Band Structure Of Crystal Research Articles

Complex band structure of two-dimensional thermal wave crystals

We investigate the complex band structure of temperature oscillations in a two-dimensional thermal wave crystal. We use the Cattaneo-Vernotte heat model to describe the thermal properties. We apply the plane wave method to calculate the complex band structure of a square lattice composed of an infinite array of square bars. We find that a complete band gap exists across the whole Brillouin zone, where temperature oscillations are forbidden. This has potential applications in thermal management, thermal cloaking, and other areas.

Ce-Doped Iron Oxide Anticorrosive Coatings: Effect of c(Ce4+):c(Fe3+) Ratio on Structure, Morphology, and Coating Anticorrosion Performance

Utilizing hydrothermal methods, Ce-doped iron oxide nanoparticles were synthesized from precursor solutions under different c(Ce4:c(Fe3+) precursor solutions. The effects of the c(Ce4+):c(Fe3+) ratio in the precursor solutions on the nanoparticle morphology and nanoparticle structure of the Ce-doped iron oxide were investigated using X-Ray diffraction, transmission electron microscopy, and scanning electron microscopy. Fourier transform infrared spectroscopy (FTIR) was used to examine the bond energy strength of the Ce-doped iron oxide nanoparticles. The electrochemical properties of the Ce-doped iron oxide nanoparticles were tested using an electrochemical workstation and a saltwater immersion resistance test. The corrosion resistance of Ce-doped iron oxide coatings at different c(Ce4+):c(Fe3+) ratios was systematically analyzed, uncovering corrosion resistance mechanisms and self-healing capabilities. The results show that as the c(Ce4+):c(Fe3+) ratio decreases, the lattice constants of the samples increase along with the average grain size. Both smaller and larger c(Ce4+):c(Fe3+) ratios are detrimental to lattice distortion in α-Fe2O3. The reduced number of valence electrons provided by cerium ions in Ce-doped iron oxide hinders the generation of holes and exerts a minor influence on the crystal band structure, leading to weaker electrochemical stability. The Ce-doped iron oxide coating prepared at a c(Ce4+):c(Fe3+) ratio of 1:60 readily generates a higher number of reactive hydroxyl radicals during corrosion, thus exhibiting enhanced self-healing capabilities and corrosion resistance.

Data-driven inverse design of a multiband second-order phononic topological insulator

Second-order phononic topological insulators (SPTIs) have sparked vast interest in manipulating elastic waves, owing to their unique topological corner states with robustness against geometric perturbations. However, it remains a challenge to develop multiband SPTIs that yield multi-frequency corner states using prevailing forward design approaches via trial and error, and most inverse design approaches substantially rely on time-consuming numerical solvers to evaluate band structures of phononic crystals (PnCs), showing low efficiency particularly when applied to different optimization tasks. In this study, we develop and validate a new inverse design framework, to enable the multiband SPTI by integrating data-driven machine learning (ML) with genetic algorithm (GA). The relationship between shapes of scatterers and frequency bounds of multi-order bandgaps of PnCs is mapped via developing artificial neural networks (ANNs), and a multiband SPTI with multi-frequency topological corner states is cost-effectively designed using the proposed inverse optimization framework. Our results indicate that the data-driven approach can provide a high-efficiency solution for on-demand inverse designs of multiband second-order topological mechanical devices, enabling diverse application prospects including multi-frequency robust amplification and confinement of elastic waves.

Microstructural and electrical properties of La0.9B0.1AlO3 (B=Pr, Nd, Sm) ceramics obtained by rare-earth ion doping

This study used the solid-phase method to prepare thermosensitive perovskite ceramics, La0.9B0.1AlO3 (B = Pr, Nd, Sm). The XRD and EDS results indicated that all components presented a single phase and all elements were uniformly distributed, formed a good solid solution. The SEM results clearly illustrated that the doped elements had enhanced the surface morphology, resulting in more uniform grain formation. The TEM results showed that linear defects were present, which led to an uneven stress distribution; consequently, this enhanced the carrier transport. The alternating current (AC) impedance showed that the grain boundary resistance determined the overall complex impedance and exhibited a different conductive mechanism with increasing temperature, from polariton to ion conduction. With the introduction of Nd3+, the conductivity of La0.9Nd0.1AlO3 increased and its temperature range increased from 600 – 1400 °C to 100–1500 °C. In La0.9Sm0.1AlO3, the presence of Sm2+ enhances the aging stability by elevating the oxygen vacancy concentration and the aging drift rate (ΔR/R0) was found to be lower than 2 %. In addition, DFT-based calculations were performed to investigate the property changes in the crystal structure and energy band structure of pure and doped LaAlO3. This study demonstrated an effective way to improve the performance of high-temperature thermistor materials using different doping strategies.

