Electrochemical properties of Ti-Ni-Sn materials predicted by <Superscript>119</Superscript>Sn Mössbauer spectroscopy

The electrochemical activity of TiNiSn, TiNi ₂Sn and Ti ₆Sn ₅ compounds considered as negative electrode materials for Li-ion batteries has been predicted from the isomer shift- Hume-Rothery electronic density correlation diagram. The ternary compounds were obtained from solid-state reactions and Ti ₆Sn ₅ by ball milling. The ¹¹⁹Sn Mössbauer parameters were experimentally determined and used to evaluate the Hume-Rothery electronic density [e _av]. The values of [e _av] are in the region of Li-rich Li-Sn alloys for Ti ₆Sn ₅ and outside this region for the ternary compounds, suggesting that the former compound is electrochemically active but not the two latter ones. Electrochemical tests were performed for these different materials confirming this prediction. The close values of [e _av] for Ti ₆Sn ₅ and Li-rich Li-Sn alloys indicate that the observed good capacity retention could be related to small changes in the global structures during cycling.     

Mössbauer study of 1% <Superscript>57</Superscript>Fe doped ferromagnetic insulator La<Subscript>0.825</Subscript>Ca<Subscript>0.175</Subscript>MnO<Subscript>3</Subscript>

We have employed magnetization measurements, M?ssbauer and ESR spectroscopic techniques, in order to study the ferromagnetic insulating (FMI) compound La_1-xCa_xMnO₃ (x=0.175) doped with 1% ⁵⁷Fe. We have used two samples; one prepared in air which has cation vacancies and a second in inert atmosphere, which is stoichiometric. An abrupt change of the experimental results is obtained, by all techniques, in the ferromagnetic insulating regime, in the temperature region of T_O/O//≈60 K, where an orbital rearrangement is suggested to occur. An analysis of these findings points to an orbital rearrangement transformation. Ferromagnetic resonance reveals considerable differences between stoichiometric and cation deficient samples, indicating anisotropy of the exchange interactions in the former sample with significant temperature dependence, most pronounced in the vicinity of T_O/O//     

<Superscript>57</Superscript>Fe emission Mössbauer spectroscopy following dilute implantation of <Superscript>57</Superscript>Mn into In <Subscript>2</Subscript>O<Subscript>3</Subscript>

Emission Mössbauer spectroscopy has been utilised to characterize dilute ⁵⁷Fe impurities in In ₂O₃ following implantation of ⁵⁷Mn (T _1/2 = 1.5 min.) at the ISOLDE facility at CERN. From stoichiometry considerations, one would expect Fe to adopt the valence state 3 + , substituting In ³⁺, however the spectra are dominated by spectral lines due to paramagnetic Fe²⁺. Using first principle calculations in the framework of density functional theory (DFT), the density of states of dilute Fe and the hyperfine parameters have been determined. The hybridization between the 3d-band of Fe and the 2p band of oxygen induces a spin-polarized hole on the O site close to the Fe site, which is found to be the cause of the Fe²⁺ state in In ₂O₃. Comparison of experimental data to calculated hyperfine parameters suggests that Fe predominantly enters the 8b site rather than the 24d site of the cation site in the Bixbyite structure of In ₂O₃. A gradual transition from an amorphous to a crystalline state is observed with increasing implantation/annealing temperature.     

<Superscript>151</Superscript>Eu Mössbauer study of multiferroic Eu<Subscript>0.75</Subscript>Y<Subscript>0.25</Subscript>MnO<Subscript>3</Subscript>

We are herewith reporting the ¹⁵¹Eu Mössbauer spectra collected on a polycrystalline powder sample of Eu_0.75Y_0.25MnO₃ from 15 K to room temperature. All the spectra consist of a single line, whose shape and related sample thickness are dependent on the temperature T. The thermal trend of the mean square displacement of Eu ion, obtained from the spectra analysis, clearly reveals a large low-temperature anharmonicity and in concomitance with the onset of the magnetic ordering consists in a linear strong decrease interrupted by two narrow wells at 29.5 K and 40 K. This behavior is interpreted in connection with the transfer of spectral weight from the 120 cm^-1 optical phonon to the electromagnonic modes. The T-trend of the central shift shows that Eu³⁺ electronic ground state in the magnetically ordered phase differs from the one in the paramagnetic state. Finally, the temperature dependence of the hyperfine field under T _N gives a contribution to interpret some controversial features regarding the phase-diagram.     

