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The powdery cobalt ferrite (CoFe2O4) is prepared by coprecipitation followed by mechanochemical synthesis in a planetary ball mill. Obtained nanomaterial has been studied using a variety of characterization techniques: X-ray diffraction (XRD), Raman spectroscopy, far infrared (FIR) reflectivity and attenuated total reflectance (ATR) in combination with Fourier transform infrared (FTIR) spectroscopy in mid IR spectra. The investigated CoFe2O4 nanomaterial showed a typical XRD pattern of cubic spinel. In the Raman and IR spectra are observed all of first-order Raman and IR active modes. Weak sub bands activated by structure disorder are seen also. Since nano-CoFe2O4 is macroscopically cubic, its main Raman and IR modes are assigned as in normal cubic spinel. Raman spectrum is fitted with 8 Lorentzian peaks. It is observed that the value of x  0.58 obtained from Raman spectrum, is in good agreement with the value obtained by XRD-structural analysis (0.51). To analyze the IR spectra, we used Decoupled Plasmon - Phonon (DPP) model of the complex dielectric function. Measurement of magnetization in the range of magnetic fields H>>Hc enable the calculation of the anisotropy coefficient K1 = 4.02·105 J cm-3 , which is very high in cobalt ferrite. The 57Fe-Mössbauer spectrum of the CoFe2O4 sample was measured at room temperature in ± 12 mm s-1 Doppler velocity range. The 57Fe-Mössbauer spectrum of the CoFe2O4 sample was fitted with the extended Voigt-based fitting method.

This study addresses the oxidation behavior of Fe38Co38Mo8B15Cu1 alloy. Amorphous, melt-spun ribbons were heat treated in an oxygen atmosphere for different times at 350 °C, 550 °C, and 800 °C. We focus on the change in structural, thermal, and magnetic properties induced by oxygen treatment. The low-temperature heat-treated samples displayed broad, continuous, and low-intensity X-ray diffraction peaks. While no structural change was observed in the heat treatments at 350 °C both 30 min and 480 min, a significant oxide formation was observed in the heat treatment at 800 °C for 480 min. DTA/TG analysis demonstrates the weight gains and oxide formation with the temperature and time of heat treatment increase. The weight gain occurs rapidly for the sample treated for 480 min at 800 °C. A remarkable change in magnetic properties was observed. Bulk oxidation is seen by Mössbauer analysis in the heat treatment of alloy in air at 800 °C. Besides hematite, a defective CoFe2O4 phase emerged after 30 min, while after 480 min this phase was well-crystallized CoFe2O4.

This document describes the initial version of the Data Management Plan (DMP) for the WaPoDe project. The overall objective of the WaPoDe project is to synthetize materials with enhanced sensitivity, selectivity, and response time as electrochemical sensors (ECS) for detection and monitoring of different pharmaceutical and pesticide pollutants in water and to reduce ECS manufacturing costs. The focus of the WaPoDe project is on ZnO-based electrochemical sensors. The database will be developed under the WaPoDe project with the main purpose to summarize the WaPoDe research results on the types, properties, and application of ZnO-based nanoparticles as selective ECS. This initial DMP provides information on the data management principles that will be implemented during and for a certain period after the WaPoDe project completion. It is based on the Data Management Plan template (https://enspire.science/wp-content/uploads/2021/09/Horizon-Europe-Data-Management-Plan-Template.pdf) which follows the guidelines from Europe Horizon calls. This DMP will be regularly updated as the implementation of the project progresses. The draft DMP was developed within the project workpackages.