Structural, magnetic, optical, and electronic properties of vanadium-doped barium hexaferrite nanoparticles: Experimental and DFT approaches

Vanadium-doped barium hexaferrite with a nanostructure is a highly valuable material in various technological fields, such as electronics, permanent magnets, and sensors. The Ba1-xFe12-xVxO19 (x = 0, 0.02, 0.04, 0.06, 0.08, and 0.1) nanoparticles derived from the aqueous solutions containing Fe:Ba molar ratio of 10:1 through the sol-gel auto-combustion method. Computational study was also performed using the first-principles density functional theory (DFT) approach. Crystal structure optimization, band structure, and density of states (DOS) calculations were conducted by CASTEP code. The variation of the structural, magnetic, optical, morphological, and electronic properties of V5+-doped barium hexaferrite was investigated. The XRD analysis combined with the Rietveld refinement showed the hexagonal structure of M-type barium ferrite (BaM), confirmed by the FT-IR analysis. The morphology of BaM nanoparticles was studied by the FE-SEM and TEM micrographs. In addition, magnetic and optical properties were analyzed through VSM and UV–Vis analysis. Crystallite size was found to be highly effective in tuning the coercivity and optical band gap of barium hexaferrites, which varied, respectively, from 3.24 to 4.83 kOe, and 2.69–3.69 eV. Magnetic results showed that several variables like cations distribution, lattice strain, and hematite secondary phase affected the nanoparticles’ magnetization. The DFT simulation results showed a sharp reduction of electronic band gap energy whether V takes the position of Ba or Fe (from 1.10 eV in undoped to 0.64 and 0.14 eV in doped structures). The projected density of states (PDOS) calculations demonstrated that the d orbitals of V and Ba mainly contribute to the valence band maximum (VBM) and conduction band minimum (CBM), respectively.

Study of inorganic perovskite RGaO3 (R = Rb and Na) oxide alloys for photocatalytic applications: A DFT insights

Photocatalytic technology has been hailed as one of the most promising ways to alleviate and potentially avoid both the global energy environment and consumption issues. In this regard, the perovskite RGaO3 (R = Rb and Na) oxides are investigated for water splitting applications. DFT based CASTEP code is utilized by employing GGA-PBE exchange-correlation functional. According to structural analysis, compounds have 221 space groups (cubic) with 5 atoms. The structural analysis and band structures of NaGaO3 and RbGaO3 crystals were described as having an indirect bandgap with 3.11 eV and 2.15 eV energy, respectively. Absorption, reflectivity, loss function, conductivity, refractive index, and dielectric function were all explored in terms of optical characteristics. According to the mechanical properties, compounds RGaO3 (R = Rb and Na) are mechanically stable, ductile, anisotropic, and hard by Born stability. These materials are best suited for photocatalytic applications to produce H2 fuel with the highest efficiency.

Band structure for relativistic charged particles immersed in a structurally chiral electromagnetic field

In this paper, we determine the band structure of an electromagnetic space-time crystal. We construct a coordinate transformation in which the matrix elements of the Dirac equation are constant. Consequently, their corresponding band structure is recovered analytically. The band structure is fragmented into three different energy regions. In the center, there is a region prohibited for all particles (universal band gap), which is symmetrically enveloped by two energy regions of the same width. These regions allow the passage of particles with a specific spin (discriminatory band gaps). Furthermore, we demonstrate that, through the appropriate combination of the refractive index, the length of the electromagnetic wave, and the amplitude of the electric field, it is possible to shorten the bandwidth of the universal gap and replace it with a discriminatory band gap. In that sense, the proposed system constitutes an alternative procedure to observe the Schwinger mechanism experimentally.

