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We report the synthesis and characterization of Fe 0.36(4) Pd 0.64(4) Se 2 with a pyrite-type structure. Fe 0.36(4) Pd 0.64(4) Se 2 was synthesized using ambient pressure flux crystal growth methods even though the space group Pa3 is high-pressure polymorph for both FeSe 2 and PdSe 2 . Combined experimental and theoretical analysis reveal magnetic spin glass state below 23 K in 1000 Oe that stems from random Fe/Pd occupancies on the same atomic site. The frozen-in magnetic randomness contributes significantly to electronic transport. Electronic structure calculations confirm dominant d-electron character of hybridized bands and large density of states near the Fermi level. Flux-grown single crystal alloys in Pd-Fe-Se atomic system therefore open new pathway for exploring different polymorphs in crystal structures and their novel properties. © 2019 American Chemical Society.

Density functional theory (DFT) calculations were performed to address the effects of 5d transition metals (TM) doping on the electronic structure properties of rutile TiO2, using both the modified Becke-Johnson (mBJ) and on-site hybrid functional. The calculations show that there is a reduction of band gap in almost all the investigated cases, except when TiO2 is doped with Ta. Some of the investigated systems (Re, W, Os, Ir) exhibit pronounced spin polarization, mainly arising from the TM atoms. In addition, a large increase of band gap is observed, when switching from a 24-atoms to 48-atoms supercell, while further enlarging the supercell size doesn’t affect the band gap significantly. Among the investigated transition metals, Pt and Ir are the best candidates for improving the photocatalytic properties of rutile TiO2 through substitutional doping.

In this paper we investigated the effects of Fe -doping of the anatase TiO 2 (1 0 1) surface on the crystal structure, electronic and optical properties, and impurity formation energy by means of density functional theory (DFT). The calculations were performed by the SIESTA DFT code and were carried out by using Troullier-Martins pseudopotentials for the 12-electron valence configuration ( 3 s 2 3 p 6 3 d 2 4 s 2 ) of Ti atom, 6-electron valence configuration ( 2 s 2 2 p 4 ) of O atom and 8-electron valence configuration ( 3 d 6 4 s 2 ) of Fe atom. We used a double- ζ basis set including polarization functions. All calculations were spin-polarized. The mechanism of narrowing the band gap and increasing the photocatalytic activity in the visible light region, of the doped TiO 2 is discussed by investigating the density of state. The band gap decreases as the concentration of the dopant increases. The Partial Density of States (PDOS) is not the same in the case of spin-up state or spin-down state. Enhanced optical absorption, for light polarized in the z direction (parallel to the surface normal) is clearly observed for Fe doped as compared to the pure anatase TiO 2 and the optical absorption is found to increase with the increase in the Fe concentration. The DFT results indicate that the source of the increasing photocatalytic activity in the visible light region of the Fe doped material is due to the introduction of additional electronic states within the band gap. Since the Fe atoms are more stable in Ti substitutional lattice positions for the entire range of Fermi energy E F over the band gap, only this substitutional position is considered. We hope that our results will highlight a route to improved electronic and optical properties of anatase TiO 2 for industrial applications.

We report the synthesis and characterization of Fe

In this paper we studied the effects of the concentration of W as a doped atom on the V lattice site on the electronic and optical properties of tetragonal zircon-type B i V O 4 structure. The calculations were performed by the first-principles density functional theory WIEN2k code. The doping strategy was targeting V atoms substituted by W atoms using the same lattice parameters as pure B i V O 4 structure. To avoid the self interaction of impurities, the supercell method was adopted ensuring a sufficient length between the impurities in all directions. For all considered concentrations, the optical properties in the visible light range of λ ≥ 550 n m are improved over the undoped B i V O 4 .

Substitutionally doped Bi2 W 1 - x M x O6 ( M = Mo, Cr, Fe, Zn; x = 0.125, 0,25, 0.5) is investigated using the density functional theory (DFT). For all the investigated transition metal dopants, the optical properties in the visible light range are improved over the undoped Bi2WO6. Irrespective of concentration, the lattice relaxation around the dopants is constrained to the first coordination shell. Mo, Fe, and Cr introduce localized defect states in the band gap, contributing to band gap narrowing. The localized states are hybridized between the impurity d–bands and host W 5d–and O 2p–states. Zn facilitates the reduction of the band gap by inducing a shift of the states near the top of the valence band toward higher energies. Our results suggest that Zn doping on the W lattice site may improve the photocatalytic properties of Bi2WO6 more than the other dopants.

