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Herein, the structural, optical, and magnetic properties of Y0.85La0.15FexAlyO3: (x; y) where x = 1; y = 0, x = 0.975; y = 0.025, x = 0.95; y = 0.05, and x = 0.9; y = 0.1 nanomaterials obtained from sol–gel method are reported. The X‐ray powder diffraction (XRD) for the structural characterization, scanning electron microscopy for crystallite size estimation, ultraviolet–visible absorption for optical studies, and vibrating‐sample magnetometer for magnetic studies are used in this investigation. An increase of orthorhombic crystal structure with an increase of Al content in the sample is observed from XRD studies. The existence of all the elements present in the samples is observed from energy‐dispersive X‐ray spectroscopy. The optical bandgap increases from 2.04 to 2.10 eV with an increase of Al concentration from 0 to 0.05. The observed magnetization value is 3.14 emu g−1 for y = 0.05, which is higher than y = 0 (2.11 emu g−1) and y = 0.024 (2.58 emu g−1). In summary, the obtained result (x = 0.95; y = 0.05) can be useful for different magnetic‐based applications. [ABSTRACT FROM AUTHOR]

Spinel oxides are a type of material that can be used in a wide range of applications, such as photocatalysis, hydrogen production and environmental protection. In this respect, calcium aluminate (CaAl2O4) and chromate (CaCr2O4) spinels were synthesized in this study by the coprecipitation method using potash solution as a precipitant. CaAl2O4 and CaCr2O4 spinels were annealed at 900 and 1100°C, respectively, for different periods. The obtained spinels were first characterized by thermal analysis, and the phase composition of the oxides was analysed using X-ray diffraction. Hydroxyl groups and absorbed water in the obtained precipitates disappeared after calcination and were observed via Fourier transform infrared spectroscopy. BET and SEM/EDS analyses were also used to determine the total surface area of the powder particles, the size of the grains and the morphology of the powders of the synthesized nanoparticles, respectively. The structural and morphological analyses revealed the formation of single-phase CaAl2O4 and dual-phase CaCr2O4, with specific surfaces for each spinel of 44.2165 and 5.7190 m2 g−1, respectively. Moreover, DFT calculations were performed on the materials, and the direct bandgaps of these spinels were found to be 4.365 eV for CaAl2O4 and 2.256 eV for CaCr2O4. The results indicated that different compositions led to different optical bandgaps. Finally, the results indicate that due to the suitable characteristics and properties of the produced spinel oxides, they are among the promising materials that may be employed as semiconductors for various applications. [ABSTRACT FROM AUTHOR]

The presented research delineates an extensive study aimed at obtaining and comparing optimal designs and geometries for one-dimensional periodic acoustic metamaterials to attenuate noise within the audible frequency range of 20 Hz to 20 kHz. Various periodic designs, encompassing diverse geometric parameters and shapes—from Basic-Periodic to Semi-Periodic, Tapered-Diverging, and Tapered-Converging unit cells of repeated patterns—are examined to identify the most effective configurations for this application. A thorough parametric analysis is executed employing FE-Bloch's theorem across these four configurations to determine their bandgaps and to identify the most effective geometry. A normalization process is utilized to extend the domain of the analysis and the range of the system parameters studied in this work, totaling 202,505 design cases. Finally, the optimal design is identified based on achieving the best bandgaps coverage. The study concludes with the presentation of frequency domain acoustic pressure responses at multiple sensing points along the filters, validating the performance and the obtained bandgaps through these optimal geometries. [ABSTRACT FROM AUTHOR]

The recent year has witnessed a flurry of activities in investigating the promising electronic, optical, and transport properties of lead‐free double perovskite halides. In the present work, the structural, electronic, optical, and transport properties of Cs2(Li/Na)GaI6 are carefully examined. The predicted negative formation energy, absence of imaginary frequency in the phonon spectra, and ab‐initio molecular dynamics calculations show that they are thermodynamically stable. Additionally, electronic studies employing generalized gradient approximation (GGA)–Perdew–Burke–Ernzerhof (PBE) + modified Becke‐Johnson + spin‐orbit coupling reveal that Cs2(Li/Na)GaI6 exhibits a direct bandgap, with values of 1.24 eV for Cs2LiGaI6 and 1.39 eV for Cs2NaGaI6. The exceptional optical properties, including a high absorption coefficient (105 cm−1) and excellent optical conductivity with low reflectivity across the entire UV–visible range, indicate that Cs2(Li/Na)GaI6 are promising materials for solar cell applications. Moreover, the ultralow thermal conductivity, high Seebeck coefficient, and substantial electrical conductivity of Cs2(Li/Na)GaI6 result in a high figure of merit over the temperature range of 200–600 K. Thus, Cs2(Li/Na)GaI6 shows strong potential as both photovoltaic and thermoelectric materials. [ABSTRACT FROM AUTHOR]

A novel metamaterial periodic multi-span beam with elastic supports and local resonators is designed and studied. The vibration characteristics of the designed metamaterial multi-span beam structure are investigated by the spectral element method (SEM) combined with the transfer matrix method (TMM). The accuracy and feasibility of the theoretical methods are validated by the finite element method (FEM) and vibration experiment. It is demonstrated that the metamaterial periodic multi-span beam with elastic supports can produce local resonance bandgaps in the low-frequency regions and Bragg bandgaps in the middle- and high-frequency regions. For some support stiffnesses, the amplitudes and widths of the bandgaps for the proposed structure are larger than those of the metamaterial multi-span beam with simply supported boundaries. Thus, the positions and ranges of the Bragg bandgaps can be adjusted by changing the stiffness of the elastic supports so as to improve the vibration reduction performance of the structure. [ABSTRACT FROM AUTHOR]