Enhanced photocatalytic removal of tetracycline by ZnO/NiCo2O4 through the construction of a p-n heterojunction

A new ZnO/NiCo2O4 photocatalyst was synthesized to develop systems for removing pharmaceutical pollutants. Various properties of the synthesized nanocomposite such as crystal structure, morphology, optical activity, chemical composition, electrochemical functions, and energy band structure were investigated. The study on tetracycline removal showed that the catalytic activity of the ZnO/NiCo2O4 nanocomposite (0.0426 min−1) is significantly higher compared to ZnO and NiCo2O4 individually. Morphology images confirmed the creation of a heterojunction between rice-shaped ZnO and NiCo2O4 nanoparticles. In photoluminescence and electrochemical impedance analyses, the nanocomposite displayed the weakest signal among its components, suggesting effective control of recombination and charge carrier transfer. The combination of NiCo2O4 with ZnO resulted in increased light absorption in the visible spectrum, contributing to its photocatalytic performance. The energy band structure of ZnO and NiCo2O4 was examined, presenting a detailed explanation of the most likely mechanism for the improved photocatalytic activity.

Optical properties of CeF3 crystal at high temperature or pressure by first principles and its application in isolators

In this work, CeF3 single crystal was successfully grown by Bridgman method. The XRD diffraction was tested and the data matched well with the standard card. Further trying its optical performance, CeF3 single crystal has very high transmittance of 90 %, the cut-off absorption edge length of the crystal is better than 300 nm. Testing the magneto-optical Verdet constant of CeF3 single crystal and trial-produced optical isolator shows that the Verdet constants of CeF3 single crystals in the magneto-optical field are similar to those of TGG crystals. The band structure, state density, optical properties and elastic constants of CeF3 crystal under different temperature and pressure are calculated by first principles. The results show that CeF3 crystal has excellent thermal stability and mechanical stability. Under high temperature conditions, light absorption and loss are small, and the optical properties are stable. Under high pressure, the crystal exhibits certain stability and impact resistance, and the optical properties are relatively stable. The results show that CeF3 crystal has significant advantages in replacing TGG crystal in laser field, and has a certain application prospect in window materials.

Prediction of Electric Load Neural Network Prediction Model for Big Data

In this study, the two-dimensional hexagonal Photonic crystal energy band structure was simulated using COMSOL Multiphysics field simulation software. The 2D hexagonal Photonic crystal structure was constructed by setting parameters such as periodic boundary conditions and air hole radius. Using the frequency domain solver of COMSOL software, the transmission and reflection spectra of the structure were calculated, and the energy band structure diagram was obtained. The effects of different parameters on the energy band structure were analyzed by adjusting the structure parameters. The results show that the fine tuning of the energy band structure of 2D hexagonal Photonic crystals can be realized by adjusting the radius of air holes and the periodic boundary conditions. This study provides a useful reference for further research on the properties and applications of 2D photonic crystals.

Resonator embedded photonic crystal surface emitting lasers

The finite size of 2D photonic crystals results in them being a lossy resonator, with the normally emitting modes of conventional photonic crystal surface emitting lasers (PCSELs) differing in photon lifetime via their different radiative rates, and the different in-plane losses of higher order spatial modes. As a consequence, the fundamental spatial mode (lowest in-plane loss) with lowest out-of-plane scattering is the primary lasing mode. For electrically driven PCSELs, as current is increased, incomplete gain clamping results in additional spatial (and spectral) modes leading to a reduction in beam quality. A number of approaches have been discussed to enhance the area (power) scalability of epitaxy regrown PCSELs through careful design of the photonic crystal atom1–3. None of these approaches tackle the inflexibility in being unable to independently modify the photon lifetime of the different modes at the Γ2 point. As a method to introduce design flexibility, resonator embedded photonic crystal surface emitting lasers (REPCSELs) are introduced. This device, combining comparatively low coupling strength photonic crystal structures along with perimeter mirrors, allow a Fabry–Pérot resonance effect to be realised that provides wavelength selective modification of the photon lifetime. We show that surface emission of different surface emitting modes may be selectively enhanced, effectively changing the character of the modes at the Γ2 point. This is a consequence of the selective modification of in-plane loss for particular modes, and is dependent upon the alignment of the photonic crystal (PhC) band-structure and distributed Bragg reflectors’ (DBRs) reflectance spectrum. These findings offer new avenues in surface emitting laser diode engineering. The use of DBRs to reduce the lateral size of a PCSEL opens the route to small, low threshold current (Ith), high output efficiency epitaxy regrown PCSELs for high-speed communication and power sensitive sensing applications.