X-ray absorption spectroscopy is employed to investigate site preference and lattice relaxation around Mo, Ru, Hf, W and Re dopants in Ni3Al. The site occupation preference and the measured distances between the refractory elements as dopants and the nearest host atoms are compared with the results of ab initio calculations within the density functional theory. Combined experimental and theoretical results indicate that Mo, Hf, W and Re atoms reside on the Al sublattice in Ni3Al, while Ru atoms occupy the Ni sublattice. A more pronounced lattice relaxation was detected in the case of Hf and Ru doping, with a strong outward relaxation of the nearest Ni and Al atoms. 2nd Workshop on FEL Photon Diagnostics, Instrumentation and Beamlines Design (PhotonDiag), Jun 08-10, 2015, Int Ctr Theoretical Phys, Trieste, Italy

The local electronic and magnetic structure, hyperfine interactions, and phase composition of polycrystalline Ni-deficient Ni3-xFexAl (x = 0.18 and 0.36) were investigated by means of Fe-57 Mossbauer spectroscopy. The samples were characterized by X-ray diffraction and magnetization measurements. The ab initio calculations performed with the projector augmented wave method and the calculations of the energies of iron point defects were done to elucidate the electronic structure and site preference of Fe doped Ni3Al. The value of calculated electric field gradient tensor V-zz = 1.6 10(21) Vm(-2) matches well with the results of Mossbauer spectroscopy and indicates that the Fe atoms occupy Ni sites. (C) 2015 Elsevier B.V. All rights reserved.

Incorporation of suitable dopants in MgH2 is widely investigated as the way of improving hydrogen storage characteristics of this material. The catalytic role of transition metal dopants on hydrogen desorption from MgH2 is very promising, but further attention is required in order to optimize the experimental methods and design materials with desired properties. In this paper we investigate the role of Ti, Fe, and Mn on the transport properties of hydrogen in MgH2, which are marked as limiting factor in the effort to lower the hydrogen desorption temperature. Taking into account the lattice relaxation around the impurities, we consider a number of different diffusion paths in the pure and doped system. Using PAW DFT calculations in combination with the NEB method, we demonstrate that the diffusion of the most relevant positively charged hydrogen vacancy and negatively charged interstitial hydrogen atom is locally hindered by the presence of the impurity atoms.

In order to study the effect of Fe cation substitution on the local structure, defect formation, and hyperfine interactions in ZnO, Mossbauer spectroscopy measurements of the microwave processed Zn 1 − x Fe x O ( x = 0.05, 0.10, 0.15, and 0.20) nanoparticles, together with ab initio calculations, were performed. Complementary information on the distribution of particle size and morphology, as well as magnetic properties, were obtained by X-ray diffraction, transmission electron microscopy, and squid-magnetometry. The selected model for analyzing the Mossbauer spectra of our samples is a distribution of quadrupole splittings. The fitting model with two Lorentz doublets was rejected due to its failure to include larger doublets. The Fe 3 + ions do not yield magnetic ordering in the samples at room temperature. The results from first-principles calculations confirm that the major component of the Mossbauer spectra corresponds to the Fe-alloyed ZnO with Zn vacancy in the next nearest neighbor environment. The magnetic measurements are consistent with the description of the distribution of iron ions over the randomly formed clusters in the ZnO host lattice. While at room temperature all the samples are paramagnetic, magnetic interactions cause a transition into a cluster spin-glass state at low temperatures.In order to study the effect of Fe cation substitution on the local structure, defect formation, and hyperfine interactions in ZnO, Mossbauer spectroscopy measurements of the microwave processed Zn 1 − x Fe x O ( x = 0.05, 0.10, 0.15, and 0.20) nanoparticles, together with ab initio calculations, were performed. Complementary information on the distribution of particle size and morphology, as well as magnetic properties, were obtained by X-ray diffraction, transmission electron microscopy, and squid-magnetometry. The selected model for analyzing the Mossbauer spectra of our samples is a distribution of quadrupole splittings. The fitting model with two Lorentz doublets was rejected due to its failure to include larger doublets. The Fe 3 + ions do not yield magnetic ordering in the samples at room temperature. The results from first-principles calculations confirm that the major component of the Mossbauer spectra corresponds to the Fe-alloyed ZnO with Zn vacancy in the next nearest neighbor en...

The hydrogen storage potential of TiNi-based shape memory alloys is an attractive but experimentally challenging issue. We employ the FP (L)APW+lo method, based on the density functional theory (DFT), in order to address the electronic structure of the low-temperature, martensitic phase of Ti0.67Zr0.33Ni and its hydrides. Further, the thermodynamics of hydride formation in the martensitic Ti-Zr-Ni alloys is studied, and some unanswered questions regarding the hydriding of martensite TiNi are resolved. The calculated formation energy of the orthorhombic beta- and gamma-hydrides of martensitic Ti0.67Zr0.33Ni is, respectively, -14.2 kJ/mol(H) and -29.6 kJ/mol(H), showing that isostructural (Ti,Zr)Ni hydrides with a larger amount of titanium have improved potential for hydrogen storage applications. Furthermore, based on the calculation results, it is unlikely that the hydriding of TiNi martensite would lead to the formation of orthorhombic beta-hydride in analogy to the pseudobinary compound. The formation of Ti0.67Zr0.33Ni hydrides leads to significant changes in electronic structure, causing shifting of some metal states to lower energies due to their interaction with hydrogen s states, and the increase of the number of states at Fermi energy. By modeling intermediate structures, the process of hydride formation in martensitic Ti0.67Zr0.33Ni is resolved to reveal the effects of crystal structure change, volume increase, and hydrogen-metal interactions on the band structure, charge transfer, and thermodynamics. A dominant, stabilizing effect in the process of hydride formation was found to come from the chemical interaction of hydrogen and metal atoms.