The powdery cobalt ferrite (CoFe2O4) is prepared by coprecipitation followed by mechanochemical synthesis in a planetary ball mill. Obtained nanomaterial has been studied using a variety of characterization techniques: X-ray diffraction (XRD), Raman spectroscopy, far infrared (FIR) reflectivity and attenuated total reflectance (ATR) in combination with Fourier-transform infrared (FTIR) spectroscopy in mid IR spectra. The investigated CoFe2O4 nanomaterial showed a typical XRD pattern of cubic spinel. In the Raman and IR spectra are observed all of first-order Raman and IR active modes. Weak sub-bands activated by structure disorder are seen also. Since nano-CoFe2O4 is macroscopically cubic, its main Raman and IR modes are assigned as in normal cubic spinel. Raman spectrum is fitted with 8 Lorentzian peaks. It is observed that the value of x 0.58 obtained from Raman spectrum, is in good agreement with the value obtained by XRD-structural analysis (0.51). To analyze the IR spectra, we used Decoupled Plasmon - Phonon (DPP) model of the complex dielectric function. Measurement of magnetization in the range of magnetic fields H>>Hc enable the calculation of the anisotropy coefficient K1 = 4.02·105 J cm-3, which is very high in cobalt ferrite. The 57Fe-Mössbauer spectrum of the CoFe2O4 sample was measured at room temperature in ± 12 mm s-1 Doppler velocity range. The 57Fe-Mössbauer spectrum of the CoFe2O4 sample was fitted with the extended Voigt-based fitting method.

Laves phases (AB2) are alloys whose metal hydrides have been proposed to improve the energy density of Ni-MH batteries. In case of ZrV2-based battery materials, various amounts of different modifiers, such as Ti and Ni are used to improve their performance. The influence of Ni modifier in ZrV2 C15 Laves phase was investigated at atomic level by the 181TaPerturbed Angular Correlation (PAC) measurements of Zr(V0.33Ni0.67)2, Zr(V0.33Ni0.67)2.4 and Zr27V18Ni55 compounds. The dominant C15-type crystallographic structures were found in all samples by the X-ray diffraction, with the minority presence of other phases, mostly various oxides. The 181Ta-PAC preliminary results showed four different electric quadrupole interactions which give similar values for electric field gradients and non-zero asymmetry parameters in all investigated compounds.

In order to provide insight into the influence of co-doping with boron (B) and transition metals (TM = Pt, Ta, V) on the photoactivity of anatase TiO2 , the electronic, structural and optical characteristics of the mentioned co-doped systems were studied using density functional theory calculations and the modified Becke–Johnson exchange potential. For each transition metal two cases were considered, with B atom either replacing O atom (B-substitutional) or imbedding interstitially (B-interstitial) into TiO2 lattice. The calculations showed that the co-doping is more favorable for the B-interstitial systems than for the B-substitutional ones and under the O-rich conditions. For the B-substitutional cases a slight decrease of the band gap is observed. In contrast, the results obtained for the B-interstitial systems exhibited no band gap narrowing. However, in these systems, the occurrence of localized states within the band gap is noticed, which could improve visible light absorption through a two-step optical transition.

Intermetallic narrow-gap semiconductors have been intensively explored due to their large thermoelectric power at low temperatures and a possible role of strong electronic correlations in their unusual thermodynamic and transport properties. Here we study the optical spectra and vibrational properties of FeGa3 single crystal. The optical conductivity indicates that FeGa3 has a direct band gap of ≈0.7 eV, consistent with density functional theory (DFT) calculations. Most importantly, we find a substantial spectral weight also below 0.4 eV, which is the energy of the indirect (charge) gap found in resistivity measurements and ab initio calculations. We find that the spectral weight below the gap decreases with increasing temperature, which indicates that it originates from the impurity states and not from the electronic correlations. Interestingly, we did not find any signatures of the impurity states in vibrational spectra. The infrared and Raman vibrational lines are narrow and weakly temperature dependent. The vibrational frequencies are in excellent agreement with our DFT calculations, implying a modest role of electronic correlations. Narrow Mössbauer spectral lines also indicate high crystallinity of the sample. © 2023 American Physical Society.

