Results 1 - 10 of 14
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[en] An expression for the surface-plasmon dispersion, using the hydrodynamical model for a cylindrical bounded electron gas, has been derived, which agrees with the theoretical and experimental work of other workers. The volume-plasmon dispersion relations have also been obtained which are found to have strong resemblance with that of Bohm and Pines dispersion relation. It is shown that the critical wave vector for exciting the plasmon oscillations is different for the hydrodynamic flow in the cylindrical boundary. The interface surface plasmons have also been discussed for the hydrodynamic cylindrical flow. (author). 39 refs., 1 fig
[en] The full potential linearized augmented plane-wave (FP-LAPW) scheme of computation is used to explore the electronic and magnetic properties of Fe doped into YN. Band structure calculations show that YN is a semicon ductor with a narrow indirect band gap of 0.08 eV along Γ-X direction. Optical properties such as reflectivity, absorption coefficient are reported and are discussed on the basis of corresponding electronic structure. Spin polarized results indicate that the ground state of Y_1_-_xFe_xN (x=0.06, 0.12, 0.25) is ferromagnetic with a high moment on Fe-atom and zero moment on Y and N atoms, except in the case of 25 % doping. A discussion of the transport properties of YN and Y_1_-_xFe_xN is given in order to get insights of the Fe substitution effects.
[en] Spinel indium sulphide exists in three phases. The tetragonal β-phase transforms to the cubic α-phase at 420 °C which further transforms to the trigonal γ-phase at 754 °C. Due to wide energy bandgap, the phases of indium sulphide have possibilities of applications in photo-electrochemical solar cell devices as a replacement of toxic CdS. The electronic, optical and transport properties of the three phases have therefore been investigated using full potential linear augmented plane wave (FP-LAPW) + local orbitals (lo) scheme, in the framework of density functional theory (DFT) with generalized gradient approximation (GGA) for the purpose of exchange-correlation energy functional. We present the structure, energy bands and density of states (DOS) for α-, β- and γ-phases. The partial density of states (PDOS) of β-In2S3 is in good agreement with experiment and earlier ab initio calculations. To obtain the fundamental characteristics of these phases we have analysed their linear optical properties such as the dynamic dielectric function in the energy range of 0–15 eV. From the dynamic dielectric function it is seen that there is no directional anisotropy for α-phase since the longitudinal and transverse components are almost identical, however the β and γ-phases show birefringence. The optical absorption profiles clearly indicate that β-phase has possibility of greater multiple direct and indirect interband transitions in the visible regions compared to the other phases. To study the existence of interesting thermoelectric properties, transport properties like electrical and thermal conductivities, Seebeck and Hall coefficients etc. are also calculated. Good agreements are found with the available experimental results. -- Highlights: ► The electronic properties of phases of In2S3 have been investigated. ► The phases exhibit luminescence properties due to vacancies in crystal structure. ► The phases of In2S3 have low thermal conductivity and high electrical resistivity. ► The thermopower and figure of merit suggest that In2S3 may find applications as thermoelectric materials.
[en] The optical response of ZnAl2X4 (X = S, Se, Te) compounds to photon energy as well as to temperature variations has been studied by using self consistent full potential linearized augmented plane wave (FP-LAPW) method with Wu-Cohen generalized gradient approximation (WC-GGA) and mBJ potential. From the energy band structures, a direct bandgap is observed in all the zinc aluminides compounds, which reduces in the order S>Se>Te. The mBJ potential brings the calculated energy band gap close to the experimental one. From the density of states, it is observed that there is a strong hybridization of Zn-d, Al-p and X-p states. The optical nature of the compounds is described in terms of the absorption coefficient, reflectivity etc. The peaks observed in the photocurrent spectra of ZnAl2Se4 corresponds to the various structures at 3.52, 3.61 and 3.717 eV observed in the calculated conductivity and absorbance spectra
[en] We present results of ab initio study of ordered vacancy compounds of mercury. The electronic structure, charge density, optical and transport properties of the semiconductor family HgGa_2X_4 (X=S, Se, Te) are calculated using the full potential linearized augmented plane wave method which is based on the density functional theory. A direct bandgap is observed in these compounds, which reduces in the order S>Se>Te. From the density of states it is observed that there is strong hybridization of Hg-d, Ga-d and X-p states. The optical properties show a red shift with increasing size and atomic no. of the chalcogenide atoms. We have also reported the transport properties of mercury thiogallates for the first time. The selenide compound exhibits n-type nature whereas HgGa_2S_4 and HgGa_2Te_4 show p-type behavior. The power factor and ZT for the HGS increases at low temperatures, the figure of merit is highest for HgGa_2Se_4 (1.17) at 19 K.