Grey SrCu2O2 with vacancy and pore structure: Dual organic degradation properties and first-principles calculations

A novel SrCu□O□ photocatalyst containing Cu vacancy and O vacancy was synthesized for the first time based on solid-phase sintering. The crystal structure, elemental composition, microscopic morphology, optical properties and energy band structure of the samples were characterized and analyzed in detail. The vacancies in the material were determined by ICP-MS and EPR, first-principles calculations showed that the introduction of vacancies extends the forbidden band of the photocatalytic to the visible band. The photocatalytic performance of SrCu□O□ was evaluated by degrading MB and TCHCI. Our results show that SrCu□O□ enhances the degradation performance of organic compounds due to rich vacancies that promote electron-hole pair separation and improve photogenerated carrier separation efficiency. Vacancy-containing metal oxide catalysts have broad application value in environmental remediation.

Simulation Computation of Two-dimensional Hexagonal Honeycomb Photonic Crystals Energy Band Structure Based on COMSOL

This study employs COMSOL software, integrating the plane wave expansion method and finite element method, to simulate and analyze the energy band structure of two-dimensional hexagonal honeycomb photonic crystals. By setting parameters and conducting scans, this paper not only maps out the electric field intensity and energy band distribution but also discovers a significant enhancement of electric field intensity at the lattice's high symmetry points, indicating a higher likelihood of electromagnetic waves' presence at these points. Furthermore, the notable energy gaps between the second and third energy bands provide directions for subsequent research. The findings of this study are of significant value for research and development in optoelectronic integration and communication, demonstrating an effective comprehensive method for analyzing the energy band structure of two-dimensional hexagonal honeycomb photonic crystals.

Complex band structure of thermal wave crystals: The plane-wave method

In this paper, we present an extension of the plane-wave method (PWM) to compute the complex band structure of thermal wave crystals (TWCs). The structural periodicity of TWC allows the possibility to manipulate non-Fourier heat via wave interference. While the Cattaneo-Vernotte (CV) heat conduction theory accurately models oscillatory wave-like propagation of heat in TWCs, obtaining an eigenvalue equation for frequency using the CV wave equation is not possible. To overcome this limitation, we propose a novel approach that solves a complex eigenvalue equation for the Bloch wave vectors

Electronic properties of the barium magnesium tantalate

BaMg1/3Ta2/3O3 (BMT) crystals belong to the family of complex perovskites and are well known for their excellent microwave dielectric properties. In this work, structural optimization of the lattice parameters was performed. Electron density functional theory calculations of the electronic band structure of BMT crystal of the trigonal phase were carried out along Г–A–K–M–L directions of the Brillouin zone. The calculated band gap energy was 3.554 eV. The partial density of states of BMT crystal in P-3 m1 phase was simulated. Top of the valence band was formed by 2p-states of O and bottom of the conduction band – by 5d-states of Ta.

Adjustable anion and cation vacancies CoSe catalysts on improving activity in photoelectrochemistry and electrocatalysis

Vacancies have a significant impact on catalysts as crystal structure, band structure and surface active sites. The effect of anion and cation vacancies on the catalytic performance of CoSe was studied. Catalysts with cation Co vacancies, anion Se vacancies and anion cation double vacancies were obtained. The results show that the single Co vacancy CovSe will form many pores as the active sites in the lattice and the position of the conduction band greatly moves from 0.55 eV of CoSe to −0.46 eV. This significantly improves the electrocatalytic hydrogen evolution performance, with overpotential of 161 mV and Tafel slope of 58 mV/dec. As a comparison, the overpotential of CoSe is 401 mV (Tafel slope of 171 mV/dec). In addition, Co vacancies can also improve carrier mobility and separation efficiency, demonstrating excellent photocurrent of 11.82 mA/cm2 at 1.23 eV (RHE), with 5.91 % conversion efficiency. The overall performance of CoSev with individual Se anion vacancies is not as good as CovSe. This indicates that cationic vacancies have a greater impact on the catalyst. There was no significant improvement in the performance of the sample with double vacancies of anions and cations, indicating that the two vacancies may have offset each other.

