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Flexible regulation of bandgap of perovskite nanocrystals (PNCs) is fundamentally critical for desirable optoelectronic functions and applications. Here, regulating chemical composition and emission wavelength of PNCs in glass by a simple heat‐treatment process are reported, which is established to rely on the thermal‐trigger phase separation and ion exchange. The first principle calculations are overall performed to reveal the mechanism of bandgap engineering and optimization of emission performance. The PNCs exhibit excellent stability against thermal, ultraviolet irradiation, and organic molecules. The bandgap of PNCs in the heat‐treated glass can also be re‐modulated by ultrafast laser irradiation. Ultrafast laser direct writing of multi‐color patterns and holographic dynamic displays are achieved, which hold great potential in the application of encryption‐decryption and emissive devices. [ABSTRACT FROM AUTHOR]

A novel non-centrosymmetric Cadmium Metal-Organic Framework (Cd-MOF) crystal with chemical formula CdC8N8H14O2S4 was synthesized and characterized. The band structure and optical limiting properties of the Cd-MOF were investigated using Band structure calculations and Optical limiting studies. The band structure analysis showed that the crystal displayed a larger, highly dispersive band, highlighting significant anisotropic n-channel charge carrier mobility. The optical limiting study demonstrated that the Cd-MOF exhibited Reverse Saturable Absorption (RSA) behaviour with an optical limiting threshold value of 1094 kW/cm2. The NLO behaviour of the Cd-MOF provides a promising potential for its application in NLO devices.

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]

Borate crystals are widely applied in solid‐state laser systems for their superior properties of wide transparency range, large nonlinear optical (NLO) coefficients, and high resistance to laser damage. Previous theoretical studies all reference the bandgaps to the UV absorption cut‐offs. Herein, through the calculated band structures of three widely applied borate NLO crystals, namely, β‐BaB2O4 (BBO), LiB3O5 (LBO), and KBe2BO3F2 (KBBF), it is found that the bandgaps are always much wider than the absorption cut‐offs by over at least 1 eV. Therefore, an excitonic mechanism is proposed for the band‐edge absorptions. From the detailed band structures of the frontier orbitals, with a Wannier−Mott type approximation to the excitons, and reduced screening from lowered effective dielectric constants, the binding energies of the excitons in the three mentioned borate crystals are obtained. It is found that the absorption cut‐offs agree with the transition energies of the excitons very well for all the three crystals. The implication of these findings helps to find ways of the absorption decrease and laser damage prevention of those crystals.

The band structure calculations were made for RMn compounds, where R is a rare-earth element, M = Fe and Co, and n = 2, 3, 23/6 and 17/2. For each series, the magnetic moments of the transition metals linearly depend on the de Gennes factor with rates determined by their local environment. Exchange interactions are analyzed starting with the 4f–5d–3d model. The contributions of local 4f–5d interactions, as well as 5d–3d short-range interactions, to the polarization M5d of R5d band is determined. Exchange interactions at unit cell level are interdependent and mediated by the R5d band polarization. A linear dependence of the Curie temperatures on the M5d values is shown for each RMn series. The results are discussed in correlation with the experimental data obtained by magnetic and neutron diffraction measurements. [ABSTRACT FROM AUTHOR]

In this paper, some electronic properties such as the electronic density of states (DOS), and energy band structure, and optical properties of the bulk and monolayer PtSe2 structure have been investigated based on the density functional theory (DFT) using full-potential linearized augmented plane wave (FP-LAPW) method and the modified Becke-Johnson potential (mBJ). By changing the PtSe2 structure size from bulk to monolayer, there have been major changes in the electronic (DOS and band structure) and optical properties such as the dielectric function. The electronic results show that PtSe2 in the bulk state exhibits a metallic property, while its nanosheet state, PtSe2 is a semiconductor with an energy gap of about 1.5 eV. Band structure calculations showed that for PtSe2 structure in the bulk state the energy distance between Γ-point and the K-point is about 0.4 eV, so it is concluded that PtSe2 is a semi-metal. The optical properties results show that the largest damping region for electromagnetic waves for a bulk PtSe2 structure in the z-direction is equal to 14.02 eV. The volume plasmon energy of the PtSe2 monolayer is smaller than the plasmon energy of the bulk PtSe2. Also, the optical reflectivity of the bulk PtSe2 is larger than the optical reflectivity of the PtSe2 monolayer. [ABSTRACT FROM AUTHOR]