An optical spectroscopy study is reported of single crystals of the LiNbO3–LiTaO3 solid solution. The spectra are dominated by the fundamental absorption edges. The direct band‐to‐band transitions in congruent LiNbO3 (LN) and LiTaO3 (LT) as well as in selected compositions of solid solutions grown from mixtures of the congruently melting end members are studied at temperatures up to 1200 °C. At room temperature, the direct optical bandgaps of congruent LN and LT assume values of about 4.0 and 4.6 eV, respectively. With rising temperatures, the absorption edges are found to shift to lower energies. The isothermal composition dependence of bandgaps is a far from linear by going through a minimum. This behavior is maintained up to the highest temperatures of our study. At about 600 °C, congruent LT undergoes a structural transition from the ferroelectric to the paraelectric phase. This is reflected by a change in the temperature dependence of the gap energy indicating structure‐related changes in electron–phonon coupling. [ABSTRACT FROM AUTHOR]

The paper studies the influence of the initial inhomogeneous thermal stresses on the dispersion of the axisymmetric longitudinal waves propagating in the bi-layered hollow cylinder within the scope of the 3D linearized theory of elastic waves in initially stressed bodies. The initial static thermal stresses are determined within the scope of the uncoupled classical linear theory of thermo-elasticity and it is assumed that the temperature change in the cylinder is caused by the heating or cooling of the inner and outer surfaces of the cylinder. The discrete analytical solution method is employed for the solution to the corresponding equations of the wave propagation. Concrete numerical results are obtained for the cylinder, the materials of the layers of which are steel and aluminum, as well for the cylinder made of steel only. Numerical results on the influence of the initial inhomogeneous thermal stresses on the dispersion curves related to the first, second and third modes are presented and discussed. In particular, it is established that the cooling or the heating of the outer and inner surfaces of the bi-layered hollow cylinder influences the dispersion curves not only in the quantitative sense, but also in the qualitative sense. [ABSTRACT FROM AUTHOR]

Copyright of National Academy of Sciences of Armenia Reports / Doklady Nacionalnaâ Akademiâ Nauk Armenii is the property of National Academy of Sciences of the Republic of Armenia and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Bandgaps, or frequency ranges of forbidden wave propagation, are a hallmark of phononic crystals (PnCs). Unlike their lattice counterparts, PnCs taking the form of continuous structures exhibit an infinite number of bandgaps of varying location, bandwidth, and distribution along the frequency spectrum. While these bandgaps are commonly predicted from benchmark tools such as the Bloch-wave theory, the conditions that dictate the patterns associated with bandgap symmetry, attenuation, or even closing in multi-bandgap PnCs remain an enigma. In this work, we establish these patterns in one-dimensional rods undergoing longitudinal motion via a canonical transfer-matrix-based approach. In doing so, we connect the conditions governing bandgap formation and closing to their physical origins in the context of the Bragg condition (for infinite media) and natural resonances (for finite counterparts). The developed framework uniquely characterizes individual bandgaps within a larger dispersion spectrum regardless of their parity (i.e., odd versus even bandgaps) or location (low versus high-frequency), by exploiting dimensionless constants of the PnC unit cell which quantify the different contrasts between its constitutive layers. These developments are detailed for a bi-layered PnC and then generalized for a PnC of any number of layers by increasing the model complexity. We envision this mathematical development to be a future standard for the realization of hierarchically structured PnCs with prescribed and finely tailored bandgap profiles. [ABSTRACT FROM AUTHOR]

The deflection and the control of the effects of the complex urban seismic wavefield on the built environment is a major challenge in earthquake engineering. The interactions between the soil and the structures and between the structures strongly modify the lateral variability of ground motion seen in connection to earthquake damage. Here we investigate the idea that flexural and compressional resonances of tall turbines in a wind farm strongly influence the propagation of the seismic wavefield. A large-scale geophysical experiment demonstrates that surface waves are strongly damped in several distinct frequency bands when interacting at the resonances of a set of wind turbines. The ground-anchored arrangement of these turbines produces unusual amplitude and phase patterns in the observed seismic wavefield, in the intensity ratio between stations inside and outside the wind farm and in surface wave polarization while there is no metamaterial-like complete extinction of the wavefield. This demonstration is done by setting up a dense grid of 400 geophones and another set of radial broadband stations outside the wind farm to study the properties of the seismic wavefield propagating through the wind farm. Additional geophysical equipment (e.g., an optical fiber, rotational and barometric sensors) was used to provide essential explanatory and complementary measurements. A numerical model of the turbine also confirms the mechanical resonances that are responsible for the strong coupling between the wind turbines and the seismic wavefield observed in certain frequency ranges of engineering interest. [ABSTRACT FROM AUTHOR]

Locally resonant phononic crystals (LRPCs) have zero group speeds along a few directions and possess bandgaps at frequencies corresponding to an order of wavelength lower than the corresponding phononic crystals of the same characteristic size. We report on a scalable, quick fabrication of metal–ceramic LRPC and its acoustic characterization using experiments and computation. Copper wires were coated with alumina by dip-coating method and assembled as a three-dimensional woodpile-kind LRPC by soldering. First, the elastic properties of alumina were estimated using a resonant ultrasound spectrometer. The properties were used to compute the bandgaps and transmission loss (TL) using the finite-element method. Ultrasonic TL measurements revealed the presence of bandgaps in the 0.6–1.2-MHz regime, which agreed with the computationally estimated TL. The computed band diagrams indicated bandgaps around 0.05 MHz, an order lower than the bandgap of an equivalent PhC of the LRPC. Furthermore, we found several directions along which the group speed was zero. This work demonstrates the use of simple, traditional fabrication methods to achieve ceramic LRPCs. [ABSTRACT FROM AUTHOR]

