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We report thermoelectric studies of FeS1-xSex (x=0,0.06) superconducting single crystals that feature high irreversibility fields and critical current density Jc comparable to materials with much higher superconducting critical temperatures (Tc's). The ratio of Tc to the Fermi temperature TF is very small, indicating weak electronic correlations. With a slight selenium substitution on sulfur site in FeS both Tc/TF and the effective mass m∗ rise considerably, implying increase in electronic correlation of the bulk conducting states. The first-principle calculations show rise of the density of states at the Fermi level in FeS0.94Se0.06 when compared to FeS, which is related not only to Fe but also to chalcogen-derived electronic states.

By means of a density functional theory (DFT) based augmented plane waves plus local orbitals (APW ​+ ​lo) method, we study the electric field gradients (EFG) in Ta and Cd-doped Zr–Al intermetallics. Comparing the obtained results with the experimental data obtained from the perturbed angular correlation (PAC) measurements, we conclude that Ta atoms always replace Zr in all the investigated compounds. Our results confirmed the previous experimental assumption that Cd substitutes exclusively for Al in ZrAl3 and Zr2Al3. In the case of Zr2Al our calculations suggest that Cd can probably substitute on both Zr and Al lattice sites, while in Zr3Al, it is most likely to occupy Al position. The effects of the distance between the impurity atoms in the supercells and the deviation of the c/a ratio are also discussed.

Charge density waves (CDWs) with superconductivity, competing Fermi surface instabilities, and collective orders have captured much interest in two-dimensional van der Waals (vdW) materials. Understanding the CDW suppression mechanism, its connection to the emerging superconducting state, and electronic correlations provides opportunities for engineering the electronic properties of vdW heterostructures and thin-film devices. Using a combination of the thermal transport, x-ray photoemission spectroscopy, Raman measurements, and first-principles calculations, we observe an increase in electronic correlations of the conducting states as the CDW is suppressed in ZrTe3 with 5% Cu and Ni intercalation in the vdW gap. As superconductivity emerges, intercalation brings not only decoupling of quasi-one-dimensional conduction electrons with phonons as a consequence of intercalation-induced lattice expansion but also a drastic increase in Zr2+ at the expense of Zr4+ metal atoms. These observations not only demonstrate the potential of atomic intercalates in the vdW gap for ground-state tuning but also illustrate the crucial role of the Zr metal valence in the formation of collective electronic orders.

In order to study the effect of Fe cation substitution on the local structure, defect formation, and hyperfine interactions in ZnO, Mössbauer 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 Mössbauer 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 Mössbauer 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. © 2019 Author(s).

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 TiO2is 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 TiO2through substitutional doping.

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.

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.

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.

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.

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.

Perturbed angular correlation measurements of the hyperfine interactions of the Ta-181 probe in the polycrystalline intermetallic Ni3Al doped with 0.5 and 5 at.% Hf were performed in the temperature range 78-1230 K. The observed local hyperfine fields at the Hf-181/Ta-181 probe showed that Hf atoms are substituting on Al sites in the L1(2) structure of Ni3Al. The two minor electric quadrupole interactions that were found for each Ni3Al alloy are discussed taking into account the L1(2) cubic structure and its two tetragonal distortions: D0(22) and L6(0). The presence of two tetragonal transformations of the parent cubic L1(2) lattice in 0.5 at.% Hf and 5 at.% Hf doped Ni3Al was revealed by X-ray diffraction. The ab initio calculations, performed with the projector augmented wave method correctly reproduce the experimental results and enable discussion on the structural and electronic properties of the polycrystalline alloys. The experimental and theoretical investigations showed that hafnium additions prefer aluminum sites in Ni3Al. (C) 2014 Elsevier B.V. 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.

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.

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.

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.

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.

