Narrow Results

In this work, the mixed system composed of Zn₂GeO₄: Mn and MgGeO₃: Mn, Eu was synthesized by the high temperature solid phase method. Under the external excitation, visual color of samples was yellow. However, after the excitation was completed, visual color turned to be red. From luminescence spectrum, it was found that Zn₂GeO₄: Mn emitted green fluorescence of 534 nm under the excitation of 375 nm light. At the same time, MgGeO₃: Mn, Eu emitted both fluorescence and persistent luminescence (PersL) of 668 nm. Moreover, the properties of PersL present samples were superior to other red PersL materials. Fine band structures from density functional theory (DFT) indicated that there were different luminescent mechanisms of Zn₂GeO₄: Mn and MgGeO₃: Mn, Eu. When Zn₂GeO₄: Mn was excited, electron transitioned from VB to CB directly. Through CB, the electron was captured by the ⁴T₂(D) of Mn ion, then the electron jumped from ⁴T₂(D) to VB and recombined at once with the previous hole and emitted a 534 nm photon. When MgGeO₃: Mn, Eu was excited, electron transitioned from ⁶A₁(S) of Mn ion to CB and left a hole. Through CB, electron was captured by ⁷F₆ levels of Eu${}^{3+}$ and remained metastable for a long time, which slowed down the recombined rate between electron and hole. Under thermal stimulation, the captured electron returned to CB from ⁷F₆ levels and was recaptured by the ⁴T₂(D) of Mn. The electron transitioned down toward ⁶A₁(S) and recombined with the hole immediately, then emitted a photon with 668 nm.

In this work, we developed a technology for growing a single crystal of a ternary compound, using the Atomic Force Microscope (AFM), we studied the surface microrelief in 2D and 3D modes, using X-ray diffraction (XRD) analysis, determined the parameters of the unit cell of this phase and revealed that it crystallizes in tetragonal symmetry with lattice parameters $a=8.345$ Å and $c=6.8352$ Å, space group I4/mcm. Using the density functional method, using the ABINIT software package, using the Troiller–Martins pseudopotentials in the basis of plane waves, the band structure was calculated, the origin of the valence and conduction bands was determined. It was revealed that this phase is a direct-gap semiconductor with a bandgap of 0.56 eV. The parameters of the InGaTe₂ unit cell were calculated by the pseudopotential and linearized attached plane wave (LAPW) methods, the theoretical and experimental values of the lattice parameters are in good agreement. Based on the band structure, the effective masses of electrons and holes are determined. It is shown that the tensors of the inverse effective mass for both extreme have a diagonal form.

A systematic theoretical investigation of structural and energetic behaviors of 55-atom Pt–Ag–Au ternary nanoalloys has been performed in two different composition systems. We have performed Gupta and Density Functional Theory (DFT) approaches on chosen systems. The Basin-Hopping algorithm is used for structural optimizations of Pt_nAg${}_{13-n}$Au${}_{42}$ ($n=0$–13) and Pt_nAu${}_{13-n}$Ag${}_{42}$ ($n=0$–13) ternary nanoalloys with Gupta many-body potential to model interatomic interactions. Local optimization results show that while the tendency of Au atoms to be located varies according to the composition system, the tendency of Pt and Ag atoms to be located does not change in both. For all compositions of Pt–Ag–Au nanoalloys, the structures with the best chemical ordering were then reoptimized by DFT relaxations and the mixing energies of the Gupta and DFT levels were compared. Our mixing energy analysis showed that Pt_nAg${}_{13-n}$Au${}_{42}$ ($n=0$–13) nanoalloys are not energetically suitable for mixing at both Gupta and DFT level. Also, mixing energy variations of Pt_nAu${}_{13-n}$Ag${}_{42}$ ($n=0$–13) nanoalloys obtained at Gupta level does not agree with the one obtained at DFT level. In addition, it has been found that the minimization energy changes when an atom in the central site is exchanging by an atom in the second shell and surface.

