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Novel Sillenites Bi25Fe(1−x)AlxO40 (x = 0.00, 0.20, and x = 0.50) have been synthesized using the SSR method. In this paper, the effect of Al-substitution on the physicochemical properties was performed. The X-ray diffraction analysis as well as both Raman and FT-IR spectroscopies indicate that all the elaborated materials have a bcc structure with the I23 space group. The increase of the cell parameters, the morphological features, and thus the decrease of the grain size with Aluminum content is also evidenced via the X-ray patterns and SEM microscopy. DSC measurements highlighted the occurrence of various phenomena related to both structural and dielectric features. The temperature dependence of electrical conductivity and the deduced activation energies pointed to the effect of temperature on the conduction process. The impedance analysis on the samples confirms the onset of relaxation phenomenon in the sample with semiconducting behavior. Furthermore, an AFM-Paramagnetic transition for x = 0.00 and 0.20, with Neel temperatures of 268 and 265 K, respectively. Otherwise, paramagnetic behavior is observed for x = 0.50. The optical measurements make these materials suitable candidates for photocatalysis and optoelectronic applications. [ABSTRACT FROM AUTHOR]

The iron-sillenite Bi25FeO40 has been synthesized using the solid-state reaction route. The elaborated material crystallizes in a cubic structure. The studied material exhibits an anomaly, noticed via the DSC analysis and dielectric measurements at 671 K. This anomaly can be attributed to the occurrence of a thermally activated relaxation in the Bi25FeO40 sample. Besides, the magnetic study revealed the antiferromagnetic behaviour of γ-Bi25FeO40 sillenite, with a 240 K of Neel temperature TN, Curie constant of 9.18 10–8 m3.K/mol, resulting in a magnetic moment of 6.37 μB. Furthermore, the band gap of Bi25FeO40 is about 2.02 eV and the magnetic behavior makes it an appropriate candidate as a photocatalyst for water and/or wastewater treatment, and degradation of pollutants, that can be simply recycled by magnetic separation. [ABSTRACT FROM AUTHOR]

The pure STiO3 has been experimentally demonstrated to catalyze H2 production using water splitting, but the reaction can only be driven by Ultraviolet (UV) radiation due to the large band gap of SrTiO3. This motivated us to search efficient strategy to tune its band gap, so that it can function in the visible region of the solar spectrum. In this study, the electronic, optical and photocatalytic properties of Se-doped, and Te-doped SrTiO3 has been investigated using density functional theory (DFT) within the generalized gradient approximation (GGA). Our results reveal that the effect of doping can lead to band gap narrowing without introducing any isolated mid-gap states. This improves greatly the visible light activity of SrTiO3 and depresses the recombination of photogenerated electron–hole pairs. Furthermore, the locations of calculated band edges relative to the water reduction and oxidation levels for doped systems meet the water-splitting requirements. Consequently, our results show that the performance of SrTiO3 for hydrogen generation by photocatalytic water splitting is significantly enhanced with Se and Te doping. In particular, Te doping can enhance greatly the visible light photocatalytic activity of SrTiO3. We expect this study can provide a theoretical basis for a prospective experimental works. [ABSTRACT FROM AUTHOR]

Structural, electronic, and optical properties of CdAl2O4, CdGa2O4, and CdIn2O4 are investigated using the first principles technique based on the new potential approximation known as the Tran-Blaha modified Becke-Johnson exchange potential approximation (TB-mBJ). We discuss the improvements in the band gap determination using TB-mBJ compared to the standard generalized gradient approximation in density functional theory. The calculated equilibrium lattice parameters are in reasonable agreement with the experimental results. Electronic properties have been studied through the calculation of band structure and density of states. Based on our electronic structure obtained using the mBJ method, we have calculated various optical properties, including the complex dielectric function ε(ω), complex index of refraction n(ω), reflectivity coefficient R(ω), absorption coefficient α(ω), and the electron energy-loss function L(ω) as functions of the photon energy. We chose these three representative oxides spinel due to their potential applications in optoelectronics and optical fields. [ABSTRACT FROM AUTHOR]

The electronic structure, magnetic, and optical properties in cubic crystalline phase of Zr1–xTMxO2 (TM=V, Mn, Fe, and Co) at x=6.25% are studied using density functional theory with the Generalized Gradient Approximation and the modified Becke-Johnson of the exchange-correlation energy and potential. In our calculations, the zirconia is a p-type semiconductor and has a large band gap. We evaluated the possibility of long-range magnetic order for transition metal ions substituting Zr. Our results show that ferromagnetism is the ground state in V, Mn, and Fe-doped ZrO2 and have a high value of energy in Mn-doped ZrO2. However, in Co-doped ZrO2, antiferromagnetic ordering is more stable than the ferromagnetic one. The exchange interaction mechanism has been discussed to explain the responsible of this stability. Moreover, it has been found that the V, Mn, and Fe transition metals provide half-metallic properties considered to be the leading cause, responsible for ferromagnetism. Furthermore, the optical absorption spectra in the TM -doped cubic ZrO2 are investigated. [ABSTRACT FROM AUTHOR]