We present first principles calculations of the electronic structure, enthalpies of formation and electric field gradients in C15 HfV2Hx (x = 1, 2, 3, 4). In C15 Laves phases, hydrogen can occupy three possible interstitial positions: 96g, 32e, and 8b. To determine which one of these interstitials is the most favorable for storing hydrogen, enthalpies of formation were calculated for every site, with different concentrations of hydrogen. In order to investigate the change in electronic structure before and after hydrogenation, we calculated the electric field gradients induced by hydrogen on the vanadium, and compared them with the existing nuclear magnetic resonance measurements. This comparison enabled us to study the distribution of hydrogen atoms in the crystal lattice, as well as the occupation of possible interstitials. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Substitutionally and interstitially Cu/Nco-doped anatase TiO2(101) surface is investigated by using density functional theory (DFT) calculations. The results suggest improved visible light photocatalytic activity over undoped anatase TiO2. Sizable lattice relaxation around the dopants is observed, followed by a formation of N-O bond. Depending on the local arrangement of atoms, localized states above the valence band maximum, deep into the band gap, and below the conduction band minimum are found. In addition, our calculation also predict band gap narrowing. The hybridization of the Cu 3d and N 2p states within the band gap and the other electronic and optical properties suggest a synergistic effect of the dopants in the enhancement of the visible light absorption on the (101) anatase surface. (C) 2017 Elsevier B.V. All rights reserved.

Magnetic ground states, local crystallographic environment of Fe, and hyperfine interaction parameters in tetragonal FeX (X = S, Se, Te) are investigated by means of density functional theory (DFT) calculations using augmented plane waves plus local orbitals (APW + lo) method. We use several different magnetic configurations to evaluate the magnetic and electronic properties of this system, as well as the hyperfine interaction parameters at Fe lattice site. The results obtained for the ground state collinear anti-ferromagnetic arrangement relatively well reproduce the quadrupole splitting and isomer shifts from the available Mossbauer measurements. The Baders atoms in molecule charge density analysis indicates bonding of closed-shell type and a sizable charge transfer from Fe to X. The system properties are sensitive to the structural optimization of the position of the chalcogen atom with respect to the iron plane. (C) 2017 Elsevier B.V. All rights reserved.

The hydrogenation properties of HfNi and Hf(2)Ni(7) intermetallics were investigated at the constant pressure of 1 bar and in the temperature ranges 373-573 K for HfNi and 323-473 K for Hf(2)Ni(7). The kinetic parameters, rate constants and activation energies of the absorption processes were determined. Maximal hydrogen absorption, i.e., number of hydrogen atoms absorbed per metal atom, HIM, are 1.05 and 0.04 achieved at 373 K for HfNi and Hf(2)Ni(7), respectively. Multiple hydriding/dehydriding was found to influence the improvement of the kinetic parameters. XRD and SEM methods were used to investigate the structural and morphological changes of the samples due to hydrogen absorption. The thermodynamic parameters of hydriding together with the structural properties of the intermetallics and their hydrides, calculated using the full-potential linearized augmented plane waves (FP-LAPW) code based on the density functional theory (DFT), were utilized for the sake of explaining the experimental investigations. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Ab initio calculations of the structural, electronic and thermodynamic properties of Hf2Ni, HfNi, HfNi2 and HfNi5 are presented. Using all-electron augmented plane waves plus local orbitals (APW+lo) method the relative stability of the selected compounds was determined by calculating their enthalpies of formation and cohesive energies. In addition, their electronic structure and bonding properties were determined. The results are discussed in view of the potential application of these intermetallics as materials for hydrogen storage. (C) 2010 Elsevier B.V. All rights reserved.

The perturbed angular correlation method has been employed to study the temperature dependence of the 181Ta hyperfine interaction parameters in the polycrystalline intermetallic compound αHfNi. At ambient temperature the frequency of the electric quadrupole interaction was ωQ = 26.0(2) Mrad/s and the asymmetry parameter η = 0.22(1). The magnitude of the observed electric field gradient decreases with increasing temperature from 78 to 900 K. The calculations were done using the augmented plane wave plus local orbitals method as implemented in the WIEN2k code, using the generalized gradient approximation. In addition, a supercell calculation with Ta impurity located at the hafnium site was performed. The obtained result is in a good agreement with the experiment.