Dynamic attenuation is a major concern in many engineering fields, and excessive energy inputs may cause fatal damages to the key devices. Therefore, there is always a demand to pursue a novel structure with the energy attenuation capacity. A metamaterial with periodic lattice-disc unit cells inspired by the tensegrity topological configuration is proposed in this study. Both theoretical and numerical modeling are conducted to examine the effects of geometrical dimensions on the bandgaps. Two types of chains are compared, including monoatomic and diatomic ones. With the increase of the number of unit cells, the dynamic attenuation effect of the bandgaps becomes prominent. This tensegrity-inspired metamaterial is 3D-printable by additive manufacturing technology. Both frequency sweep experiment and low-speed impact test are conducted. The torsional vibration mode is identified, which is decoupled with the axial vibration mode. Both improved spring-mass model and finite element model to describe the dual modes are developed to match well with the experiments. The behaviors of metamaterial bandgaps are fully verified by both numerical simulation and experiments. This study provides a novel idea for the design of additively-manufactured metamaterials for energy dissipation. [ABSTRACT FROM AUTHOR]

Bulk ferroelectrics hold tremendous potential for the rapidly growing field of photovoltaic applications due to the separation of charge carriers caused by polarization, resulting in a high photovoltage. However, the wider bandgap in ferroelectrics limits their photoresponse. Attempts to tune the bandgap degrade ferroelectric polarization, while increased oxygen vacancy (Vo¨$\overset{\cdot\cdot}{\text{o}}$) in oxide perovskite hinders electron conduction and undermines ferroelectricity. Therefore, controlling Vo¨$\overset{\cdot\cdot}{\text{o}}$ and maintaining polarization in reduced bandgap ferroelectric photovoltaics remains challenging. To address this, aliovalent Fe3+ and Nb5+ are co‐substituted on the B‐site of Na0.5Bi0.5TiO3 ceramics. Various techniques confirm the controlled Vo¨$\overset{\cdot\cdot}{\text{o}}$ concentration, and UV‐absorption data reveal a reduction in bandgap energy from 3.01 to 2.38 eV through metal substitution. Density functional theory calculations identify a localized intermediate gap state within the bandgap, created by Fe–O hybridization, acting as a charge carrier scaffold and further reducing the bandgap energy to 2.47 eV. Remarkably, the Al/NBFNT75/Ag configuration achieves an augmented short‐circuit current density of 18.92 nA cm−2, while the open‐circuit voltage of the Al/NBFNT50/Ag device reaches 4.13 V. The resulting Al/NBFNT75/Ag device exhibits a maximum photovoltaic power density of 0.725 mW m−2 which is 9.5 times greater than Al/Na0.5Bi0.5TiO3/Ag. This approach successfully reduces Vo¨$\overset{\cdot\cdot}{\text{o}}$ and achieves narrow bandgap conditions through suitable aliovalent substitution, leading to enhanced photovoltaic power, photosensing response, photoresponsivity, and specific detectivity. [ABSTRACT FROM AUTHOR]

The presented research delineates an extensive study aimed at obtaining and comparing optimal designs and geometries for one-dimensional periodic acoustic metamaterials to attenuate noise within the audible frequency range of 20 Hz to 20 kHz. Various periodic designs, encompassing diverse geometric parameters and shapes—from Basic-Periodic to Semi-Periodic, Tapered-Diverging, and Tapered-Converging unit cells of repeated patterns—are examined to identify the most effective configurations for this application. A thorough parametric analysis is executed employing FE-Bloch’s theorem across these four configurations to determine their bandgaps and to identify the most effective geometry. A normalization process is utilized to extend the domain of the analysis and the range of the system parameters studied in this work, totaling 202,505 design cases. Finally, the optimal design is identified based on achieving the best bandgaps coverage. The study concludes with the presentation of frequency domain acoustic pressure responses at multiple sensing points along the filters, validating the performance and the obtained bandgaps through these optimal geometries.

The deflection and the control of the effects of the complex urban seismic wavefield on the built environment is a major challenge in earthquake engineering. The interactions between the soil and the structures and between the structures strongly modify the lateral variability of ground motion seen in connection to earthquake damage. Here we investigate the idea that flexural and compressional resonances of tall turbines in a wind farm strongly influence the propagation of the seismic wavefield. A large-scale geophysical experiment demonstrates that surface waves are strongly damped in several distinct frequency bands when interacting at the resonances of a set of wind turbines. The ground-anchored arrangement of these turbines produces unusual amplitude and phase patterns in the observed seismic wavefield, in the intensity ratio between stations inside and outside the wind farm and in surface wave polarization while there is no metamaterial-like complete extinction of the wavefield. This demonstration is done by setting up a dense grid of 400 geophones and another set of radial broadband stations outside the wind farm to study the properties of the seismic wavefield propagating through the wind farm. Additional geophysical equipment (e.g., an optical fiber, rotational and barometric sensors) was used to provide essential explanatory and complementary measurements. A numerical model of the turbine also confirms the mechanical resonances that are responsible for the strong coupling between the wind turbines and the seismic wavefield observed in certain frequency ranges of engineering interest.