This paper discusses the structural, electronic, magnetic, and half-metallic properties of half-Heusler alloy KCaB. First-principles calculation based on density functional theory is successfully used to determine properties at bulk and on the (111) and (001) surfaces of KCaB. KCaB is half-metallic ferromagnet with a magnetic moment of 1 ${\mu }_{\mathrm{\text{B}}}$ and an energy gap equal to 0.82 eV in the lower spin channel. The $n$-type doped exhibits higher Seebeck coefficient, electrical conductivity, thermal conductivity, and figure of merit than the $p$-type-doped KCaB at room-temperature 300 K. The half-metallic property is preserved in each of the ends Ca and B on the (111) surface and is lost in the ends K (111) and B and KCa (001) slab surface. The relaxation effect on the electronic spin states decreases the magnetic moment of some atoms on the end surface because the relaxation of the atomic sites is affected and the loss of the nearest neighbors affects exchange–correlation interactions. The surface end with Ca is more stable than the surface end with B on the (111) surface and can maintain the property of half metallic under relatively large stress.

The geometries, structural stability, electrical and magnetic characteristics of pure and multiple palladium (Pd)-adsorbed graphene, followed by hydrogen adsorption, are investigated using first-principles calculations with the density functional theory. In the DFT-D2 technique, first-principles computations with the van der Waals interaction are done using the generalized gradient approximation. In a $4\times 4$ supercell, the adsorption energy per Pd atom is found to be 1.20 eV in the optimal adsorption shape. The bandgap of 51 meV has opened in multiple Pd-decorated graphene, according to band calculations. This band’s opening is ascribed to a symmetry break. The binding energy for hydrogen adsorption in optimal double Pd-decorated graphene was determined to be in the range of (0.14–0.73) eV per hydrogen molecule, indicating that Pd-decorated graphene might be used as a hydrogen storage material.

Gupta and Density Functional Theory (DFT) calculations were performed to investigate of structural and magnetic behaviors of 19 atom Fe_nRh${}_{19\text{-}n}$ ($n=0$–19) nanoalloys. A double icosahedron structure was considered for Fe_nRh${}_{19\text{-}n}$ ($n=0$–19) nanoalloys. Significantly, the effects of Fe atom addition on the chemical ordering, stability and total magnetic moments of the nanoalloys were investigated. Local optimization results at the Gupta level show that the Fe atoms are located in the center of the double icosahedron structure and finally in the equatorial region on the surface. The mixing energy analysis obtained that Fe${}_{12}$Rh₇ and Fe₄Rh${}_{15}$ nanoalloys are the most stable compositions at Gupta and DFT levels, respectively. It was found that Fe_nRh${}_{19\text{-}n}$ ($n=0$–19) nanoalloys are energetically suitable for mixing at both Gupta and DFT levels. Also, the bond order parameter result is compatible with the mixing energy analysis result. The total magnetic moments of the Fe_nRh${}_{19\text{-}n}$ ($n=0$–19) nanoalloys increase with the addition of the Fe atom, which is a ferromagnetic metal.

Solar cells convert electricity from the solar spectrum to more than 60%. Researchers focused on this promising field because of the most demanding renewable source of electrical energy. Based on the demand, we focused our study on bismuth-doped tin chalcogenide materials for the optoelectronic and solar cell applications. The effect of bismuth concentration on structural, electronic, thermodynamic and optical properties of Sn${}_{0.75}$Bi${}_{0.25}$Te and Sn${}_{0.25}$Bi${}_{0.75}$Te materials is studied based on density functional theory (DFT). Generalized gradient approximation (GGA) was proposed to calculate structural parameters, density of states and band structure. Here the lattice parameter increases when increasing bismuth concentration. The parent binary SnTe is in semiconducting behavior with a narrow direct bandgap of 0.234 eV (L-L). From the calculated thermal and optical results, the Gruneisen parameter is maximum for Sn${}_{0.25}$Bi${}_{0.75}$Te and Debye temperature is maximum for Sn${}_{0.75}$Bi${}_{0.25}$Te. The studied materials are consistent in IR, visible and UV regions and they are adorable for IR optical detectors and solar cell applications.