In this paper, some electronic properties such as the electronic density of states (DOS), and energy band structure, and optical properties of the bulk and monolayer PtSe2 structure have been investigated based on the density functional theory (DFT) using full-potential linearized augmented plane wave (FP-LAPW) method and the modified Becke-Johnson potential (mBJ). By changing the PtSe2 structure size from bulk to monolayer, there have been major changes in the electronic (DOS and band structure) and optical properties such as the dielectric function. The electronic results show that PtSe2 in the bulk state exhibits a metallic property, while its nanosheet state, PtSe2 is a semiconductor with an energy gap of about 1.5 eV. Band structure calculations showed that for PtSe2 structure in the bulk state the energy distance between Γ-point and the K-point is about 0.4 eV, so it is concluded that PtSe2 is a semi-metal. The optical properties results show that the largest damping region for electromagnetic waves for a bulk PtSe2 structure in the z-direction is equal to 14.02 eV. The volume plasmon energy of the PtSe2 monolayer is smaller than the plasmon energy of the bulk PtSe2. Also, the optical reflectivity of the bulk PtSe2 is larger than the optical reflectivity of the PtSe2 monolayer. [ABSTRACT FROM AUTHOR]

Copyright of Metallophysics & Advanced Technologies / Metallofizika i Novejsie Tehnologii is the property of G.V. Kurdyumov Institute for Metal Physics, N.A.S.U and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Metallophysics & Advanced Technologies / Metallofizika i Novejsie Tehnologii is the property of G.V. Kurdyumov Institute for Metal Physics, N.A.S.U and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Motivated by current interest in the materials with heavy elements, we perform theoretical calculations on two 5 d -electron compounds, Sr M 2 Ge 2 (M = Ir, Pt), which are observed superconductivity by former experiments. The electronic and phonon properties are obtained by ab initio calculations. The results show that the Pt/Ir-5 d orbital are strongly hybridized with Ge-4 p orbital, which contribute mainly to electronic states near the Fermi level (E F). Two (four) bands in SrIr 2 Ge 2 (SrPt 2 Ge 2) cross E F to construct rather three-dimensional Fermi surfaces. In SrPt 2 Ge 2 , novel Dirac cones around Σ point are observed, which are related to the band inversion between Ge-4 p and Pt-5 d orbital. When spin-orbit coupling (SOC) is considered, the Dirac cone along Z-Σ becomes fully gapped, but the cone along Γ − Σ line is stable. The lattice dynamics and electron-phonon coupling (EPC) are also studied with and without SOC. We find EPC is quite weak in SrIr 2 Ge 2 but strong in SrPt 2 Ge 2. Unstable phonon modes are observed in SrPt 2 Ge 2 with ThCr 2 Si 2 -type structure, corresponding to metastable phase observed by experiments. • The electronic structure and lattice dynamics of two 5d -electron potential superconductors SrIr 2 Ge 2 and SrPt 2 Ge 2 are investigated. • In SrPt 2 Ge 2 , novel Dirac cones are around Σ point, caused by the band inversion between Ge- 4p and Pt- 5d orbital. • It is found that the electron-phonon coupling (EPC) is quite weak in SrIr 2 Ge 2 but strong in SrPt 2 Ge 2. [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]

We investigate the electronic band structure properties for different arrangements of infinite horizontal boron nitride (BN) lines in the (6,6) armchair carbon nanotube. Depending on the arrangement of the boron and nitrogen atoms, the horizontal BN lines can be viewed as single or multiple BN segments along the contour of the host carbon nanotube. According to the geometrical orientation of the BN segment(s) in the circular direction, the band gap energy can be tuned providing semiconducting properties for the parallel geometries and metallic behaviors for the antiparallel geometries respectively. For the non-equilibrium transport properties, the current-voltage characteristics for such structures are also examined. Conventional fluctuations in the current are obtained for the high bias voltage as a sign of the resonant tunneling effects in the electronic transport process. However, unusual current-voltage characteristics are reported for particular BN segment configurations in the anti-parallel multiple geometry. The transmission functions and the local currents are respectively presented pointing out more details about such discrepancy in both the electronic transport process near the Fermi level and the nature of the corresponding wave functions. All calculations are performed by means of the density functional tight-binding approach as implemented in the DFTB+ software package. I-V characteristics for the multiple anti parallel (BN) x C x' heteronanotube with 2 ≤ x ≤ 10 under direct polarization (0 V < V b < 3V). The threshold values are directly observed on the V b axis. [Display omitted] [ABSTRACT FROM AUTHOR]

