Structural and Optoelectronic Properties of Cubic CsPbF3 for Novel Applications

Chemical bonding as well as structural,electronic and optical properties of CsPbF3 are calculated using the highly accurate full potential linearized augmented plane-wave method within the framework of density functional theory(DFT).The calculated lattice constant is found to be in good agreement with the experimental results.The electron density plots reveal strong ionic bonding in Cs-F and strong covalent bonding in Pb-F.The calculations show that the material is a direct and wide bandgap semiconductor with a fundamental gap at the R-symmetry point.Optical properties such as the real and imaginary parts of the dielectric function,refractive index,extinction coefficient,reflectivity,optical conductivity and absorption coefficient are also calculated.Based on the calculated wide and direct bandgap,as well as other optical properties of the compound,it is predicted that CsPbF_(3) is suitable for optoelectronic devices and anti-reflecting coatings.

Glow Discharge Plasma Nitriding of AISI 304 Stainless Steel

Glow discharge plasma nitriding of AISI 304 austenitic stainless steel has been carried out for different processing time under optimum discharge conditions established by spectroscopic analysis. The treated samples were analysed by X-ray diffraction （XRD） to explore the changes induced in the crystallographic structure. The XRD pattern confirmed the formation of an expanded austenite phase （TN） owing to incorporation of nitrogen as an interstitial solid solution in the iron lattice. A Vickers microhardness tester was used to evaluate the surface hardness as a function of indentation depth （μm）. The results showed clear evidence of surface changes with substantial increase in surface hardness.

Investigations of the half-metallic behavior and the magnetic and thermodynamic properties of half-Heusler CoMnTe and RuMnTe compounds: A first-principles study

First-principles spin-polarized density functional theory （DFT） investigations of the structural, electronic, magnetic, and thermodynamics characteristics of the half-Heusler, CoMnTe and RuMnTe compounds are carried out. Calculations are accomplished within a state of the art full-potential （FP） linearized （L） augmented plane wave plus a local orbital （APW ＋ lo） computational approach framed within DFT. The generalized gradient approximation （GGA） parameterized by Perdew, Burke, and Ernzerhof （PBE） is implemented as an exchange correlation functional as a part of the total energy calculation. From the analysis of the calculated electronic band structure as well as the density of states for both compounds, a strong hybridization between d states of the higher valent transition metal （TM） atoms （Co, Ru） and lower valent TM atoms of （Mn） is observed. Furthermore, total and partial density of states （PDOS） of the ground state and the results of spin magnetic moments reveal that these compounds are both stable and ideal half-metallic ferromagnetic. The effects of the unit cell volume on the magnetic properties and half-metaliicity are crucial. It is worth noting that our computed results of the total spin magnetic moments, for CoMnTe equal to 4 ~tB and 3 p-B per unit cell for RuMnTe, nicely follow the rule μ2tot = Zt - 18. Using the quasi-harmonic Debye model, which considers the phononic effects, the effecs of pressure P and temperature T on the lattice parameter, bulk modulus, thermal expansion coefficient, Debye temperature, and heat capacity for these compounds are investigated for the first time.

Trace-Rare-Gas Optical Emission Spectroscopy of Nitrogen Plasma Generated at a Frequency of 13.56 MHz

Optical emission spectroscopic measurement of trace rare gas is carried out to determine the density of nitrogen （N） atom, in a nitrogen plasma, as a function of filling pressure and RF power applied. 2% of argon, used as an actinometer, is mixed with nitrogen. In order to normalize the changes in the excitation cross section and electron energy distribution function at different operational conditions, the Ar-I emission line at 419.83 nm is used, which is of nearly the same excitation efficiency coefficient as that of the nitrogen emission line at 493.51 nm. It is observed that the emission intensity of the selected argon and atomic nitrogen lines increases with both pressure and RF power, as does the nitrogen atomic density.