Based on the density functional theory (DFT), the electronic, optical and thermoelectric properties of the MoS₂-GaN interface at three different distances have been investigated. In all configurations, we see the semiconductor behavior at the MoS2-GaN interface. Their direct bandgaps at the MoS₂-GaN interface with 2.8782, 4.0870 and 5.3330 $\mathrm{\text{Å}}$ distances are 1.50, 1.12 and 1.15 eV, respectively. The optical properties of these structures were investigated with three Random Phase Approximation (RPA), Time-Dependent Density Functional Theory (TDFT) and Bethe-Salpeter Equation (BSE) approximations, and their semiconductor properties were confirmed, especially with the BSE one.

In this paper, the hydrogen storage performance of Sc (Ti, Li)-modified $\mathrm{\Psi }$-graphene ($\mathrm{\Psi }$-g) is investigated by density functional theory (DFT). Sc and Ti can be stably adsorbed on $\mathrm{\Psi }$-g with the binding energies of 4.78 eV and 4.83 eV, respectively. Li atoms can also be stably absorbed on B-doped $\mathrm{\Psi }$-g with the binding energy of 2.51 eV. In addition, Sc and Ti atoms attached on $\mathrm{\Psi }$-g can adsorb up to ten and eight hydrogen molecules, and the hydrogen gravimetric storage capacity reaches 7.93 wt.% and 6.20 wt.%, respectively. Li atoms attached on B-doped $\mathrm{\Psi }$-g can adsorb up to eight hydrogen molecules with the hydrogen gravimetric storage capacity 9.32 wt.%, all meeting DOE standards. On the whole, Bader charge analysis shows that the charge is transferred from C atoms to H atoms, which is more conducive to hydrogen adsorption. All the researches prove that the Sc, Ti-decorated $\mathrm{\Psi }$-g and Li-decorated B-doped $\mathrm{\Psi }$-g are potential hydrogen storage materials.

Thin films of pure and Mg-doped ZnO (Zinc Oxide) were successfully elaborated on glass substrates using the sol–gel technique. X-Ray diffraction patterns show that all grown films have good crystallinity and a hexagonal wurtzite structure, the (002) direction is the most preferred for thin-film growth. Atomic force microscopy (AFM) analysis showed that the surface is homogeneous and more compact with little change in surface morphology with increasing Mg doping rate, which agreed with the crystallite sizes obtained from the XRD results. The structural parameter “$a$” measured and calculated using functional density increases while “$c$” decreases. The electronic and optical bandgap and transmittance improve by increasing the concentration of Mg. The physical origin of the energy gap bowing parameter is investigated using the Zunger approach, which examines the microscopic origins of the energy bandgap bowing. In contrast, the reflectivity and electrical conductivity are reduced with increasing concentration of Mg. The experimental and theoretical results have the same tendency therefore, the Mg-doped ZnO (ZnO:Mg) is an essential candidate material for thin films in many optoelectronic devices.

This work investigates the effect of band structure, optical spectra, computed elastic coefficients, Bulk-to-Shear modulus ratio, Young’s modulus and Poisson’s ratio in metal selenide compounds and their influence on electronic, optical, and elastic properties of bulk crystals using density functional theory (DFT). By studying the structural and geometrical parameters, we show that the V–VI group compound has a direct bandgap of 0.887eV and the band structure can be explained by a partial density of states (PDOS) plot. By using Pugh’s formation, the bulk-to-shear ratio can be significant in precisely determining the ductility of a material. Poisson’s ratio can provide information to examine whether the lattice crystal is ionic or covalent. Our elastic data show that the orthorhombic system is found to be unstable. The optical spectra (high absorption coefficient of $1.78\times 10^5$cm${}^{-1}$, dielectric coefficient of 8.61 and reflective index of 2.93) of our current work would be beneficial to explore the applications of optoelectronic devices, especially in light-harvesting materials, covering the UV region. Our findings advance the knowledge of the structural, electronic, optical, vibrational, and mechanical properties of Sb₂Se₃, the key to their use, and explained the potential applications in photovoltaics perspectives.

