Physics of the Solid State最新文献

Lead-free 0.7BiFeO₃–0.3(BaTi_1–xCe_xO₃) ceramics with compositions of (x = 0, 0.01, 0.03, 0.05, and 0.07) were produced using a conventional solid-state reaction method. X-ray diffraction analysis was performed to examine the crystal structure and phases of the samples, verifying the rhombohedral perovskite structure of the compound. The lattice parameter and unit cell volume varied with the addition of Ce ions. Temperature and frequency variation impedance spectroscopic studies confirmed that the relaxation time and impedance real and imaginary parts decreased with increasing temperature, suggesting a normal conductive nature of the samples. The resistance values for both the grain and grain boundary followed a similar trend as the temperature varied. As the Ce doping level increased, the resistance within the grains surpassed that of the grain boundaries in all the samples. This is indicated by the reduction in the activation energy (E_τ) of the Ce-doped sample. The electric modulus and AC conductivity studies also followed a trend similar to that of the impedance studies. These studies confirm that the 0.7BiFeO₃–0.3(BaTi_1–xCe_xO₃) sample is suitable for relaxor applications.

Researches on Ba_0.85Ca_0.15Zr_0.1Ti_0.9O₃ (BCZT) ceramics revealed that their low energy storage density and efficiency limit their applications. This study prepared (1–x)Ba_0.85Ca_0.15Zr_0.1Ti_0.9O₃–xBi(Mg_0.5Ti_0.5)O₃ (abbreviated as (1–x)BCZT–xBMT, x = 0, 0.01, 0.05, 0.07, and 0.1) ceramics using the solid-state method. We looked closely at how the degree of BMT doping affected the BCZT ceramics’ structures and characteristics. The results indicate that all samples with different compositions exhibit the pure phase and dense microstructures. The doping with BMT significantly improves both energy storage efficiency and density. 0.93BCZT-0.07BMT ceramics achieve an efficiency of 65.9% and an energy storage density of 1.09 J/cm³. The improvement in energy storage performances can be attributed to appropriate BMT doping, which densifies the system, refines grain size and facilitates the transition of the system from ferroelectric to relaxor ferroelectric.

Developing efficient polycrystalline silicon (pc-Si) thin-film solar cells offers a promising route to reducing photovoltaic costs, but their performance is strongly constrained by carrier recombination. In this work, a two-dimensional device simulation is developed to analyse recombination mechanisms in pc-Si thin-film solar cells, incorporating Gaussian and tail-distributed donor- and acceptor-like traps for bulk recombination and delta-distributed traps for interface recombination. Both Shockley–Read–Hall (SRH) and auger recombination, along with interface recombination, are examined in detail. Results show that increasing defect density enhances both SRH and auger recombination, with SRH dominating below emitter doping densities of 10¹⁶ cm^–3 and auger recombination prevailing above this level; however, SRH remains dominant across absorber defect densities from 10¹⁴ to 10¹⁹ cm^–3. Interface trap densities between 10¹¹ and 10¹³ cm^–2 are found to significantly degrade performance, underscoring the need for bulk and interface trap passivation. Device performance metrics; short-circuit current density (J_SC), open-circuit voltage (V_OC), fill factor (FF), and efficiency are further evaluated against variations in absorber bandgap, absorber thickness, and emitter doping concentration. For an optimized absorber thickness of 3 μm, absorber bandgap of 1.3 eV, emitter doping of 10¹⁸ cm^–3, and interface trap density of 10¹² cm^–2, the model predicts a maximum efficiency of ~9.6%. The developed model is in good agreement with reported experimental results.

Many Heusler alloys are half-metals because of the band structure with one of the spin projections insulating and another one being metallic that provides a possibility for 100% spin-polarized current. We present the first-principles calculations of the electronic structure and magnetic properties of M-n₂Co_1‒xNi_xSn Heusler alloys for x = 0–1. The alloys crystallize in the XA-type Heusler structure. For x = 0, Mn₂CoSn is found to be a half-metal with a band gap of less than 1 eV in the majority spin direction, thus the spin-polarization of current is almost full. The other compositions are found to be metallic in the density of states with spin polarization near 0.3. The presence of Ni in Mn₂Co_1–xNi_xSn Heusler alloys results in the band gap shift to the lower energies. In Mn₂CoSn, the total magnetic moment equal to 3 µ_B satisfies the Slater–Pauling rule. With the increasing nickel concentration, the total magnetic moment decreases, however, the magnetic moment of all Mn ions become large. The Mn–Co–Ni-based alloys are promising for spintronic applications due to the high spin polarization and composition-dependent total magnetic moment.

This paper investigates the DC characteristics of a two-dimensional (2D) analytical model of AlGaN/GaN High Electron Mobility Transistor (HEMT), based on the solution of Poisson’s equation and incorporating the effects of spontaneous (({{P}_{{text{S}}}}_{{text{P}}})) and piezoelectric (({{P}_{{{text{PZ}}}}})) polarization. The behaviour of the sheet carrier density (({{n}_{s}})) is studied using a non-linear model of the Fermi level, and the two-dimensional electron gas (2DEG) current–voltage characteristics incorporate the effects of velocity saturation, field-dependent mobility, and parasitic resistances. Additionally, variations in the threshold voltage (({{V}_{{{text{th}}}}})) and ({{n}_{s}}) are examined in relation to barrier thickness (({{d}_{{{text{AlGaN}}}}})), aluminum mole fraction (n), and the doping density (({{N}_{{text{D}}}})) of the barrier layer. In predicting the 2DEG density and ({{V}_{{{text{th}}}}}) with varying n, ({{d}_{{{text{AlGaN}}}}}) and N_D, both ({{P}_{{text{S}}}}_{{text{P}}}) and ({{P}_{{{text{PZ}}}}}) polarization effects were considered. The ({{n}_{s}}) increased with ({{d}_{{{text{AlGaN}}}}}), from 1.3 × 10¹³ cm^–2 at 20 nm to 1.4 × 10¹³ cm^–2 at 34 nm, while ({{V}_{{{text{th}}}}}) shifted negatively from –4.7 to –9.4 V due to reduced gate control at higher thickness. For n, ({{n}_{s}}) rose from 1.0 × 10¹³ to 1.7 × 10¹³ cm^–2 as n increased from 0.20 to 0.30, with ({{V}_{{{text{th}}}}}) moving from –4.0 to –6.2 V, driven by enhanced polarization and carrier confinement. Similarly, increasing ({{N}_{{text{D}}}}) from 1 × 10¹⁸ to 6 × 10¹⁸ cm^–3 elevated ({{n}_{s}}) from 1.3 × 10¹³ to 1.4 × 10¹³ cm^–2 and shifted ({{V}_{{{text{th}}}}}) from –4.3 to ‒6.1 V, due to a higher supply of free electrons. The results obtained from this work closely match simulated data, confirming the validity of the model.