Mössbauer effect study of Bi<Subscript>0.8</Subscript>La<Subscript>0.2</Subscript>FeO<Subscript>3</Subscript> multiferroic on <Superscript>57</Superscript>Fe nuclei

The parameters of hyperfine interactions in the Bi_0.8La_0.2FeO₃ multiferroic have been measured by Mössbauer spectroscopy in the temperature range of 87–850 K. It has been found that the spatial spin-modulated structure that exists in BiFeO3 is destroyed in the substitution of La for 0.2 mol % of Bi and the homogeneous antiferromagnetic structure appears. The temperatures of the magnetic (Néel temperature, T _N = 677 ± 3 K) and ferroelectric (Curie temperature, T _C = 773 ± 3 K) transitions and the Debye temperature (Θ = 431 ± 12) have been measured.     

Mössbauer studies of spatial spin-modulated structure and hyperfine interactions in multiferroic Bi<Superscript>57</Superscript>Fe<Subscript>0.10</Subscript>Fe<Subscript>0.85</Subscript>Cr<Subscript>0.05</Subscript>O<Subscript>3</Subscript>

Results of Mössbauer investigations on ⁵⁷Fe nuclei in multiferroic material Bi⁵⁷Fe_0.10Fe_0.85Cr_0.05O₃ in the temperature range from 5.2 to 300 K are presented. Bulk rhombohedral samples were obtained by solidstate synthesis at high pressure. Mössbauer spectra were analyzed using the model of spatial incommensurate spin-modulated structure of the cycloidal type. Information on the influence of substituting Cr cations for Fe cations on hyperfine spectral parameters was obtained: the shift and quadrupolar shift of a Mössbauer line, and isotropic and anisotropic contributions into the hyperfine magnetic field. The anharmonicity parameter m of the spatial spin-modulated structure increases almost 1.7 times at 5.2 K when BiFeO₃ is doped with chromium. The data on m were used for calculation of the uniaxial magnetic anisotropy constants and their temperature dependences for pure and chromium-doped BiFeO₃.     

Structural and Mössbauer studies of nanocrystalline Mn<Superscript>4+</Superscript>-doped Li<Subscript>0.5</Subscript>Fe<Subscript>2.5</Subscript>O<Subscript>4</Subscript> particles prepared by mechanical milling

The structure and magnetic properties of spinel-related Mn⁴⁺-doped Li_0.5Fe_2.5O₄ nanocrystalline particles of the composition Li_0.5Fe_2.25Mn_0.1875O₄, prepared by milling a pristine sample for different times, were investigated. The average crystallite and particle size, respectively, decreased form ～40 nm to ～10 nm and ～2.5 μm to ～10 nm with increasing milling time from 0 h to 70 h. Rietveld refinement of the XRD data of the non-milled sample show the Mn⁴⁺ dopant ions to substitute for Fe³⁺ at the octahedral B-sites of the spinel-related structure. The Mössbauer spectra of the milled ferrites indicate that more particles turn superparamagnetic with increasing milling time. The Mössbauer data collected at 78 K suggest that while in the non-milled sample the Mn⁴⁺ ions substitute for Fe³⁺ at the octahedral B-sites, this is reversed as milling proceeds with doped Mn⁴⁺ ions, balancing Fe³⁺ vacancies and possibly Li⁺ ions progressively migrate to the tetrahedral A-sites. This is supported by the slight increase observed in the magnetization of the milled samples relative to that of the non-milled one. The magnetic data suggest that in addition to the increasing superparamagentic component of the milled particles, thermal spin reversal and/or spin canting effects are possible at the surface layers of the nanoparticles.     

O<Subscript>2</Subscript> photodesorption from AuO<Stack><Subscript>2</Subscript><Superscript>−</Superscript></Stack> and Au<Subscript>2</Subscript>O<Stack><Subscript>2</Subscript><Superscript>−</Superscript></Stack>

Using time-resolved photoelectron spectroscopy, the decay channels of AuO₂⁻ and Au₂O₂⁻ following photoexcitation with 3.1-eV photons have been studied. For AuO₂⁻, a state with a rather long lifetime of 30 ps has been identified. Its decay path could not be determined but photodesorption can be excluded. For Au₂O₂⁻, the spectra indicate O₂ desorption after 3.1-eV photoexcitation on a time scale of 1 ps. While comparing these results on Au _n O₂⁻ with analogous data on Ag _n O₂⁻ clusters, a discernible pattern emerges: for dissociatively bound O₂(AuO₂⁻, Ag₃O₂⁻), there are long-living excited states which do not decay by oxygen desorption, while for molecular chemisorption (Au₂O₂⁻, Ag₂O₂⁻, Ag₄O₂⁻, Ag₈O₂⁻), the 3.1-eV photoexcitation triggers fast O₂ desorption with a high quantum yield.     

