not only to the central spin-5/2 plane but also directly to one another through a direct interlayer exchange J3 — a next-nearest-layer path whose registry, coordination and sublattice sign are fixed by the Bernal (ABA) stacking, and which has not been retained in the adjacent-coupled trilayer models studied so far. Using a variational mean-field formulation based on the Bogoliubov–Peierls inequality, we determine the sublattice magnetizations self-consistently and compute the total magnetization, susceptibility, internal energy, entropy, specific heat and the magnetocaloric entropy change. The direct coupling J3 emerges as the decisive control parameter of the ferrimagnetic response: it generates a Néel N-type compensation point that is absent at J3 = 0 for the same exchange couplings and crystal fields, drives a ground-state reorientation, and produces a genuine first-order reorientation transition at J3 ≈ −0.75 where two free-energy branches cross at t1 ≈ 2.60. The crystal field of the high-spin layer triggers a sharp first-order spin-state collapse (|7/2| → |1/2|) at DC ≈ −2.25, whereas the order–disorder transition at TC ≈ 11.20 remains second order, marked by a divergent susceptibility (χ ≈ 28.6) and a λ-anomaly in the specific heat. The entropy saturates exactly at S∞ = (ln4 + ln6 + ln8)/3 ≈ 1.7525, and the hysteresis loops show multi-step reversal whose topology is reshaped by J3. Crucially, the magnetocaloric entropy change exhibits an inverse (ΔSM > 0) response that appears only once J3 is switched on, identifying it as a thermodynamic signature of the J3A systematic survey of the J3 = 0 limit shows that compensation can be recovered there only by reversing the sign of one nearest-layer bond, by collapsing the high-spin moment with a strong crystal field, or by enhancing the middle-layer exchange by more than 75%; with both nearest-layer bonds antiferromagnetic and all three sublattices saturated, the direct outer-layer coupling is the only parameter of the model that produces a compensation point. These results establish the direct outer-layer coupling as a versatile route to tune compensation, magnetic switching and magnetocaloric response in layered mixed-spin ferrimagnets.
Interfacial engineering of two-dimensional van der Waals heterostructures is a key strategy for controlling their optoelectronic properties. This study uses density functional theory to analyze how hydrogen (H) atom intercalation in the FeCl3/WSi2N4 heterostructure affects its structural stability, electrical characteristics, and optical absorption. The results indicate that hydrogen intercalation induces an effective redistribution of charge carriers, consequently leading to a gradual transformation of the electronic band structure. As the intercalated H-atom number increases from 0 to 3, the system transitions from a semiconductor (with a band gap of 0.49 eV) through a semimetallic state towards a pseudo-metallic state. Meanwhile the band alignment of the heterostructure shifts from Type-I to Type-II. H-atom intercalation significantly increases the heterostructure's work function (from 5.69 eV to 5.95 eV) and enhances the built-in electric field, as indicated by the rise in the electrostatic potential difference (ΔΦ) from 0.54 eV to 2.70 eV due to the reconstruction of the interface dipole moment. Furthermore, compared with intrinsic heterostructure, H-intercalation can modulate dipole matrix elements, thereby improving the optical absorption. In the visible range (λ = 496.6 nm), the absorption coefficient decreases with the increase in the number of H-atoms. This behavior is dictated by the competition between band-edge state density and carrier screening. In the UV region (λ= 285.1 nm) the absorption reaches to 24.8% by inserting hydrogen atom owing to the density of states increasing. This work provides important theoretical insights for the design of high-performance, spectrally tunable two-dimensional optoelectronic devices via precise interfacial hydrogenation engineering in the FeCl3/WSi2N4 heterostructure.
Two-dimensional (2D) heterostructures have garnered significant attention in the design of novel optoelectronic devices due to their exceptional device performance. In this work, we systematically investigate the electronic structures and optical properties of Pt(Pd)Se2 lateral heterostructures and graphene/Pt(Pd)Se2 vertical heterostructures. The Pt(Pd)Se2 lateral heterostructure is an indirect-gap semiconductor with a band gap of 1.229 eV, whereas vertical integration with graphene yields a narrow indirect band gap of 0.0135 eV, as determined using the Heyd–Scuseria–Ernzerhof screened hybrid functional (HSE06). The optimized graphene/Pt(Pd)Se2 heterostructure has an interlayer distance of 3.430 Å and a binding energy of −0.859 eV per supercell, indicating energetically favorable interlayer assembly. Its valence-band maximum is predominantly localized on graphene, whereas the conduction-band minimum is localized on the Pt(Pd)Se2 layer, resulting in a staggered Type-II band alignment. Compared with the isolated Pt(Pd)Se2 layer, the graphene-containing heterostructure exhibits markedly enhanced broadband optical absorption, with calculated absorption coefficients exceeding 106 cm-1 in the ultraviolet region.
