A novel investigation of tin-doped ferrihydrite nanoparticles

Tin-doped ferrihydrite was synthesized and characterized with powder X-ray diffraction and ⁵⁷Fe and ¹¹⁹Sn Mössbauer spectroscopy to obtain diagnostic and structural information. Samples were prepared with doping concentrations (molar percentages) of 0, 10, 25, 40, 50, 60, 75, and 90% tin. As Sn concentration increases, the 110 reflection plane of ferrihydrite shifts to higher d-values, while the 300 plane d-values increase, reach a maximum and then sharply drop. The δ (isomer shift) and Δ (quadrupole splitting) values for ⁵⁷Fe Mössbauer spectra increase, while the Γ (line width) values stay constant. In ¹¹⁹Sn Mössbauer spectra, δ values decrease with increasing tin substitution while Δ and Γ values increase. After 50% Sn has been substituted, the ferrihydrite becomes oversaturated with surface tin and a secondary tin structure is proposed to develop.     

Study of Au/SnO x –Al2O3 catalysts used in CO oxidation by in situ Mössbauer spectroscopy

The active catalytic components in tin oxide containing alumina-supported gold catalyst were examined by comparing and analysing the in situ Mössbauer spectra of the SnO _x –Al₂O₃ support and the 3 wt.% Au/SnO _x –Al₂O₃ catalyst (1.1 wt.% Sn, Au/Sn = 3:2 atomic ratio). Samples were prepared by using organometallic precursor of ¹¹⁹SnMe₄ (enriched). First tin was grafted to the alumina surface from the organometallic precursor compound. In the next step the grafted complexes were decomposed in flowing oxygen. Gold was deposited onto the SnO _x –Al₂O₃ support in the subsequent step. Analysis of in situ spectra shows that in Au/SnO _x –Al₂O₃ catalyst after activation in hydrogen at 620 K tin may occur in three different oxidation states [Sn (IV), Sn(II) and Sn(0)] simultaneously. The metallic tin is a component of the bimetallic AuSn alloy phase. Data presented provide the first evidence for the formation of alloy-type supported Sn–Au catalyst on alumina. Furthermore, from the spectra recorded at different temperatures, values of the Debye temperatures and recoilless fractions were also determined for the various species. The results show that in catalytic oxidation of carbon monoxide at room temperature the dominant part of Sn(II) and the AuSn alloy is oxidized.     

In situ 119Sn Mössbauer spectroscopy study of Sn-based electrode materials

Sn-based composite materials were synthetized by a conventional melt-quenching method, and studied by X-ray diffraction, electrochemistry and in situ ¹¹⁹Sn Mösssbauer spectroscopy. Tin was dispersed ex situ into a matrix formed from B₂O₃:P₂O₅. XRD and ¹¹⁹Sn Mössbauer spectroscopy show the formation of an interface between the active species (Sn⁰) and the matrix. This amorphous interface acts as a “buffer-zone” which compensates volume changes during the tin–lithium alloy formation and avoids aggregation of tin particles.     

Mössbauer studies of negative-U tin centers in lead chalcogenides

Experimental data on identification of negative-U tin centers in lead chalcogenides and related solid solutions by means of ¹¹⁹Sn Mössbauer spectroscopy are discussed.     

Investigation of isomeric ratios in high-energy reactions

Experimental data on the isomeric ratios of cross sections for products originating from the interaction of ¹²C ions (E 12 _C = 26.4 GeV), protons (E _p = 3.65 GeV), and deuterons (E _d = 7.3 GeV) with targets enriched in the tin isotopes ¹¹²Sn, ¹¹⁸Sn, ¹²⁰Sn, and ¹²⁴Sn are presented. The dependence of the isomeric ratios on the interaction mechanism, projectile type and energy, and nuclear properties of the final-state nucleus are discussed. The dependence of the isomeric ratios on the degree of deformation of the product nucleus is also considered.     

Tin U ?-centers formed through nuclear transformations in vitreous arsenic sulfides and selenides

It has been shown using the M?ssbauer emission spectroscopy for isotope ¹¹⁹Sn that impurity tin atoms formed after the radioactive decay of ¹¹⁹Sb atoms in vitreous arsenic sulfide and selenide are localized in arsenic sites and play the role of two-electron centers with negative correlation energy. The most of daughter ^119m Sn atoms formed after the radioactive decay of the ^119m Te atoms in glasses are arranged in chalcogen sites; they are electrically inactive. Considerable recoil energy of daughter atoms in the case of decay of ^119m Te leads to the appearance of ^119m Sn atoms shifted from chalcogen sites.     