Introduction of chirality in the field of molecular conductors has received increasing interest in recent years in the frame of modulation of the crystal packing, and hence conducting properties, with the number of stereogenic centers and absolute configuration, e.g., racemic or enantiopure forms. Here, we describe the preparation by electrocrystallization of chiral radical cation salts, based on the donors methyl-ethylenedithio-tetrathiafulvalene (Me-EDT-TTF) 1 and ethyl-ethylenedithio-tetrathiafulvalene (Et-EDT-TTF) 2 containing one stereogenic center, with the perchlorate anion. Donor 1 provided the series of crystalline materials [(rac)-1]ClO4, [(S)-1]2ClO4 and [(R)-1]2ClO4, while for donor 2 only the 1:1 salts [(rac)-2]ClO4 and [(R)-2]ClO4 could be prepared as suitable single crystals for X-ray analysis. The enantiopure salts of 1 show β-type packing and metallic conductivity in the high temperature regime, with room temperature conductivity values of 5–10 S cm−1, whereas compound [(rac)-2]ClO4 is a very poor semiconductor. Tight-binding extended Hückel band structure calculations support the metallic conductivity of the enantiopure salts of 1 and suggest that small structural changes, possibly induced by thermal contraction or pressure, could lead to a pseudo-elliptic closed Fermi surface, typical for a 2D metal.

Abstract In this paper electron momentum density of CaCl 2 using 241Am Compton spectrometer is reported. The experimental Compton profile is compared with the corresponding theoretical profiles, computed using different exchange and correlation potentials within linear combination of atomic orbitals (LCAO) scheme. The hybrid WC1LYP approximation within LCAO scheme shows a better agreement with experimental CP than other reported theoretical profiles. Going beyond Compton line shapes, the energy bands, density of states using LCAO scheme and modified Becke-Johnson (mBJ) potential within full potential linearized augmented plane wave (FP-LAPW) method are also reported. The optical properties like, dielectric tensors, absorption spectra, reflectivity and refraction are also discussed using FP-LAPW method. Energy band gaps computed using LCAO-WC1LYP and FP-LAPW-mBJ methods are found to be 6.89 and 6.76 eV, respectively which are in reasonable agreement with the available experimental data. Highlights • Experimental Compton profile (CP) of CaCl 2 is measured using 241Am source. • Experimental CP is compared with LCAO based profiles. • Energy bands & DOS are computed using LCAO & FP-LAPW schemes. • Optical properties of CaCl 2 are deduced from mBJ schemes. [ABSTRACT FROM AUTHOR]

Theoretical investigations were made into the band gap, band structure and optical properties of tin sulphide (SnS) crystal with C2mb symmetry. The SnS crystal with this symmetry though has many properties similar to the well documented SnS crystal with Pnma symmetry, it does exhibit some uniqueness in band structure. The purpose of this study was to verify and confirm the recent experimental results of p-SnS thin films with C2mb symmetry. The p-type conductivity in SnS films is obtained due to Tin vacancies. These defects invariably gives rise to residual stress in the crystal. Theoretical investigations allow to address the question as to which of the two factors, stress or vacancies with stress, influences the electrical and optical properties more. Results of our calculations confirm that reported p-SnS films were oriented such that the incident light of UV–visible spectroscope fell perpendicular to the ‘ab’ plane and that shallow levels appear just above the valence band edge along with a spread in the conduction band edge on introduction of defects in the lattice. The spread in conduction band edge and appearance of shallow levels manifest themselves as Urbach spread or tail in UV–visible absorption spectra, which results in a decrease in band-gap with increasing number of Tin vacancies. Calculations also show that while optical properties are essentially due to the Tin vacancies, the residual stress also affects the p-SnS optical properties. The theoretical results are in good agreement with the experimental results. [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]