In this paper, we used the first-principles method to investigate the structural, electronic, mechanical and thermodynamic parameters of the ternary $\beta$-Ti–15Nb–xSi alloys with $x=0.6,0.8,1,1.2,1.4,1.6$wt.%. We have carried out theoretical computations inside the density functional theory (DFT) utilizing the generalized gradient approximation (GGA) with the Perdew–Burke–Ernzerhof (PBE) model. The random distribution of Nb atoms in the alloy was described by using both virtual crystal approximation (VCA), special quasirandom structure (SQS) and the coherent potential approximation (CPA) techniques, in combination with first-principles plane-wave pseudopotential (PW-PP) and exact muffin-tin orbital (EMTO) methods. We determined the elastic constants as well as the bulk, shear, Young’s modulus and Poisson’s ratio. Our structural results are in good agreement with the available experimental and theoretical results for the pure structure of the titanium. In addition, we have estimated the band structure and the density of state (DOS) for the electronic computations. Our findings demonstrate that all of the compounds are metallic, stable and meet the requirements for stability. Young’s modulus of Ti–15Nb–0.6Si and Ti–15Nb–1.6Si is 86.5GPa and 15.11GPa, respectively, which are similar to Young’s moduli of human bone (10–30GPa). All calculated parameters of the alloys decreased with increasing of Si concentration except for Poisson’s ratio, anisotropy and B/G ratio. Furthermore, all of the materials investigated showed ductile nature, and Young’s modulus values are needed for further applications. Excitations from the quasi-harmonic Debye approximation’s vibrational part were applied to the 0K free energy calculated via ab-initio calculations. The influence of temperatures up to 800 K on phase stability was investigated. These findings can be utilized to help designers create alternative low-modulus alloys for biomedical applications.

By using the first-principles calculations established on density functional theory (DFT), the electronic aspects of the tetrahexcarbon (TH-carbon) monolayer as a two-dimensional carbon allotrope which is a direct bandgap semiconductor have been investigated under variations of buckling parameter ($\sigma =0,2,4,6$) by the PBE-GGA. Also, optical properties of this nanosheet are projected in out-of-plane polarization in buckling variation situations up to $\sigma =6$. Its optic behaviors in the visible light spectrum match its electronic ones. The results propose that the TH-carbon monolayer is an appropriate material for designing optoelectronic devices.

Based on density functional theory (DFT), the structural and physical properties of NaCaZ (Z$=$N, P, As) half-Heusler (HH) semiconductor materials have been studied under pressure up to 20GPa. The ground state results show that the NaCaZ are chemically stable in $\alpha$-phase structure and exhibit semiconducting behavior with an indirect bandgap. The optical parameters like the real and imaginary components of complex dielectric function, the absorption coefficient and refractive index are investigated and discussed. The obtained results show that NaCaZ have low value of reflectivity and high absorption coefficient in low ultraviolet and visible regions and exhibit small changes under pressure. Pressure-based elastic constants and their derivative parameters show that NaCaZ are mechanically stable and have brittle nature. Above 10GPa, NaCaP and NaCaAs have ductile nature. The phonon dispersions calculations with pressure show that NaCaN and NaCaP are dynamically stable, in contrast, NaCaAs is dynamically unstable at ambient pressure. Above 10GPa, the studied compounds are dynamically stable. The mechanically, dynamically stable with low reflectivity and high absorption coefficient in the low ultraviolet and visible regions make these materials more promising as absorbers of solar cells, optoelectronic and 2D applications.