Electronic Band Structure and Optical Response of Spinel SnX_(2)O_(4)(X=Mg,Zn)through Modified Becke-Johnson Potential

The modified Becke–Johnson exchange potential approximation is applied to predict the band structure,optical parameters and electron density of SnMg_(2)O_(4)and SnZn_(2)O_(4).The local density approximation,generalized gradient approximation(GGA),EV-GGA significantly underestimate the direct band gap values compared to modified Becke–Johnson approximation.The band gap dependent optical parameters such as dielectric constant,index of refraction,reflectivity,and optical conductivity are calculated and analyzed.A prominent feature of cation replacement is observed and analyzed for these studied compounds.The replacement of the cation Mg by Zn leads to a significant reduction in the value of band gap and consequently affects its dependant optical parameters.This variation is of crucial importance for device fabrication in different regions of the spectrum.

Electronic and Optical Properties of Spinel GeMg2O4 and GeCd2O4

Oxide spinels have potential applications in optoelectronics and optics fields.In this work the electronic band structure and optical properties of GeMg2O4 and GeCd2O4 are calculated by first principles technique based on the new potential approximation known as the modified Becke-Johnson exchange potential approximation(mBJ).The local density and generalized gradient approximations significantly underestimate the direct band gap values compared to the mBJ.The band gap dependent optical parameters such as dielectric constant,refractive index,reflectivity and optical conductivity are calculated and analyzed.The replacement of the cation is observed and analyzed for the compounds studied and a prominent change is noticed.The replacement of the cation Mg by Cd reduces the band gap and its dependent optical parameters.For device fabrication in different regions of the spectrum this variation is strongly recommended.

Electronic Band Profile and Optical Response of Spinel MgIn_(2)O_(4)through Modified Becke-Johnson Potential

We employ the first-principles technique based on the modified Becke–Johnson(BJ)exchange potential for the prediction of the electronic band structure,optical properties,and electron density of the cubic MgIn_(2)O_(4)spinel compound.It is found that the calculated band gap value with the modified BJ approximation is significantly improved over the results based on the generalized gradient approximation and the local density approximation in comparison to the experimental data.The band gap dependent optical parameters such as the dielectric constant,refractive index,reflectivity,optical conductivity,and electron density are predicted.The optical response suggests that MgIn_(2)O_(4)is an applicant material in optoelectronic devices in various parts of the energy spectrum like MgAl_(2)O_(4)and MgGa_(2)O_(4).

FirstPrincipleCalculations of the Ground and Excited State Properties of RbPbF_(3)

Structural,elastic,electronic,chemical bonding and optical properties of the cubic RbPbF 3 compound under pres-sure are studied using a highly accurate state-of-the-art full potential linearized augmented plane wave method.The exchange correlation effects are included through the generalized gradient and modified Becke–Johnson ex-change potential.The lattice constant and band gap of the cubic RbPbF 3 decreases with enhanced pressure.RbPbF 3 is brittle,elastically anisotropic,and a direct bandgap material.Its optical properties such as refractive index𝑜(ω),extinction coefficient𝑙(ω),reflectivity𝑆(ω),and optical conductivity𝜏(ω)are predicted.

Optoelectronic Response of GeZn_(2)O_(4) through the Modified Becke-Johnson Potential

A first-principles technique capable of describing the nearly excited states of semiconductors and insulators,namely the modified Becke–Johnson(mBJ)potential approximation,is used to investigate the electronic band structure and optical properties of spinel oxides:GeZn_(2)O_(4).The predicted band gaps using the mBJ approximation are significantly more accurate than the proposed previous theoretical work using the common LDA and GGA.Band gap dependent optical parameters,like the dielectric constant,index of refraction,reflectivity and optical conductivity are calculated and analyzed.The results from the dielectric constant shows that the numerical value of the static dielectric,after dropping constantly,becomes less than zero and the material exhibits metallic behavior.The refractive index also drops below unity for photons higher than 18 eV,which indicates that the velocities of incident photons are greater than the velocity of light.However,these phenomena can be explained by the fact that a signal must be transmitted as a wave packet rather than a monochromatic wave.This comprehensive theoretical study of the optoelectronic properties predicts that these materials can effectively be used in optical devices.

