Sharif Digital Repository

The search for cathode materials with fast oxygen reduction reaction (ORR) catalytic activities and high ionic conductivity is the key obstacle to SOFCs commercialization and its operation at low temperatures. In order to search for a cathode with enhanced catalytic functionality, herein we report a single-phase CoFe2O4 (CFO) and CoGd0.2Fe1.80O4 (CGFO), which can be employed as an active cathode to improve electrocatalytic ORR functionalities at low temperature. It is found that CGFO having enriched oxygen vacancies exhibits the least polarization resistance (RP) of 0.42 Ωcm2 compared to the pure CFO which shows polarization resistance of 0.56 Ω cm2 under H2/air conditions. Furthermore,... 

With the advent of the Internet of Things (IoT), the development of self-powered sensors has received much attention. Introducing triboelectric nanogenerators (TENGs) as a power source that converts mechanical movement into electrical signals has been admired recently. Moreover, the monitoring of humidity has become enormously essential in several technological contexts from environment monitoring to biomedical applications, thus joining these two subjects provides a huge benefit in achieving self-powered humidity sensors. Here, in this research, facile, low-priced and self-powered humidity sensors are fabricated utilizing transition-metal dichalcogenides (TMD) nanosheets. Semi-vertical SnS2... 

In this paper, a sufficient reciprocity condition for general time-periodic modulated bianisotropic media is extracted from first principles. Reciprocity of various cases of significant importance, including stationary bianisotropic media, time-varying (TV) isotropic media, TV anisotropic media, and TV bianisotropic media, are investigated using this condition. We prove that synchronous time modulation of stationary bianisotropic yet reciprocal media (chiral, pseudochiral, and achiral) does not lead to nonreciprocity, unless the modulation function breaks time reversal symmetry. This is in contrast to recently published research. The theoretical results are validated using in-house finite... 

Very recently, two-dimensional (2D) iodinene, a novel layered and buckled structure has been successfully fabricated (Qian et al 2020 Adv. Mater. 32 2004835). Motivated by this latest experimental accomplishment, for the first time we conduct density functional theory, first-principles calculations to explore the structural, electronic, and optical properties of monolayer, few-layer and bulk iodinene. Unlike the majority of monoelemental 2D lattices, iodinene is predicted to be an intrinsic semiconductor. On the basis of calculations using the generalized gradient approximation of Perdew-Burke-Ernzerhof for the exchange-correlation functional and the Heyd-Scuseria-Ernzerhof (HSE06)... 

Herein we describe the synthesis and characterization of the first platinum(IV) metal-organic cage [(Me3PtIV)8(byp)12](OTf)8 (2), in which the organometallic moieties trimethylplatinum(IV) (PtMe3) occupied the corners of a cubane structure and 4,4′-bipyridine ligands used as linkers. The first-principles density functional theory calculations showed that the highest occupied molecular orbitals were localized on the PtMe3 moieties, while the lowest unoccupied molecular orbitals were distributed on the organic linkers. © 2021 American Chemical Society  

Tunable microwave absorption characteristics are highly desirable for industrial applications such as antenna, absorber, and biomedical diagnostics. Here, we report BiNdxCrxFe1-2xO3 (x = 0, 0.05, 0.10, 0.15) nanoparticles (NPs) with electromagnetic matching, which exhibit tunable magneto-optical and feasible microwave absorption characteristics for microwave absorber applications. The experimental results and theoretical calculations demonstrate the original bismuth ferrite (BFO) crystal structure, while Nd and Cr injection in the BFO structure may cause to minimize dielectric losses and enhance magnetization by producing interfacial defects in the spinel structure. Nd and Cr co-doping plays... 

The fabrication of the C6N7 monolayer [Zhao et al., Sci. Bull. 66, 1764 (2021)] motivated us to discover the optical, structural, mechanical, and electronic properties of the C6N7 monolayer by employing the density functional theory (DFT) method. We find that the shear modulus and Young's modulus of the C6N7 monolayer are smaller than the relevant values of graphene. However, Poisson's ratio is more significant than that of graphene. Applying the PBE (HSE06) functional bandgap of the C6N7 monolayer is 1.2 (1.97) eV, and the electronic dispersion is almost isotropic around the Γ point. C6N7 is more active in the ultraviolet region as compared to the visible light region. This study provides... 

