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TaSb2, a candidate material for thermoelectric conversion, is studied to establish a method for the synthesis of polycrystalline bulk materials with a diameter greater than 10 mm. Polycrystalline TaSb2 materials with relative densities exceeding 97% are successfully prepared by combining the solid‐state reaction method with the spark plasma‐sintering process. The prepared TaSb2 sample is identified to be a semimetal with a pseudogap‐like electronic structure near the Fermi level using hard X‐ray photoelectron spectroscopy and band structure calculation. [ABSTRACT FROM AUTHOR]

The Compton profile of tetragonal BaTiO 3 is measured using 20Ci 137Cs Compton spectrometer. The experimental data have been analyzed using theoretical electron momentum densities computed using linear combination of atomic orbitals (LCAO) with density functional theory (DFT) and the hybridization of Hartree-Fock and DFT (WC1LYP scheme). It observed that hybrid scheme WC1LYP provides a better agreement with the experimental data than other approximations of exchange-correlation (with generalized gradient approximation like PBESol, SOGGA and local density approximation like LDAPZ) as considered in the present work. In addition, the energy bands and density of states have been reported using LCAO-WC1LYP scheme. The WC1LYP hybrid method confirms wide band gap semiconducting nature of tetragonal BaTiO 3. Further, a relative nature of bonding among CaTiO 3 , SrTiO 3 and BaTiO 3 has also been discussed using equal-valence-electron-density profiles and Mulliken's population analysis which predict a trend of increasing iconicity in the order CaTiO 3 →BaTiO 3 →SrTiO 3. • Measured first-ever Compton profile (CP) of tetragonal BaTiO 3 using high energy γ-rays. • Compared experimental CPs with those from LCAO-DFT and hybrid calculations. • Discussed applicability of hybrid functionals for BaTiO 3. • Discussed relative nature of bonding using Mulliken's population and EVED profiles. [ABSTRACT FROM AUTHOR]

In the course of our search for unconventional superconductors amidst the 1:2:2 phases, we have re-investigated the Lu TE 2 Si 2 compounds with TE = Fe, Co, Ni, Ru, Pd and Pt. In this paper, we present the results of our fully relativistic ab initio calculations of the band structures, performed using the full-potential local-orbital code. The theoretical data are supplemented by the results of low-temperature electrical transport and specific heat measurements performed down to 0.35 K. All the materials studied but LuPt 2 Si 2 crystallize with the body–centered tetragonal ThCr 2 Si 2 –type structure (space group I 4/ mmm ). Their Fermi surfaces exhibit a three-dimensional multi–band character. In turn, the Pt–bearing compound adopts the primitive tetragonal CaBe 2 Ge 2 –type structure (space group P 4/ nmm ), and its Fermi surface consists of predominantly quasi–two–dimensional sheets. Bulk superconductivity was found only in LuPd 2 Si 2 and LuPt 2 Si 2 (independent of the structure type and dimensionality of the Fermi surface). The key superconducting characteristics indicate a fully-gapped BCS type character. Though the electronic structure of LuFe 2 Si 2 closely resembles that of the unconventional superconductor YFe 2 Ge 2 , this Lu–based silicide exhibits neither superconductivity nor spin fluctuations at least down to 0.35 K. [ABSTRACT FROM AUTHOR]

We report synthesis, crystal and electronic structures, and optical properties of two new Hg-based zero-dimensional hybrid organic-inorganic halides (HIm) 2 Hg 3 Cl 8 and (HIm)HgI 3 (HIm = imidazolium). (HIm) 2 Hg 3 Cl 8 crystallizes in the triclinic P -1 space group with a pseudo-layered structure made of organic imidazolium cation layers and anionic inorganic layers containing [Hg 2 Cl 6 ] 2- units and linear [HgCl 2 ] 0 molecules. (HIm)HgI 3 crystallizes in the monoclinic P 2 1 /c space group featuring anionic [HgI 3 ] - units that are surrounded by imidazolium cations. Based on density functional theory calculations, (HIm) 2 Hg 3 Cl 8 has an indirect band gap, whereas (HIm)HgI 3 has a direct band gap with the measured onsets of optical absorption at 3.43 and 2.63 eV , respectively. (HIm) 2 Hg 3 Cl 8 and (HIm)HgI 3 are broadband light emitters with broad photoluminescence peaks centered at 548 nm (2.26 eV) and 582 nm (2.13 eV), respectively. Following the crystal and electronic structure considerations, the PL peaks are assigned to self-trapped excitons. [ABSTRACT FROM AUTHOR]