Polycrystalline samples of Y TE 2 Ge 2 with TE = Co, Ni, Ru, Rh, Pd and Pt were synthesized and characterized by means of X-ray powder diffraction and low-temperature electrical resistivity and specific heat measurements, supplemented by fully relativistic full-potential local-orbital band structure calculations. We confirm that most of the compounds studied crystallize in a body-centered tetragonal ThCr 2 S 2 -type structure (space group I 4 / mmm ) and have three-dimensional Fermi surfaces, while only one of them ( YPt 2 Ge 2 ) forms with a primitive tetragonal CaBe 2 Ge 2 -type unit cell (space group P 4 / nmm ) and possesses quasi-two-dimensional Fermi surface sheets with some nesting. Physical properties data show conventional superconductivity in the phases with TE = Co, Pd and Pt, i.e. independently of the structure type (and hence the dimensionality of the Fermi surface). [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]

The low bandgap semiconductor, SnTe is receiving significant attention as a thermoelectric material because of its low toxicity and environment-friendly nature. In this study, we report the effect of co-doping dilute concentrations of Ag and Cu ions in SnTe that suppresses the Sn vacancies leading to optimized thermoelectric properties. Samples of nominal chemical composition Sn 1.03–2x Ag x Cu x Te (x = 0, 0.01, 0.02, 0.04) were prepared by the solid-state route. The Rietveld refinement of powder XRD of these compounds showed a fcc (Fm 3 ¯ m) structure with no other impurity phases. Diffuse reflectance IR spectroscopy showed an increase in the bandgap upon Ag-Cu co-doping in SnTe, associated with valence band convergence. Electronic band structure calculations confirmed an increase in the bandgap along with a reduction in the energy difference between light and heavy valence bands having maxima at the L and Σ points. Partial density of states (P-DOS) calculations showed that Ag-Cu doping in SnTe does not contribute towards the formation of resonant energy levels. The Seebeck coefficient S of the Sn 1.01 Ag 0.01 Cu 0.01 Te reached a maximum value of ∼ 95 μ V/K at 783 K, compared to 86 μ V/K of pure SnTe. The power factor increased with the doping concentration, reaching ∼ 10.8 μ WK−2cm−1 at 783 K for x = 0.04. The lattice thermal conductivity κ L decreased on Ag-Cu co-doping, with κ L = 0.44 W m − 1 K − 1 above 750 K for x = 0.04, which is close to the Cahill model. The combination of higher power factor and reduced lattice thermal conductivity in the Ag-Cu co-doped samples resulted in enhanced ZT = 0.24–0.29 at 773 K. • A single-phase fcc (Fm-3 m) structure is maintained through the range of substitution. • The band-gap increases from 0.18 eV for SnTe to 0.25 eV on doping indicative of band convergence effects. • First-principles calculations show band convergence introduced by Ag-Cu co-doping. • Our calculations do not find any signature of resonant level formation upon Ag-Cu doping in the SnTe system. • The enhanced power factor and reduced lattice thermal conductivity on doping result in a maximum ZT = 0.29 at 773 K. [ABSTRACT FROM AUTHOR]

We investigate the structural, electronic and magnetic properties of LaMnO _3 /BaTiO _3 heterostructure by means of ab initio calculations within the GGA+ U approach. We consider the heterostructure when ferroelectric polarization in the BaTiO _3 film is oriented perpendicular to the LaMnO _3 substrate. We present atom and spin-resolved density of states calculations for LaMnO _3 /BaTiO _3 heterostructure with different number of BaTiO _3 overlayers as well as layer-resolved spectra for the conducting heterostructure. We found that the LaMnO _3 /BaTiO _3 heterostructure becomes conducting with a significant spin polarization indicating that the interface becomes ferromagnetically ordered. The propose concept of a ferroelectrically controlled interface ferromagnetism that offers the possibility to design novel electronic devices.