In the present work, the electronic and optical properties of (B, TM) co-doped ( TM = Pt, Ta, V) anatase TiO 2 were investigated using modified density functional theory (DFT) calculations, in order to provide insight into the synergistic effect of co-doping with various elements on the photoactivity of TiO 2. We considered two combinations for each co-doped sample, with TM atom replacing Ti atom and B atom either replacing O atom or embedding interstitially into TiO 2 lattice. The calculations showed that for all studied transition metals, the co-doping is more favorable in the case of interstitially doped boron than for the substitutional one and under the O-rich conditions. For the co-doped systems with B atom substitutionally replacing O atom, a small reduction of the band gap is observed in all the investigated cases. In contrast, the results obtained for the co-doped systems with boron embedded interstitially into TiO 2 lattice, exhibited no band gap narrowing. However, in these systems, the doping induced localized states within the band gap, which could enhance visible light absorption through a two step optical transition from the valence to conduction band

LiAlH4 is a promising material for hydrogen storage, having the theoretical gravimetric density of 10.6 wt% H2. In order to decrease the temperature where hydrogen is released, we investigated the catalytic influence of Fe2O3 on LiAlH4 dehydrogenation, as a model case for understanding the effects transition oxide additives have in the catalysis process. Quick mechanochemical synthesis of LiAlH4 + 5 wt% Fe2O3 led to the significant decrease of the hydrogen desorption temperature, and desorption of over 7 wt%H2 in the temperature range 143–154 °C. Density functional theory (DFT)-based calculations with Tran-Blaha modified Becke-Johnson functional (TBmBJ) address the electronic structure of LiAlH4 and Li3AlH6. 57Fe Mössbauer study shows the change in the oxidational state of iron during hydrogen desorption, while the 1H NMR study reveals the presence of paramagnetic species that affect relaxation. The electron transfer from hydrides is discussed as the proposed mechanism of destabilization of LiAlH4 + 5 wt% Fe2O3. © 2021 Hydrogen Energy Publications LLC

Fly and bottom ash(es) are the most abundant generated by-products of coal combustion in thermal power plants. This investigation offers a sustainable solution of a double and circular use of industrial waste material in civil engineering practices; i.e., fly ash (FA) as an eco-efficiently, low-cost material for As(V) adsorption, as well as an additive in building materials. A goethite impregnated sample (FAG) was synthesized and optimized using the column precipitation procedure, then thoroughly, structurally and morphologically characterized using liquid nitrogen porosimetry (BET), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) and Mössbauer spectroscopy (MS) techniques. The data from the equilibrium adsorption were fitted by linear and non-linear isotherm models; the optimal capacity of FAG/As(V) removal was calculated from the Langmuir model at 31.742 mg g−1 for 45 °C. The kinetics of adsorption process has shown the pseudo-second-order kinetic model (PSO). The Weber-Morris model was applied to determine the intra-particle diffusion as a limiting step of reaction. The low pH dependant FAG leaching confirmed the efficient use of non-hazardous waste material in arsenic removal; furthermore, it also validated the new added value of the used/spent adsorbent as an adhesive in building materials possessing advanced mechanical properties. © 2021 Elsevier Ltd

Substitutionally doped Bi2W1-xMxO6 (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.

Iron oxide, in the form of magnetite (MG)–functionalized porous wollastonite (WL), was used as an adsorbent for heavy metal ions (cadmium and nickel) and oxyanions (chromate and phosphate) removal from water. The porous WL was synthesized from calcium carbonate and siloxane by controlled sintering process using low molecular weight submicrosized poly(methyl methacrylate) as a pore-forming agent. The precipitation of MG nanoparticles was carried out directly by a polyol-medium solvothermal method or via branched amino/carboxylic acid cross-linker by solvent/nonsolvent method producing WL/MG and WL-γ-APS/MG adsorbents, respectively. The structure/properties of MG functionalized WL was confirmed by applying FTIR, Raman, XRD, Mössbauer, and SEM analysis. Higher adsorption capacities of 73.126, 66.144, 64.168, and 63.456 mg g−1 for WL-γ-APS/MG in relation to WL/MG of 55.450, 52.019, 48.132, and 47.382 mg g−1 for Cd2+, Ni2+, phosphate, and chromate, respectively, were obtained using nonlinear Langmuir model fitting. Adsorption phenomena were analyzed using monolayer statistical physics model for single adsorption with one energy. Kinetic study showed exceptionally higher pseudo-second-order rate constants for WL-γ-APS/MG, e.g., 1.17–13.4 times, with respect to WL/MG indicating importance of both WL surface modification and controllable precipitation of MG on WL-γ-APS.

