Search

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.

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.

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

Connections between crystal chemistry and critical temperature Tc have been in the focus of superconductivity, one of the most widely studied phenomena in physics, chemistry, and materials science alike. In most Fe-based superconductors, materials chemistry and physics conspire so that Tc correlates with the average anion height above the Fe plane, i.e., with the geometry of the FeAs4 or FeCh4 (Ch = Te, Se, or S) tetrahedron. By synthesizing Fe1–ySe1–xSx (0 ≤ x ≤ 1; y ≤ 0.1), we find that in alloyed crystals Tc is not correlated with the anion height like it is for most other Fe superconductors. Instead, changes in Tc(x) and tetragonal-to-orthorhombic (nematic) transition Ts(x) upon cooling are correlated with disorder in Fe vibrations in the direction orthogonal to Fe planes, along the crystallographic c-axis. The disorder stems from the random nature of S substitution, causing deformed Fe(Se,S)4 tetrahedra with different Fe–Se and Fe–S bond distances. Our results provide evidence of Tc and Ts suppression by disorder in anion height. The connection to local crystal chemistry may be exploited in computational prediction of new superconducting materials with FeSe/S building blocks.

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.

APSTRAKT: U ovoj disertaciji su prikazani rezultati ispitivanja legure Fe72Cu1V4Si15B8, koja pripada familiji FINEMET-tipa legura. Legura je izrađena ultrabrzim hlađenjem rastopa legure na rotirajućem disku. Dobijena legura ima već formirane nanokristalne faze (α-Fe(Si) i Fe23B6 faze), koje se nalaze u amorfnoj matrici, što je ustanovljeno XRD analizom i Mesbauerovom spektroskopijom. Pored toga, Mesbauerovom spektroskopijom je ustanovljeno postojanje znatno više kristalnih faza koje zbog male zastupljenosti nisu detektovane XRD analizom. Legura je termički tretirana, što je indukovalo strukturne promene koje su doprinele promeni magnetnih svojstava. DTA analizom je legura zagrevana do 1073 K, različitim brzinama (β= 5K/min, 10K/min i 20 K/min), kojom su ustanovljena dva kristalizaciona pika: (i) od 750 K do 780 K i (ii) od 875 K do 900 K (za β= 5 K/min). Oba pika su nesimetrična, što ukazuje na složenost procesa kristalizacije. Ovi pikovi odgovaraju jednom termomagnetnom piku u intervalu od 745 K do 875 K (za H=7960 A/m i β= 4 K/min). Termomagnetnim merenjima je ustanovljena Kirijeva temperatura amorfne faze legure koja iznosi oko 615 K i Kirijeva temperatura iskristalisane legure koja iznosi oko 875 K. Nakon toga su uzorci oblika trake odgrevani različitim temperaturama (Tan= 573 K – 973 K). Ustanovljeno je da je pri Tan= 773 K došlo do najvećeg povećanja magnetizacije zasićenja, Ms uz minimalno povećanje koercitivnog polja, Hc. Povećanje Ms se objašnjava uvećanjem zastupljenosti α-Fe(Si) faze, sa porastom Tan, usled transformacije amorfne u kristalnu fazu. Prosečna veličina novoformiranih kristalita α-Fe(Si) faze ista je kao i veličini kristalita u neodgrevanoj leguri do Tan=773 K. Pri Tan>773 K dolazi do naglog povećavanja prosečne veličine kristalita ove faze, što uzrokuje slabiju pokretljivost magnetnih domena, zbog čega se smanjuje Ms. Isti trend promena Ms uočen je i za longitudinalnu i normalnu (perpendikularnu) orijentaciju uzorka u magnetnom polju u odnosu, This dissertation presents the results of examination of the alloy Fe72Cu1V4Si15B8, which belongs to the FINEMET-type family of alloys. The alloy was prepared with a rapid quenching of the melt on a rotating disc. The as-prepared alloy already contains nanocrystals of α-Fe(Si) and Fe23B6 phases, in an amorphous matrix, that is observed by XRD analysis and by Mössbauer spectroscopy. In addition, Mössbauer spectroscopy revealed the existence of significantly more crystal phases that, due to their low presence, were not detected by XRD analysis. The alloy was thermally treated, which induced structural changes that contributed to the changes in magnetic properties. First, the alloy was heated to 1073 K, at different rates (β = 5K/min, 10K/min and 20 K/min), and two crystallization peaks were found by DTA analysis: (i) from 750 K to 780 K, and (ii) from 875 K to 900 K (for β = 5 K/min). Both peaks are asymmetric, which indicates the complexity of the crystallization process. These peaks correspond to a single thermomagnetic peak in the range from 745 K to 875 K (for H = 7960 A/ m and β = 4 K/ min). Thermomagnetic measurements revealed the Curie temperature of the amorphous phase of the alloy at 615 K, and the Curie temperature of the crystallized alloy at 875 K. After that, the ribbon-shaped samples were annealed at different temperatures (Tan = 573 K - 973 K). It was found that at Tan = 773 K there was the huge increase in saturation magnetization (Ms) with a minimal increase in the coercive field (Hc). The increase in Ms is explained by the increase of the abundance of α-Fe (Si) phase, with the increase of Tan, due to the transformation of amorphous into crystalline phase. The average size of the evolved crystallites of α-Fe (Si) phase is the same as the size of crystallites in the as-prepared alloy up to Tan = 773 K. At Tan > 773 K there is a sharp increase in the average size of crystallites of this phase, which causes slow mobility of magnetic domains due

The study of an effect of iron doping on the structural, microstructural and mechanical properties of sintered iron-doped mullite is presented. The results of phase composition, performed in detail by Mössbauer spectroscopy and XRD analysis, revealed that all added iron was inside the mullite lattice forming the single phase up to 12% by weight of Fe2O3 and 1300 °C. Samples, which were processed at 1550 °C, contained secondary phases, hematite or magnetite, regardless of the amount of added iron. Furthermore, the addition of iron decreases the values of relative linear shrinkage comparing to the values of undoped one (~18%) while the densities of the sintered samples rise as well as their values of microhardness. Even though the density values were not too high (90 TD%), the obtained values of microhardness were excellent, 1634 HV0.1 for maximum iron content due to the characteristic mullite microstructure.

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).

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.

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.