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[Display omitted] • A DFT study using Quantum-Espresso. • Transition metal doped rare earth neodymium sesquioxide (Nd 2 O 3). • Perdew–Burke–Ernzerhof exchange correlation functional. • Density of states specify enhanced magnetic properties in doped Nd 2 O 3. • Optical properties are well modulated by transition metal atom. The structural, electronic, magnetic, and optical properties of transition metal doped rare earth neodymium sesquioxide (Nd 2 XO 3 , where X = Co, Cr, Mn, Ni, and Zn) were investigated here by first-principles simulations considering the density functional theory (DFT) framework. Comparing the energy band structures, density of states, and the overall charge density distribution, we have seen that the transition metal doping improves the application of the Nd 2 O 3 (NDO) in many technological aspects. Spin-polarized calculations were quite satisfactorily described, and from this theoretical interpretation using DFT we've fruitfully explained the mechanism behind the magnetic behavior of all doped samples. The electronic and optical properties of doped NDO samples were well-tuned by transition metal atoms. Finally, we have observed that the values of total magnetization of transition metal substituted NDO samples were substantially enhanced compared to that of pure NDO, which would be very attractive in diverse applications. [ABSTRACT FROM AUTHOR]

La 3 Co and La 3 Ni are reported superconductors with transition temperatures of 4.5 and 6 K, respectively. Here, we reinvestigate the physical properties of these two intermetallic compounds with magnetic susceptibility χ, specific heat C p and electrical resistivity ρ measurements down to 1.9 K. Although bulk superconductivity is confirmed in La 3 Co, as observed previously, only a trace of it is found in La 3 Ni, indicating that the superconductivity in La 3 Ni originates from an impurity phase. Superconducting state parameters for La 3 Co, including lower and upper critical fields and the superconducting gap, are estimated. Results of the theoretical calculations of the electronic structure for both materials are also presented, and comparison of the Fermi level location in La 3 Co versus La 3 Ni explains its larger superconducting T c . A major discrepancy between band structure calculations and the experimentally measured Sommerfeld coefficient is found. The measured electronic density of states is about 2.5 times larger than the theoretical value for La 3 Co. This effect cannot be explained by the electron-phonon interaction alone. Renormalization of γ, as well as an ∼T 2 behavior of the resistivity, suggests the presence of spin fluctuations in both systems. [ABSTRACT FROM AUTHOR]

We report the first ever Compton scattering study of ZnWO 4 and CdWO 4 using 20 Ci 137 Cs Compton spectrometer at momentum resolution of 0.34 a.u. To compare the experimental Compton profiles, we have also deduced the momentum densities using density functional theory (DFT) within linear combination of atomic orbitals (LCAO) methods. It is seen that the experimental Compton profiles of both the tungstates give a better agreement with LCAO–DFT calculations within generalized gradient approximation (GGA) employing Perdew–Becke–Ernzerhof (PBE) exchange and correlation energies than other approximations included in the present work. Further, energy bands, density of states (DOS) and band gaps have also been calculated using LCAO–DFT–GGA–PBE scheme and full potential linearized augmented plane wave method. Both the computational schemes show a semiconducting nature of both the tungstates, with a direct band gap at Y point of Brillouin zone. Further, a relative nature of bonding on equal-valence-electron-density scale shows more covalent character in ZnWO 4 than CdWO 4 which reconciles with the conclusions drawn using integrated DOS and Mulliken’s population data. [ABSTRACT FROM AUTHOR]

Ti 2 AlC x N y solid solutions are synthesized using hot isostatic pressing. The X site solid solution effects are investigated, focusing on the microstructure, electronic structure and transport properties of the Ti 2 AlC x N y MAX phases. Combining X-ray diffraction with scanning electron microscopy and wavelength dispersive X-ray spectroscopy measurements, it is shown that solid solutions can be synthesized with well-controlled chemical compositions in the entire composition range ( x = 0–1). The measured a and c lattice-parameter values are shown to be in good agreement with those calculated using the cluster-expansion formalism. Combining electron energy-loss spectroscopy (EELS) and band structure calculations, it is demonstrated by Arroyave et al. that solid solution effects induce weak perturbations on the electronic structure. The solid solution effect thus results mainly in a rigid shift of the Fermi energy in a flat part of the electron density of states of Ti 2 AlC (or Ti 2 AlN). From these observations, the variations in two key parameters of the conductivity are rationalized. The relative variations in the residual resistivity in the whole composition range are shown to be small, which agrees well with the weak disorder evidenced by EELS. However, the values of the slope of the variation in resistivity vs. temperature are shown to vary quite significantly, evidencing a deviation from Matthiessen’s rule in these systems. By comparing the experimental data with calculations based on the semi-classical Boltzmann equation, it is demonstrated that the observed variations are due to a combination of band structure effects and changes in the scattering mechanisms. Finally, vacancies are also shown to have a prominent effect on the transport properties of Ti 2 AlC x N y solid solutions. In particular, both residual resistivity and dρ( T )/d T values are shown to be significantly higher than those of the corresponding stoichiometric compounds. [ABSTRACT FROM AUTHOR]