Stability of Zn–Ni–TiO<Subscript>2</Subscript> and Zn–TiO<Subscript>2</Subscript> nanocomposite coatings in near-neutral sulphate solutions

Zn–Ni–TiO₂ and Zn–TiO₂ nanocomposites were prepared by galvanostatic cathodic square wave deposition. X-ray diffraction analysis and scanning electron microscopy revealed that the occlusion of TiO₂ nanoparticles (spherical shaped with diameter between 19.5 and 24.2 nm) promotes the formation of the γ-Ni₅Zn₂₁ phase, changes the preferred crystallographic orientation of Zn from (101) and (102) planes to (002), and decreases the particle size of the metallic matrices. The stability of the nanocomposites immersed in near-neutral 0.05 mold m⁻³ Na₂SO₄ solution (pH 6.2) was investigated over 24 h. The initial open circuit potential for the Zn–Ni–TiO₂ and Zn–TiO₂ coatings were −1.32 and −1.51 V (vs. Hg/Hg₂SO₄), respectively, and changed to −1.10 and –1.49 V (vs. Hg/Hg₂SO₄) after 24 h of immersion. Data extracted from the steady state polarization curves demonstrated that the metal–TiO₂ nanocomposites have, with respect to the metal coatings, a higher corrosion potential in the case of the Zn–Ni alloy composite; a lower corrosion potential in the case of Zn-based nanocomposite albeit the predominant (002) crystallographic orientation; and a lower initial corrosion resistance due to the smaller grain size and higher porosity in the Zn–Ni–TiO₂ and Zn–TiO₂ nanocomposites. Morphological and chemical analyses showed that a thicker passive layer is formed on the surface of the Zn–Ni–TiO₂ and Zn–TiO₂ deposits. After 24 h of immersion in the sulphate solution, the Zn–Ni–TiO₂ coating has the highest corrosion stability due to the double-protective action created by the deposit’s surface enrichment in Ni plus the higher amount of corrosion products.     

Mössbauer spectroscopy of <Superscript>57</Superscript>Fe in <Emphasis Type="Italic">α</Emphasis>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> following implantation of <Superscript>57</Superscript>Mn<Superscript>*</Superscript>

Two Fe/MCM-41 systems, one of them sylilated, were obtained to be used as catalysts in Fischer–Tropsch reaction. They have more than 90% of the iron species located inside the support channels, leading to a narrow crystal size distribution accessible to reactive gases. The samples were characterized by X-ray diffraction, atomic absorption spectroscopy, N₂ adsorption, Mössbauer spectroscopy and Fourier transformer infrared spectroscopy. Mössbauer spectroscopy allowed us to demonstrate that the catalytic active species were the same in both catalysts. The only difference between them was the surface hydrophobicity, which decreases the “water gas shift reaction” in the sylilated catalyst. Besides, this solid is more active for hydrocarbon production, with a lower methane yield.     

Synthesis and photocatalytic activity of polyaniline–TiO<Subscript>2</Subscript> composites with bionic nanopapilla structure

Polyaniline (PANI)–TiO₂ nanocomposites possessing both nano and microscale structures were prepared through a facile hydrothermal route in the presence of PANI. The nanopapilla particles were characterized by scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray analysis, X-ray photoelectron spectra, X-ray diffraction, FTIR spectra, UV–Vis spectroscopy, and N₂ adsorption analysis, etc. The results show that the composites possess both nano and microscale structures. The TiO₂ nanorods are dispersed on PANI with one end fixed to the surface. The photocatalytic properties of the powders were verified by the photodegradation of gaseous acetone under UV (λ = 254 nm) and visible-light irradiation (λ > 400 nm). In fact, the photocatalytic effects exhibited by the composite particles were superior to that of pure TiO₂ and P25 samples. This excellent behavior is attributed to the structural features of PANI–TiO₂ microspheres and the synergistic effect between PANI and TiO₂ which facilitates a larger amount of surface active sites. This in turn causes a faster charge separation and slower charge recombination which results in a more efficient decomposition of gaseous pollutants.     

Magnetic and119Sn Mössbauer studies on a new Heusler alloy Co2ScSn

A new alloy, having the formula, Co₂ScSn, has been prepared. This is found to have the cubic Heusler L2₁ type structure (a = 6.19A). Magnetization measurements reveal a large drop in magnetization around 270K. Low field ac susceptibility also shows a transition at 268K which we take to be the Curie temperature of the alloy. The magnetic moment at 5K is found to be 0.55 _B per cobalt atom.¹¹⁹Sn Mössbauer measurements at 8K show a hyperfine split spectrum with a hyperfine field of about 40 kOe. Attempts to prepare other Co₂RSn alloys particularly with R=Lu, were not successful.     