The presented main studies of point defects in CdGa₂Se₄ chalcopyrite are considered to quantify the formation energies of three possible models of Cd, Ga and Se vacancy defects using various local density approximation (LDA) and general gradient approximation (GGA) approximations. Using supercells with 56 atoms, interatomic distances were calculated both for an ideal cell and a supercell containing vacancies. It was found that interatomic distance does not change only in a supercell containing Ga vacancy. Investigation shows that the Ga vacancy has a high defect formation energy (DFE) among other intrinsic vacancies and is therefore unstable. We found that for all vacancies, $-2$ charge states are favorable.

Based on the density functional theory (DFT) calculations, the structural, electronic, optical and thermoelectric properties of the MnFeTe Heuslerene compound have been investigated. The total energy change curve in terms of volume refers to the ground state point and equilibrium volume. By applying mBJ approximation, this compound has perfect half-metallic behavior of 100% spin polarization at the Fermi level with 7${}_{\mu B}$ magnetic moment. Optical calculations show that the semiconductor behavior with an optical absorption gap occurred by incident light perpendicular to the MnFeTe Heuslerene plane. The figure of merit coefficient (ZT) has reached 3.5 at 50K temperature, which makes it an excellent candidate for thermoelectric applications. Also, the power factor (PF) of this compound has reached its maximum value at room temperature.

It is well known that hexagonal Ge has a direct bandgap and exhibits excellent light emission. The structure and electrical characteristics of hex-GeSn alloys are investigated using an ab initio computation and the PBEsol-meta-GGA-mBJ function. In all alloys, the direct bandgap is observed. Due to the high radius of the Sn atom, when Sn content increases, the bandgap decreases and lattice parameters expand. Their spin–orbit, crystal field splitting and effective mass of electron and hole were also determined, indicating that the direct bandgap of hex-GeSn alloys has significant application in optoelectronic.

This paper reports density functional theory (DFT) on LiMgP half Heusler alloy doped by the transition metal elements (Ti, V, Fe and Ni) determined by present results, in which the half-metallicity besides ferromagnetism behavior is estimated. The electron spin polarization of Ti(3$d)$ is around the $E_F$ and the Ti${}^{2+}$ will have two electrons, of which two electrons occupied the $e^{+}$. Then, this orbital is set on the Fermi level. When the conduction band of the orbitals $e^{-}$, $t_2^{+}$ and $t_2^{-}$ is empty, LiMg${}_{0.95}$Ti${}_{0.05}$P displays the half-metallic characteristic, where the ferromagnetic (FM) conduct fits the double-exchange coupling. For LiMg${}_{0.95}$V${}_{0.05}$P alloy, the charge state is closer to V${}^{2+}$ electron configuration, which predicts the following configuration, in which two electrons are occupied by $e^{+}$ and one electron is occupied by $t_2^{+}$ at the upside of $E_F$. Based on LiMg${}_{0.95}$Fe${}_{0.05}$P alloy, the presence of the half metallicity at the downside of $E_F$ due to (3$d)$orbital is clear. A hybridization between the Fe(3$d)$ and the P(3$p)$ orbitals is in the range −0.35 — −0.04 Ry. For LiMg${}_{0.95}$Ni${}_{0.05}$P alloy, the predicted charge is Ni${}^{2+}$ and exhibits the half-metallic on the downside of the $E_F$ which is occupied by $t_2^{-}$ minority state. For LiMg${}_{0.95}$TM${}_{0.05}$P alloy, (TM = Ti, V, Fe and Ni), the half-metallic conduct is estimated with 100% spin polarized on the Fermi level. The spin moment of TM is $\parallel M^{\mathrm{\text{Ni}}}\parallel <\parallel M^{\mathrm{\text{Ti}}}\parallel <\parallel M^{\mathrm{\text{V}}}\parallel <\parallel M^{\mathrm{\text{Fe}}}\parallel$, where their total magnetic moments $\parallel M^{\mathrm{\text{Tot}}}\parallel$ are in correlation for those Ni, Ti, V and Fe, where the trend also is $\parallel M_{{\mathrm{\text{LiMg+}}}_{0.95}{\mathrm{\text{Ni}}}_{0.05}\mathrm{\text{P}}}^{\mathrm{\text{Tot}}}\parallel <\parallel {\mathrm{\text{M}}}_{{\mathrm{\text{LiMg}}}_{0.95}{\mathrm{\text{Ti}}}_{0.05}\mathrm{\text{P}}}^{\mathrm{\text{Tot}}}\parallel <\parallel M_{{\mathrm{\text{LiMg}}}_{0.95}{\mathrm{\text{V}}}_{0.05}\mathrm{\text{P}}}^{\mathrm{\text{Tot}}}\parallel <\parallel M_{{\mathrm{\text{LiMg}}}_{\mathrm{\text{0.95}}}{\mathrm{\text{Fe}}}_{0.05}\mathrm{\text{P}}}^{\mathrm{\text{Tot}}}\parallel$. Likewise, based on LiMg${}_{0.95}$TM${}_{0.05}$P alloys, the crystal field splitting ($e,t_2)$ observation stated that the doped elements conduct a trend having the following range ${\mathrm{\Delta }}_{(e,t_2)}^{\mathrm{\text{Ni}}}<{\mathrm{\Delta }}_{(e,t_2)}^{\mathrm{\text{Ti}}}<{\mathrm{\Delta }}_{(e,t_2)}^{\mathrm{\text{V}}}<{\mathrm{\Delta }}_{(e,t_2)}^{\mathrm{\text{Fe}}}$. From these observations, it is predicted to have a correlation between magnetic moments of (Ti, V, Fe and Ni) and the crystal field splitting.