The electronic, magnetic and magnetocaloric properties of the Iron-Selenite Bi25FeO40 compound have been investigated using first-principles calculations and Monte Carlo simulations (MCs). It was found that Bi25FeO40 is a p-type semiconductor with an indirect bandgap of about 2.16 eV which is in good agreement with the previous experimental and theoretical results. The studied compound displays a ferromagnetic behaviour with a spin moment of the unit cell of about 4.06 μB. The Bi25FeO40 compound exhibits a weak ferromagnetic behaviour around TC = 271.96 K; this value is in good agreement with experimental results. In addition, it shows a magnetocaloric effect (MCE) around the Curie temperature (TC), with the maximum values of the magnetic entropy change (Δ S m M a x ) and relative cooling power (RCP) are 2.56 J.kg−1.K−1and 55.01 J/Kg, respectively, under applied an external magnetic field of h = 5.00 T. The good magnetocaloric properties reveal the applicability of Bi25FeO40 compound to the magnetic refrigeration around TC. [ABSTRACT FROM AUTHOR]

Nanostructured chalcopyrite CuAlGaTe ( x = 0.25, 0.50, and 0.75) has been prepared by ball milling of Cu, Al, Ga, and Te precursors. Preliminary ab initio calculations of the main properties have been performed on the prototype chalcopyrite semiconductor CuAlGaTe. The simulation method used is based on the density functional theory within the framework of pseudo-potentials and plane waves. Band Structure calculations suggest that CuAlGaTe is a direct bandgap semiconductor having a band gap = 1.35 eV. In the experimental part, x-ray diffraction analysis revealed the presence of (112), (220)/(204), (312)/(116), and (400) reflections for all the milled powders characteristic of the chalcopyrite structure. A shift in peaks towards a higher value of 2 θ is observed with the increase in Al composition. With increasing Al content, it is found that the average crystallite size decreases whereas the bandgap energy increases from 1.34 eV to 1.51 eV. Compared with experimental data, calculated results by GGA-mBJ functional quantitatively agree with experimental data. [ABSTRACT FROM AUTHOR]

CdS(Se)/graphene oxide (GO) heterostructures have received significant attention due to their potential application in optoelectronic devices with tunable bandgap, efficient charge transfer, and enhanced photocatalytic and photovoltaic activity. In this work, Density Functional Theory (DFT) calculations of the photocatalytic properties of CdS(Se)/GO heterostructures were performed. The results of work function, band gap, optical absorption, and band edges of CdS and CdSe in the (001) and (110) directions on graphene oxide are presented. Various approaches to simulate graphene oxide with a different concentration of oxygen, and their subsequent integration into CdS (Se)-GO heterostructures are discussed. DFT calculations were employed to determine the equilibrium value and adhesion energy for various compositions of layers at the interface, as well as different stacking arrangements between graphene oxide and CdS slabs. The results revealed that some oxygen atoms migrate to the CdS matrix and form bonds with Cd atoms. It was observed that the semiconductor band gap can be controlled by the oxidation degree in graphene oxide, and the electronic properties of CdS(Se) depend on the semiconductor orientation and slab number. Notably, surface states are found to be responsible for the negative part of the dielectric function at low frequencies, significantly influencing the electronic properties and charge transfer dynamics. The results show that both structures form type II heterostructures, which is promising for photocatalytic hydrogen generation., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

First of all, we show that two kinds of sandwich bilayers (BLs) are dynamically, thermally, and mechanically stable, which are degenerate p-type materials with intercalated Ca atoms, i.e. , Nb-doped MoS 2 homobilayers (HoBLs) and Nb-doped WS 2 -MoS 2 heterobilayers (HtBLs) with 25% Nb content. Specifically, their interlayer bindings are five times stronger than van der Waals interactions in their pristine counterparts. Both of them are semiconductors with indirect band gaps in the visible region within the HSE06 exchange-correlation functional. Depending upon the presence and absence of centrosymmetry, they display interesting spin-valley coupling effects in such a way that opposite hidden spin polarization or opposite spin splitting is observed at opposite k -points. They can be easily engineered into direct gap materials under compressive (>2%) strain along the zigzag direction even with an explicit consideration of giant spin splitting. Under strain, they satisfy thermodynamic conditions for bifunctional catalysis in photocatalytic water splitting. In addition, the photoholes of the BLs can be subjected to lower overpotentials than those of pristine BLs for the oxygen evolution reaction. Electrons and holes in the sandwich HtBL can be separated into different layers under photon irradiation, allowing it to be more efficient than the corresponding HoBL in solar energy harvesting.