[en] The structural, electronic, thermal, and optical properties of cubic non magnetic CeX_3(X=Pd, Rh) compounds which crystallize in the Au_3Cu structure have been studied using the projected augmented wave (PAW) method within the density functional theory (DFT) with generalized gradient approximation (GGA) for exchange correlation potential. In this paper we have calculated the band structure which are interpreted using the density of states. The optical properties such as extinction coefficients clearly illustrate the changes in CeX_3 due to intercalation of boron. Lattice instability is observed in CePd_3B from the calculated dynamical properties.
[en] The structural, electronic, thermal, and optical properties of borides of cubic non-magnetic YX_3 (X=Rh, Pd) compounds and their borides which crystallize in the AuCu_3 structure have been studied using the density functional theory (DFT). The flat bands in the vicinity of E_F which are associated with superconductivity appear in YPd_3 and YRh_3 band structures. However, the B s-states enhance the flat band only in YRh_3B. The optical properties clearly show that boron insertion modifies the absorption and transmittance. The YX_3 alloys and their borides exhibit valuable changes in the thermopower and ZT. It is observed that the properties of the Y-X intermetallics change significantly for the Y-Rh and Y-Pd alloys and the presence of single boron atom modifies the properties to a great extent.
[en] We have studied the electronic, transport and vibrational properties of low temperature superconductor β-PdBi_2. The band manifold clearly demonstrates the 2D-layered structure with multiple gaps. The intersection of bands at E_F in the Γ-P, Γ-N directions gives rise to complicated Fermi surface topology, which contains quite complicated multiple connected sheets, as well as hole and electron-like pockets. From the low temperature specific heat, we have estimated the electron-phonon coupling constant λ_e_l_-_p_h which has a very high value of 3.66. The vibrational properties clearly illustrates that the strong coupling makes the lattice unstable. The calculated properties confirm that β-PdBi_2 is an intermediate coupling superconductor
[en] Amongst the family of anti-perovskites, the materials with general formula RM3X (R and M are metals, X=B, C, N) are isostructural with superconducting MgCNi3. From a survey of literature it was found that the Y-Pd-C-B system has one of the highest superconducting transition temperatures (∼ 23 K) amongst the intermetallic compounds. Since YPd3 with AuCu3 structure has good hydrogen storage properties, boron and carbon can also be easily incorporated at its interstitials sites. The electronic properties of borides and carbides of Y-Pd have therefore been investigated by density functional theory based full potential linearized augmented plane wave (FP-LAPW) and projector augmented wave (PAW) methods. The energy bands, Fermi surfaces and density of states as well as the transport and vibrational properties were calculated to study the stability and superconducting properties of these alloys
[en] In this paper we report the electron momentum density of a layered transition-metal dichalcogenide WSe2. The Compton profile measurements have been made using our 20 Ci 137Cs Compton spectrometer. The energy bands, density of states, Compton profiles and Mulliken's populations of WSe2 are computed using pseudopotential scheme within linear combination of atomic orbitals as embodied in CRYSTAL03 rode. The band structure calculations show that WSe2 is an indirect-gap semiconductor having its top most valence band at Γ point and bottom of the conduction band in Γ -K branch of the first Brillouin zone. It is found that the theoretical electron momentum density for hybrid (Hartree-Fock and density functional theory) pseudopotential scheme is relatively in better agreement with the experiment. (author)