Abstract: In the present work, we have studied electron momentum density of CaCO3 using a Compton scattering technique. The experiment has been performed using a 100mCi 241Am (59.54keV) Compton spectrometer. The experimental data have been interpreted in terms of theoretical Compton profiles. To compute the theoretical momentum densities, energy bands and density of states, we have used linear combination of atomic orbitals method as embodied in CRYSTAL09 code. We have used local density approximation, generalized gradient approximation (GGA) and second order GGA (SOGGA) within the frame work of density functional theory. It is seen that the GGA gives a better agreement with the experimental data than other approximations. We have also discussed the energy bands and density of states of CaCO3. [Copyright &y& Elsevier]

Abstract: From the refined atomic positions obtained by Belmal et al. (2004) using X-ray diffraction for Li0.50Co0.25TiO(PO4), we have performed a structural optimization by minimizing the forces acting on the atoms keeping the lattice parameters fixed at the experimental values. With this relaxed (optimized) geometry we have performed a comprehensive theoretical study of electronic properties and dispersion of the linear optical susceptibilities using the full potential linear augmented plane wave (FP-LAPW) method. The generalized gradient approximation (GGA) exchange-correlation potential was applied. In addition, the Engel-Vosko generalized gradient approximation (EVGGA) was used for comparison with GGA because it is known that EVGGA approach yields better band splitting compared to the GGA. We have calculated the band structure, and the total and partial densities of states. The electron charge densities and the bonding properties were analyzed and discussed. The complex dielectric optical susceptibilities were discussed in detail. [Copyright &y& Elsevier]

Abstract: We have investigated spin-doping effects on the valence-band electronic structure of Sr1−(x+y)La x+y Ti1−x Cr x O3 at y =0.2 using high-resolution photoemission spectroscopy and first-principles band structure calculations. The Cr 3d photoemission spectral weight located between 2.0 and 3.5eV increased with x, indicating that x works as a rough measure of the spin density. However, the increase in the spectral weight was actually more rapid than the band theory prediction. The near-Fermi level (E F) weight due to the Ti 3d states showed significant reduction with x. Considering that the band theory predicted nearly constant density of states near E F, this reduction of the near-E F weight should be interpreted as a manifestation of strong Ti–Cr site disorder effects. [Copyright &y& Elsevier]

High-pressure angle-dispersive X-ray diffraction experiments were performed on UGa3 up to 30 GPa within a diamond-anvil cell. UGa3 remains in its cubic AuCu3 type structure up to the maximum pressure studied and does not show any structural phase transition. To understand the structural stability of UGa3, band structure calculations were performed as a function of reduced volume using the full-potential linear augmented plane wave (FP-LAPW) method. The results show that the Fermi level coincides with a deep valley in the density of states (DOS) curve in the antiferromagnetic state, whereas it lies near a valley (towards the bonding side) in the nonmagnetic state. At high pressures, the DOS near EF does not show much variation in both the cases. The experimental and theoretical equation of state, bulk modulus, and its pressure derivative values are also reported. The pressure dependence of magnetic moment shows a linear decrease at the rate of dμ/dP = -0.027 μB/GPa. [ABSTRACT FROM AUTHOR]

