The study of electronic, elastic, magnetic and optical response of Zn1-xTixY (Y=S, Se) through mBJ potential

Q. Mahmood,M. Hassan,M.A. Faridi,B. Sabir,G. Murtaza,Asif Mahmood 한국물리학회 2016 Current Applied Physics Vol.16 No.5

To explore the structural, electronic, magnetic and optical properties of Zn1-xTixY (Y=S, Se) alloys, in the composition range 0 ≤ x ≤ 1, we have applied full-potential linearized augmented plane wave plus local orbital (FP-LAPW + lo) scheme, which is based on the density functional theory (DFT). Structural optimizations have been done in ferromagnetic (FM) and antiferromagnetic (AFM) phase by using Wu eCohen generalized gradient approximation (WC-GGA), whereas recently developed modified Becke and Johnson (mBJ) potential was employed to study electronic and optical properties. The lower value of ground state energy and negative enthalpy of formation confirm stability in the FM phase. Due to the spin polarization of electrons in the Ti-d orbital, origin of half-metallic ferromagnetism has been expressed by the calculated band structures, electronic density of states (DOS) and magnetic moments. We also have calculated the exchange splitting energy Dx (d), crystal field energy (DEcrystal = Et2g Eeg) and exchange constants (N0a and N0b). The negative value of exchange constant (N0b) and large splitting of 3d-states of Ti show that the down spin potential is more effective than up spin. Finally, the results of optical parameters such as complex dielectric constant ε (u), refractive index n (u), normal incident reflectivity R (u), absorption coefficient ɑ (u), optical conductivity s (u) and optical loss factor L (u) are discussed in the energy range 0e14 eV. Moreover, we have verified the Penn's model by showing the inverse relation between the static dielectric constant and the optical band gap. The direct relation between static dielectric constant and static refractive index has been observed by increasing the composition of Ti. The calculated parameters provide valuable theoretical information for optical and spintronics device applications.

First principle study of vanadium doped ZnS: Structural, electronic, elastic, magnetic and optical properties using mBJ approximation

Q. Mahmood,G. Murtaza,R. Ahmad,T. Hussain,I.G. Will 한국물리학회 2016 Current Applied Physics Vol.16 No.3

The structural, electronic, magnetic, mechanical and optical properties of ternary Zn1xVxS (x ¼ 0.0, 0.25, 0.50, 0.75 and 1.0) ferromagnetic semiconductor alloys have been studied in the zinc blende (ZB) phase, by first principle approach. Density functional theory has been employed to calculate the fundamental properties of the alloys using full-potential linearized augmented plane-wave plus the local orbitals (FPLAPW þ Lo) method. In addition, the electronic and magnetic properties are investigated by the local spin density approximation coupled with the modified BeckeeJohnson exchange potential (mBJLDA). Structural analysis revealed that the structure of the three alloys Zn0.75V0.25S, Zn0.50V0.50S, and Zn0.25V0.75S are stable in the ferromagnetic phase. It is noted that the calculated lattice constant decreases, while the bulk modulus increases with the increase of V content. The density of states and spin polarized band structure investigation demonstrated the half-metallic ferromagnetic characteristics of the investigated alloys and are also used to determines ped exchange constants N0a and N0b, due to S (p) eV(3d) hybridization. These results reveal that magnetic moment of V dopant element reduced from its free space value of 3 mB, because the Zn and S sites acquire minor atomic magnetic moments. The energy band gap analysis show an increasing trend with V doping that makes our compound a suitable candidate for the fabrication of devices operating in the ultraviolet region. Moreover, the static dielectric constant, ε1 (u), and static refractive index, n (u), increases with V contents. The incorporation of V generates some new peaks in the energy regions of 0e2.83 eV and 4e10 eV. The substitution by V increases the intensity of the peaks, and a slight red shift has been observed in the absorption peak. The extinction coefficient k (u) and optical conductivity also follow a similar trend to that of the dielectric constants. These results give deep insight into the design of devices for optical and spintronics applications using V doped ZnS.

Compositional dependence of the alignment of three-dimensionally macroporous architectures assembled by two-dimensional hybrid nanosheets

Yu, X.,Mahmood, Q.,Kang, Y.B.,Kim, W.S.,Park, H.S. Elsevier Sequoia 2016 JOURNAL OF ALLOYS AND COMPOUNDS Vol.677 No.-

The composition and pore alignment of three-dimensional (3D) internetworked materials may be a critical parameter for determining the electrochemical properties, but it has yet to be explored. Herein, hierarchically structured reduced graphene oxide (rGO)/MoS<SUB>2</SUB> frameworks (GMfs), as lithium ion batteries (LIB) electrode, are assembled via an ice-templating process on a basis of the interaction between 2D MoS<SUB>2</SUB> and 2D rGO. The morphology and chemical structure of GMfs are investigated by various microscopic and spectroscopic methods and their alignment is dependent on the compositional variations. The as-obtained GMfs exhibit randomly networked and crumpled morphology, achieving the enhanced electrochemical performances for LIB anodes due to the redox-active MoS<SUB>2</SUB> deposited on the 3D macroporous internetworks. The GMfs with 16% MoS<SUB>2</SUB> (GMfs-16) shows high discharge capacity of 1362 mAh g<SUP>-1</SUP> at the specific current of 100 mA g<SUP>-1</SUP> along with a reasonable rate capability of 53.4% from 50 to 1000 mA g<SUP>-1</SUP> and good cycle capability of 86.4% after 100 charge/discharge cycles. It is concluded that for the case of the randomly networked GMfs-16 composites, MoS<SUB>2</SUB> is the key active component to lithium ions storage, while rGO is the skeleton to improve conductivity and maintain the structural stability for MoS<SUB>2</SUB> nanosheets.