Hafnium-based interriletallics Hf(2)Fe, Hf(2)Co and Hf(2)Ni are investigated as hydrogen absorbers at atmospheric pressure and their electrocatalytic activities are compared. The absorption process is carried out in typical volumetric apparatus. Their crystal structures and morphological characteristics are investigated by X-ray difractometry (XRD) and scanning electron microscopy (SEM). According to the absorption abilities, the investigated intermetallics can be ordered as follows: Hf(2)Fe GT Hf(2)Co GT Hf(2)Ni. Ab initio calculations, within the framework of the density functional theory (DIFT), as implemented in the full-potential (linearized) augmented plane-wave (FP/LAPW) method, confirms the experimental investigations. The calculations are important as a way of predicting the best cathode and storage materials. (C) 2009 Elsevier B.V. All rights reserved.

The hyperfine quadrupole interaction parameters and their temperature dependences for (181)Ta and (111)Cd probes in Ti(2)Pd compound were determined experimentally by means of the perturbed angular correlation (PAC) technique. In addition, ab initio calculations using all-electron augmented plane wave plus local orbitals (APW + lo) method have been performed. Through the comparison of the calculated and measured electric field gradients (EFG) it was established that both Ta and Cd occupy 4(e) Ti position in the Ti(2)Pd compound. (C) 2008 Elsevier B.V. All rights reserved.

A detailed theoretical study of the structure and electric field gradients (EFG) of the Hf2Ag, HfAg, Zr2Ag and ZrAg compounds is presented. Using all-electron augmented plane waves plus local orbitals (APW + lo) formalism, the equilibrium volumes and EFGs for the mentioned compounds are calculated. We have also performed supercell calculations with Cd and Ta impurities. Through the comparison of theoretical and experimental EFGs in these cases, we elucidate the role played by the Cd probe in the time-differential perturbed angular correlation (TDPAC) measurements of Hf-Ag and Zr-Ag compounds. (c) 2008 Elsevier B.V. All rights reserved.

The hyperfine magnetic field (H-hf) in 0.2 at.% Hf-Ni alloy is measured at the Ta-181 probe using the time-differential perturbed angular correlation (TDPAC) method, in the temperature range 78-675 K. The obtained value of 8.6 (3) T at room temperature is in good agreement with the previously reported measurements for similar Hf concentrations in Ni. X-ray powder diffraction (XRPD) experiments confirmed that small atomic concentrations of Hf atoms ( LT 1 at.%) mainly substitute on Ni lattice sites in the fee crystal lattice without forming any intermetallic phase. In addition, ab-initio calculation using all-electron augmented plane waves plus local orbitals (APW + lo) formalism is performed and the obtained result for the hyperfine magnetic field at Ta site is in accordance with the measurement. (C) 2008 Published by Elsevier Ltd.

The stability and structure of titanium doped gold clusters (AunTi; n = 1-32) are studied by density functional theory calculations, as implemented in the first principles code SIESTA. The exchange and correlation effects were calculated within the generalized gradient approximation (GGA) parametrized by Perdew, Burke and Ernzerhof (PBE). We used norm conserving Troullier-Martins pseudopotentials for the 10-electron valence configuration of Ti and 11-electron valence configuration of Au. All calculations were spin-polarized. The global energy minimum geometries of the clusters were searched for by using the simulated annealing technique. The stability of the clusters is discussed on the basis of the binding energy per atom, second-order energy difference, vertical ionization potential, vertical electron affinities, HOMO-LUMO energy gap and vibrational frequencies. Based on the simultaneous criteria of high binding energy, high band gap, high vertical ionization potential, and low electron affinity, it is found that Au4Ti and Au14Ti clusters have a higher stability and are candidates for magic clusters, which confirms the already known results from previous works. The new result presented in this paper is that the Au20Ti and Au30Ti clusters have a higher stability too. In general, the clusters with even n are more stable than the clusters with odd n. Most of the clusters with even n are non-magnetic (total magnetic moment is zero). Our results also suggest that only the Au3Ti, Au7Ti and Au8Ti clusters have a planar structure. (C) 2016 Elsevier B.V. All rights reserved.

Hypervalent molecules of Li3F and Li4F were detected experimentally for the first time. Ionization energies determined by the thermal ionization mass spectrometry were 3.8 +/- 0.2 eV for Li2F, 4.0 +/- 0.2 eV for Li3F and 3.9 +/- 0.2 eV for Li4F. The ionization energies obtained by ab initio calculations support the experimental findings. The lowest energy structures of the LinF (n = 2-4) molecules and their cations were also predicted. (C) 2007 Elsevier B.V. All rights reserved.

