Physics of the Solid State最新文献

This manuscript explores the magnetocaloric properties of the antiperovskite compound AsNCr₃, emphasizing its potential for sustainable refrigeration applications. Employing a combination of phenomenological modeling and density functional theory, the research reveals that the material’s low magnetization, arising from antiferromagnetic spin alignment, contributes to reduced hysteresis losses and enhanced thermal stability. Key findings include moderate entropy changes, a relatively narrow operational temperature span, and field-dependent phase transitions, indicating suitability for precise thermal management. The insights offer a pathway to designing efficient, environmentally friendly refrigeration systems based on low-magnetization materials.

In this work, two Copper(II) complexes that were produced and structurally studied were obtained from salicylaldehyde benzoyl hydrazine ligands. These complexes are (1) Cu(L¹)₂Cl₂·2H₂O, and (2) Cu(L²)₂Cl₂·2H₂O. L¹ stands for Salicylaldehyde Benzoyl Hydrazine (SBH), and L² for 3-nitro salicylaldehyde benzoyl hydrazine (3NSBH). Calculations using density functional theory (DFT) were used to predict bond properties, examine electronic structures, and optimize geometries. EXAFS and XANES, two types of experimental X-ray absorption fine structure (XAFS) spectroscopy, were used to examine the oxidation state and local coordination environment of the copper centers. To examine and confirm the different coordination geometries of two Copper(II) complexes, a combined DFT and XAFS investigation was conducted. The results showed a distorted square pyramidal structure and a distorted square planar structure, respectively. Copper in both complexes is confirmed to be in a +2 oxidation state by XANES and Mulliken charge studies, which also point out variations in metal–ligand covalency depending on electron density delocalization. Moreover, two Copper(II) complexes exhibit clear structural rigidity as revealed by DFT and EXAFS investigations using vibrational modes and Debye–Waller factors. For in-depth understanding of the structural and electrical characteristics of transition metal complexes, this integrated approach shows that both computational and spectroscopic methods may be used.

Sintering (ZnO−ZnS):Ga₂O₃ alloys ([ZnS] = 0–50 mol %) has been developed using chemical vapor transport with an HCl + H₂ gas mixture as the transport agent. It has been demonstrated that this complex transport agent can form a dense gaseous medium with Zn-, O-, and S-containing species, which promotes mass transport of the sintered material, enhances the dissolution rate of Ga₂O₃ dopant, and allows to control stoichiometric deviation. Key benefits of the proposed method include a low sintering temperature of 900°C, the use of cost-effective micropowders as a material source, minimal loss of the sintered material, increased conductivity (by one order of magnitude) due to improved dissolution of Ga impurities and stoichiometric deviation in the sintered material. Additionally, the resistivity of the thin films decreases by up to one order of magnitude as a results of stoichiometric deviation of the targets. A high ZnS content in the films promotes the growth of crystallites with (100) orientation, reduces transparency, conductivity, surface roughness and increases the wettability of the coatings.

The introduction of lithium-ion solid electrolytes significantly escalates the safety risks associated with liquid electrolytes. Among various solid electrolytes, aluminium-doped Li_1.3Al_0.3Ti_1.7(PO₄)₃ (LATP) has gained attention in research due to its impressive ionic conductivity and stability in air. However, the conventional high-temperature sintering technique presents challenges like lithium loss and the formation of secondary phases. As a result, producing high-quality LATP solid electrolytes is quite challenging. Analysis of the X-ray diffraction patterns revealed that the LATP samples synthesized in this study exhibited a rhombohedral structure, consistent with the R-3c space group, and a novel method of excess lithium compensation sintering was introduced. This method utilizes lithium compensation (LiNO₃) effectively to mitigate the effects of lithium volatility. Furthermore, it serves as a sintering additive to enhance the densification of LATP during the sintering process. In this study, the optimal sample for sintering at 1050°C was identified by assessing the microstructure and electrochemical characteristics of the electrolyte, alongside an investigation of lithium doping. The lithium-doped LATP solid electrolyte, containing 10 wt% lithium, demonstrated a conductivity of 8.7 × 10⁻³ S/cm and low activation energy of 0.278 eV. On survey, the obtained results are proven to be one among the best solid electrolytes for lithium ion batteries.

This work focuses on the photoelectrical and photovoltaic characteristics of Au/δ-GaN/n-GaAs Schottky barrier diodes (SBDs), aiming to evaluate the influence of an ultra-thin GaN interlayer on their performance. The devices were experimentally fabricated and examined through current–voltage (I–V) measurements under both dark and illuminated conditions, while complementary numerical simulations were employed to gain deeper insight into their behavior. The fabricated structure exhibited good electrical quality, attributed to the GaN interlayer, with a reduced ideality factor of 1.15 and an increased Schottky barrier height of 0.81 eV. Under illumination, the device exhibits a strong wavelength-dependent photoresponse, with optimal performance in the UV-visible range (200–400 nm), as confirmed by enhanced photocurrent generation and surface photovoltage (SPV) measurements. The extracted excess carrier concentration (δn) and interface state density (N_ss) indicate that the GaN interlayer effectively passivates interface defects, minimizing recombination losses, and improving carrier collection. In addition, photovoltaic measurements indicate a pronounced short-circuit current density (J_sc) and open-circuit voltage (V_oc) at shorter wavelengths, accompanied by a consistently stable fill factor (FF) across the different wavelengths. These results highlight the device’s effectiveness in converting optical energy into electrical power. These findings contribute to the advancement of GaN/GaAs heterostructures for high-performance photodetectors and energy harvesting applications, emphasizing the crucial role of interface engineering in optimizing optoelectronic device performance.

