Search Results (316)

GaAs_1-xN_x/GaAs (001) (0 < x ≤ 0.037) tensile-strained epilayers are of considerable importance in optoelectronics due to their ability to offer large and resilient band structure engineering. Strain causes valence-band splitting, giant bandgap reduction and phonon frequency shifts. Optimum performance of III-V-Ns in long-wavelength lasers, infrared photodetectors, optical modulators, and multi-junction solar cells is contingent on their distinctive vibrational and optical characteristics. We report results of meticulous simulations of GaAs_1-xN_x alloys to validate Fourier transform infrared (FTIR) reflectivity and spectroscopic ellipsometry (SE) data in the far-infrared and ultraviolet regions. The FTIR spectra showed strong reflectivity peaks and dips in the reststrahlen band region, linked to the transverse optical ${\omega }_{\mathrm{T}\mathrm{O}1}$ and longitudinal optical ${\omega }_{\mathrm{L}\mathrm{O}1}$ modes of the Ga-As bond and a high-frequency ${\omega }_{\mathrm{T}\mathrm{O}2}$ local vibrational mode of GaAs:N. Modified dielectric functions of GaAs_1-xN_x/GaAs epilayers are carefully evaluated using an improved Adachi’s semiemperical method to study the x and E-dependent optical constants. Focusing on the electronic band structures at critical points, this approach provided accurate analytical formulation to evaluate complex dielectric $\tilde{\epsilon }$(E) and refractive indices $\tilde{\mathrm{n}}$(E) for simulating reflectance spectra in a wide energy range with good agreement to the SE data. Full article

This study investigated context-associated variation in vocalizations in Malinois dogs through acoustic parameter analysis. Vocalizations from thirty adult Malinois dogs (15 males, 15 females) aged 2 to 3 years were recorded across 11 behaviourally defined contexts. Using Praat software, key acoustic parameters—fundamental frequency (F0), harmonic-to-noise ratio (HNR), and formant frequencies—were extracted and analyzed. Results indicated that different vocalization types (barking, whimpering, growling, snarling, howling) exhibited distinct acoustic profiles. Whimpering and howling showed significantly higher F0 values than barking (p < 0.05), with whimpering uniquely displaying both low and high F0 components. Dogs in contexts expected to be positively valenced (e.g., food anticipation) showed lower HNR than those in contexts expected to be negatively valenced (e.g., separation) (p < 0.05). However, the actual internal states were not independently verified. Formant analysis revealed that snarling and howling had lower Formant 1 (F1) values (p < 0.05), while formant dispersion varied with emotional state. These findings suggest that acoustic analysis of dog vocalizations can provide objective insights into dogs’ motivational and arousal changes, thereby improving our understanding of canine vocal communication, social behavior, and the human–dog bond. This approach has potential applications for working-line Malinois breeding programs and for enhancing human–working dog interactions. Full article

Ten compounds have been prepared among them six different dioxido(pyridine-2,6-dicarboxylato)vanadate(V) compounds with piperazinium (H₂pip²⁺) (1·6H₂O), methylpiperazinium (H₂mepip²⁺) (2·5H₂O), ethylpiperazinium (H₂etpip²⁺) (3·3H₂O), isopropylpiperazinium (H₂isopip²⁺) (4·H₂O), phenylpiperazinium (Hphepip⁺) (5∙H₂O) and thiomorpholinium 1-oxide (HtmorO⁺) (6·2,6-H₂pydc·2H₂O) cations as counterions as well as methylpiperazinium (H₂mepip²⁺) salt of a mixed valence vanadium [VO(2,6-pydc)-(μ-O)-VO(H₂O)(2,6-pydc)]⁻ complex (7), thiomorpholin-4-ium vanadate (Htmor)VO₃ (8), hexa(thiomorpholin-4-ium) decavanadate hexahydrate (Htmor)₆[V₁₀O₂₈]·6H₂O (9·6H₂O) and organic salt cocrystal thiomorpholin-4-ium 6-carboxypicolinate pyridine-2,6-dicarboxylic acid (Htmor)⁺(2,6-Hpydc)⁻∙(2,6-H₂pydc)·2H₂O (10·2H₂O) via different pathways starting either from pyridine-2,6-dicarboxylic acid or its esters, and were structurally characterized by single-crystal X-ray diffraction. Extended hydrogen bonding interactions are present due to the presence of organic cations as well as due to the diverse roles of water molecules in the hydrogen bonding network. Centrosymmetric hydrogen bonding was found to be an important motif, and diverse supramolecular patterns were also observed due to a wide variety of C–H···O and π···π interactions stabilizing the crystal lattices. Full article