The role of Ti, Fe, and Mn on H diffusion in MgH2 is studied by DFT calculations using the PW91 generalized gradient functional on a 71 atom 2 x 2 x 3 supercell of rutile-type MgH2 in which one Mg host atom is replaced by the dopant.

In order to investigate Hf-TM (TM = Fe, Co, Rh, Ru) phase diagrams in the region of 50:50% atomic ratio, we performed an initio Full-Potential Linearized Augmented Plant Waves calculations of the most stable Hf and TM elemental phases and HfTM compounds of the CsGl and CuAu structure types. The obtained electronic structures, cohesive energies and enthalpies of formation are discussed and compared to some of the existing models and available experimental data. The non-existing compound HfFe is found to be at least metastable and the reason for its absence from the phase diagram is discussed. (c) 2006 Elsevier Ltd. All rights reserved.

Magnetization M as a function of applied magnetic field H up to 50 kOe was measured at low temperature T = 5K, using an SQUID magnetometer, for HfCo2 and Hf2Co intermetallic compounds. Both samples showed paramagnetic behaviour with a weak ferromagnetic contribution due to impurities (0.01-0.001 wt%). The values of the mass susceptibilities chi were deduced from the measurements. In addition, calculations using full-potential linearized augmented plane wave (FP-LAPW) WIEN 97 programme package were done, in order to check their agreement with the experimental results. Recent Developments in Advanced Materials and Processes, 7th Conference of the Yugoslav-Materials-Research-Society (Yu-MRS), Sep 12-16, 2005, Herceg Novi, Montenegro

The magnetic properties and hyperfine interaction parameters for Laves phase HfFe2 with C14 type structure are studied using SQUID magnetometer and Mossbauer measurement. The saturation magnetization, remanent magnetization, coercive field, magnetic moment per unit formula and the hyperfine magnetic field at Fe site are reported. In addition, a detailed theoretical study of the electronic structure and hyperfine magnetic fields of the two possible HfFe2 structures, C15 and C14, is presented. Using the full-potential linearized augmented plane wave (FP-LAPW) method as implemented in the WIEN 97 package, the equilibrium volume, bulk moduli, magnetic moments and hyperfine magnetic fields for the two structures are calculated. The obtained results are compared with the measured data.

Despite the fact that the magnetic properties of the intermetallic compounds with C15- type Laves phase structure have so far been studied intensively, the nature of magnetism in some of them is still a matter of controversy. In order to establish and understand the magnetism in the HfCo2 Laves phase with C15 (MgCu2-type) structure, calculations using FP-LAPW WIEN 97 program package for non-polarized and spin-polarized cases were made. They have shown that the spin-polarized case is more stable, i. e. the energy of its ground state is lower by about 0.15 eV. This is in collision with the measured TDPAC spectra, which show no sign of magnetic interaction, as well as with the earlier reported magnetization and susceptibility measurements, which claim that HfCo2 is Pauli paramagnet. Probable explanation for the obtained contradiction is the deviation of the real structure from the ideal one.

The electric field gradients (EFG) of the Hf2Fe intermetallic compound were calculated Using the full-potential linearized augmented plain-wave (FP-LAPW) method as embodied in the WIEN 97 code. The obtained values are compared with other ab-initio calculations and on a qualitative basis with the previously reported experimental data obtained from TDPAC. The calculated results, -23.1.10(21) V/m(2) and 2.7.10(21) V/m(2) for Hf 48f and Fe 32e position, respectively, are in excellent agreement with experimental data (23.4.10(21) V/m(2) and 2.7.10(21) V/m(2)), better than those reported in earlier calculations. The calculated EFG for Hf 16c position (4.2.10(21) V/m(2)) is stronger than the experimental one (1.1.10(21) V/m(2)). Joint Meeting of the 13th International Conference on Hyperfine Interactions/17th International Symposium on Nuclear Quadrupole Interactions (HFI/NQI 2004), Aug 22-27, 2004, Bonn, Germany

We have investigated the development of local bond lengths with composition in the Cd1−xZnxTe mixed system by measuring the fine structure in X-ray absorption (EXAFS) at all three constituent atoms. The bond strength is found to dominate over the averaging of the bulk so that the local bond length deviates only slightly from its natural value determined for the pure binary components ZnTe and CdTe, respectively. The deviations are significantly less than predicted by a simple radial force constant model for tetrahedrally co-ordinated binary systems, and the bond-length variation with concentration is significantly non-linear. For the second shell, bimodal anion–anion distances are found while the cation–cation distances can already be described by the virtual crystal approximation. In the diluted regime close to the end-point compounds, we have complemented our experimental work by ab initio calculations based on density functional theory with the WIEN97 program using the linearised augmented plane wave method. Equilibrium atomic lattice positions have been calculated for the substitutional isovalent metal atom in a 32-atom super cell, Zn in the CdTe lattice or Cd in the ZnTe lattice, respectively, yielding good agreement with the atomic distances as determined in our EXAFS experiments.