Iron oxide, in the form of magnetite (MG)–functionalized porous wollastonite (WL), was used as an adsorbent for heavy metal ions (cadmium and nickel) and oxyanions (chromate and phosphate) removal from water. The porous WL was synthesized from calcium carbonate and siloxane by controlled sintering process using low molecular weight submicrosized poly(methyl methacrylate) as a pore-forming agent. The precipitation of MG nanoparticles was carried out directly by a polyol-medium solvothermal method or via branched amino/carboxylic acid cross-linker by solvent/nonsolvent method producing WL/MG and WL-γ-APS/MG adsorbents, respectively. The structure/properties of MG functionalized WL was confirmed by applying FTIR, Raman, XRD, Mössbauer, and SEM analysis. Higher adsorption capacities of 73.126, 66.144, 64.168, and 63.456 mg g−1 for WL-γ-APS/MG in relation to WL/MG of 55.450, 52.019, 48.132, and 47.382 mg g−1 for Cd2+, Ni2+, phosphate, and chromate, respectively, were obtained using nonlinear Langmuir model fitting. Adsorption phenomena were analyzed using monolayer statistical physics model for single adsorption with one energy. Kinetic study showed exceptionally higher pseudo-second-order rate constants for WL-γ-APS/MG, e.g., 1.17–13.4 times, with respect to WL/MG indicating importance of both WL surface modification and controllable precipitation of MG on WL-γ-APS.

Lithium iron phosphate (LiFePO4, LFP) is one of the widely used cathode materials for rechargeable lithium ion batteries. LFP batteries are widely used for electric vehicles and backup power due to their important advantages such as low cost, lifetime, efficiency, and reliability. There are still several technical challenges that need to be addressed: The increase of energy density or further reduction of their final cost. This paper concerned with the characterization of carbon coated LiFePO4 nanopowder cathode materials produced under different conditions by pulse combustion for providing energy to the reactor for the synthesis. The reactor was built according to the principles of the thermoacoustic burner on the basis of the Helmholtz resonator. The investigated nanopowders are synthesized by complete and incomplete combustion and calcined at 700 °C. The obtained samples were characterized by X-ray diffraction, Fourier transform infrared, Raman, and Mössbauer spectroscopy. Observed low-Temperature magnetic phase transitions definitively identified the crystal phases. The morphology of samples was controlled by scanning electron microscopy. The aim of this work is to show that it is possible to achieve a desired crystal phase by pulse combustion in a relatively cheap and fast way. The extremely rapid synthesis of almost pure phase material is possible due to the reduction in size of interacting particles and to an enormous number of collisions between them as a result of strong turbulent flow associated with explosive combustion. © 2019 Author(s).

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).

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.

Stability, magnetic properties, electric field gradients and hyperfine fields of YCo(5)Hx compounds were investigated by using DFT based calculations. Two computational approaches were employed in the study-ultrasoft pseudopotentials with plane waves and all-electron FP(L) APW + lo method. It was found that H atoms prefer off-centered or centered octahedral sites. Enthalpies of formation for alpha - GT beta transition were calculated. Inclusion of zero-point correction reduces agreement between theoretical values of enthalpy of formation obtained from spin-polarized calculations and experimental value. Comparison of theoretical and experimental spin magnetic moments of different YCo5Hx compounds resulted in a reasonable agreement between present theoretical results and previous experimental and theoretical data. Magnetocrystalline anisotropy energy (MAE) was calculated for intermetallic compound YCo5. Reasonable agreement was found between MAE obtained in the present study and the corresponding theoretical and experimental values obtained in earlier studies. (C) 2017 Elsevier B.V. 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.