The polymorphism of nanostructures is of paramount importance for many promising applications in high-performance nanodevices. We report the chemical vapor deposition synthesis of Ga 2 S 3 nanowires (NWs) that show the consecutive phase transitions of monoclinic (M) → hexagonal (H) → wurtzite (W) → zinc blende (C) when lowering the growth temperature from 850 to 600 °C. At the highest temperature, single-crystalline NWs were grown in the thermodynamically stable M phase. Two types of H phase exhibited 1.8 nm periodic superlattice structures owing to the distinctively ordered Ga sites. They consisted of three rotational variants of the M phase along the growth direction ([001] M = [0001] H/W ) but with different sequences in the variants. The phases shared the same crystallographic axis within the NWs, producing novel core-shell structures to illustrate the phase evolution. The relative stabilities of these phases were predicted using density functional theory calculations, and the results support the successive phase evolution. Photodetector devices based on the p-type M and H phase Ga 2 S 3 NWs showed excellent UV photoresponse performance., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

α-Fe 2 O 3 nanoparticles were synthesized via a straightforward method. XRD, FTIR, SEM, ESR, and DRS techniques investigated the influence of various calcination temperatures on the crystal structure, optical, and photocatalytic properties of the samples. The obtained results demonstrated that the average crystallite size increased with the increase in the calcination temperature. Measured and computed optical properties were in accordance and the bandgap energy decreased with the increase in the calcination temperature. The highest photocatalytic degradation efficiency for diclofenac (DCF) was obtained with the sample calcinated at 300 °C (96%). The photocatalytic process occurs because of the presence of OH• radicals. The addition of H 2 O 2 led to the inhibition of OH• radicals that H 2 O 2 scavenged., (© 2021. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Background: Obstructive sleep apnea (OSA) may lead to myocardial preconditioning by increasing coronary collateral vessel recruitment in patients with acute coronary occlusion., Aim: To determine the relationship between the severity of obstructive sleep apnea and coronary collaterality during acute myocardial infarction., Methods: This study prospectively included 71 patients with an inaugural myocardial infarction who had undergone a coronary angiography within 24h of onset. All patients underwent an overnight polygraph before discharge and were classified according to the apnea-hypopnea index (AHI). Coronary collaterals were scored by visual analyses and according to the Rentrop grading system., Results: Mean age was 59±11years and 83% of patients were men. All patients had complete or subtotal occlusion of the infarct-related artery. After the sleep study, patients were divided into two groups: 25 were suffering from OSA (AHI>15/h). Patients with OSA showed better collateral vessel development (Rentrop score≥1) compared to non-OSA patients (68 vs. 41%, P=0.032). AHI was significantly higher in patients with developed coronary collaterals (Rentrop≥1) compared to those without collaterality (17.74±13.2 vs. 12.24±10.9, P=0.025)., Conclusion: Coronary collateral development may be increased in OSA patients who are presenting with a first myocardial infarction., (Copyright © 2015 Elsevier Masson SAS. All rights reserved.)

Atrial fibrillation can expose to thrombo-embolic complications. Many biomarkers have been tested to refine the stratification of thrombo-embolic risk. The study aim was to assess the interest of the d-dimer testing in this pathology. We conducted a prospective observational study including 50 cases and 19 controls, enrolled at the cardiology department of the Mongi Slim Hospital, from July to November 2012. The d-dimer assay was performed on mini-VIDAS(®) and analyzed according to clinical, echocardiographic and biological data. The mean age of patients was 61.8±10.6years. The mean CHA2DS2-VASc score was 2.58±1.31. The average of D-dimer levels was 590±506ng/ml in patients and 225.26±112.95ng/ml in controls (P=0.02). No significant difference has been found between the d-dimer level and age, sex, type and etiology of atrial fibrillation, the CHA2DS2-VASc score, the left atrial surface. Among patients on acenocoumarol, d-dimer levels was significantly higher in patients with an INR<2 compared to those with an INR≥2 (P=0.004). We identified a positive d-dimer threshold (300ng/ml) in patients distinguishing them significantly with controls (P<0.001). In conclusion, the measurement of d-dimers could help clinicians to identify patients with atrial fibrillation having an increased coagulability and, therefore, an increased thrombo-embolic risk. It could be complementary to the determination of INR in monitoring anticoagulation therapy: d-dimers level refines the thrombo-embolic risk and INR measurement assesses the level of anticoagulation and the bleeding risk., (Copyright © 2015 Elsevier Masson SAS. All rights reserved.)