Growth, optical and thermal properties of YbxHo1-xCa4O(BO3)3 crystals

YbxHo1-xCa4O(BO3)3 (Yb:HoCOB, x = 0, 0.1, 0.2, 0.3) crystals were grown by the Bridgman method for the first time. The crystal structure, rocking curve, transmission spectra, absorption spectra, band structure and thermal properties of Yb:HoCOB were characterized in detail. The maximum half peak width (FMHW) of Yb0.1Ho0.9COB and Yb0.2Ho0.8COB is 26.7″ and 23.8″, respectively, and the effective segregation coefficient is greater than 0.9. In addition, the transmittance of Yb:HoCOB is 88 %. New absorption peaks are introduced by doping Yb3+ at 850–1000 nm. The UV absorption cut-off edge of Yb:HoCOB is red-shifted with increasing Yb3+ doping. The thermal diffusivity and thermal conductivity of Yb:HoCOB decrease with increasing temperature. The specific heat increases with the increasing temperature and finally approaches a constant value. The specific heat of Yb:HoCOB crystal are above 0.670 J/gK at room temperature. Yb:HoCOB with good crystallization quality, high transmittance and high specific heat has the application potential in laser frequency and QPCPA. This work provides a useful exploration for the study of nonlinear optical materials in solid state lasers.

Effect and Regulation Mechanism of Post-deposition Annealing on the Ferroelectric Properties of AlScN Thin Films.

Integrating ferroelectric AlScN with III-N semiconductors to enhance the performance and tunability of nitride devices requires high-quality AlScN films. This work focuses on the effect and regulation mechanism of post-annealing in pure N2 on the crystal quality and ferroelectric properties of AlScN films. It is found that the crystal quality improves with increasing annealing temperatures. Remarkably, the leakage current of AlScN films caused by grain boundaries could be reduced by four orders of magnitude after annealing at 400 °C. The crystal growth dynamics simulations and band structure calculations indicate that the energy supplied by the temperature facilitates the evolution of abnormally oriented grains to have a better c-axis orientation, resulting in the defect states at the Fermi-level disappearing, which is mainly the reason for the leakage current decrease. More interestingly, the reduction of leakage current leads to the previously leaking region exhibiting ferroelectric properties, which is of great significance to improve the ferroelectricity of AlScN and ensure the uniformity of devices. Furthermore, annealing enhances the tensile strain on the film, which flattens the energy landscape of ferroelectric switching and reduces the coercive field. However, the risk of incorporation of oxygen will also be increased if the annealing temperatures are higher than 400 °C, which will not only reduce the relative displacement of metal atoms and nitrogen atoms in AlScN but also enhance the ferroelectric depolarization field, leading to the remnant polarization decreasing dramatically. These discoveries facilitate a deeper understanding of the influencing mechanism on the ferroelectric properties of AlScN films and provide a direction for obtaining high-quality AlScN.

A rasterized plane wave expansion method for complex 2-D phononic crystals

This paper introduces a computer image processing-based method called the rasterized plane wave expansion method (RPWEM). This method improves the conventional plane wave expansion method (CPWEM) and reduces its formula derivation cost in the case of 2-D phononic crystals with complex inclusions. In addition, for 2-D phononic crystals with arbitrary multiphase materials, this method can also simplify the calculation process. By employing the proposed RPWEM, successful calculations of band gaps are conducted for planar phononic crystals with the hexagonal unit cell as well as phononic crystals featuring integrated circuit-like structures. The results further validate the expanded applicability of the RPWEM in comparison to the CPWEM. In the end, a potential application similar to DIC (Digital Image Correlation) for predicting band structures of phononic crystals is proposed, and its feasibility is briefly validated.

Enhancing Electrical Transport Performance of Polycrystalline Tin Selenide by Doping Different Elements

In the face of ever‐evolving energy and environmental challenges, tin selenide (SnSe) has garnered significant attention due to its outstanding thermoelectric performance. The article focuses on the research of easily accessible and highly practical polycrystalline SnSe thermoelectric materials, providing an overview of their crystal structure, band structure, and electrical transport performance. Compared with previous studies, this research classifies elements based on their own properties, mainly dividing them into alkali metals, transition metals, main group metals, halogens, and rare earth (Re) elements. The study systematically summarizes the experimental results of doping SnSe with these elements and analyzes the mechanisms by which different elements enhance the electrical transport performance and thermoelectric figure of merit of polycrystalline SnSe. The enhanced mechanism is mainly achieved by increasing the conductivity and Seebeck coefficient. Finally, a systematic analysis is conducted to identify the factors that improve electrical transport performance, and strategies for enhancing the electrical transport and thermoelectric properties of polycrystalline SnSe through precise doping techniques are discussed, with a prospect for their application in the future.