Abstract: Detailed theoretical and experimental investigations of the electronic and magnetic properties of the RCo5−x M x compounds (R=Y, Pr and M=Si, Al) have been performed. All theoretical investigations of the electronic and magnetic properties of the system have been done using the Korringa–Kohn–Rostoker (KKR) band structure method. The Si for Co substitution in RCo5 does not change the magnetic ordering: the RCo5−x Si x with R=Y, Nd and Pr is ferromagnetic, whilst the heavy rare-earth containing compounds are ferrimagnetic. The important modifications induced by this substitution concerns the magnetic properties of the system: the Curie temperature and the magnetic moments of Co decrease with Si content, indicating the weakening of the Co–Co exchange interaction. The band structure calculations evidence the hybridization between the 3d electronic states of Co and the 3p states of Si as possible reason for the diminishing of Co–Co exchange interaction. Also, the volume effect on the magnetic properties of the YCo4Si was investigated using theoretical methods. The results are compared with the experimental measurements in order to distinguish the origin of magnetization reduction in YCo4Si compared with YCo4Al. [Copyright &y& Elsevier]

Abstract: Total and partial densities of states of the constituent atoms of iron tungstate, FeWO4, and cobalt tungstate, CoWO4, have been calculated using the first-principles self-consistent full potential linearized augmented plane wave (FP-LAPW) method. The results obtained reveal that the O 2p-like states are the dominant contributors into the valence band of the tungstates under consideration, whilst the bottom of the conduction band of FeWO4 and CoWO4 is dominated by contributions of the empty Fe 3d- and Co 3d-like states, respectively. The FP-LAPW data indicate that the O 2p-like states contribute mainly into the top of the valence band, with also significant contributions throughout the whole valence-band region, of FeWO4 and CoWO4 compounds. Other significant contributors into the valence-band region are the Fe 3d- and W 5d-like states in FeWO4 and the Co 3d- and W 5d-like states in CoWO4. All the above d-like states contribute throughout the whole valence-band region of the tungstates under consideration, however maximum contributions of the W 5d-like states occur in the lower, whilst the Fe (Co) 3d-like states in the upper portions of the valence band, respectively. To verify the above FP-LAPW data, the X-ray emission bands representing the energy distributions of mainly the valence O p-, Fe (Co) d-, Fe (Co) p- and W d-like states were measured and compared on a common energy scale with the X-ray photoelectron valence-band spectrum of the corresponding tungstate. The experimental data were found to be in good agreement with the theoretical FP-LAPW results for the electronic structure of FeWO4 and CoWO4 compounds. [Copyright &y& Elsevier]

Abstract: In this paper, we present the first-ever experimental Compton line shapes of HgBr2 and HgI2 using 137Cs Compton spectrometer. To compare our experimental momentum densities, we have computed the Compton profiles using Hartree–Fock and density functional theory within linear combination of atomic orbitals. We have also computed the energy bands and density of states using the linear combination of atomic orbitals and full potential linearized augmented plane wave method. On the basis of equal-valence-electron-density profiles, it is seen that HgI2 is more covalent than HgBr2 which is in agreement with the valence charge densities. The experimental isotropic profiles are found to be relatively in better agreement with the Hartree–Fock data. We have also discussed the photoluminescence and detection properties of both the halides. [Copyright &y& Elsevier]

Abstract: Three new ternary potassium(I) zinc(II) or cadmium(II) tellurides, namely, K2Cd2Te3, K6CdTe4 and K2ZnTe2, were synthesized by solid-state reactions of the mixture of pure elements of K, Cd (or Zn) and Te in Nb tubes at high temperature. K2Cd2Te3 belongs to a new structure type and its structure contains a novel two-dimensional [Cd2Te3]2− layers perpendicular to the b-axis. K(5) cation is located at the center of five member rings of the 2D [Cd2Te3]2− layer, whereas other K+ cations occupy the interlayer space. K6CdTe4 with a K6HgS4 type structure features a “zero-dimensional” structure composed of isolated CdTe4 tetrahedra separated by the K+ ions. K2ZnTe2 in the K2ZnO2 structural type displays 1D [ZnTe2]2− anionic chains of edge sharing [ZnTe4] tetrahedra separated by the potassium(I) ions. K2Cd2Te3, K6CdTe4 and K2ZnTe2 revealed a band gap of 1.93, 2.51 and 3.0eV, respectively. [Copyright &y& Elsevier]