A $4\times 4\times 4$ and 765eV (sufficient to converge the results) have been used to explore the electronic, optical, mechanical, and vibrational properties using ab initio code CASTEP with hybrid functionals. A wide indirect F–Z bandgap energy of 3.77eV has been reported. Our partial density of states plot further shows the valence band is made of O 2p and Ag 4d electron orbitals, while Ag S orbitals and N O 2p states contribute to the conduction band bottom (CBM), among the upper conduction band consisting of Ag 4p, O 2$s2p$ and N 2p electron orbitals. In our optical data, a high absorption coefficient of $2.57\times 10^5$ cm${}^{-1}$ has been found, and a relatively low 20% reflectivity simply indicates a high absorption of the material. Although our mechanical data cannot determine the material ductility/brittleness with the B/G ratio, we can report a Poisson’s ratio value of −2.04 in this work. On the other hand, the phonon dispersion and the density of the phonon state plot report may indicate the mechanical instability of the system. The negative Poisson’s ratio (NPR) we provide may hint at the possibility of using AgNO₃ as a promising anode in a group I/II elements (Mg, K, Na)-ion battery.

This study focuses on zinc oxide by both computational and experimental methods. Pure and In-doped ZnO thin films were produced by spray pyrolysis at 300^∘C onto glass substrate. X-ray patterns reveal the polycrystalline structure according to wurtzite along the (002) direction recording a smaller grain size in nanometric scale. This aspect is confirmed by AFM scanned pictures. High transparency of thin film is observed in spite of the indium insertion into ZnO lattice which decreases it slightly. A wide bandgap exceeds 3eV of such as-grown films were recorded. Blue and orange emissions were detected as confirmed by photoluminescence analysis. Computational result analysis is used to demonstrate the ideal geometries in the ground states of pure and doped ZnO. The UV–visible absorption band shifts from 360nm to 448nm as a result of In-doping. The HUMO and LUMO diagrams demonstrate a drop in energy E as a result of doping, and the DOS profiles validate and confirm this detail. Also, the effect of indium on the linear and nonlinear optical parameters of zinc oxide was discussed.