Because of the possibility of various types of vacancies in cementite due to its crystalline structure, the focus of this paper was only on vacancies. In this regard, the formation energies of single, two, three and four vacancies of over than 120 different cases were calculated using first-principles method. For the case of single vacancy, the results were in three values of ~1.63, 1.39 and 0.78 eV according to iron vacancies at general positions, iron vacancies located on mirror planes and carbon vacancies in the interstitial positions, respectively. The results for the case of two, three and four vacancies were between from 2.10 to 3.34 eV, from 3.92 to 5.10 eV and from 4.77 to 6.33 eV,... 

One of the most elusive problems in quantum mechanics is the transition between classical and quantum physics. This problem can be traced back to Schrödinger's cat thought experiment. A key element that lies at the center of this problem is the lack of a clear understanding and characterization of macroscopic quantum states. Our understanding of macroscopic quantumness relies on states such as the Greenberger-Horne-Zeilinger (GHZ) or the NOON state. Here we take a first-principle approach to this problem. We start from coherence as the key quantity that captures the notion of quantumness and require the quantumness to be collective and macroscopic. To this end, we introduce macroscopic... 

In transportation literature, User Equilibrium (UE) has been widely studied since early 1950's, many studies of which define equilibrium flow of traffic for uncapacitated networks based on Wardrop's first principle, implying also a Nash Equilibrium (NE). Although, in general, the two equilibria (UE and NE) are not explicitly the same, they are shown to be equivalent under special conditions for uncapacitated UE, when volume delay functions are separable, continuous, non-decreasing and non-negative. A good deal of research is devoted to explain UE in capacitated networks based on Wardrop's first principle and the concept of generalized costs. However, UE for capacitated networks, even under... 

In transportation literature, User Equilibrium (UE) has been widely studied since early 1950's, many studies of which define equilibrium flow of traffic for uncapacitated networks based on Wardrop's first principle, implying also a Nash Equilibrium (NE). Although, in general, the two equilibria (UE and NE) are not explicitly the same, they are shown to be equivalent under special conditions for uncapacitated UE, when volume delay functions are separable, continuous, non-decreasing and non-negative. A good deal of research is devoted to explain UE in capacitated networks based on Wardrop's first principle and the concept of generalized costs. However, UE for capacitated networks, even under... 

In this paper, by using first-principle density functional theory (DFT) combined with non-equilibrium Green's function (NEGF), thermally induced spin current in zigzag and armchair Antimonene Nanoribbon (SbNR) is investigated. Also, we obtain higher spin current in Armchair nanoribbon (ANR) than zigzag nanoribbon (ZNR), because the start energy of transmission for ANR is closer to the Fermi level than ZNR. The results show that the device has a perfect spin Seebeck effect under temperature difference without gate voltage or bias voltage. For the ANR configuration, the competition between spin up holes and spin down electrons leads to negative differential behavior of charge current, which is... 

It is well-known that helicopters descending fast may enter the so-called Vortex Ring State (VRS), a region in the velocity space where the blade's lift differs significantly from regular regions and high amplitude fluctuations are often present. These fluctuations may lead to instability and, therefore, this region is avoided, typically by increasing the horizontal speed. This paper researches this phenomenon in the context of small-scale quadcopters. The region corresponding to the VRS is identified by combining first-principles modeling and wind-tunnel experiments. Moreover, we propose that the so-called Windmill-Brake State (WBS) or autorotation region should also be avoided for... 