Abstract: The electronic structure and the magnetic properties of Sr2FeMoO6/SrTiO3(SFMO/STO) multilayers using the Full Potential Linearized Augmented Plane Wave method are investigated in order to discuss the role played by the Fe deficiency at the interface between SFMO and STO layers. The superlattice cell is built with (i) an STO layer consisting on five atomic layers for which the in plane lattice is taken equal to the one of bulk SFMO, (ii) a bulk-like SFMO layer consisting of seven atomic layers ending with Sr2O2 and (iii) an interfacial atomic layer consisting on FeMoO4 (stoichiometric SFMO layer) or Mo2O4 (Fe deficient SFMO layer). The present calculations show that the interface has a very limited impact on the electronic and magnetic properties for the stoichiometric SFMO layer. On the other hand, the polarization of the evanescent states into the STO layer is strongly reduced and the gap into the majority spin band is recovered only for the most inner FeMoO4 atomic plane of SFMO for the Fe deficient SFMO layer as compared to the other case. [Copyright &y& Elsevier]

The electronic band structure and stability of extended nanocrystallites (NCs) of titanium monocarbide TiC were investigated by the electron density functional-tight binding (DFTB) technique. The stability of prismatic NCs increases with the number of atomic layers; the electronic spectrum of these compounds changes from semiconductor (for NC of minimal atomic size) to metallike type inherent in crystalline titanium carbide. [ABSTRACT FROM AUTHOR]

Abstract: We analyzed the atomic and electronic structures in relaxed Si1−y C y crystals using the local density approximation (LDA) as implemented within the full-potential linearized augmented plane wave (FP-LAPW) basis. The band gaps are compared with those calculated with nonlocal corrections for the exchange-correlation energy functional and those calculated by using a GW approach. For small concentrations of carbon, it is found that carbon–silicon alloys are semiconducting with a very small band gap. These results are consistent with earlier LDA calculations, which predicted that the band gap of carbon–silicon alloy at low carbon concentrations is smaller than that of pure silicon. The optical band gap bowing is found to be strongly composition dependent. Furthermore, we found that the SiC alloys are characterized by a strong competition between structural (volume deformation) and chemical (charge transfer) effects leading to a giant optical gap bowing. [Copyright &y& Elsevier]

We have previously shown that a division of the f‐shell into two subsystems gives a better understanding of the cohesive properties as well the general behavior of lanthanide systems. In this article, we present numerical computations, using the suggested method. We show that the picture is consistent with most experimental data, e.g., the equilibrium volume and electronic structure in general. Compared with standard energy band calculations and calculations based on the self‐interaction correction and LDA + U, the f‐(non‐f)‐mixing interaction is decreased by spectral weights of the many‐body states of the f‐ion. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005 [ABSTRACT FROM AUTHOR]

Computational and experimental studies using linear muffin tin orbital methods and UV-visible diffuse reflectance spectroscopy, respectively, were performed to quantitatively probe the relationships between composition, crystal structure and the electronic structure of oxides containing octahedrally coordinated d0 transition metal ions. The ions investigated in this study (Ti4+, Nb5+, Ta5+, Mo6+, and W6+) were examined primarily in perovskite and perovskite-related structures. In these compounds the top of the valence band is primarily oxygen 2p non-bonding in character, while the conduction band arises from the π* interaction between the transition metal t2g orbitals and oxygen. For isostructural compounds the band gap increases as the effective electronegativity of the transition metal ion decreases. The effective electronegativity decreases in the following order: Mo6+>W6+>Nb5+∼Ti4+>Ta5+. The band gap is also sensitive to changes in the conduction band width, which is maximized for structures possessing linear M–O–M bonds, such as the cubic perovskite structure. As this bond angle decreases (e.g., via octahedral tilting distortions) the conduction band narrows and the band gap increases. Decreasing the dimensionality from 3-D (e.g., the cubic perovskite structure) to 2-D (e.g., the K2NiF4 structure) does not significantly alter the band gap, whereas completely isolating the MO6 octahedra (e.g., the ordered double perovskite structure) narrows the conduction band width dramatically and leads to a significant increase in the band gap. Inductive effects due to the presence of electropositive “spectator” cations (alkali, alkaline earth, and rare-earth cations) tend to be small and can generally be neglected. [Copyright &y& Elsevier]

We present electronic properties of CrSi2 under isotropic and anisotropic stress. Theoretical calculations were performed using the full-potential linearized-augmented-plane-wave method. The isotropic stress of the crystal leads to an almost linear variation of the direct and indirect transitions as a function of the lattice parameter, whereas anisotropic deformations result in more complicated dependencies. Uniaxial stretching of the lattice up to 106% converts chromium disilicide into a direct-gap semiconductor with a fundamental gap of about 0.3 eV. The compression of the lattice up to 94% changes the symmetry of the transitions. [Copyright &y& Elsevier]