This study investigates the structural, electronic, elastic, and optical properties of Y_xB_1–xAs ternary alloys using first-principles calculations based on the well-established full-potential linearized augmented plane-wave (FP-LAPW) method. The equilibrium structural, phase stability, and bulk moduli were analyzed in both zinc blende and NaCl structures. Results show that NaCl is the most stable structure for the YAs (x = 1) compound, while other compositions (x = 0, 0.25, 0.50, and 0.75) favor the zinc blende phase, indicating a phase transition near x ≈ 0.79. The electronic properties were predicted using the GGA and modified Becke–Johnson (mBJ) approximations, demonstrating a transition from semiconductor to metallic behavior as yttrium content increases. The alloys exhibit significant bowing in lattice constants and band gaps caused by lattice mismatch and electronic differences between the constituent binaries. Elastic constant calculations reveal a change in mechanical behavior with composition, emphasizing yttrium’s role in tuning the ductility of Y_xB_1–xAs alloys. Optical properties such as the dielectric function, refractive index, and reflectivity were also examined, showing strong composition-dependent behavior. These findings provide insights for tailoring the properties of Y_xB_1–xAs compounds for potential optoelectronic applications.

The pseudo-potential approach (EPM) in the virtual crystal approximation (VCA) is used to estimate the mechanical and lattice dynamic properties of GaAs_1–xP_x alloys as a function of temperature. The results show a generally good agreement with the experimental data, which are available only for the binary compounds of interest. These results include the elastic constants, bulk modulus, Young’s modulus, shear modulus, bond bending constant, bond stretching constant, and sound velocity. Our findings show that the investigated alloy achieves mechanical stability at various temperatures. To the best of our knowledge, no previous research of this type has been reported for GaAs_1–xP_x alloys under temperature effects. According to the results, the alloy under investigation may provide a greater range of possibilities for obtaining the required properties with the right temperature setting, which would make it easier to create new materials with the required properties.

Kinetic regularities of hydroxychloroquine sulfate (HCQ) degradation in an aqueous medium during UV radiation and also in the presence of an oxidizer in the UV/HCQ/H₂O₂ system and a catalyst in the photo-Fenton system are established. The degree of degradation for 1 h of irradiation is found to reach up to 50.4% in the dependence on the concentration prepared. The kinetics of HCQ degradation follows the kinetics of pseudo-monomolecular reaction. The calculated reaction rate constants vary in the range of (0.4‒8.4) × 10^–3 min^–1. The degree of drug degradation in the presence of H₂O₂ reaches 78.9% at optimal conditions ([Н₂О₂] = 85 mg/L, t = 25°C, λ = 220 nm, pH = 4.5). During the degradation in the photo-Fenton system, the dependence of the reaction rate on molar [H₂O₂]/[Fe²⁺] ratio is also studied. The study revealed that, in the concentration range ([Fe²⁺] = 0.28–1.12 mg/L, [H₂O₂] = 85 mg/L, t = 25°C, λ = 220 nm, the optimal [H₂O₂]/[Fe²⁺] ratio = 80 at pH = 4.5, and the degree of hydroxychloroquine sulfate degradation in the photo-Fenton system is 86.1%. The apparent reaction rate constants calculated at various [H₂O₂]/[Fe²⁺] ratios from 1 : 50 to 1 : 200 have values in the range of (4.1–5.5) × 10^–2 min^–1.

Zinc oxide (ZnO) thin films are known for their remarkable optical and electrical properties, m-aking them highly suitable for a wide range of applications in electronics, optoelectronics, and sensing devices (detectors). The current research carried out a detailed study on the deposition and characterization of zinc oxide thin films using the pulsed laser deposition (PLD) technique on two different substrates: silicon (p‑type) and glass (amorphous). Depositions were carried out at a base pressure of  (8 times {{10}^{{ - 6}}}) mbar in a vacuum, and in an oxygen environment at a pressure of (1.5 times {{10}^{{ - 1}}}) mbar. A solid ZnO target was ablated using the third harmonics (355 nm) of a Q-switched Nd:YAG laser operated at a laser pulse energy of 38 mJ with a corresponding laser fluence of 47 J/cm². Substrate temperature was maintained at 500°C for a deposition time of 40 min. The structural, morphological, optical, and electrical properties of the thin films were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, and the four-probe method. The thin film grown in an oxygen environment on the silicon substrate shows the best crystalline structure, while both thin films grown in a vacuum exhibit an amorphous nature. Electrical characterization performed using the four-probe method revealed a decrease in resistivity with increasing temperature for all deposited films; however, the thin film grown on a glass substrate in an oxygen atmosphere exhibited comparatively higher resistivity.