The development of advance energy storage technology relies on preparation of electrode materials with enhanced electrochemical properties. Among various energy storage technology, supercapacitors (SCs) are a viable option for future energy storage technologies due to characteristics like better power density, non-flammability and environmental compatibility. In this work, CaFe2O4/rGO nanohybrid was successfully prepared via a hydrothermal procedure and evaluated as advance electrode compound for SCs applications. Incorporating two-dimensional rGO into the CaFe2O4 matrix significantly improved electrical conductivity and charge-transfer characteristics by forming an interconnected conductive framework. The electrochemical behavior of CaFe2O4 /rGO nanocomposite was evaluated in 3 M KOH alkaline electrolyte and demonstrated superior electrochemical behavior. The CaFe2O4/rGO nanohybrid exhibited high specific capacitance (Cs) of 1015 F/g at standard current density (j) of 1 A/g. The nanohybrid revealed electrochemical durability of 50 h and long-term cyclic stability after 5000 cycles. Moreover, the low solution resistance (Rs) of 1.1 Ω indicates reduced ohmic resistance and facilitates efficient charge transport within the electrochemical system. Furthermore, the fabricated CaFe2O4/rGO//AC device achieved Cs of 158 F/g, energy density (Ed) of 46 Wh/kg and power density (Pd) of 725 W/kg. These outcomes show novelty and effectiveness of CaFe2O4/rGO nanohybrid as potential electrode compound for sustainable energy storage applications.
Lithium-ion battery thermal runaway is accompanied by the release of characteristic gases, including H2, CO, CO2, CH4, and C2H4, whose adsorption-induced electronic perturbations provide useful signals for early safety assessment. In this work, density functional theory calculations were performed to investigate the adsorption behavior and electronic response of Pd1–Pd4 cluster-decorated Janus NbTeSe monolayers toward these gases, with emphasis on the Janus-surface asymmetry and Pd-cluster-size effect. The results show that Pd clusters can be stably anchored on both Te-up and Se-up surfaces and act as dominant active centers for gas adsorption. The overall adsorption strength decreases in the sequence of CO, C2H4, H2, CH4, and CO2, indicating selective interactions with CO and C2H4. CO adsorption on Se-up-Pd3/NbTeSe exhibits the strongest interaction, with an adsorption energy of −1.85 eV and a large charge-transfer magnitude, but its overly strong binding is unfavorable for desorption. In contrast, C2H4 adsorption provides a more balanced adsorption-recovery behavior. Charge-density difference and DOS/PDOS analyses reveal that Pd-4d states dominate the adsorption-induced electronic modulation, and the orbital hybridization between CO- and C2H4-derived molecular states and Pd-4d states accounts for the enhanced interaction. Notably, the C2H4/Te-up-Pd1–Pd4 systems exhibit a nonmonotonic cluster-size dependence, with Pd3 producing the strongest molecule-cluster electronic coupling. These findings clarify the surface-dependent recognition mechanism of Pd-cluster-decorated Janus NbTeSe and highlight C2H4/Pdn/NbTeSe systems as promising candidates with balanced adsorption strength, electronic response, and recoverability.
Experimental studies have demonstrated that Bi alloying simultaneously enhances the electrical transport and reduces the lattice thermal conductivity of Mg3Sb2 based thermoelectrics, yet the underlying microscopic mechanisms remain insufficiently understood at the atomic scale. Here, we combine density functional theory and first-principles molecular dynamics simulations to systematically investigate how Bi alloying regulates the electron and phonon transport properties. We find that Bi alloying reduces the conduction band effective mass, activates multi-valley transport, and lifts band degeneracy, leading to a substantial enhancement in electrical conductivity and power factor. Simultaneously, the larger atomic radius and higher mass of Bi induce local bond length fluctuations, reduced coordination numbers, and broadening of pair correlation function peaks, significantly increasing atomic-scale structural disorder. This disorder, together with phonon spectrum softening, reduces the phonon group velocity and enhances scattering, thereby effectively suppressing lattice thermal conductivity. These results elucidate the physical origin of Bi-alloying induced performance enhancement from both electronic and phononic perspectives, providing a comprehensive atomic-scale foundation for the rational design of Mg3(Sb,Bi)2 based thermoelectrics.