Luminescent, optical and electronic properties of Na 2 Mo 2 O 7 single crystals grown by two different procedures, the conventional Czochralski method and the low-temperature gradient Czochralski technique, are presented. The band structure calculations were performed in generalized gradient and local density approximations and allowed to determine the composition and structure of the valence and conduction bands. It is shown that the bottom of the conduction band is formed by the 4d states of Mo in octahedral oxygen coordination while the contribution of 4d states of Mo in tetrahedral oxygen coordination starts at 0.7 eV above the bottom of the conduction band. The optical bandgap of the crystals was estimated from absorption spectra to E g opt = 3.2 eV. The absorption band observed below the fundamental absorption edge at 370 nm is connected with the presence of oxygen vacancies. The luminescence spectrum is represented by a single emission band at 1.82 eV (T = 10 K), which is ascribed to the excitons self-trapped at oxyanionic complexes. The origin of charge carrier traps was studied using the combination of the methods of electron paramagnetic resonance and thermostimulated luminescence. Several electron and hole trapping centers were revealed including self-trapped holes and F + centers. The influence of trapping centers on the excitation energy transfer to the emission centers is discussed. [ABSTRACT FROM AUTHOR]

Materials research is currently one of the most interdisciplinary fields that drive scientific exploration of functional and usable structures. In addition to experimental approaches, computational studies are becoming ever more important in predicting compounds with desired properties. In particular two-dimensional materials have received enormous interest in recent years. Herein, we study the energy landscape of silicon-carbon compounds in two-dimensions. Predicting energetically (meta)stable structures is the foundation upon which in a second step the electronic structure of some selected networks is explored. We show how topology, geometry, and stoichiometry in the networks can be used as parameters to design 2D silicon carbide materials with tunable band structure, ranging from metallic, to semimetallic, and to finite bandgaps. [ABSTRACT FROM AUTHOR]

The structural, electronic and mechanical properties of Ga 1−x B x P ternary alloys are carried out by the first-principles based on density functional theory. We studied the effect of composition on the ground state properties such as lattice parameter, band gap and elastic modulus and anisotropy. The elastic anisotropy of Ga 1−x B x P alloys have been described through different anisotropic factors. We analyzed elastic anisotropy by depicting the three-dimensional surface structure of elastic modulus. Due to the introduction of boron atoms, the Ga 1−x B x P alloys become direct-gap semiconductors at x = 0.25, 0.50 and 0.75. At last, we calculated the average acoustic velocity in different directions and the Debye temperatures for the Ga 1−x B x P alloys. [ABSTRACT FROM AUTHOR]

R 3 AlC x (R = Ce, Pr and Nd; x = 0–1) series has been synthesized by arc melting. Rietveld analysis of x-ray powder diffraction reveals cubic (Pm-3m) structure. A Kondo temperature T K ~ 1 K is estimated for Ce 3 AlC 0.65 from the susceptibility and resistivity data. Magnetic susceptibility measurements indicate antiferromagnetic (AFM) order for R = Pr (x = 0.8 and 1) and Nd (x = 0.6, 0.8 and 1) and ferromagnetic (FM) for Nd 3 Al. Metamagnetic behaviour in the magnetization curve indicates complex magnetic structure. Band structure calculations indicate growth of a pseudo-gap in the density of states (DOS) from Ce 3 AlC to Pr 3 AlC to Nd 3 AlC. The DOS calculations predict a metallic behaviour which is consistent with the resistivity measurements. [ABSTRACT FROM AUTHOR]

The structural, electronic and magnetic behavior of the as-cast and annealed Mn 52 Al 46 Ti 2 and Mn 50 Al 46 Ti 4 alloys have been studied through electronic band structure calculations, X-ray diffraction and magnetic measurements in the temperature range 4–850 K and magnetic field up to 7 T. Band structure calculations show a preference for Ti atoms to occupy the Mn sites in the plane of Al atoms with their magnetic moments (−0.68 μ B /Ti) coupled antiparallel relative to the Mn magnetic moments in the plane of Mn atoms (2.33 μ B /Mn). The as-cast and annealed samples were phase mixtures with different values of the hard ferromagnetic τ phase content. Except the as-cast and annealed at 1050 °C Mn 52 Al 46 Ti 2 alloys, all the analyzed samples include, along with the τ and γ 2 phases, a soft κ phase (CsCl - structure type) with T C around 530 K. The best magnetic characteristics were obtained for Mn 52 Al 46 Ti 2 alloy annealed at 470 °C for 6 h: M S = 116 A m 2 /Kg at 4 K and T C = 668 K, in good agreement with the values reported in the literature for the τ phase of the MnAl system. The effects of the composition and of the preparation route on the electronic and magnetic properties are discussed in comparison with the properties of Mn 54 Al 46 parent alloy. [ABSTRACT FROM AUTHOR]