In this paper we investigated the effects of Fe-doping of the anatase TiO2 (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 (3s(2)3p(6)3d(2)4s(2)) of Ti atom, 6-electron valence configuration (2s(2)p(4)) of O atom and 8-electron valence configuration (3d(6)4s(2)) of Fe atom. We used a double- zeta 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 TiO2 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 TiO2 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 TiO2 for industrial applications. (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.

Yttrium orthoferrite (YFeO3) powder was prepared by a mechanochemical synthesis from a mixture of Y2O3 and alpha-Fe2O3 powders in a planetary ball mill for 2.5 h. The obtained YFeO3 powder sample was characterized by X-ray diffraction (XRD), Raman and infrared spectroscopy. The average crystallite size calculated by the Scherrer equation was 12 nm. The Mossbauer spectroscopy at room temperature confirms the superparamagnetic character of YFeO3 orthoferrite sample.

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.

У овом раду истраживана су поликристална интерметална једињења γ′–Ni3Al са примесама атома хафнијума и γ′–Ni3Al са примесама атома гвожђа. Испитивања локалне структуре, магнетних и електричних особина γ′–Ni3Al једињења допираних атомима Hf или атомима Fe извршена су методама дифракције Х–зрачења, мерењима магнетизације, као и применом временски разложених пертурбованих угаоних корелација и спектроскопије Mössbauer–овог ефекта, које су омогућиле истраживања хиперфиних интеракција на језгрима примеса Hf и на језгрима примеса Fe. Ова експериментална истраживања испитиваних система су употпуњена прорачунима енергије дефеката, као и параметара структуре и хиперфиних интеракција на основу првих принципа. Главни циљ експерименталних истраживања и теоријских прорачуна интерметалне γ′– Ni3Al фазе са примесама атома хафнијума, односно гвожђа био је да се одреди преферентно позиционирање атома Hf, односно атома Fe у γ′–Ni3Al решетки, као и њихов утицај на кристалну решетку у коју се уграђују. Aнализoм дифракције Х–зрака испитиваних Hf допираних Ni3Al узорака утврђено је присуство кубне γ′ фазе (ознака L12) у испитиваним Hf–Ni3Al легурама, као и њене две тетрагоналне трансформације L60 и D022. Анализа је показала да је кубна L12 фаза доминантна у односу на тетрагоналне фазе испитиваних Hf–Ni3Al узорака. Мерења хиперфиних интеракција на проби 181Та, језгру–потомку 181Hf, у легурама 0.2, 0.5 и 5 at.% Hf – Ni3Al извршена су у температурском опсегу од 78 K до 1230 K. Измерене вредности хиперфиних параметара приписане су одређеним позицијама атома Hf у присутним Ni3Al фазама: L12, D022 и L60. Присуствo 181Ta–сигнала који је константан у времену кореспондира атомима Hf на позицији Al атома у доминантној L12 фази. За све три испитиване легуре, измерена нижа вредност спин независне електричнеiiiквадруполне фреквенције додељена је електричној квадруполној интеракцији којадејствује на атоме Hf који су заменили атоме Al у тетрагоналној D022 фази.Измерена виша вредност фреквенције кореспон, The dissertation addresses the local crystal structure and hyperfine interactions of hafnium or iron doped polycrystalline intermatallic γ′–Ni3Al alloys.The local structure, magnetic and electrical properties of γ′–Ni3Al compounds doped with Hf atoms or Fe atoms were investigated by the X ray diffraction, magnetization, time differential perturbed angular correlation spectroscopy and Mössbauer–effect spectroscopy. The last two experimental methods provided insight into hyperfine interactions of Hf– and Fe–nucleus. This was complemented by the calculations of the energy of the defects, as well as with ab initio calculations of structural and hyperfine interactions parameters.The main goal of the experimental and theoretical investigations of the intermetallic γ′–Ni3Al phase doped with Hf or Fe atoms was to determine the site preference of dopant atoms in the γ′–Ni3Al matrix, as well as their influence on the host lattice.The X–ray diffraction measurements of the Hf doped Ni3Al samples revealed the presence of the cubic γ′ phase (usually denoted by L12) and its two tetragonal distortions: D022 and L60. The refinement of XRD data showed the dominant presence of the cubic L12 phase in the Hf–Ni3Al samples, with the minority presence of the two tetragonal phases. The measurements of the hyperfine interactions of the 181Та–probe in the 0.2, 0.5 and 5 at.% Hf – Ni3Al alloys (181Та–nucleus is the daughter–nucleus of the 181Hf–parent nucleus) were done in the temperature range 78 K to 1230 K. The measured hyperfine parameters values were assigned to the various Hf atom sites in the different crystal structures (cubic and tetragonal) present in the Ni3Al alloys. The presence of 181Та–signal constant in time is ascribed to Hf atoms at the Al sites in dominant L12 phase. For all investigated alloys, the lower value of the spin independent electric quadrupole frequency was ascribed to the electric quadrupole interaction of the Hf nuclei substituting on the Al sites in the tetrag