Electronic and thermoelectric properties of YbMg_(2)X_(2)(X=P,As,Sb,Bi)zintl compounds by first-principles method

In this work the structural,electronic and thermoelectric properties of YbMg_(2)X_(2)(X=P,As,Sb,Bi)zintl compounds were investigated comprehensively using first principles study.The electronic properties were studied using PBE GGA,TB-mBJ and hybrid(YS-PBE0)potentials.All the structural parameters of optimized structures are in harmonious agreement to the available data.The band structure study illustrates that the titled materials manifest metallic and semi metallic nature using PBE and TB-mBJ potentials while they show wide band gap semiconducting behavior by following hybrid(YS-PBE0)potential.Total density of states(TDOS)and partial density of states(PDOS)were also calculated to glimpse the contribution of orbitals of atoms in the formation of bands.Transport properties were studied by using BoltzTraP2 code employed to WIEN2k.We get enormous values of Seebeck coefficient(S),power factor(PF)and thermoelectric figure of merit(ZT)for all the samples YbMg_(2)X_(2)(X=P,As,Sb,Bi),Moreover,the overwhelming transport properties for the titled compounds indicate the optimum level of carriers’concentration which pinpoints these materials to be better thermoelectrics in the 1-2-2 zintl family.

Kinetic Instability of Anisotropic Drift Wave Accompanied by Field Aligned Currents in Solar Coronal Loop

Solar coronal loops are frequently accompanied by the field-aligned currents, which drive instabilities if the drift velocity u0 > v A the Alfv′en velocity. For our choice of parameters, the critical threshold value of u0/v A is ～ 3.0 for growth and the corresponding current filling factor ～ 10-3-10-4. Below this value we are no longer in the kinetic regime.The coronal loops also have short-scale density gradients within each loop. The electron resonance in the presence of density gradient causes the drift mode to grow. We study the effect of these two free energy sources, the electron drift and the density gradient, in the presence of temperature anisotropy T⊥_α > T∥_α. These effects simultaneously exist in the coronae. Using gyrokinetic theory, we investigate the influence of these effects, examine how they interplay with each other and study the consequent growth of the magnetosonic wave. We observe that kinetic instability driven by density gradient can be suppressed by field-aligned currents. The temperature anisotropy with chosen signatures causes further stabilizing effect. The results may prove useful to study the heating mechanism of solar coronal loops, acceleration of particles and confinement of particles in the thermonuclear reactors.

Ordinary Mode Instability in a Cairns Distributed Electron Plasma

Employing the linearized Vlasov-Maxwell equations, a generalized dispersion relation for the ordinary mode is derived by employing the Cairns distribution function. The instability of the mode and its threshold condition is investigated. It is found that the temperature anisotropy χ= TⅡ I⊥〉 1 required to excite the instability varies with density values whereas the growth rate is dependent on various parameters like non-thermMity A, equilibrium number density no and temperature anisotropy. It is found that with the increase in the values of any of the parameters A, no and X, the growth rate is enhanced and the k-domain is enlarged. The results are applicable for space plasma environments like solar wind.

Linear Analysis of Obliquely Propagating Longitudinal Waves in Partially Spin Polarized Degenerate Magnetized Plasma

Linear analysis of low frequency obliquely propagating electrostatic waves in a partially spin polarized degenerate magnetized plasma is presented. Using Fourier analysis, a general linear dispersion relation is derived for low frequency electrostatic lower hybrid(LH) wave, ion acoustic(IA) wave and ion cyclotron(IC) wave in the presence of electron spin polarization. It is found that the electron spin polarization gives birth to a new spin-dependent wave(spin electron acoustic wave) in the spectrum of these waves. Further, the electron spin polarization also causes drastic shifts in the frequency spectrum of these waves. These effects would have a strong bearing on wave phenomena in degenerate astrophysical plasmas.