The effect of the halide-ion (F<Superscript>–</Superscript>, Cl<Superscript>–</Superscript>) dopant nature on the local structure and hydration processes of brownmillerite Ba<Subscript>2</Subscript>In<Subscript>2</Subscript>O<Subscript>5</Subscript>

Halogen-substituted barium indate Ba₂In₂O₅ based brownmillerites Ba_1.95In₂O_4.9F_0.1 and Ba_1.95In₂O_4.9Cl_0.1 have been synthesized. It has been verified radiographically that the single-phase condition is satisfied. The effect of the substituent ion nature on parameters of the crystalline lattice and lengths of In–O bonds has been revealed. The propensity of the phases under study for hydration and formation of energetically unequal ОН^– groups in the structure has been proved. In both the cases of doping, the degree of hydration decreased as compared to barium indate Ba₂In₂O₅, which is caused by the participation of the halide ion in the tetrahedral site of indium.     

Mössbauer study of SnO<Subscript>2</Subscript> powders doped with dilute <Superscript>57</Superscript>Fe prepared by a sol-gel method

SnO₂ powders, doped with various ⁵⁷Fe contents were prepared by a sol-gel method, and annealed finally at 500 °C and 650 °C. These samples were characterized by Mössbauer spectroscopy, vibrating sample magnetometer (VSM), scanning electron microscopy (SEM), and X-ray diffraction (XRD) to investigate the relationship of magnetic properties, grain sizes, annealing temperatures and Mössbauer parameters. The particle sizes of SnO₂ powders reduced to less than 100 nm with the increase of Fe contents up to 5%. Rutile SnO₂ was the only phase obtained for all samples. Room temperature Mössbauer spectra suggest the presence of two different paramagnetic iron sites for all samples and one magnetically relaxed species for those samples with the lowest iron concentrations. The magnetization increased with the Fe content, but was reduced for the samples annealed at 650 °C perhaps due to a segregation of α-Fe₂O₃ doped with tin.     

NMR and Mössbauer study of multiferroic BiFeO<Subscript>3</Subscript>

Pulse nuclear magnetic resonance (NMR) was applied in studying the effect of ⁵⁷Fe isotope content in multiferroic BiFeO₃ on the shape of NMR spectra at 4.2 K. Strong dependences of the NMR line shape on the isotope content and transverse relaxation time were found. Consideration of these effects on NMR line shape shows that there is an undisturbed (with no anharmonicity effect) space spin-modulated structure of the cycloid type in BiFeO₃. The Mössbauer effect was also used to investigate the perovskite BiFeO₃ at 650, 295, and 87 K. Experimental spectra allowed us to obtain the distribution of hyperfine fields, which was found to be consistent with studies of the NMR line shape. The local electronic and magnetic states of the iron ion were measured.     

<Superscript>57</Superscript>Fe Mössbauer,SEM/EDX,p-XRF and μ-XRF studies on a Dutch painting

The painting of a rich Jewish merchant “Bildnis eines jüdischen Kaufmanns” from the Netherlands is dated presumably to the 16^th century. After a vivid historical background, i.e. robbed by the Nazis by order of Hermann Göring, it was recently discovered on an Austrian flea market. Different analysis methods were combined to identify the time of the production of this historically interesting looted art. Non-destructive MIMOS II Fe-57 Mössbauer spectroscopy was utilised for mesurements in selected spots. This mainly revealed haematite (α-Fe₂O₃) in the red curtain. In spots of the brown jacket Mössbauer spectra indicated the presence of mainly Iron(III) in super-paramagnetic oxide or oxide-hydroxide. Consecutively SEM measurements revealed a restoration by partly over-painting. The elementary composition of the pigments was examined by a portable-X-ray fluorescence. μ-XRF analysis for element distribution at different areas was performed. The look into a crack showed Zinc-white at the bottom of the crack. Traces of Titanium-white could be found within some locations on the surface of the painting. In terms of provenance of the artwork, the presence of Zink-white suggests that the painting was painted around the 19^th century. Titanium-white indicates a reconstruction during the 20^th century, approximately between 1917 and 1958.     