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.

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.

The Time Differential Perturbed Angular (TDPAC) measurements of nuclear quadrupole interactions (NQIs) at Ta-181 ion probe in the polycrystalline intermetallic alloy gamma-Ni3Al doped with 0.2 at. % Hf were performed in the temperature range 78-1230K, in order to determine the lattice location of Hf atoms in the ordered gamma-Ni3Al structure. The two NQIs obtained are discussed within the present L1(2) cubic structure and a tetragonal distortion of L1(2) to another two DO22 and L6(0) type structures. The first low frequency NQI at the site of the Ta-181 ion-probe after substitution of aluminum for hafnium in DO22 at ambient temperature, is v(Q1)(300 K) = 39(1) MHz with eta(1) = 0. The corresponding high frequency value on the second crystallographic site in L6(0), is v(Q2)(300 K) = 204(14) MHz with eta(2) = 0.47(11). These two NQIs have different temperature behavior. The presence of both DO22 and L6(0) tetragonal distortions of the parent cubic L1(2) lattice, detected after adding 0.2 at. % Hf, are with modulations to the lattice constant (a) with a ratio (c/a), 2.04 and 0.87, respectively. Ab initio calculations of electronic and structural properties and hyperfine parameters at the Ta-181 ion probe of the gamma-Ni3Al-0.2 at. % Hf alloy were performed using the full potential augmented plane wave plus local-orbital (APW+lo) method as implemented in the WIEN2k code. The accuracy of the calculations and comparison with the experimental results enabled us to identify the observed hyperfine interactions and to infer the EFG sign that cannot be measured in conventional TDPAC measurements. (C) 2013 AIP Publishing LLC.

The perturbed angular correlation method was employed to study the temperature dependence of electric field gradients at the Ta-181 probe in the polycrystalline Hf2Ni7 compound. The temperature evolution of the sample content was measured using high-temperature X-ray diffraction. To check the magnetic order of the sample, magnetization measurements and additional perturbed angular correlation measurements with externally applied magnetic field were performed. All obtained spectra showed no evidence of magnetic order of the Hf2Ni7 phase. Within the experimental resolution of the apparatus, the measured electric field gradients at Ta-181 probe for the two inequivalent Hf-181/Ta-181 sites in the Hf2Ni7 compound appeared as one in the range of 78-944 K. A single quadrupole interaction implies that the electric field gradients at the two Hf sites must be quite similar. At 293 K, the measured quadrupole interaction parameters are v(Q) = 433(1) MHz and eta = 0.300(4). An increase of the quadrupole frequency and a gradual rising of the asymmetry parameter were observed with increasing temperature. The high-temperature X-ray diffraction indicated a build up of HfO2 above 693 K.