Abstract Multifunctionality as a paradigm requires materials exhibiting multiple superior properties. Integrating second‐order optical nonlinearity and large bandgap with piezoelectricity can, for example, enable broadband, strain‐tunable photonics. Though very different phenomena at distinct frequencies, both second‐order optical nonlinearity and piezoelectricity are third‐rank polar tensors present only in acentric crystal structures. However, simultaneously enhancing both phenomena is highly challenging since it involves competing effects with tradeoffs. Recently, a large switchable ferroelectric polarization of ≈80 μC cm−2 was reported in Zn1‐xMgxO films. Here, ferroelectric Zn1‐xMgxO is demonstrated to be a platform that hosts simultaneously a 30% increase in the electronic bandgap, a 50% enhancement in the second harmonic generation (SHG) coefficients, and a near 200% improvement in the piezoelectric coefficients over pure ZnO. These enhancements are shown to be due to a 400% increase in the electronic anharmonicity and a ≈200% decrease in the ionic anharmonicity with Mg substitution. Precisely controllable periodic ferroelectric domain gratings are demonstrated down to 800 nm domain width, enabling ultraviolet quasi‐phase‐matched optical harmonic generation as well as domain‐engineered piezoelectric devices.

Halide perovskites have broad bandgap tunability, making them suitable for diverse applications in optoelectronics and photovoltaics. The optical bandgap of halide perovskites varies almost linearly with the halide ionic size, and therefore, it can be controlled through compositional engineering. However, the mechanism underlying this low‐bandgap variation is not yet fully understood. Thus, this study comprehensively investigates the bandgap bowing of cesium–lead mixed‐halide perovskites using compositional engineering and demonstrates that bandgap bowing is extremely small in a variety of compositions including Cl, Br, and I. Subsequently, through density functional theory calculations, it is suggested that the antibonding character of the valence band maximum, tilt distortion of halide ions, and entropy effect leading to equal participation of various halide ions around Pb are collectively responsible for the small bandgap bowing. [ABSTRACT FROM AUTHOR]

The existence of an ultra-wide acoustic bandgap of novel nanophononic crystal in gigahertz (GHz) frequency ranges for a one-dimensional (1D) in the "out-of-plane" modes, and a two-dimensional (2D) in the "out-of-plane" modes is investigates. The maximum bandgap ratio up-to 141% for ultra-high frequency range of phononic crystal is also investigated. The results demonstrate that the transmission spectrum amplitude and bandgap of phononic crystal strongly agree in the same frequency region. It has been investigated that when the resonator is employed with phononic crystal the Qanchor increase from 6340 to 7.65 × 1010. So the quality Q of resonator is boost very high, and the insertion loss is reduced to 91.98% by employing the proposed nanophononic crystal to resonator. Furthermore, this work verifies the propagation of acoustic waves is completely banned through proposed nanophononic crystal, and the transmission response of this phononic crystal is also verified by delay line configurations. [ABSTRACT FROM AUTHOR]

Bifacial perovskite (PVK)/crystalline silicon (c‐Si) tandem photovoltaic (PV) modules provide an effective strategy to further improve the efficiency and energy yield (EY) of c‐Si PV modules. In this work, the energy outputs of bifacial tandem PV modules under outdoor conditions are analyzed by combining optical modeling, one‐diode equivalent circuit model, module tilt angle, and meteorological data, and a detailed comparative study with bifacial silicon heterojunction (SHJ) PV modules is also performed. The bifacial PVK/c‐Si tandem modules exhibit higher EY in locations with strong direct normal irradiance regardless of the ground type with any albedo, while bifacial SHJ modules exhibit similar or even higher EY than tandem modules in locations with strong diffuse horizontal irradiance (DHI) such as Chengdu. Considering factors such as EY and levelized cost of electricity, Eg_PVK in the range of 1.58–1.62 eV is suitable for most application scenarios, while the deployment of bifacial SHJ PV modules is preferred in areas dominated by DHI, as represented by Chengdu. Herein, important implications for policy making in determining the cost‐effective type of PV modules are provided to generate renewable electricity. [ABSTRACT FROM AUTHOR]

Using a microscopic model, the magnetic and electric properties of pure and ion‐doped (on the Lu or Fe sites) hexagonal LuFeO3 (LuFO) are studied and compared with the properties of ion‐doped LaFeO3 (LaFO). The magnetization increases by Sr and Sc doping which is caused by the strain and the changes of the exchange interaction constants at the doped states. It is observed that by Sm doping of LuFO the polarization decreases, whereas by Sm doping of LaFO, the polarization increases with increasing Sm concentration. By Ir or Co ion doping on the Fe site, the magnetization and the phonon energy increase whereas the bandgap energy decreases. By doping on the Fe sites with the same ion, for example, Sc, there are no differences between LuFO and LaFO. A good agreement with the experimental data is observed. The doping effects can be used for different applications. [ABSTRACT FROM AUTHOR]

Using a microscopic model, the magnetic and electric properties of pure and ion‐doped (on the Lu or Fe sites) hexagonal LuFeO3 (LuFO) are studied and compared with the properties of ion‐doped LaFeO3 (LaFO). The magnetization increases by Sr and Sc doping which is caused by the strain and the changes of the exchange interaction constants at the doped states. It is observed that by Sm doping of LuFO the polarization decreases, whereas by Sm doping of LaFO, the polarization increases with increasing Sm concentration. By Ir or Co ion doping on the Fe site, the magnetization and the phonon energy increase whereas the bandgap energy decreases. By doping on the Fe sites with the same ion, for example, Sc, there are no differences between LuFO and LaFO. A good agreement with the experimental data is observed. The doping effects can be used for different applications. [ABSTRACT FROM AUTHOR]