Основу истраживања ове докторске дисертације чине компјутерскипрорачуни базирани на теорији функционала густине, односно методилинеаризованих проширених равних таласа са комплентим потенцијалом. Ово јерелативно нова теоријска метода имплементирана у програмском пакету Wien2k,којим су рађени сви прорачуни.Истраживања су конципирана тако да се докторска дисертација састоји издва сегмента. У првом делу испитивана је локална структура, електронскеособине и градијенти електричних поља интерметалних једињења HfV2 и ZrV2,без и са убаченим допантима танталом и кадмијумом. Проучаване су тритемпературске модификације HfV2 (кубна, тетрагонална и орторомбична), и једнаZrV2 (кубна), а након анализе чистих једињења испитивана је променаелектронских особина која се јавила након имплантације допаната. Израчунатиградијенти електричних поља и параметри асиметрије упоређивани су саодговарајућим експерименталним вредностима, добијеним методом временскиразложених пертурбованих угаоних корелација гама зрачења, чиме је утврђенокоје атомске позиције заузимају убачени допанти. На основу добијених резултатанепобитно су утврђене просторна група и атомске позиције хафнијума иванадијума у нискотемпературској орторомбичној модификацији HfV2, које сураније биле спорне услед постојања противречних резул тата у литератури.Такође, потврђено је да ненулти градијент електричног поља измерен на позицијитантала у кубној решеци HfV2 потиче због његове измештености из равнотежногположаја.Други део докторске дисертације односи се на испитивање променеелектронске структуре кубне Лавес фазе једињења HfV2, настале због убацивањаводоника на једну од три интерстицијалне позиције у кристалној решеци. На овајначин симулиран је интерстицијални хидрид HfV2Hx у коме је број водоника појединици формуле износио од један до четири. Приказани су резултатиИнститут за нуклеарне науке „Винча“ Факултет за физичку хемијуистраживања ефеката које улазак водоника има на јединичну ћелију, електронскуструктуру кристала и градијен, This doctoral dissertation consists of density functional theory basedcalculations, conducted with Wien2k computational code, which implements fullpotentiallinearized augmented plane wave plus local orbital method. The dissertation isdivided into two segments. First part addresses the local structure, electronic properties,and electric field gradients of pure and doped intermetallic compounds HfV2 and ZrV2.Three temperature modifications of HfV2 – cubic, tetragonal and orthorhombic – andonly one, cubic, modification of ZrV2 were investigated. After the analysis of electronicstructure and electric field gradients of pure intermetallic compounds, crystal latticeswere doped with impurities tantalum or cadmium. Electric field gradients werecalculated on the atomic site of the inserted probe-atoms, and results were comparedwith the existing experimental data from the time differential perturbed angularcorrelation and nuclear magnetic resonance measurements. This comparison enabled usto determine the lattice site occupied by impurities in every examined structure, exactspace group, and crystallographic positions of hafnium and vanadium in the lowtemperatureorthorhombic modification of HfV2. In addition, we have confirmed thatthe measured, nonzero electric field gradient in the tantalum-doped cubic HfV2 structureoriginates from the displacement of tantalum from its equilibrium position in the cubicenvironment.In the second part of the thesis, first principles calculations of the electronicstructure, formation enthalpies, and electric field gradients in the cubic hydride HfV2Hxare presented. In cubic, C15 Laves phases, hydrogen can occupy three possibleinterstitial positions: 96g, 32e, and 8b. To investigate the change in electronic structurebefore and after hydrogenation, and effects that hydrogen has on the unit cell, electricfield gradients induced by this atom on the surrounding vanadium were calculated, andcompared with the existing nuclear magnetic resonance measureme