Mössbauer and magnetic studies of the phase state of SrFe<Subscript>12</Subscript>O<Subscript>19</Subscript>/La<Subscript>0.9</Subscript>Ca<Subscript>0.1</Subscript>MnO<Subscript>3</Subscript> composites

The formation of an intermediate phase in SrFe₁₂O₁₉/La_0.9Ca_0.1MnO₃ composites was demonstrated for the first time using only Mössbauer spectroscopy. The SrFe₁₂O₁₉/La_0.9Ca_0.1MnO₃ composite was prepared by the two-stage (sol–gel and hydrothermal) synthesis with varying initial conditions. The X-ray diffraction studies showed that the composite consisted of two phases: well-formed structures of manganite La_0.9Ca_0.1MnO₃ and hexagonal ferrite SrFe₁₂O₁₉. It was found that nanocrystalline La_0.9Ca_0.1MnO₃ particles with size d ? 150 nm formed in the composites at the surface of plate-like SrFe₁₂O₁₉ crystallites. The Mössbauer studies showed that the composite contained additional (intermediate) phase La_0.9Ca_0.1Mn(Fe)O₃ that formed at the interface between SrFe12O19 and La_0.9Ca_0.1MnO₃ phases. The intermediate phase concentration increased with the molar content of La_0.9Ca_0.1MnO₃; in this case, the fraction of the surface of SrFe₁₂O₁₉ crystallites coated with La_0.9Ca_0.1MnO₃ increased, which led to the increase in the total area of the interface surface and the intermediate phase concentration.     

Oxidation and passivating effect in tin(II) fluoride and chloride fluoride solid solutions: a <Superscript>119</Superscript>Sn Mössbauer study

Divalent tin fluorides and chloride fluorides appear to be stable relative to oxidation to tetravalent tin at ambient temperature. X-ray diffraction shows only the line of the tin(II) compound, however the ¹¹⁹Sn Mössbauer spectrum of all tin(II) polycrystalline samples has a small broad peak at ca. 0 mm/s. This is the case of polycrystalline α ?SnF₂, while the spectrum of a large single crystal polished sufficiently thin shows only the tin(II) doublet, with no SnO₂ peak at 0 mm/s. This shows that there is surface oxidation of each solid particle, to give a thin amorphous layer of SnO₂ stannic oxide. However, the Mössbauer peak of SnO₂ does not grow with prolonged exposure to air at ambient temperature, therefore it must be assumed that the layer of SnO₂ has a passivating effect, however oxidation increases at higher temperatures. We have investigated in this work the passivating effect of a layer of SnO₂ in two types of solid solutions: (i) in the fluorite type M_1?xSn_xF₂, where the amount of tin at low x values is not sufficient to provide full coverage of the surface of the particles, and (ii) in the PbClF type doubly disordered solid solution, Ba_1?xSn_xCl_1+yF_1?y. It was found that passivation works well in the M_1?xSn_xF₂ solid solution, however most of the time, it does not work so well for Ba_1?xSn_xCl_1+yF_1?y where it is strongly dependent on the method of preparation and the bonding strength, as shown by the variation versus the tin(II) recoil-free fraction.     

The development of the physical and electrical characteristics of multi-layer TiO<Subscript>2</Subscript>–W–TiO<Subscript>2</Subscript> thin films

In this study, two different thin films, TiO₂ thin film and TiO₂–W–TiO₂ multi-layer thin films (W, tungsten), are prepared by RF magnetron sputtering onto glass substrates. The crystal structure, morphology, and transmittance of TiO₂ and TiO₂–W–TiO₂ multi-layer thin films are investigated by X-ray diffraction, SEM, and UV-Vis spectrometer, respectively. The amorphous, rutile, and anatase TiO₂ phases are observed in the TiO₂ thin film and in the TiO₂–W–TiO₂ multi-layer thin films. The deposition of tungsten as the inter-layer will have large effect on the transmittance and phase ratios of rutile and anatase phases in the TiO₂–W–TiO₂ multi-layer thin films. The crystal intensities of amorous TiO₂ will decrease as the tungsten is used as the middle layer in the multi-layer structure. The band gap energy values of TiO₂ thin film and TiO₂–W–TiO₂ multi-layer thin films are evaluated from (αhν)^1/2 versus energy plots, and the calculated results show that the energy gap decreases from 3.21 eV (TiO₂ thin film) to 3.08∼3.03 EV (TiO₂–W–TiO₂ multi-layer thin films).     

EIT Ground State Cooling Scheme of <Superscript>171</Superscript>Yb<Superscript>+</Superscript> Based on the <Superscript>2</Superscript>S<Subscript>1/2</Subscript>→<Superscript>2</Superscript>P<Subscript>1/2</Subscript> Cooling Transition

We propose a method for EIT ground state cooling of ¹⁷¹Yb+ ion, which involves three light fields with detuning on a MHz scale. The steady-state mean vibrational quantum number is calculated to be less than 0.005. Efficient cooling is achievable in a motional-mode frequency range of 2π · (1.5 ± 0.5 MHz).