In this work, the structural, electronic, elastic, and optical properties of X3Sb2Au3 (X = K, Rb) ternary compounds have been investigated using the density-functional theory method as implemented in the quantum espresso package. The generalized gradient approximation has been adopted in performing the calculations. The computed lattice parameters have been found to be in agreement with the available experimental and theoretical results. The K3Sb2Au3 and Rb3Sb2Au3 compounds have been found to be semiconductors with direct bandgaps of 1.236 eV and 1.353 eV, respectively. The compounds have also been found to be mechanically stable at zero pressure, ductile, and nearly metallic and therefore possess suitable attributes for industrial applications. The complex dielectric functions, absorption coefficients, reflectivity, refractive index, and energy loss spectra have also been presented. Refractive indices of 3.41 and 3.11 for K3Sb2Au3 and Rb3Sb2Au3 have also been calculated. The high refractive indices, high absorption coefficients, as well as the wide energy coverage of the absorption spectra, mostly in the ultraviolet–visible (UV–Vis) regions make the K3Sb2Au3 and Rb3Sb2Au3 compounds excellent UV–Vis light absorbers which are some of the essential characteristics for materials for photovoltaic applications. [ABSTRACT FROM AUTHOR]

We present the general conditions to realize a fourth-order exceptional point of degeneracy (EPD) in two uniform (i.e., invariant along z) lossless and gainless coupled transmission lines (CTLs), namely, a degenerate band edge (DBE). Until now the DBE has been shown only in periodic structures. In contrast, the CTLs considered here are uniform and subdivided into four cases where the two TLs support combinations of forward propagation, backward propagation, and evanescent modes (when neglecting the mutual coupling). We demonstrate, for the first time, that a DBE is supported in uniform CTLs when there is proper coupling between: 1) propagating modes and evanescent modes, 2) forward and backward propagating modes, or 3) four evanescent modes (two in each direction). We also show that the loaded quality factor of uniform CTLs exhibiting a fourth-order EPD at k=0 is robust to series losses due to the fact that the degenerate modes do not advance in phase. We also provide a microstrip possible implementation of a uniform CTL exhibiting a DBE using periodic series capacitors with very subwavelength unit-cell length. Finally, we show an experimental verification of the existence DBE for a microstrip implementation of a CTL supporting coupled propagating and evanescent modes.

Light‐harvesting materials with dynamical management of light transmittance hold great promise in smart photovoltaics (PV). Here, a novel organic–inorganic halide, MVBi2I8 (MV = methyl viologen cation), exhibiting reversible thermochromism and constant bandgap of ≈1.65 eV over a wide temperature range of 77–453 K, is presented as a candidate. The compound consists of 0D (Bi4I16)4– clusters and MV2+ cations. And the adjacent (Bi4I16)4– clusters are in touch with each other, forming a 3D interaction for the inorganic part. The experimental and theoretical studies reveal that the ionic and covalent interactions in the crystal undergo a self‐adjusting process in response to temperature changes. The self‐adjustment and electron transfer between inorganic clusters and organic cations enable excellent reversible thermochromism and constant narrow bandgaps over a wide temperature range, which is expected for smart PV windows integrated with information displays and potentially other technologies. [ABSTRACT FROM AUTHOR]

2D materials that possess multifunctional properties are of great interest for applications in semiconducting devices. Herein, a series of novel Janus XYP2 (X/Y = Si, Ge, Sn, and Pb; X ≠ Y) monolayers with good stability, electronic, mechanical, piezoelectric properties, as well as ferromagnetic properties are predicted based on density functional theory. They are all indirect‐bandgap semiconductors with bandgaps varying from 0.56 to 2.18 eV. The monolayers exhibit in‐plane and out‐of‐plane piezoelectricity with large piezoelectric coefficients, suggesting that they are promising piezoelectric materials for nanoelectromechanical systems. In SiGeP2, GeSnP2, and SnPbP2 monolayers, hole doping is found to be an effective approach in inducing or tuning different ferromagnetic states resulting from electronic instability as reflected by van Hove singularity of band structures in the 2D systems. The results suggest that Janus XYP2 monolayers can be promising 2D materials for applications in nanoelectronic, spintronic, and nanoelectromechanical devices. [ABSTRACT FROM AUTHOR]

Suture joints contribute to the exceptional combination of stiffness, strength, toughness and efficient load bearing and transmission of many biological structures like the cranium or ammonite fossil shells. However, their role in the attenuation of vibrations and effect on dynamic loads is less clear. Moreover, the self-similar hierarchical geometry often associated with suture joints renders its treatment with standard numerical approaches computationally prohibitive. To address this problem, this paper investigates the dynamic response of periodic layered media with suture joints using an analytical approach based on material homogenization. A general trapezoidal suture geometry is considered together with the fundamental ingredients of hierarchy and viscoelasticity. The Spectral Element Method and Bloch theorem are used to derive the dispersion relation and band diagram of the system, including propagating and evanescent dispersion modes. A strong influence of the suture morphology and material properties emerges, and the analysis reveals an important advantage of adding hierarchy, i.e. the possibility of simultaneously obtaining wider bandgaps and their shift to higher frequencies. A synergy between hierarchy and structure is also observed, providing superior levels of wave attenuation. These findings suggest a possible design concept for bioinspired devices with efficient and tailorable wave attenuation properties. [ABSTRACT FROM AUTHOR]

We present the results of a numerical study on a seismic metasurface that achieves wide bandgap for low frequencies and with relatively smaller resonators. The metasurface consists of periodic concrete pillars with rigid caps supported on rubber between the caps and pillars and placed above ground. The study shows that such a metasurface creates a barrier against elastic waves having frequencies in the seismic frequency range. The results are further validated by a frequency-domain and time-transient study. The proposed metasurface configuration is simple and can be realized with readily available materials.