Copyright of Metallophysics & Advanced Technologies / Metallofizika i Novejsie Tehnologii is the property of G.V. Kurdyumov Institute for Metal Physics, N.A.S.U and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

[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]

Y 3 AlC has been synthesized by arc melting and subsequent annealing. Rietveld analysis of the powder x-ray diffraction (XRD) data confirms cubic Pm -3 m structure. Electrical resistivity ( ρ ) of Y 3 AlC exhibits metallic behaviour. No sign of superconductivity is observed down to the lowest measurement temperatures of 4.2 K in ρ , and 2 K in magnetic susceptibility ( χ ) and specific heat ( C p ) measurements. The value of the electronic specific heat coefficient γ is 1.36 mJ/K 2 mol from which the density of states (DOS) at the Fermi energy ( E F ) is obtained as 0.57 states/eV.unit cell. The value of Debye temperature θ D is estimated to be 315 K. Electronic band structure calculations of Y 3 AlC reveal a pseudo-gap in the DOS at E F leading to a small value of 0.5 states/eV unit cell which matches quite well with that obtained from γ . Non-zero value of the DOS indicates metallic behaviour as confirmed by our ρ data. Covalent and ionic bonding seem to co-exist with metallic bonding in Y 3 AlC as indicated by van Arkel- Ketelaar triangle for Zintl-like systems. [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]

The subnitridometalates Ba23Na11(MN4)4 (M=V, Nb, Ta) crystallize in a new structure type, which shows ionic ortho-nitridometalate anions and motifs from simple (inter)metallic packings: Na-centered [Na8] cubes as cutouts of the bcc structure of elemental Na and Na-centered [Ba10Na2] icosahedra as found in Laves phases, for example. Single-crystal and powder X-ray diffraction studies in combination with quantum-chemical calculations of the electronic structure and Raman spectroscopy support the characterization of the subnitridometalates as 'chemical twins'. They consist of independent building units with locally prevalent ionic or metallic bonding in an overall metallic compound. [ABSTRACT FROM AUTHOR]

We present the first ever studies on Compton profiles of AWO 4 (A=Co, Ni and Cu) using 661.65 keV γ-rays emitted by 137 Cs source. The experimental momentum densities have been employed to validate exchange and correlation potentials within linear combination of atomic orbitals (LCAO) method. Density functional theory (DFT) with local density approximation and generalized gradient approximation and also the hybridization of Hartree-Fock and DFT (B3LYP and PBE0) have been considered under LCAO scheme. The LCAO-B3LYP scheme is found to be in better agreement with the experimental data than other approximations considered in this work, suggesting applicability of B3LYP approach in predicting the electronic properties of these tungstates. The Mulliken’s population (MP) data show charge transfer from Co/Ni/Cu and W to O atoms. The experimental profiles when normalized to same area show almost similar localization of 3d electrons (in real space) of Ni and Cu which is lower than that of Co in their AWO 4 environment. [ABSTRACT FROM AUTHOR]

The structural, electronic and magnetic behavior of the as-cast and annealed Mn 50 Al 46 Ni 4 and Mn 54 Al 46 alloys was investigated. It was found that annealing at 470 °C promotes the formation of the τ phase in both alloys, however, all of the prepared samples were phase mixtures. The τ phase was found along with the κ phase (CsCl-type structure) only in the Mn 50 Al 46 Ni 4 alloy. M ( T ) curves show two transitions at 437 K and 634 K corresponding to the ferromagnetic κ and τ phases, respectively. A maximum τ phase content of 76 wt% for Mn 54 Al 46 and 74 wt% for Mn 50 Al 46 Ni 4 was found for the samples annealed at 470 °C for 6 h. Saturation magnetization values at 4 K of 112 Am 2 /Kg and 106 Am 2 /Kg were obtained for Mn 54 Al 46 and Mn 50 Al 46 Ni 4 respectively, in good agreement with the values reported in the literature. Band structure calculations show a preference for Ni to occupy the Mn 1 a and 1 c crystallographic sites, the calculated magnetic moments for Mn 54 Al 46 and Mn 50 Al 46 Ni 4 being in good agreement with the experiment. The electronic, structural and magnetic properties of these alloys are discussed as a function of composition and preparation route. [ABSTRACT FROM AUTHOR]