We have measured the lattice relaxation around As in Si at a homogeneous As concentration of 4×1018 cm−3 by EXAFS spectroscopy. From the absorption spectra, distances up to the 4th shell could be extracted. A sizeable misfit due to an increased distance is only observed for the 1st shell. Complementing our experimental work we have performed ab initio calculations based on the density functional theory with the WIEN97 package which uses the linearised augmented plane wave method and with the FHI96md program which uses first-principles pseudo-potentials and a plane wave basis set to investigate the size dependence of the super-cells constructed around one substitutional As atom. The calculations yielded good agreement with our EXAFS experiment so that the determined relaxations can be used as a solid basis for further interpretations of derived parameters such as hyperfine interaction parameters in defect complexes.

Thermodynamics of hydride formation is one of the key properties of metal-hydrogen system and determines its applicability. Therefore, numerous researches are focused on the use of first-principles calculations as the predictive tool when investigating the stability of the hydrides. In this paper we use density functional theory to address two-step process of hydride formation in the MNi (M = Ti, Zr, Hf). Through systematic study of experimentally verified and hypothetical hydride phases, we examine the influence of crystal structure and intermetallic composition on electronic structure, stability and bonding of the hydrides. The unique properties and advantages of gamma-phase hydrides having orthorhombic crystal structure (space group Cmcm) for near-ambient hydrogen storage applications are pointed out, as well as the importance of further investigation of the crystal structure of the beta-phase hydrides. Calculated enthalpies of hydride formation/decomposition and desorption temperatures show good agreement with the wide range of experimental data taken from literature, demonstrating predictive power of the used approach for addressing structure-property relationship and giving complete overview of the important representatives of AB class of intermetallic compounds. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

First principles calculations were performed in the framework of the density functional theory (DFF) using the Full Potential-Linear Augment Plane Wave method (FP-LAPW) within the generalized gradient approximation (GGA) to predict the structural, electronic, elastic and thermal properties of NiTi2 intermetallic compound. By using the Wien2k all-electron code, calculations of the ground state and electronic properties such as lattice constants, bulk modulus, presure derivative of bulk modulus, total energies and density of states were also included. The elastic constants and mechanical properties such as Poissons ratio, Youngs modulus and shear modulus are estimated from the calculated elastic constants of the single crystal. Through the quasi-harmonic Debye model, the preasure and temperature dependences of the linear expansion coefficient, bulk modulus and heat capacity have been investigated. Finally, the Debye temperature has been estimated from the average sound velocity according to the predicted polycrystal bulk properties and from the single crystal elastic constants. (C) 2015 Elsevier Ltd. All rights reserved.

The evolution of the environment of Hf sites in a hafnium-alkoxide-modified polysilsesquioxane upon polymer-to-ceramic transformation was investigated via the perturbed angular correlation (PAC) method. The results of the PAC measurements on samples thermally treated at temperatures from 400 to 1300 degrees C indicate that Hf is surrounded only by oxygen at all studied temperatures. This finding is in agreement with the evolution pathway of polymer-derived SiHfOC ceramics, which were reported to be generated as single-phase amorphous materials upon pyrolysis of alkoxide-modified polysiloxanes and subsequently to phase separate and crystallize towards HfO2/SiOC nanocomposites. Thus, the results presented here support our previous statement that there is a thermodynamic control on the phase separation and crystallization behavior of Si-M-O-C (M = metal) ceramics (Ionescu et al. 96;2013:1899-1903), which in the case of Hf leads to the precipitation and crystallization of hafnia nanoparticles within a SiOC matrix. (C) 2014 Elsevier Ltd. All rights reserved.

Substitutional N to O and M to Ti (M = Pt, V, Sb) codoped rutile TiO2 was investigated using density functional theory (OFT) based calculations with both standard and hybrid exchange-correlation functionals. The band gaps calculated using generalized gradient approximation (GGA) exhibited narrowing compared to the pure rutile TiO2 in all the investigated cases. In contrast, the results obtained with hybrid exchange-correlation functional showed that there was no band gap narrowing, but doping induced localized states within the band gap just above the valence band, as well as below the conduction band for Pt doped TiO2. The presence of broad intermediate states (IS) in the band gap could enhance visible light absorption through a two step optical transition from the valence to the conduction band via the IS and at the same time lower recombination of the photo-generated charges. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

X-ray absorption spectroscopy has been used to obtain information on the local structure around Zn atoms in CdTe. The Zn–Te distance is 5% smaller than the Cd–Te bond-length in the bulk, but slightly larger than in pure ZnTe. A similar effect is predicted by FLAPW calculations.