Herein, a structural design for labyrinthine acoustic metamaterial is proposed using a topology optimization method to realize a subwavelength bandgap preventing the transmission of low‐frequency sounds. The optimized design is composed of air‐filled channels of different widths, which exhibit the subwavelength bandgap based on the monopole resonance induced in the meta‐atom. In addition to the optimized meta‐atom design, a simplified meta‐atom design with a small coiling coefficient is proposed by extracting structural features of the optimized design. The bandwidth and central frequency of the subwavelength bandgap can be controlled by adjusting the size parameters of the simplified meta‐atom. Numerical analysis for acoustic waves based on the finite‐element method is conducted to demonstrate the low transmission coefficients of the obtained designs for a wide‐ and low‐frequency range. Furthermore, using a 3D printer, experimental specimens of optimized and simplified meta‐atoms are constructed, and impedance tube experiments are performed to show their functionality. [ABSTRACT FROM AUTHOR]

Locally resonant (LR) metamaterial structures possess bandgaps in which wave propagation is significantly attenuated. In this paper, we discuss flexural wave bandgaps in an LR beam subjected to a global axial force and multiple vertical elastic supports. An array of inerter-based dynamic vibration absorbers (IDVAs) was periodically attached to the LR beam. The flexural wave band structure of this prestressed multisupported LR beam was first derived using the transfer matrix method (TMM) and then explicitly illustrated through a numerical example. Four bandgaps were identified: a bandgap located in the low-frequency zone, a Bragg band generated by Bragg scattering, and two LR bands generated by the local resonance of the IDVAs. The effects of the IDVA parameters, axial force, and vertical elastic support on the properties of the bandgaps were evaluated. In particular, the bandgaps merged accompanied by an exchange of their edge frequencies. The bandwidth of the merged bandgap was nearly equal to the sum of the bandwidths of the bandgaps involved, indicating a method for controlling broadband flexural vibration through the bandgap splicing mechanism. [ABSTRACT FROM AUTHOR]

Herein, a novel star‐shaped hybrid acoustic metamaterial structure is proposed. Based on Bloch's theorem and the finite element method, the bandgap characteristics and the bandgap formation mechanism of different combinations of structures are first analyzed. Then, the propagation characteristics of elastic waves in Model C2 are studied with focus on equal frequency contours, phase velocity, and group velocity. And the attenuation of elastic waves in the finite size structure of Model C2 illustrates that the elastic waves are effectively suppressed in the bandgap frequency range, which further confirms the perfect correspondence between the bandgap and the vibration attenuation region. Finally, the influence of structural parameters on the bandgap is analyzed, as well as the change of the bandgap when the structure undergoes large deformation, which can realize the tunability and flexibility of the bandgap. This study provides important clues for the design of vibration isolators and metamaterials, and shows the good engineering application potential of the structure for vibration isolation. [ABSTRACT FROM AUTHOR]

Designing artificial microstructural metamaterials that fulfill the single‐phase vibration dampening and lightweight twin goals is challenging and critical. 2D curved and chiral hybrid star‐shaped metamaterials (CCHSM) are proposed to perform vibration reduction filtering in the midfrequency region by combining the properties of chiral structure and concave structure. The generating process of the bandgap of in‐plane elastic waves, the properties of directional attenuation, and the flow direction of energy in the dispersion curve are examined using the modal shape, dispersion surface, and group velocity. In a specific frequency range, the equivalent medium parameters satisfy the conditions of negative refraction transverse and longitudinal waves, so the structure also has double‐negative characteristics. The filtering performance is validated using the CCHSM periodic plate structure and a finite‐element simulation of transmission loss. In addition, the correlation between wave attenuation characteristics and structural parameters is explored. The radius of the circular arc and the deflection angle of the connecting rod have a significant impact on the frequency range of the structural bandgap. The results show that the created simple‐configured, single‐phase lightweight acoustic metamaterials exhibit strong local resonance properties and double‐negative features. [ABSTRACT FROM AUTHOR]

In solid state physics, a bandgap (BG) refers to a range of energies where no electronic states can exist. This concept was extended to classical waves, spawning the entire fields of photonic and phononic crystals where BGs are frequency (or wavelength) intervals where wave propagation is prohibited. For elastic waves, BGs are found in periodically alternating mechanical properties (i.e., stiffness and density). This gives birth to phononic crystals and later elastic metamaterials that have enabled unprecedented functionalities for a wide range of applications. Planar metamaterials are built for vibration shielding, while a myriad of works focus on integrating phononic crystals in microsystems for filtering, waveguiding, and dynamical strain energy confinement in optomechanical systems. Furthermore, the past decade has witnessed the rise of topological insulators, which leads to the creation of elastodynamic analogs of topological insulators for robust manipulation of mechanical waves. Meanwhile, additive manufacturing has enabled the realization of 3D architected elastic metamaterials, which extends their functionalities. This review aims to comprehensively delineate the rich physical background and the state‐of‐the art in elastic metamaterials and phononic crystals that possess engineered BGs for different functionalities and applications, and to provide a roadmap for future directions of these manmade materials. [ABSTRACT FROM AUTHOR]