Based on density functional theory, the structural, mechanical, and photoelectric properties of the perovskite material Cs₂SeCl₆ were systematically studied under pressures ranging from 0 to 50 GPa. Analysis of structural parameters indicates that the lattice constant, unit cell volume, and bond length decrease progressively with increasing pressure. Notably, the material maintains structural stability across the entire pressure range. Electronic property calculations show that Cs₂SeCl₆ retains an indirect band gap under pressure, with the band gap value monotonically decreasing as pressure increases. The orbital contributions remain almost unchanged at different pressures. The conduction band is mainly composed of Cl-p and Se-p orbitals, while the valence band is dominated by Cl-p orbitals. The analysis of the effective mass indicates that the transport capability of charge carriers is enhanced under compression. Mechanical stability and ductility were evaluated by calculating the elastic constants and derived mechanical moduli, confirming that the material remains mechanically stable under high pressure. Optical properties were investigated by computing the dielectric function, reflectivity, refractive index, optical absorption coefficient, and extinction coefficient. Collectively, the findings of this work demonstrate that the pressurized Cs₂SeCl₆ exhibits excellent structural robustness, improved charge transport, and promising photoelectric performance, making it a strong candidate for applications in solar cells and other photoelectronic devices. Full article

In this study, density functional theory (DFT) within the generalized gradient approximation (GGA) is employed to investigate the structural, electronic, mechanical, and thermoelectric properties of perovskite hydrides XZrH₃ (X = Mg, Ca, Sr, Ba). Mechanical stability and ductility are evaluated through the Cauchy pressure, Pugh’s ratio, and Poisson’s ratio, all of which point to ductile behavior with a dominant ionic-bonding character. Electronic structure calculations reveal metallic behavior arising from band overlap at the Fermi level. Equilibrium energy–volume data are fitted with the Murnaghan equation of state, and transport coefficients are extracted using the BoltzTraP package as implemented in WIEN2k. The absence of a band gap and the overlap between valence and conduction bands confirm conductor-like behavior. Lattice thermal conductivity for MgZrH₃, CaZrH₃, SrZrH₃, and BaZrH₃ increases monotonically with temperature. Overall, the results identify MgZrH₃ in particular as a promising candidate for thermoelectric devices and solid-state hydrogen storage, thereby supporting progress toward a sustainable hydrogen economy. Full article

The pursuit of high-energy-density cathode materials has positioned LiNiO₂ as a promising candidate due to its high theoretical capacity. However, its practical application is hindered by structural instability, cation mixing, and sluggish Li-ion mobility. This study presents a strategic co-doping approach to enhance the electrochemical performance of R3m-structured LiNiO₂ by introducing Na at the Li site and Nb/Al/W at the Ni site. First-principles calculations based on density functional theory (DFT), combined with the bond valence sum energy (BVSE) method, were employed to evaluate the structural, electronic, and transport properties of the doped systems. The optimized lattice parameters reveal that co-doping induces lattice expansion and suppresses cation disorder, thereby improving structural integrity. Formation energy validates the thermodynamics of the modified structures. Furthermore, BVSE-based ion migration mapping shows that Na/Nb and Na/Al co-doping significantly broadens Li-ion diffusion pathways and lowers migration barriers compared to pristine LiNiO₂. These results demonstrate that dual-site doping is an effective strategy to overcome intrinsic limitations of Ni-rich layered oxides, offering a rational design route cathode for next-generation Li-ion battery. Full article

For the first time, the ternary Zintl phases RbCaBi and CsCaBi have been synthesized and structurally characterized via single-crystal X-ray diffraction methods. These two compounds, alongside KCaBi, are confirmed to crystallize in a tetragonal crystal system with the space group P4/nmm (no. 129) with two formula units per cell. The lattice constants increase monotonically from a = 5.3812(10) Å and c = 8.410(3) Å for KCaBi, to a = 5.4139(7) Å and c = 8.6180(17) Å for RbCaBi, and to a = 5.4709(11) Å and c = 8.914(3) Å for CsCaBi. The crystal structure can be visualized as an array of square prisms formed of Bi atoms, which are centered by alkali metal atoms, while the Ca atoms fill tetrahedra formed of Bi atoms. There are no direct Bi–Bi interactions in the crystal structure; therefore, with full cation ordering present, the chemical bonding in the ACaBi compounds can be rationalized within the fully ionic approximation as A⁺Ca²⁺Bi³⁻ (A = K, Rb, Cs). This suggests the opening of an (narrow) energy gap between the valence and conduction bands, i.e., semiconducting behavior. Full article