The paper addresses the issue of health risk associated with the presence of chrysotile in the soil type ranker formed on massive serpentines occurring in the area of Bubanj Potok, a settlement located in the southern Belgrade environs, Serbia. Characterization of the ranker soil was conducted by scanning electron microscopy, X-ray diffraction, micro-Raman spectroscopy and transmission Fe-57 Mossbauer spectroscopy. Scanning electron microscopy figures showed regular shaped smectite (montmorillonite) particles, aggregates of chlorite, and elongated sheets of serpentines minerals antigorite. X-ray diffraction analysis confirmed the presence of detrital mineral quartz polymorph as well as minor amounts of other mineral species. Micro-Raman spectroscopy identified the presence of dominant minerals, such as montmorillonite, kaolinite, muscovite, gypsum, calcite, albite, amphiboles (hornblende/kaersutite) and orthoclase. Important polymorph silica modifications of quartz, olivine (forsterite), pyroxene (enstatite/ferrosilite, diopside/hedenbergite), and serpentine (antigorite/lizardite/chrysotile) were identified.

The paper addresses the issue of health risk associated with the presence of chrysotile in the soil type ranker formed on massive serpentines occurring in the area of Bubanj Potok, a settlement located in the southern Belgrade environs, Serbia. Characterization of the ranker soil was conducted by scanning electron microscopy, X-ray diffraction, micro-Raman spectroscopy and transmission 57Fe Mössbauer spectroscopy. Scanning electron microscopy figures showed regular shaped smectite (montmorillonite) particles, aggregates of chlorite, and elongated sheets of serpentines minerals antigorite. X-ray diffraction analysis confirmed the presence of detrital mineral quartz polymorph as well as minor amounts of other mineral species. Micro-Raman spectroscopy identified the presence of dominant minerals, such as montmorillonite, kaolinite, muscovite, gypsum, calcite, albite, amphiboles (hornblende/kaersutite) and orthoclase. Important polymorph silica modifications of quartz, olivine (forsterite), pyroxene (enstatite/ferrosilite, diopside/hedenbergite), and serpentine (antigorite/lizardite/chrysotile) were identified., Rad se bavi pitanjem zdravstvenog rizika povezanog sa prisustvom hrizotila u rankeru (tip zemljišta) formiranom na masivnom serpentinitu u oblasti Bubanj Potoka, naselju koje se nalazi u južnoj okolini Beograda. Karakterizacija rankera je izvršena skenirajućom elektronskom mikroskopijom, rendgenskom difrakcijom praha, mikro-Raman spektroskopijom i transmisionom 57Fe Mesbauer spektroskopijom. Slike dobijene skenirajućim elektronskim mikroskopom pokazuju čestice smektita regularnog oblika montmorionita, agregata hlorita i izdužene listove serpentinskog minerala antigorita. Rendgenska difrakciona analiza potvrdila je prisustvo detrital minerala kvarcnog polimorfa kao i manje količine drugih mineralnih vrsta. Mikro-Raman spektroskopija identifikovala je prisustvo dominantnih minerala, kao što su montmorionit i kaolinit, muskovit, gips, kalcit, albit, amfibol (kaersutit/hornblenda) i ortoklas. Važni polimorfi silika modifikacije kvarca, olivina (forsterit), piroksena (enstatit, ferosilit, hedenbergit, diopsid), i serpentina (antigorit, lizardit, hrizotil) su bili identifikovani.

Among novel magnetic intermetallics based on rare earth-transition compounds, the Nd2Fe14B/alpha-Fe isotropic nanocomposites have been obtained by recrystallization from an amorphous phase, prepared by melt spinning. For variable 5 wt.% Fe and 10 wt.% Fe contents we recorded transmission Fe-57 Mossbauer spectra at the room temperature, hardened of the alpha-Fe phase by exchange interactions. The spectra have been analyzed in terms of ten Zeeman sextets and one paramagnetic doublet related to the Nd1.1Fe4B4 phase. One sextet corresponds to the alpha-Fe phase, whereas others are attributed to six non-equivalent Fe sites in the Nd2Fe14B structure, namely 16k(1), 16k(2), 8j(1), 8j(2), 4c, and 4e. The three remaining sextets belong to the Fe3B structure with three inequivalent Fe sites Fe-I(8g), Fe-II(8g) and Fe-III(8g). All relevant parameters for both nanocomposites: the magnetic hyperfine field, the isomer shift and the quadrupole splitting are determined for each of these sites.