A discrete breather (DB) is a spatially localized, large-amplitude vibrational mode in a defect-free nonlinear lattice. The discovery of DBs raised the question of how they can be excited in nonlinear lattices. One possible mechanism is supratransmission, whereby energy is transferred to the lattice from an external source at a frequency outside the phonon spectrum of the lattice. When the amplitude of the external driving is large enough, the DBs are excited and transfer energy to the lattice. In a recent study, we analyzed the supratransmission effect for the β-FPUT square lattice and demonstrated that DBs can be emitted from a pair of periodically driven particles along close-packed directions. The present work demonstrates that DBs can also be excited along the diagonal directions of the lattice. The results confirm the existence of moving DBs propagating either along a close-packed direction or a diagonal direction in the square lattice. This finding is significant because it reveals the mechanisms of energy transport in a square lattice via nonlinear excitations.

Phonon properties of CuInS₂ crystals are studied experimentally by the Raman scattering method and also theoretically from first principles using the density functional theory (DFT). From the Raman scattering studies, the frequencies of Raman-active modes have been determined. From the first principles, the phonon mode dispersion, the origin of energy states, partial densities of states (PDOS) projected on atoms, and the optical phonon frequencies have been calculated. In addition, six elastic constants с₁₁, с₁₂, с₁₃, с₃₃, с₄₄, and с₆₆ are calculated and the bulk modulus, the shear modulus, the Young’s modulus, and the Poisson ratio are determined. The Grüneisen parameter and the Debye temperature are estimated. The velocity of propagation of longitudinal and transverse acoustic waves in CuInS₂ crystals in various crystallographic directions and also temperature dependences of the thermodynamic functions (free energy, phonon part of the internal energy, entropy, and specific heat) are also calculated from the first principles.

In this study, Layered Double Hydroxide (LDH) derivative ZnCr-LDH, ZnCr-DS-LDH, and 2‑Furoyl Thiourea (FT) modified novel ZnCr-FT-LDH composites were synthesized. The structures of these composites were elucidated using FTIR, XRD, and solid-state ¹³C-NMR techniques. Thermal analysis studies were carried out using a combined TG/DTG/DTA system. Particle sizes, morphology and elemental analyzes were determined by SEM/EDX, and pore sizes and volumes were investigated by BET analysis. According to SEM analysis, the average grain sizes of ZnCr-DS-LDH, ZnCr-APTES-LDH, and ZnCr‑FT‑LDH were found to be in the range of 1.1–0.8, 0.8–0.4, and 0.6–0.4 µm, respectively. Furthermore, SEM images revealed that the particle size distribution is uniform and the particles have a lamellar structure. XRD patterns of ZnCr-LDH, ZnCr-DS-LDH, ZnCr-APTES-LDH, and ZnCr-FT-LDH confirmed that LDHs have a hydrotalcite structure (JCPDS: 00-052-0010). The basal space of ZnCr-LDH was calculated as 8.08 Å, that of ZnCr-DS-LDH was 9.59 Å, ZnCr-APTES-LDH was 9.29 Å, and the basal spacing of ZnCr-FT-LDH was calculated to be 8.65 Å based on XRD data.

In this paper, we present luminescence spectra for three types of light-emitting diodes (LEDs) with rectangular, trapezoidal and triangular InGaN/GaN multiple quantum wells (MQWs), analyzed under various bias conditions through extensive numerical analysis. The nature of luminescence spectra is analyzed on the light of energy band structure, electric field profile, carrier distribution in well and peak shifting of electron and hole concentrations. Our observation reports that the peak of emission spectra for trapezoidal QW (TQW) LED remains at the same wavelength under different bias conditions, unlike rectangular QW (RQW) and triangular QW (TNQW) LEDs. The shifting of luminescence peak towards the longer wavelength is only 1 nm for TQW LED, whereas 6 nm for RQW and 3 nm for TNQW LEDs when bias voltage changes from 0 to ±10 V. Moreover, the efficiency droop of TQW LED is very low and it is equal to 3.7%, in contrast of 27.8% for RQW and 7.4% for TNQW LEDs. Therefore, this high efficiency and color-stable lighting performance of TQW LED is useful for different photonic and optoelectronic applications.

This study investigates the quantum capacitance (({{C}_{Q}})) of a monolayer ({text{WS}}{{{text{e}}}_{2}}) under the influence of an electric field ({{Delta }_{z}}) and spin/valley Zeeman fields ({{M}_{z}}) and ({{M}_{{v}}}). The results demonstrate that at low temperatures (10, 30 K), the electric field and Zeeman fields eliminate the abrupt sharp jump in ({{C}_{Q}}), leading to a series of smoother, gradual steps. This behavior arises from the increased number of sublevels in the energy structure of ({text{WS}}{{{text{e}}}_{2}}), induced by external fields. In contrast, at room temperature (approximately 300 K), the thermodynamic effects dominate, resulting in a smooth ({{C}_{Q}}) curve, regardless of the presence of electric or Zeeman fields. The dip in ({{C}_{Q}}) within the energy gap region remains a characteristic feature of ({text{WS}}{{{text{e}}}_{2}}), reflecting its semiconductor nature with a band gap modulated by ({{Delta }_{z}}). These findings highlight the pivotal role of external fields in tuning the quantum capacitance of ({text{WS}}{{{text{e}}}_{2}}), offering potential insights for the development of advanced nanoelectronic and spintronic devices based on two-dimensional materials.