First principles investigations of electronics, magnetic, and thermoelectric properties of rare earth based PrYO3(Y¼Cr, V) perovskites

B. Sabir,G. Murtaza,Q. Mahmood,R. Ahmad,K.C. Bhamu 한국물리학회 2017 Current Applied Physics Vol.17 No.11

The structural, electronic, magnetic, optical and thermoelectric properties of PrYO3(Y¼Cr, V) have been studied by using density functional based FP-LAPWþ lo method as implemented into WIEN2k code. The analysis of band structures and density of states confirm the half metallic ferromagnetism in studied compounds. The nature and origin of ferromagnetism has been depicted in terms of crystal field energies, exchange energies involved and exchange constants. Moreover, the reduction of magnetic moment from V/Cr, Pr sites and generation of small magnetic moments on oxygen and interstitials sites leads to negative value of indirect exchange energy Dx(pd) and strong hybridization. Finally, the thermoelectric behavior has been explained by discussing the electrical conductivity, thermal conductivity, Seebeck coefficient, power factor and thermal efficiency. Moreover, evaluation of PrYO3 on the basis of its magnetic and thermoelectric properties conform that the compounds are much suitable for spintronic and thermoelectric applications.

The study of electronic, magnetic, magneto-optical and thermoelectric properties of XCr2O4 (X = Zn, Cd) through modified Becke and Johnson potential scheme (mBJ)

Shahid M. Ramay,M. Hassan,Q. Mahmood,Asif Mahmood 한국물리학회 2017 Current Applied Physics Vol.17 No.8

The electronic structure is analyzed to elucidate the magnetic and optical characters and the thermoelectric response of XCr2O4 (X ¼ Zn, Cd) stabilized in the cubic phase by using DFT based FP-LAPW method. The modified BeckeeJohnson (mBJ) functional is utilized to compute precise band structures (BS) and density of states (DOS), which confirm ferromagnetic semiconducting behavior. The origin of ferromagnetism explored by computing crystal field energy ðDCF Þ, John-Teller energy ðDJT Þ and exchange splitting energies DEXðdÞ and DEXðpdÞ. It is found that strong hybridization results in decay in Cr the magnetic moment and creates the magnetic moments at the nonmagnetic sites. The optical parameters reveal the suitability for energy harvesting devices. Finally, the BoltzTraP code has been implemented to study the thermoelectric properties, which show that increase in temperature increases the electrical conductivity, thermal conductivity and the power factor, while Seebeck coefficient reduces. Hence, the studied compounds are also suitable for thermoelectric devices to realize useful alternative energy sources.

Investigation of ferromagnetic semiconducting and opto-electronic properties of Zn1-xMnxS (0 ≤ x ≤ 1) alloys: A DFT-mBJ approach

M. Hassan,N.A. Noor,Q. Mahmood,B. Amin 한국물리학회 2016 Current Applied Physics Vol.16 No.11

In this study, we report the mechanical, structural, electronic, magnetic and optical behaviors in Zn1-xMnxS (0 ≤ x ≤ 1), which are determined by employing Wein2K code. The ferromagnetic (FM) state stability of the Zn1-xMnxS alloys has been elucidated from the calculated values of enthalpy of formation. The elastic constant (C11, C12, C14) are calculated to find various useful mechanical parameters, which depend upon Mn concentrations. The calculated electronic band structure and density of states (DOS) have demonstrated that exchange splitting through p-d hybridization, arising due to Mn impurities, stabilize a ferromagnetic state. The exchange splitting of the bands is further elucidated from the sharing of magnetic moment, charge and spin, between the impurity cations and the host lattice anions. Various parameters like direct spin-exchange splitting Dx(d), exchange constants N0a and N0b have also confirmed a stable ferromagnetic state. Various calculated optical parameters have indicated that the studied compounds respond to visible and ultraviolet energies. Moreover, the calculated optical band gap and static dielectric constant 31 (0) verify Penn's model. The studied compounds of Zn1-xMnxS have been shown theoretically that they find potential spintronic and optical device applications.

Study of optoelectronic, thermoelectric, mechanical, and thermodynamic properties of Cs2NaTlX6 (X = Cl, Br, I) for energy harvesting

Hedhili Fekhra,Hassan Belqees,Rashid M.S.,Bakr Mohammed,Mahmood Q.,M. Al-Shomar Shereen,Alahmad Waed,Alimi Fathi,Mechi Lassaad 한국물리학회 2023 Current Applied Physics Vol.53 No.-

The inorganic double perovskites are remarkable materials for renewable energy which can be realized through solar cells and thermoelectric generators. Here, we have comprehensively elaborated the stability, mechanical, thermodynamic, optical and transport characteristics. The formation energy is computed to ensure thermodynamic validity and the tolerance factor is assessed for structural existence. The elastic constants satisfied the Born criteria and mechanical stability. Naviera’s velocities have been used to study the Debye temperature and directional lattice conductivity. Modifying the band gap from 3.1 to 0.58 eV by halide ions (Cl to I) probes the distinct optoelectronic characteristics. Absorption bands, dispersion of light energy, refraction, and optical loss explain the optical characteristics. In addition, the above thermoelectric factors like conductivities, Seebeck effect, and performance are studied in the temperature range of 100–600 K. Large figure of merit and extremely low lattice vibration at room temperature indicate their significance for thermoelectric devices.