Mossbauer spectrum measured on ferromagnetic HfFe2 at 296 K, consists of four six-line components and one doublet. The Laves phase HfFe2 has three kinds of crystal structures: cubic MgCu2(C15), hexagonal MgZn2(C14) and MgNi2(C36). We assigned two sextets to the 2a and 6h sites of C14, one to the C15 and the fourth sextet to the minor presence of alpha-Fe. The doublet originates from small amount of FeO, apparently a corrosion product. The pseudobinary compound of Hf0.75Ta0.25Fe2 (C14) undergoes the first - order transition to antiferromagnetic (AFM) state at about 180 K due to the strong spin fluctuation. Therefore, a magnetic sextet and a doublet were observed for the spectra assigned to the 6h and 2a site. The second sextet is attached to the minor presence of Fe3O4.

The perturbed angular correlation method has been employed to study the temperature dependence of the Ta-181 hyperfine interaction parameters in the poly-crystalline intermetallic compound alpha HfNi. At ambient temperature the frequency of the electric quadrupole interaction was omega(Q) = 26.0(2) Mrad/s and the asymmetry parameter eta = 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.

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.

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.

The hyperfine interactions of Ta-181 probe in the nickel-2 at.% hafnium alloy have been studied by the perturbed angular correlation method in the temperature range 78-1131K. The magnitude of the magnetic dipole interaction of Hf-181/Ta-181 substituting in ferromagnetic Ni(Hf) solid solution decreases with increasing temperature. As a result of the restricted solid solubility of Hf in Ni, a second phase (HfNi5) in the Ni-Hf sample was detected. Hf-181/Ta-181 which resides in HfNi5 senses weak electric quadrupole interaction. The observed anomalous temperature behavior was ascribed to distortions in the HfNi5 cubic phase. The third measured hyperfine interaction corresponds to the quadrupole interaction of Hf-181/Ta-181 positioned in HfO2 contamination originating from an annealing procedure above 900 K. (C) 2008 Elsevier B.V. All rights reserved.

The hyperfine interactions of Ta-181 probe in the nickel-2 at.% hafnium alloy have been studied by the perturbed angular correlation method in the temperature range 78-1131K. The magnitude of the magnetic dipole interaction of Hf-181/Ta-181 substituting in ferromagnetic Ni(Hf) solid solution decreases with increasing temperature. As a result of the restricted solid solubility of Hf in Ni, a second phase (HfNi5) in the Ni-Hf sample was detected. Hf-181/Ta-181 which resides in HfNi5 senses weak electric quadrupole interaction. The observed anomalous temperature behavior was ascribed to distortions in the HfNi5 cubic phase. The third measured hyperfine interaction corresponds to the quadrupole interaction of Hf-181/Ta-181 positioned in HfO2 contamination originating from an annealing procedure above 900 K.

The high-resolution time-differential perturbed angular correlation technique (TDPAC) has been used to study the electric field gradient at Ta-181 impurities in the polycrystalline intermetallic compound Hf2Ni in the wide temeperature range 78-1314 K. The single-phase BCT CuAl2 (C16)-type structure of the compound was confirmed by X-ray diffractogram, with lattice constants found to be a = 6.479(3) angstrom and c = 5.271(3) angstrom at room temperature. The coincidence measurements between gamma rays in the cascade were recorded with a time resolution better than 0.75 ns for the 133-482 keV y-y cascade of Ta-181 nuclei. The results of measurements reveal the presence of a single nuclear quadrupole interaction (NQI) WO and its linear dependence with temperature in the range 78-1134 K. In the high temperature region (1134-1314 K) the significant appearance of disordering in the lattice structure of Hf2Ni was revealed, in the vicinity of the melting point of 1473 K. The XRPD measurements in the high temperature range can help in better interpretation and understanding of this complex structural and microdinamic behavior of the Hf2Ni phase.

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.