This review presents the covalent chemistry of carbon from the point of the spin-radical concept of electron interaction in the framework of the unrestricted molecular orbitals (UHF MO) theory. Using the language of valence bond trimodality, the regions of classical spinless spin-symmetric covalence and its spin-dependent asymmetric counterpart are defined. Carbon is the only element exhibiting spin covalent chemistry. Classical covalent chemistry of carbon of molecular substances whose valence bond structure includes segregate or chained single sp³$C-C$ bonds meet its spin counterpart only at these bonds breaking. Substances with double sp²$C=C$ and triple sp¹$C\equiv C$ bonds are the subject of spin covalent chemistry of carbon. The mathematical apparatus of the UHF MO allows forming algorithms controlling the chemical modification of carbon substances, polymerization processes, and catalysis involving them, making it possible to supplement the empirical spin covalent chemistry of carbon with its virtual analog. Full article

The high salt content in saline–alkali soil has a significant impact on plant nutrient absorption and water transport, severely inhibiting crop growth. Through esterification reactions, silicic acid is grafted onto humic acid to form an organic silicon fertilizer (OSiF). The unique Si-O-C bond in the material endows this new type of organic silicon-based fertilizer with the ability to effectively alleviate the harm of high-salt soil to plants. In this study, a soil column experiment was designed to systematically evaluate and compare the effects of organic silicon fertilizers with different organic silicon contents (0%, 5%, and 10%) and traditional compound fertilizers on soil water characteristics, salt ion concentration, pH value, and electrical conductivity. The results showed that the addition of an appropriate amount of organic silicon fertilizer could significantly reduce the activity of salt ions in the soil solution. Experimental data indicated that the 5% and 10% organic silicon fertilizers had the most significant effect on the consumption of major salt ions such as sodium and chloride ions. X-ray photoelectron spectroscopy (XPS) analysis revealed that the reaction of Si-O-C bonds in the soil with Lewis bases led to a shift in the valence state of the 1S electrons of silicon atoms, providing a theoretical basis for the mechanism by which silicon fertilizers alleviate high-salt stress. Full article

The development of lithium-ion batteries necessitates cathode materials that possess excellent mechanical and thermal properties in addition to electrochemical performance. As a prominent functional ceramic, the properties of spinel LiMn₂O₄ are governed by its atomic-level structure. This study systematically investigates the impact of Ni doping concentration on the mechanical and thermal properties of spinel LiNi_xMn_2−xO₄ via first-principles calculations combined with the bond valence model. The results suggest that when x = 0.25, the LiNi_xMn_2−xO₄ shows excellent mechanical properties, including a high bulk modulus and hardness, due to the favorable ratio of bond valence to bonds length in octahedra. Furthermore, this optimized composition shows a lower thermal expansion coefficient. Additionally, Ni doping concentration has a very minimal influence on the maximum tolerable temperature of the cathode material during rapid heating. Therefore, from the perspective of mechanical and thermal properties, this composition could be beneficial for improving the cycling life of the battery, since comparatively inferior mechanical properties and a higher thermal expansion coefficient make it prone to microcrack formation during charge–discharge cycles. Full article

We studied the changes of martensite average temperature T_M in a wide range of Heusler alloys derived from a Ni-Mn-Ga multifunctional compound prepared by arc melting. Based on prepared alloys and supplemented by the literature data, we demonstrated that criteria based on valence electron or non-bonding electron concentration per atom often failed in many different cases, in particular for isoelectronic compounds and Heusler alloys with Sb and Sn. Thus, we suggest an empirical criterion for estimating the temperature of martensitic transformation T_M in Ni-Mn-based Heusler alloys. It is built on valence electron concentration per atomic volume. Suggested criterion well-describes the experiment and data available in literature. Although it can be used for predicting T_M in complexly alloyed Ni-Mn-based Heusler alloys. Full article

Diffusion bonding is an exciting technology expected to open new fields of application. To further develop this technology, it is necessary to investigate the inter-diffusion phenomena that occur at the atomic level at the interface of bonded junctions. A homogeneous Cu-Cu junction and heterogeneous Cu-Al junction were fabricated using the direct diffusion bonding method. Using XPS, we investigated the phenomena of recrystallization and inter-diffusion at the interface of the bonded junction. The Cu valence band spectrum observed using XPS measurements at the interface of the homogeneous Cu-Cu direct diffusion-bonded junction revealed that diffusion-induced recrystallization occurred. In a heterogeneous Cu-Al direct diffusion-bonded junction, the valence band spectrum observation using XPS measurements showed that the valence bands of Cu and Al overlapped at the interface of the bonded junction. Using a heterogeneous Cu-Al direct diffusion-bonded junction, we investigated the inter-diffusion at the interface of the bonded junction and found that the diffusion lengths of Al atoms in the Cu region and Cu atoms in the Al region were approximately 11.8 μm and 7.85 μm, respectively. Full article