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We report comprehensive work on the fabrication of alumina-based phononic crystals (PhCs) using direct ink writing (DIW), measurement of anisotropic properties, and identification of acoustic bandgaps. Woodpile-structure-kind PhCs of characteristic size 1.1 mm and 10 periods were fabricated from alumina and polyvinyl alcohol (PVA) solution, and processed by freezing under vacuum. Next, the anisotropic elastic constants of alumina were obtained from bulk specimens using resonant ultrasound spectroscopy. Band diagrams and transmission loss were computed using the finite-element method and good correlations were found between the bandgaps estimated by these methods. Multiple partial bandgaps and several local resonances were observed in many directions for frequencies below 2 MHz. This work is the first step toward developing ceramic PhC using additive manufacturing methods for high-temperature applications. [ABSTRACT FROM AUTHOR]

• Enhancement of low-frequency bandgaps of locally resonant lattices. • Amplification of resonating masses utilizing a dynamic directional amplification (DDA) mechanism. • Practical metabarrier design for seismic wave protection of structures. Locally resonant metamaterials (LRMs), with unit-cells exhibiting local resonance, present extraordinary wave propagation properties as a result of their spatial periodicity. However, these structures present certain limitations when wide bandgaps are sought, such as the need of heavy resonating masses. In this paper, a simple dynamic directional amplification (DDA) mechanism is proposed as a means to artificially increase inertia of the resonating mass. The DDA is realized by imposing kinematic constraints to the model's degrees of freedom (DoFs), hence inertia is increased by coupling the horizontal and vertical motion of a reference two-dimensional (2D) mass-in-mass lattice. A discrete element lattice model based on mass, stiffness, and damping elements, is used to establish dispersion behavior and frequency response, while results indicate broader bandgaps and significant improvements compared to the reference LRM. At last, a preliminary design of a DDA-metabarrier is presented as a proof of concept, showcasing the potential application of the mechanism as a seismic wave mitigation measure. [ABSTRACT FROM AUTHOR]

This study explores surface-wave propagation through periodic arrangements of multilayered piles in a single-layer soil medium from the viewpoint of bandgaps. The influence of the geometrical parameters of the model on the bandgaps is discussed. The periodic theory of solid-state physics is imposed to derive the dispersion equation. The finite-element method is implemented to calculate the dispersion relation and attenuation zones for surface waves in a periodic pile and soil system. The results show that the bandgaps are sensitive to the size and arrangement of the piles. The practicability of ground vibration-isolation by periodic pile barriers are verified in the time domain. The location and width of bandgaps are further authenticated through finite unit cell–based frequency response analyses. It is found that the frequency range of the Rayleigh wave reduction agrees well with the theoretical attenuation zone. This work provides new insights into the design of periodic piles as wave barriers. This approach has scope for protecting infrastructures, such as nuclear power plants, which pose high environmental risks. It is found that the dispersion analysis gives essential information for Rayleigh wave isolation using piles, including the frequency range and the form of decline. [ABSTRACT FROM AUTHOR]

Minimal cost, huge area, high throughput, high performance of photovoltaic panels, prolonged lifespan, and less toxicity are vital aspects when transitioning photovoltaic technology from lab‐scale production to industrial implementations. A new class of materials typically known as hybrid halide double perovskites (HHDPs) has emerged as a possible alternative for the replacement of toxic lead in crystal lattice for realizing lead‐free, stable, and high‐performance perovskite solar cells (PSCs). An ab initio analysis of (MA)2AgInBr6 HHDP via the WIEN2K code is conducted. It is found that this material has a direct bandgap of 3.85 eV having excellent optical properties in the UV region. The calculated thermodynamic parameters confirm its thermal stability at different temperatures and pressure. Its figure of merit is more than unity at room temperature as well as higher temperature ranges, so this material will be useful in thermoelectric (TE) devices as a TE material. [ABSTRACT FROM AUTHOR]

Double perovskite halide materials have been widely used in batteries, light‐emitting diodes, and solar cells. Thus, investigations of the fundamental properties of the double perovskite halide to search for an ideal structure are crucial. In this study, a surrogate model is developed to predict the formation energy, convex hull energy, and bandgap of A2BB′X6 type double perovskite halide structures. The material properties of 13 542 candidate structures are predicted and validated through first‐principles calculations. Without double perovskite halide information during training, the prediction accuracy for the formation energy is obtained as an R‐squared value of 0.770 and Root Mean Square Error (RMSE) of 0.404 eV atom−1. For the convex hull energy, an accuracy of 0.642 is obtained. For the bandgap, R‐squared score of 0.427 and an RMSE of 1.235 eV are achieved. Furthermore, the optimization process confirms that adding only 850 (6%) double perovskite halide structures to the training set increases the R‐squared value to 0.90 for the formation energy. In the bandgap, more data are needed; 3550 data (68.2%) are added to achieve an R‐squared score of 0.9. The current study successfully predicts the fundamental properties of double perovskite halides for the accelerated discovery of ideal structures. [ABSTRACT FROM AUTHOR]

In this paper, an innovative tetrachiral and star-shaped hybrid metamaterial (TSHM) composed of periodic assembly of single-phase lightweight materials is proposed. Based on the finite element method, the band structure of TSHM and the correlation between the bandgaps and geometric parameters are investigated. In addition, the visualization mode provided by the finite element software COMSOL Multiphysics 5.5 is used to explore the formation mechanism of the bandgaps. Furthermore, by drawing iso-frequency contours and group velocities, the directionality of elastic wave propagation in TSHM and the anisotropic behavior of metastructure are intuitively expressed. Finally, the wave regulation effect of the two-dimensional (2D) sandwich panel formed by the TSHM core is studied and the frequency response functions (FRFs) are plotted, which is another way to characterize the bandgap properties. Our research shows that the proposed periodic metamaterial has excellent wave attenuation performance in multiple frequency ranges, which will provide a valuable reference for vibration and noise reduction projects. [ABSTRACT FROM AUTHOR]