Electromigration of gold and silver in single crystal tin

Measurements of electromigration have been performed for gold and silver in single crystal tin. The electromigration measurements of Ag in single crystal Sn along the c-axis give for Z_Ag¹ a value of around −2.15±0.25. The temperature dependence of Z¹_Ag is small, but there is a large Soret effect which may account for the considerable irreproducibility evinced by earlier measurements of Z_a¹ in this system. The electromigration studies of Au in Sn show that the orientation of Sn has little effect on the Z_a¹ values. The Z_a¹ parameters are around −9.5 ± 0.33. The temperature gradient across the sample has less influence than that in the electroinigration of Ag in Sn.     

Evolution of the negative electrode (tin/silicate) for Li-ion batteries studied by 119 Sn Mössbauer spectroscopy

A novel tin composite Sn/CaSiO₃ for the anode of Li-ion batteries was prepared by solid-state reaction. The CaSiO₃ matrix was synthesized by a sol-gel route. The crystalline structures and morphology were determined by X-ray diffraction (XRD) and ¹¹⁹Sn Mössbauer spectroscopy; the electrochemical properties were evaluated by galvanostatic charge and discharge. The results obtained show that the Sn/CaSiO₃ composite presents very interesting electrochemical performances in terms of specific capacity in the first discharge (591 mAh/g) and a good reversibility due to both the formation of an interface between active and inactive materials and the reversible formation of Li _x Sn alloys. We have also highlighted, by ¹¹⁹Sn Mössbauer spectroscopy, the various tin species constituting the material of the starting electrode, as well as the chemical evolutions occurring during the discharge and the charge of the electrode.     

On the microwave absorption of superconducting Nb3Sn

Measurements ofdc-resistance, surface resistance at 9.6 GHz and x-ray diffraction were made on Nb₃Sn layers having thicknesses between 4 and 7 μ. Samples were prepared by condensing tin on niobium foil which was then annealed at high temperature. This process was repeated, in some cases as many as twenty times. The best samples showed steep transition curves close to 18.2 K. X-ray measurements indicated a high degree of stoechiometry. The surface resistance decreased from 5 · 10^?2Ω atT _c to a residual value of 3 · 10^?4 Ω. This relatively high value can be due to minor deviations from stoechiometry or possibly to similar mechanisms as proposed for pure elements.     

Bonding in the Doubly Disordered Ba1−x Sn x Cl1+y F1−y Solid Solution

New materials were prepared in the SnF₂/BaCl₂ system by precipitation, and in the SnF₂/BaCl₂/BaF₂ system by direct reactions at high temperature in dry conditions. Stoichiometric BaSn₂Cl₂F₄ and BaSnClF₃?0.8H₂O, and a wide Ba_1?x Sn _x Cl_1+y F_1?y solid solution were prepared for the first time. Elemental analysis, X-ray diffraction and ¹¹⁹Sn Mössbauer spectroscopy were used for the characterization and study of bonding in the new materials. Mössbauer spectroscopy was shown to be an excellent method for probing both the type of bonding at tin(II) (ionic or covalent) and the bond strength at the tin sublattice. Tin(II) is covalently bonded in the stoichiometric phases and ionic (Sn²⁺ stannous ion) in the precipitated Ba_1?x Sn _x Cl_1+y F_1?y solid solution. The case of Ba_1?x Sn _x Cl_1+y F_1?y prepared in dry conditions is more complex. At negative y values (Cl: F <1) and more particularly at high x (solid solution rich in tin), a mixture of Sn²⁺ and covalent Sn(II) is observed, with a normal sublattice strength for Sn(II). At positive y values (Cl:F >1) and more particularly at low x (poor in tin), all the tin(II) is in the ionic form. Furthermore, at high x and high y, the tin(II) sublattice strength decreases so drastically that the tin recoil free fraction at ambient temperature is nearly zero. The bonding type and tin sublattice strength can be explained in terms of preference of covalent bonding with F and when tin clustering occurs, whereas an excess Cl around Sn(II) forms ionic bonding and tin rattling due to ionic size mismatch.     