Some properties of the Hf-X (X-transition metal) systems obtained by x-ray diffraction, hyperfine interaction measurements by time differential perturbed angular correlations of gamma rays (TDPAC), and Faraday method magnetic susceptibility chi measurements, are investigated. Special attention is paid to the influence of the ordering of the X ions microstructure and their arrangement in the crystal lattice, on the magnetic properties of the Hf-X systems. Its shown up that X ions in the systems with different crystal structures (Ti2Ni, MgCu2, quasicrystalline) form almost identical, close-packed tetrahedral microstructures, but that their arrangement in the crystal lattice is essentially different. Obtained results suggest that besides the mentioned arrangement of the X-ions microstructures, magnitude of Hf-X e.g. X-X coupling substantially influence the magnetic properties of the systems. Trends in Advanced Materials and Processes, 3rd Yugoslov-Materials-Research-Society Conference, Sep 20-24, 1999, Herceg Novi, Yugoslavia

The time differential perturbed angular correlation technique has been used to measure the electric field gradient at impurities in the intermetallic compound . The results of the measurements show the presence of two independent quadrupole interactions. At room temperature the interaction frequencies are and . The electric field gradient , the corresponding asymmetry parameter and the distribution parameter exhibit a pronounced temperature dependence from 78 to 1223 K.

Mg2FeH6 is a promising hydrogen storage material with one of the highest volumetric hydrogen density among the known hydrogen storage materials. However, its complicated synthesis and high temperature of hydrogen desorption limit wider applications. In this paper we study the influence of transition metal (Ni, Co, Mn) doping on the structural, electronic and hydrogen sorption properties of Mg2FeH6, using first-principles density functional theory calculations. The thermodynamics of three different synthesis routes is addressed, and all of the mentioned transition metals are found to destabilize Mg2FeH6. In addition, a detailed study of electronic structure properties, including densities of states (DOS) and charge transfer analysis (AIM), reveals that the doping with Ni, Mn and Co leads to the reduction of the direct band gap of Mg2FeH6. This is a peer-reviewed version of the article: Batalović, K., Radaković, J., Belošević-Čavor, J., & Koteski, V. (2014). Transition metal doping of Mg 2 FeH 6–a DFT insight into synthesis and electronic structure. Physical Chemistry Chemical Physics, 16(24), 12356-12361 [http://dx.doi.org/10.1039/c4cp01020e]

The aim of this study is to evaluate the size and stability of radiolytically produced silver clusters. The clusters obtained by the gamma irradiation of a mixture of a silver salt and polyvinyl alcohol (PVA) were studied both theoretically and by mass spectrometry. MALDI TOF mass spectrometry of the Ag-n clusters showed the presence of clusters containing between 5 and 29 atoms. Both the theoretical and experimental results of this paper show that the most stable clusters are small clusters with an odd number of atoms. The stability of these clusters is correlated with the clusters electronic configuration. (C) 2012 Elsevier Ltd. All rights reserved.

The lattice relaxation around Ga in CdTe is investigated by means of extended X-ray absorption spectroscopy (EXAFS) and density functional theory (DFT) calculations using the linear augmented plane waves plus local orbitals (LAPW+lo) method. In addition to the substitutional position, the calculations are performed for DX- and A-centers of Ga in CdTe. The results of the calculations are in good agreement with the experimental data, as obtained from EXAFS and X-ray absorption near-edge structure (XANES). They allow the experimental identification of several defect structures in CdTe. In particular, direct experimental evidence for the existence of DX-centers in CdTe is provided, and for the first time the local bond lengths of this defect are measured directly. 7th International Workshop on X-Ray Damage to Biological Crystalline Samples, Mar 14-16, 2012, England

We present first principles calculations of the electric field gradients (EFGs) in the pure cubic, tetragonal and orthorhombic phases of HfV2 and in the cubic phase of ZrV2. Band structure calculations of orthorhombic and tetragonal HfV2 are presented for the first time. EFGs are also calculated on the inserted Ta and Cd probe atoms, and results are compared with the existing experimental data from time differential perturbed angular correlations and nuclear magnetic resonance measurements. By this comparison, it was possible to determine the exact space group and crystallographic positions of orthorhombic HfV2, and the site preferences of the Ta and Cd probe atoms. We have also confirmed that the measured nonzero EFG in the Ta-doped cubic HfV2 structure originates from the displacement of Ta atoms from their equilibrium positions in the cubic environment. (C) 2012 Elsevier Ltd. All rights reserved.