Имајући у виду значај енергије за људско друштво, проналажењеодрживог система њеног добијања, транспорта и коришћења је један од основнихзадатака модерне науке. Пре нешто више од пола века започета су испитивањаметалних хидрида као начина складиштења водоника. Време ће показати да ли ћебаш водоник бити гориво будућности, али оно што је сигурно је да су свадосадашња испитивања металних хидрида у великој мери допринела разумевањупроцеса интеракције гасовитог водоника са металима (легурама) и развоју бројнихпрактичних примена метал-водоничних система. Истраживања на овом пољу сенастављају, а поред незаобилазних експерименталних испитивања врло значајнуулогу имају и методе засноване на теорији функционала густине (DFT), јеромогућавају испитивање модела идеалних или контролисаних система иразумевање фундаменталних веза између састава и структуре материјала ињегових особина.Предмет испитивања у овој тези су хидриди легура метала 4. групе (Ti, Zr,Hf) са Ni и Fe као потенцијални материјали за складиштење водоника. МетодомFP-(L)APW+lo, која примењује DFT у прорачунима bulk кристалних система,испитана је стабилност легура и хидрида, њихова електронска структура,стабилност различитих кристалних решетки и интерстицијалних позиција.Додатно, применом експерименталних метода испитана је апсорпција идесорпција водоника у легурама HfNi и TiFe1-xNix (x = 0.2 – 0.6).На основу експерименталних испитивања у овој тези и литературних података,испитиване легуре су поређене по особинама од интереса за складиштењеводоника: разматрана је термодинамика формирања хидрида (енталпијаформирања хидрида, положај равнотежног притиска, температура десорпцијеводоника...), кинетика процеса апсорпције водоника, капацитет за складиштење.На основу поређења електронске структуре легура и хидрида, размотрена јеприрода интеракције водоника са металима и трансфер наелектрисања.Термодинамичке величине добијене на основу израчунатих енергија формирањахидридних фаза показују задовољавајуће слагање са експеримента, Due to the large significance of energy for human society, one of the main goalsof modern science is the discovery of sustainable energy supplies: sources, storage andutilization methods. Research of metal hydrides for hydrogen storage application startedover a half century ago. Time will tell whether hydrogen is the fuel of the future; butwithout doubt the research of metal hydrides conducted so far has contributed to theunderstanding of metal-hydrogen interaction and led to many practical applications ofmetal hydrides we have today. Ongoing research in this field includes, besidesunavoidable experimental methods, computational methods based on density functionaltheory (DFT), which allow investigation of ideal or controlled systems andunderstanding of structure-property and composition-property relations in materials.In this dissertation, hydrides of transition metal alloys (formed between groupIV metals – Ti, Zr, Hf, and Ni and Fe) are considered as potential materials forhydrogen storage. Electronic structure, stability of alloys and their hydrides and stabilityof different crystal structures and interstitial hydrogen positions are studied by the FP-(L)APW+lo method, based on DFT implementation for bulk crystals. Also,experimental methods are used to study absorption and desorption of hydrogen in HfNiand TiFe1-xNix (x = 0.2 – 0.6).Combining the experimental results from this dissertation and the ones availablein literature, studied alloys are compared on the basis of their properties important forhydrogen storage applications: thermodynamics of hydride formation (hydrogenformation enthalpy, equilibrium pressure, desorption temperature…), kinetics ofhydrogen absorption and storage capacity. The nature of the metal-hydrogen interaction,as well as charge transfer, is also considered based on the calculated electronic structureof alloys and hydrides. Thermodynamical quantities obtained from the calculatedformation energies of hydride phases are in satisfactory agreem

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.

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.

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.

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.

We report the evolution of structural and magnetic properties in La2O3(Fe1-xMnx)(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.

Auger-electron spectra associated with Be atoms in the pure metal lattice and in an oxide have been investigated for 1.8 MeV/u Au-129(41+) ions and 2.7 keV primary electrons. The excitation and local energy transfer by such fast primary particles in solids is dominated by electronic processes. The electron-induced spectrum is compared to calculated band-structure results and it is relatively well understood. For the heavy-ion case, however, we observe a significant variation of the Auger electron spectrum, related to a variation of the electronic band structure. This spectrum points to a formation of a metal-like meta-stable electronic density of states. (c) 2010 Elsevier B.V. All rights reserved.

Local structures of amorphous and quasicrystalline phases in Zr-Ti-Ni and Zr-Ti-Ni-Cu alloys have been studied by means of x-ray absorption spectroscopy. The amorphous phases show a high degree of icosahedral short-range order. In all investigated systems local order around Cu and Ni atoms was found to be nearly identical pointing to site substitution of Ni by Cu as the reason for an improved glass forming ability when Ni is partly substituted by Cu. The results strengthen an icosahedral cluster based approach for the structure of metallic glasses and indicate the importance of the medium-range order on glass formation. (C) 2010 American Institute of Physics. [doi:10.1063/1.3467265]

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.

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.

The quadrupolar hyperfine interactions of in-diffused In-111 - GT Cd-111 probes in polycrystalline isostructural Zr4Al3 and Hf4Al3 samples containing small admixtures of the phases (Zr/Hf)(3)Al-2 were investigated. A strong preference of In-111 solutes for the contaminant (Zr/Hf)(3)Al-2 minority phases was observed. Detailed calculations of the electric field gradient (EFG) at the Cd nucleus using the full-potential augmented plane wave + local orbital formalism allowed us to assign the observed EFG fractions to the various lattice sites in the (Zr/Hf)(3)Al-2 compounds and to understand the preferential site occupation of the minority phases by the In-111 atoms. The effects of the size of the supercell and relaxation around the oversized In and Cd probe atoms were investigated in detail.

Auger-electron spectra associated with Be atoms in the pure metal lattice and in the stoichiometric oxide have been investigated for different incident charged particles. For fast incident electrons, for Ar(7+) and Ar(15+) ions as well as Xe(15+) and Xe(31+) ions at velocities of 6% to 10% the speed of light, there are strong differences in the corresponding spectral distributions of Be-K Auger lines. These differences are related to changes in the local electronic band structure of BeO on a femtosecond time scale after the passage of highly charged heavy ions.