P doping in Co 2 As induces two structural transitions, resulting in an enhanced ferromagnetic state at intermediate P compositions. In Co 2 As 1− x P x , doping induces a room temperature α -to- β structural distortion around x =0.04, similar to what temperature ( T =725 K) does in the parent compound ( x =0). The resulting β phase displays an enhanced ferromagnetic ground state. Close to x =0.85, a hexagonal-to-orthorhombic phase transition occurs, concomitant with the quenching of the magnetic order. Band structure calculations for the three different phases confirm the experimental observations while revealing remarkably high charge carrier polarization rate for the β phase. [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]

Short period superlattices of the form m GaN/ n AlN, where m , n denote integer numbers of monolayers, and with growth direction along the wurtzite c -axis are studied by ab initio calculations. The dependence of the band gaps on composition is compared with results obtained previously for m InN/ n GaN superlattices. The strain caused by mismatch to the substrate leads to significant deformations of bonds in InN/GaN superlattices, whereas this effect is smaller in GaN/AlN superlattices. The general trends in gap behavior can to a large extend be related to the strength of the internal electric field, E , in the respective GaN and InN quantum wells. In the GaN/AlN superlattices E reaches values as high as 8 MV/cm, while in the InN/GaN superlattices E ≈ 15 MV/cm may be reached. The strong electric fields are caused by spontaneous and piezoelectric polarizations. The latter contribution dominates in InN/GaN superlattices. [ABSTRACT FROM AUTHOR]

The structural and physical properties of nickel-diluted Tb 0.27 Dy 0.73 ( Fe 0.7 − x Ni x Co 0.3 ) 2 intermetallics were studied by X-ray diffraction, four-probe dc electrical measurements and standard strain gauge method. X-ray analysis shows that all samples crystallize in a cubic Laves structure. The lattice parameter decreases linearly with the nickel content. Electrical resistivity was measured in a temperature range of 15–1100 K. The parameters involved in the dependence of resistivity on temperature and composition were determined. Residual, phonon and magnetic resistivity were separated from the electrical resistivity using both the Matthiessen and Bloch-Grüneisen formulas. The compounds’ Curie temperatures, which decrease nonlinearly with x , were obtained from the magnetic resistivity curves. The maximum values of magnetostriction attained for the Tb 0.27 Dy 0.73 ( Fe 0.6 Ni 0.1 Co 0.3 ) 2 compound exceed about 851 ppm. Electronic 3d-band structure and magnetic moment calculations were performed using the Full-Potential Linearized Augmented Plane Waves method. The distribution function for the densities of 3d-states was used to characterise the transition metal subbands. [ABSTRACT FROM AUTHOR]

We present the first ever Compton profile measurement of WO 2 using a 20 Ci 137 Cs γ-ray source. The experimental data have been used to test different approximations of density functional theory in linear combination of atomic orbitals (LCAO) scheme. It is found that theoretical Compton profile deduced using generalized gradient approximation (GGA) gives a better agreement than local density approximation and second order GGA. The computed energy bands, density of states and Mulliken׳s populations (MP) data confirm a metal-like behavior of WO 2 . The electronic properties calculated using LCAO approach are also compared with those obtained using full potential linearized augmented plane wave method. The nature of bonding in WO 2 is also compared with isoelectronic WX 2 (X=S, Se) compounds in terms of equal-valence-electron-density profiles and MP data, which suggest an increase in ionic character in the order WSe 2 →WS 2 →WO 2 . [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]