Using a tight-binding approach and first-principles calculations combined with the nonequilibrium Green’s function method, the thermal spin transport in a zigzag molybdenum disulfide (MoS 2) nanoribbon in the proximity of a ferromagnetic insulator that induces a local exchange magnetic field in the center of the nanoribbon is investigated. It is found that a pure spin current and perfect spin Seebeck effect with zero charge current can be generated by applying a thermal gradient and local exchange magnetic field without a bias voltage near room temperature. Furthermore, it is shown that this nanoscale device can act as a spin Seebeck diode for the control of thermal and spin information in... 

The interactions between four different gas molecules (methanol, o-xylene, p-xylene and m-xylene) and Ni-decorated monolayer MoS2 were investigated by means of density functional computations to exploit its potential application as a gas sensor. The electronic properties of the Ni-decorated monolayer MoS2 and gas molecule (adsorbent–adsorbate properties) strongly depend on the Ni-decorated monolayer MoS2 structure and the molecular configuration of the adsorbate. The adsorption properties of volatile organic compound (VOC) molecules on Ni-decorated MoS2 has been studied taking into account the parameters such as adsorption energy, energy bandgap, density of states, and Mulliken charge... 

Density functional theory (DFT) calculations have been performed to investigate the electronic structure and photocatalytic activity of a hybrid Ag3PO4(111)/g-C3N4 structure. Due to Ag(d) and O(p) states forming the upper part of the valence band and C(p), N(p), and Ag(s) the lower part of the conduction band, the band gap of the hybrid material is reduced from 2.75 eV for Ag3PO4(111) and 3.13 eV for monolayer of g-C3N4 to about 2.52 eV, enhancing the photocatalytic activity of the Ag3PO4(111) surface and g-C3N4 sheet in the visible region. We have also investigated possible reaction pathways for photocatalytic CO2 reduction on the Ag3PO4(111)/g-C3N4 nanocomposite to determine the most... 

Siligraphene belonging to the family of two-dimensional (2D) materials has great potential in optoelectronics due to its considerable excitonic effects. In this study, the strain effects on the electronic structure and the real-space exciton wave functions of g - SiC 7 are investigated using the first-principles calculations based on the ab initio many-body perturbation theory. Alongside the increase (decrease) of the bandgap with compressive (tensile) strain, our results show that the exciton in the siligraphene monolayer under in-plane biaxial compressive strains is much more localized than that in the case of tensile one, leading to the higher and lower exciton binding energies,... 

Using the first-principles procedure of density-functional-theory within tight-binding approximation and nonequilibrium Green's function formalism, this paper reports on the impact of vacancy defects on the structural, electronic and transport properties of hydrogen-passivated graphene atomic sheet. After the introduction of vacancy defects in graphene atomic sheet passivated with hydrogen atoms, apart from increase in band gap, a suppression is noted in the intensity of transmission channels and density of states arising from the long array deformations of the graphene sheet and a corresponding shift of the Fermi level. This in turn decreases the conductance of the defected graphene atomic... 

We have studied the pressure-induced structural, magnetic and electronic properties of AeFe 2 As 2 (Ae = Ba, Sr, Ca) compounds in the framework of density functional theory within the GGA-PBE method. The effects of chemical pressure generated by Sr and Ca substitutions in BaFe 2 As 2 have been investigated. We have found a magnetic transition at the same primitive unit cell volume, around 81 Å 3 for the (Ba⧹Ca)Fe 2 As 2 compounds, which predicts a magnetic transition pressure of 12 GPa for SrFe 2 As 2 . The structural parameters of FeAs 4 tetrahedra are obtained after ionic relaxation and compared with the existing experimental results. The change of these internal parameters is ascribed to... 

Owing to the exceptional properties of graphene and the crucial role of substrate on the performance of electrochemical biosensors, several graphene-based hybrid structures have recently emerged, yielding improved selectivity and sensitivity. To date, most of the reported biosensors utilize solution-driven graphene flakes with drawbacks of low conductivity (due to high inter-junction contact resistant) and structural fragility. Herein, we present a conductive three-dimensional CeO2 semiconductor nanoparticles/graphene nanocomposite, as a platform for sensitive detection of hydrogen peroxide, an important molecule in fundamental biological processes. The 3D conductive graphene architecture is...