Tennantite (Cu₁₂As₄S₁₃) and enargite (Cu₃AsS₄) are two important minerals that simultaneously contain copper and arsenic. Detailed studies of their structure and properties are crucial for understanding their oxidation, flotation, and leaching. This study investigates the crystal structures, electronic properties, and reactivity of these two copper-arsenic minerals from the perspectives of atomic bonding, charge, density of states, and d-orbital splitting. The results indicate that tennantite is a crystal with mixed Cu valence states of +2 and +1 (predominantly +1), while the Cu in enargite is in the +1 state. The valence state of As in tennantite (+3) is lower than that in enargite (+5). Orbital energy level calculations show that the energy gaps between the copper d-orbitals are small in both minerals, indicating strong electron delocalization and, consequently, strong covalent character in the crystals, which is also confirmed by Mulliken bond population calculations. The presence of arsenic is the reason for the enhanced covalency. It is noteworthy that tennantite exhibits stronger covalency. The Cu 3d and As 4p electrons in tennantite are more electronically active than those in enargite. In tennantite, the strong d-electron delocalization caused by d-p hybridization between Cu and S leads to similar 3d electronic properties between 3-coordinated and 4-coordinated Cu. The energies of the five d-orbitals of the 4-coordinated Cu in enargite are lower than those of the 4-coordinated Cu in tennantite, which may affect the ability of Cu 3d electrons to enter the empty orbitals of S atoms in sulfur-containing collectors to form π back-bonding, thereby reducing the collecting ability of enargite. On the other hand, the splitting energy of the 4-coordinated Cu 3d orbitals in enargite is significantly smaller than that in tennantite, making the structure less stable and, thus, potentially more prone to dissolution. Full article

Charge-trapping memory (CTM) is a viable contender to supersede the floating gate technology in high-density flash memory applications. To this end, very reliable charge storage in CTM should be secured. This requires optimization of trap density, their energy and spatial location as well as a deep understanding of their origin. In this work, we used X-ray photoelectron spectroscopy (XPS) to investigate chemical bonds in nanolaminated and doped HfO₂/Al₂O₃ stacks in an effort to gain insight into the nature of defects in the electron/hole trapping processes. The impact of Al incorporation into the HfO₂ and rapid thermal annealing (RTA) in O₂ on the composition, stoichiometry and bonding configurations was studied. Incorporation of Al into HfO₂ leads to an increased concentration of Hf-suboxides. Subsequent RTA effectively reduces suboxides, enhances the stoichiometry of the HfO₂/Al₂O₃ stacks and facilitates intermixing at the dielectric interface, resulting in the formation of Hf–Al–O bonds. The valence band spectra indicate that both Al incorporation and RTA change the dielectric/Si band alignment in a similar way, lowering the valence band offset. The observed changes were considered in relation to the electrically active defects and traps in the structures. Full article

Photoactivatable nitric oxide donors (photoNORMs) are promising agents for controlled NO release and real-time optical tracking in biomedical theranostics. Here, we report a comprehensive density functional theory (DFT) and time-dependent DFT (TDDFT) study on a series of hybrid ruthenium–gold nanocluster systems of the general formula [(L)Ru(NO)(SH)@Au₂₀], where L = salen, bpb, porphyrin, or phthalocyanine. Structural and bonding analyses reveal that the Ru–NO bond maintains a formal {RuNO}⁶ configuration with pronounced Ru → π*(NO) backbonding, leading to partial reduction of the NO ligand and an elongated N–O bond. Natural Bond Orbital (NBO), Natural Energy Decomposition Analysis (NEDA), and Extended Transition State–Natural Orbitals for Chemical Valence (ETS–NOCV) analyses confirm that Ru–NO bonding is dominated by charge-transfer and polarization components, while Ru–S and Au–S linkages exhibit a delocalized, donor–acceptor character coupling the molecular chromophore with the metallic cluster. TDDFT results reproduce visible–near-infrared (NIR) absorption features arising from mixed metal-to-ligand and cluster-mediated charge-transfer transitions. The calculated zero–zero transition and reorganization energies predict NIR-II emission (1.8–3.8 μm), a region of high biomedical transparency, making these systems ideal candidates for luminescence-based NO sensing and therapy. This study establishes fundamental design principles for next-generation Ru-based photoNORMs integrated with plasmonic gold nanoclusters, highlighting their potential as multifunctional, optically trackable theranostic platforms. Full article