A new metastable compound Cr3Sb was synthesized as thin film starting from modulated elemental reactant layers. The new compound is cubic and crystallizes in the A15 structure (Cr3Si-type). A variation of the occupancy of the Sb position (0, 0, 0) was observed leading to a Cr-rich sample with formula Cr∼6Sb. In-situ X-ray diffraction and reflectivity investigations indicate an interdiffusion of the multilayers and crystallization of the new compound below 350°C. Calculations of the crystal structure and lattice parameter agree well with the experimental results. In addition the existence of a further metastable phase, a Heusler-like alloy, is discussed and supported by DFT calculations. [ABSTRACT FROM AUTHOR]

A detailed theoretical investigation on the electronic and magnetic properties of τ-phase of Mn54Al46 alloys with the CuAu tetragonal type of structure has been performed. All theoretical investigations of the electronic and magnetic properties have been done using the Korringa-Kohn-Rostoker (KKR) band structure method. The disorder in the system has been accounted for by means of the Coherent Potential Approximation (CPA). The spin resolved density of states (DOS) reflects the covalent nature of the interatomic bands. The calculated magnetic moments for the system Mn54-xAl46Znx show a non-linear variation with Zn content ranging between 4.06 μB/unit cell for Mn54Al46 (x = 0) to 4.68 μB /unit cell for Mn50Al46Zn4 (x = 4), suggesting an optimum Zn doping of 4% for Mn, close to the value of 2.9 % determined by experiment. On the other side, the SPR-KKR calculations do not confirm the existence of an optimum Zn for Al substitution which maximizes the magnetic moment of the samples. [ABSTRACT FROM AUTHOR]

Hierarchical SnO2 nanoflowers, assembled from single-crystalline SnO2 nanosheets with high-index (11 $ \bar 3 $) and (10 $ \bar 2 $) facets exposed, are prepared via a hydrothermal method using sodium fluoride as the morphology controlling agent. Formation of the 3D hierarchical architecture comprising of SnO2 nanosheets takes place via Ostwald ripening mechanism, with the growth orientation regulated by the adsorbate fluorine species. The use of Sn(II) precursor results in simultaneous Sn2+ self-doping of SnO2 nanoflowers with tunable oxygen vacancy bandgap states. The latter further results in the shifting of semiconductor Fermi levels and extended absorption in the visible spectral range. With increased density of states of Sn2+-doped SnO2 selective facets, this gives rise to enhanced interfacial charge transfer, that is, high sensing response, and selectivity towards oxidizing NO2 gas. The better gas sensing performance over (10 $ \bar 2 $) compared to (11 $ \bar 3 $) faceted SnO2 nanostructures is elucidated by surface energetic calculations and Bader analyses. This work highlights the possibility of simultaneous engineering of surface energetics and electronic properties of SnO2 based materials. [ABSTRACT FROM AUTHOR]

Abstract: We have reported the first-ever experimental Compton profile (CP) of TaB2 using 20 Ci137Cs Compton spectrometer. To compare the experimental data, we have also computed the theoretical CPs using density functional theory (DFT) and hybridization of DFT and Hartree–Fock (HF) within linear combination of the atomic orbitals (LCAO) method. In addition, we have reported energy bands and density of states of TaB2 using LCAO and full potential-linearized augmented plane wave (FP-LAPW) methods. A real space analysis of CP of TaB2 confirms its metallic character which is in tune with the cross-overs of Fermi level by energy bands and Fermi surface topology. A comparison of equal-valence-electron-density (EVED) experimental profiles of isoelectronic TaB2 and NbB2 show more covalent (or less ionic) character of TaB2 than that of NbB2 which is in agreement with available ionicity data. [Copyright &y& Elsevier]

Abstract: URh3 stabilizes in the cubic AuCu3 type structure at normal temperature and pressure. High-pressure angle-dispersive X-ray diffraction experiments were performed on URh3 up to 25GPa using a diamond-anvil cell. URh3 remains in its cubic AuCu3 type structure up to the maximum pressure studied. The Birch–Murnaghan equation of state fit to the P–V data yields the bulk modulus to be 133GPa. The Villars structural stability map gives a clue of a possible high pressure phase transition to a Ni3Sn type structure. The electronic structure calculations were carried out for both the ambient AuCu3 type cubic phase and the expected Ni3Sn type hexagonal high pressure phase. However, the total energy curves of these two structures do not intersect even at pressure as high as 360GPa, removing the possibility of transition to Ni3Sn type structure. [Copyright &y& Elsevier]

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]