We report the evolution of structural and magnetic properties in La${}_{2}$O${}_{3}$(Fe${}_{1\ensuremath{-}x}$Mn${}_{x}$)${}_{2}$Se${}_{2}$. Heat capacity and bulk magnetization indicate an increased ferromagnetic component of the long-range magnetic order and possible increased degree of frustration. Atomic disorder on Fe(Mn) sites suppresses the temperature of the long-range order whereas intermediate alloys show a rich magnetic phase diagram.

By means of a density functional theory approach, we studied the electric field gradients (EFG) in Ta and Cd-doped Ti-Pd intermetallics. Our results confirmed the previous experimental findings that the TiPd2 low-temperature structure is orthorhombic and established that Ta substitutes for Ti in this structure. The temperature increase above 650 K changes the Ta impurity position in the lattice. Similar changes for the Cd doped system were not confirmed, as Cd is most likely to occupy Pd lattice sites in both low and high-temperature phases. In the case of TiPd, our calculations suggested that Ta substitutes for Ti in the low-temperature phase, while Cd probably can substitute on both Ti and Pd crystallographic sites. (C) 2012 Elsevier Ltd. All rights reserved.

Intermetallic compound TiFe, known for its hydrogen storage applications, is modified by substituting iron by nickel and related changes of properties and applicability of the obtained compounds are studied. Samples TiFe 1− x Ni x ( x = 0.2–0.6) are synthesized by melt-spinning and their crystal structure, desorption characteristics and electronic structure are investigated by TPD, 1 H NMR and Mossbauer spectroscopy. State-of-the-art DFT calculations give further insight into the changes in electronic structure and bonding related to the hydrogen absorption and substitution of iron by nickel. The increase of Ni/Fe ratio in the TiFe 1− x Ni x is found to result in the increase of hydride cohesive energies and in the systematic shifting of Fermi energy ( E F ) to lower values, in both pure intermetallics and appropriate hydrides. Hydride formation was found to influence the Fermi energy lowering and the increase of number of states at E F .

Hydrogen induced modifications to the structural, electronic and bonding properties of HfNi are investigated by performing first principles calculations. The full-potential linearized augmented plane waves (FP-LAPW) code based on the density functional theory (DFT) was used. The charge transfer and bonding between the constituent atoms is examined by means of the Baders atoms in molecule (AIM) theory. The calculated enthalpies of formation of HfNi, HfNiH and HfNiH(3) are -53.5 kJ/mol atom, -17.3 kJ/molH and -34.6 kJ/molH. They are found to be in a good agreement with the experimental and semi-empirical values. The calculated stability of the hydrides is in agreement with their hydrogen absorption ability. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.

A detailed theoretical study of the structure and electric field gradients (EFG) of the Zr2Ni compound is presented. Using all-electron augmented plane waves plus local orbitals formalism, the equilibrium volume, bulk modulus, and EFGs at both non-equivalent crystallographic positions, Zr and Ni, are calculated. The possible mechanism of formation of the EFGs at both sites are analyzed and discussed. We have also performed supercell calculations with Cd and Ta impurities. Through the comparison of theoretical and experimental EFGs in these cases, we elucidate the role played by the Cd and Ta probe atoms in the time-differential perturbed angular correlation measurements of this compound. 11th International Symposium on Physics of Materials (ISPMA), Aug 24-28, 2008, Charles Univ, Fac Math and Phys, Prague, Czech Republic

Using ab initio density-functional theory approach the electric field gradients (EFGs) and hyperfine magnetic fields (HMFs) for the isostructural $C14$ Laves-phase compounds ${\text{HfCr}}_{2}$, ${\text{HfFe}}_{2}$, ${\text{HfMn}}_{2}$, ${\text{ZrCr}}_{2}$, and ${\text{ZrMn}}_{2}$ are calculated and compared with the available experimental data from time differential perturbed angular-correlation (TDPAC) spectroscopy. In addition, supercell calculations of the hyperfine interaction parameters at the nucleus of the substitutional Ta impurity are used to elucidate the role played by the Ta probe in the TDPAC measurements of Hf and Zr $C14$ Laves phases and solve the controversy related to the origin of the HMF in the $C14$ ${\text{HfFe}}_{2}$ compound.

The time differential perturbed angular correlation technique was used to observe the magnetic dipole and electric quadrupole interactions of (181)Ta probe in the Ni-5 at.% Hf alloy from 78 to 1131 K. The presence of the Larmor precession frequency of (181)Ta in the Ni(Hf) solid solution phase confirms the Ni dominant concentration for the onset of ferromagnetism in the Ni-Hf alloys. A very weak quadrupole interaction originates from imperfections in the HfNi(5) phase formed during melting procedure. The third observed quadrupole interaction corresponds to the Ta probe in the HfO(2) contamination due to internal oxidation of the sample. (C) 2008 Elsevier B.V. All rights reserved. 16th International Conference on Solid Compounds of Transition Elements, Jul 26-31, 2008, Dresden, Germany