In situ 119Sn Mössbauer spectroscopy used to study lithium insertion in c-Mg2Sn

The electrochemical reactions of Li with c-Mg₂Sn have been investigated by in situ Mössbauer spectroscopy of ¹¹⁹Sn and X-ray diffraction. The lithiation transforms initially c-Mg₂Sn part into Li _x Mg₂Sn alloy (x?2MgSn ternary alloy. In situ Mössbauer spectroscopy provides valuable information on local environment of tin and swelling behavior and cracking of the particles during discharge and charge processes.     

Magnetic hyperfine interactions of 119Sn probe atoms in the binary perovskite CaCu3Mn4O12

The manganite CaCu₃Mn₄O₁₂ doped by ¹¹⁹Sn atoms (about 1 at % with respect to Mn atoms) is studied by Mössbauer spectroscopy. The introduction of diamagnetic tin atoms is found not to affect the structure of the manganite. Tetravalent tin atoms are shown to substitute for the isovalent manganese atoms that are located in an octahedral oxygen surrounding. The cluster method of molecular orbitals is used to calculate the contributions of Mn⁴⁺ and Cu²⁺ cations that belong to different structural sublattices to the hyperfine magnetic field at ¹¹⁹Sn nuclei (H _Sn = 105 kOe at T = 77 K). These partial contributions are analyzed, and the intrasublattice Mn⁴⁺-O-Mn⁴⁺ exchange interactions are found to play a significant role in the formation of the magnetic structure of the manganite.     

Absence of the resonant environment effect on the half-life of the <Superscript>119<Emphasis Type="Italic">m</Emphasis></Superscript>Sn isomer in the standard Mössbauer <Emphasis Type="Italic">γ</Emphasis>-ray source

Nine sets of measurements aimed at searching for the influence of resonant environment on the half-life of the ^109m Sn isomer have been performed during 14.7 months. The intensities of γ and X rays, emitted by two 261Mössbauer sources of identical design and size, were compared in these experiments. One of the sources was kept in the resonant environment of tin dioxide between measurements. No difference was found in the half-lives of ^119m Sn that would be beyond the experimental errors (0.35%).     

Interpretation of the 119Sn Mössbauer parameters

The variations of the ¹¹⁹Sn Mössbauer isomer shift δ are interpreted for tin compounds from a semi-empirical tight-binding calculation of the electronic density at the nucleus ρ(0). A molecular model is proposed in order to relate the variations of ρ(0) for the Sn(IV) chalcogenides to the changes in the Sn environment. The variations of the experimental values of the quadrupole splitting δ are linearly correlated to the values of the electric field gradients (EFG) calculated by the full-potential linearized-augmented-plane-wave (FP-LAPW) method. The value of the ¹¹⁹Sn nuclear quadrupole moment is found to be |Q| = 10.5 ± 0.2 fm². Finally, the relation between the EFG and the Sn environment is discussed for SnO.     

Sn interaction with the CeO2(1 1 1) system: Bimetallic bonding and ceria reduction

A tin layer 0.8 nm thick was deposited onto the CeO₂(1 1 1) surface by molecular beam deposition at a temperature of 520 K. The interaction of tin with cerium oxide (ceria) was investigated by X-ray photoelectron spectroscopy (XPS), ultra-violet photoelectron spectroscopy (UPS) and resonant photoelectron spectroscopy (RPES). The strong tin-ceria interaction led to the formation of a homogeneous bulk Ce-Sn-O mixed oxide system. The bulk compound formation is accompanied by partial Ce⁴⁺ → Ce³⁺ reduction, observed as a giant 4f resonance enhancement of the Ce³⁺ species. CeO₂ and SnO₂ oxides were formed after oxygen treatment at 520 K. The study proved the existence of strong Ce-Sn interaction and charge transfer from Sn to the Ce-O complex that lead to a weakening of the cerium-oxygen bond, and consequently, to the formation of oxygen deficient active sites on the ceria surface. This behavior can be a key for understanding the higher catalytic activity of the SnO_x/CeO_x mixed oxide catalysts as compared with the individual pure oxides.     