To investigate the properties of elastic waves propagating in the periodic ballasted track, a double-rail phononic crystal (DRPC) model which consists of two parallel rails fastened on equally spaced sleepers supported by ballast is proposed in this study. The presented numerical results show that there are twelve characteristic waves occurring in the DRPC. These waves can be divided into three kinds. Within the calculated frequency range, the first kind of characteristic wave always propagates except an initial lower frequency range. The second kind of characteristic wave has alternative pass bands and stop bands, showing obvious phononic property of the DRPC. The wavenumbers of the third kind of characteristic wave have larger imaginary parts, implying that this kind of wave is evanescent wave and can only propagate a few spans of the track away from the source. The numerical results show more advantages of the DRPC for explaining the elastic wave propagation mechanism in the ballasted track than the single-rail phononic crystal (SRPC) model. [ABSTRACT FROM AUTHOR]

Sonic crystals (SCs) are unique periodic structures designed to attenuate acoustic waves in tunable frequency bands known as bandgaps. Though previous works on conventional uniform SCs show good insertion loss (IL) inside the bandgaps, this work is focused on widening their bandgaps and achieving better IL inside the bandgaps by using a gradient-based sonic crystal (GBSC). The GBSC applies property gradient to the conventional SC array by varying its basic properties, i.e., the distance between the scatterers/resonators (lattice constant), and resonator dimensions between the columns and hence the name GBSC. The design of the GBSC is backed by the results of acoustic beamforming experiments conducted over the uniform SCs of hollow scatterers and Helmholtz resonators (HRs) having two-dimensional (2D) periodicity prepared by using Polyvinyl chloride (PVC) pipes without any property gradient and their respective 2D finite element (FE) studies. The experimental and FE simulation results of the uniform SCs were found to be in good agreement and therefore, the GBSC was modeled and analyzed using FE method considering the viscothermal losses inside the resonators. The results indicated that the property gradient improves both Bragg scattering and Helmholtz resonance compared to that of the uniform SCs and therefore, the GBSC exhibits wider attenuation gaps and higher attenuation levels. An array of 30 microphones was used to conduct acoustic beamforming experiments on the uniform SCs. Beamforming was found to be an advanced and fast method to perform quick measurements on the SCs. [ABSTRACT FROM AUTHOR]

In recent years, conjugated microporous polymers (CMPs) have become important precursors for environmental and energy applications, compared with inorganic electrode materials, due to their ease of preparation, facile charge storage process, π-conjugated structures, relatively high thermal and chemical stability, abundance in nature, and high surface areas. Therefore, in this study, we designed and prepared new benzobisthiadiazole (BBT)-linked CMPs (BBT–CMPs) using a simple Sonogashira couplings reaction by reaction of 4,8-dibromobenzo(1,2-c;4,5-c′)bis(1,2,5)thiadiazole (BBT–Br2) with ethynyl derivatives of triphenylamine (TPA-T), pyrene (Py-T), and tetraphenylethene (TPE-T), respectively, to afford TPA–BBT–CMP, Py–BBT–CMP, and TPE–BBT–CMP. The chemical structure and properties of BBT–CMPs such as surface areas, pore size, surface morphologies, and thermal stability using different measurements were discussed in detail. Among the studied BBT–CMPs, we revealed that TPE–BBT–CMP displayed high degradation temperature, up to 340 °C, with high char yield and regular, aggregated sphere based on thermogravimetric analysis (TGA) and scanning electron microscopy (SEM), respectively. Furthermore, the Py–BBT–CMP as organic electrode showed an outstanding specific capacitance of 228 F g−1 and superior capacitance stability of 93.2% (over 2000 cycles). Based on theoretical results, an important role of BBT–CMPs, due to their electronic structure, was revealed to be enhancing the charge storage. Furthermore, all three CMP polymers featured a high conjugation system, leading to improved electron conduction and small bandgaps. [ABSTRACT FROM AUTHOR]

In this paper, we investigated the bandgaps of two-dimensional phononic crystals with quasi- Sierpinski carpet unit cells in a metacomposite based solid–solid phononic crystal. Finite element method was used to analyze the properties of two-dimensional phononic bandgaps (2D PBGs) in a quasi-fractal structure. Two new types of quasi-Sierpinski fractal unit cells whose constituents are homogeneous and isotropic were proposed to obtain larger full bandgaps. The results show that the PBGs of the proposed quasi-Sierpinski fractals are suitable to tune the PBG’s without changing the size of the phonic crystal. The new quasi-Sierpinski fractals also retain the selfsimilarity as in the third-order Sierpinski fractal unit cell. The investigated quasi-fractals can be easily modified to increase the filling fraction of the constituents, which can be effectively used to enlarge existing PBG by preserving degree of self-similarity structure. [ABSTRACT FROM AUTHOR]

Metal chalcohalides have recently been highlighted as so‐far overlooked semiconductors that could play an important role in the future of photovoltaics (PV). Indeed, the blooming field of emergent PV technologies is still in search for stable, efficient, and environmentally‐friendly light‐harvesting materials to be used either in single‐junction solar cells or multijunction devices in combination with silicon or another absorbers. Under the broad terms of metal chalcohalides, there exists a plethora of semiconductor materials with different chemical, structural, and optoelectronic characteristics. While some have already been implemented in solar cells with power conversion efficiencies up to 4–5%, others are only theoretically described. This perspective article offers a general overview of these materials as potential next‐generation absorbers in PV and also discusses possible limitations, not only related to intrinsic materials' properties but also to processing conditions. [ABSTRACT FROM AUTHOR]