The rapid formation of tin oxide pillared laponite by microwave heating: Characterisation by tin-119 Mössbauer spectroscopy,X-ray photoelectron spectroscopy and nuclear magnetic resonance

The intercalation of organotin-compounds into laponite and the formation of tin(IV) oxide pillars is rapidly achieved when performed in a microwave oven.¹¹⁹Sn Mössbauer- and x-ray- photoelectron-spectroscopy suggest that Ph₃SnCl and Ph₂SnCl₂ undergo hydrolysis on the surface once sorbed. The treatment of Ph₃SnCl/laponite with microwave radiation also induces the formation of a metallic phase which contains both tin and magnesium.     

Auger spectroscopic study of the surface composition of Pt/Sn alloys in ultrahigh vacuum and in the presence of oxygen and hydrogen

The surface composition of two Pt/Sn alloys, viz. PtSn and Pt₃Sn, has been followed by means of AES, as a function of annealing in ultrahigh vacuum, oxygen chemisorption and reduction with hydrogen.The results, which were quantitatively interpreted with the aid of a novel calibration technique, reveal the following features: - The surface of PtSn and Pt₃Sn becomes enriched with tin by annealing in vacuum. Ultimate values of 68±5 at% Sn for PtSn and 41±5 at% Sn for Pt₃Sn were attained after annealing at 500°C. - The adsorption of oxygen on the annealed surface of PtSn and Pt₃Sn causes a further enrichment with tin, while severe oxidation of PtSn at 500°C leads to complete disappearance of Pt from the surface. - Oxygen is more strongly and differently bound on a surface containing about 40 at% Sn than on a surface containing about 70 at% Sn. Activated adsorption of oxygen takes place only on the latter. The results suggest the formation of SnO₂ surface complexes on the exposed surface of Pt₃Sn. - Reduction of the alloys at 500°C carries the excess of tin into the bulk and reduces its surface concentration to 35±5 at% for Pt₃Sn and 64±5 at% for PtSn, which is an enrichment of the surface with platinum relative to the annealed state.     

Mössbauer study of Tl containing highT c superconductors

Mössbauer spectroscopy, X-ray diffractometry, ESR and electrical resistivity measurements, were used to study highT _c (above 100 K) superconducting materials in order to get information about the effect of the preparation circumstances as well as about the anomalous behaviour in⁵⁷Fe and¹¹⁹Sn doped TlBaCaCu(⁵⁷Fe)O_4.5+δ and TlBaCuCu(¹¹⁹Sn)O_4.5+δ superconductors. We have found that the Mössbauer parameters strongly depend on the preparation circumstances. In many cases the presence of Mössbauer lines of nonsuperconducting oxide phases indicated that the iron and tin could not entirely built in into the lattice of superconductor. Four valence state tin and four valence state iron sites were identified in the superconducting phases. We have found anomalous temperature dependent changes in the⁵⁷Fe Mössbauer spectra of TlBaCaCu(⁵⁷Fe)O_4.5+δ samples around theT _c between 105–135 K. In this temperature range the total area of the spectrum temporary increases.     

On the Mössbauer isomer shift studies of the electronic structure of Sn implanted AIIIBV compounds

Recent Mössbauer isomer shift (IS) measurements on¹¹⁹Sn impurities substitutionally implanted in several A^IIIB^V compounds are interpreted in terms of their electronic structure. Since tin can replace both the A and the B atoms, two different IS lines arise corresponding to the donor and acceptor Sn impurities. To calculate the electronic configuration of ionized tin donors and acceptors and the relevant electron contact densities, a Green-function procedure is used based on the parametrized tight-binding approximation including relativistic wave functions. It turns out that with ionized Sn acceptors, the impurity is formed by a small cluster containing the tin atom in its neutral configuration rather than by a single negative Sn ion as might be anticipated at first sight. On the other hand, in the donor case the positive Sn ion plays the dominant role.     

Photodisintegration of Sn isotopes

Yields of (γ, n) reactions on tin isotopes ¹²⁴Sn, ¹¹⁸Sn, ¹¹⁴Sn, and ¹¹²Sn and yields of (γ, p) reactions on ¹¹⁷Sn, ¹¹⁶Sn, and ¹¹²Sn were measured in the present study. The obtained results are compared to those from earlier experiments and theoretical calculations. The yields of reactions with the production of nuclei in isomeric states are presented.