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.     

Local environment and dynamic characteristics of the 119Sn(II) and 119Sn(IV) Mössbauer probes on the surface of Cr2O3 exposed to hydrogen sulfide atmosphere

Tin dopant located on the surface of Cr₂O₃ crystallites interacts easily, at room temperature, with adsorbed H₂S molecules. Contrary to the initial oxygen-surrounded tin species, the resulting Sn(II) and Sn(IV) sulfur-surrounded entities exhibit no spin polarization, at least down to 4.6 K, which shows that they are more distant from the magnetically ordered oxide substrate. Additionally, their thermal vibration amplitudes are greater than in oxygen-surrounding, which denotes a weaker bonding of the tin within the H₂S adsorbed layer. Moreover, for Sn(II), sufficiently large quadrupole splitting allows the Goldanski-Karyagin effect to be seen. Thermal vibration amplitudes of Sn(II) are then found to be greater in the plane of the three neighbouring sulfur atoms than in the perpendicular direction.     

119Sn Mössbauer study of the implantation behaviour of119In,119Sn,119mSn,119Sb and119mTe ions in SiC

The implantation behaviour of stable¹¹⁹Sn⁺ ions and radioactive¹¹⁹In⁺,^119mSn⁺,¹¹⁹Sb⁺ and^119mTe⁺ ions in SiC has been investigated by, respectively, conversion-electron Mössbauer spectroscopy on the 24 keV transition of¹¹⁹Sn, and by Mössbauer emission spectroscopy on the 24 keV radiation emitted by the¹¹⁹Sn daughter after the decays of the radioactive isotopes. The Mössbauer spectra could be decomposed in most cases into two groups of lines, one originating from¹¹⁹Sn atoms on substitutional Si sites, the other from various Sn-vacancy complexes distinguished by their Mössbauer parameters. Annealing experiments reveal a strong dependence of the structure of the defects and the formation and annealing kinetics on the chemical nature of the impurities. Defects formed in 297 K implantations with^119mSn and¹¹⁹Sb anneal above 500 C, resulting in a preferential location of the impurities on substitutional Si sites, whereas^119mTe atoms are efficient defect-trapping centres and no stable, substitutional fraction is observed on either lattice site. Possible structures for the Sn-vacancy complexes are discussed and comparison is made to similar defect complexes in group IV and in III–V semiconductors.     

Light-perturbed hysteresis in an iron(II) spin-crossover compound observed by the Mössbauer effect

The compound [Fe(phy)₂](BF₄)₂ (phy = 1,10-phenanthroline-2-carbaldehyde phenylhydrazone) shows spin-transition with a hysteresis of 10 K width around room temperature. Continuous irradiation of the compound during heating and cooling with green light (514 nm) shifts the hysteresis in temperature. This revised version was published online in August 2006 with corrections to the Cover Date.     

Determination of the change of nuclear charge radius of the119Sn Mössbauer transition by internal conversion

Radioactive¹¹⁹Sb was implanted into six host matrices (CaSnO₃, Pt, Y, Au,-Sn, Pb) and internal conversion electrons of the 23.87 keV transition in¹¹⁹Sn were measured with an iron-free magnetic spectrometer as well as Mössbauer spectra. In the analysis of the conversion spectra of outermost electrons, the overlapping K-LM Auger lines were subtracted using the Auger spectrum of tin measured with another source of^117mSn, and the shake-off effect accompanying the conversion process was considered. From the correlation between the Mössbauer isomer shifts and the intensity ratios of O-shell to N₁-shell conversion electrons, the change of the nuclear charge radius of the 23.87 keV transition of¹¹⁹Sn was deduced to be R/R=(0.87 ± 0.25) × 10^–4 for a uniform charge distribution ofR= 1.2 ×A ^1/3 fm or, equivalently, r²>—=(3.6 ± 1.0) ×10^–3 fm².     

Decay of 161m1,m2Dy isomers under conditions of a resonance environment (Mössbauer Screen)

The half-lives of the isomers ^161m1Dy and ^161m2Dy (E = 25.6 keV and T _1/2 ～ 30 ns for the former and E = 74.6 keV and T _1/2 ～ 3 ns for the latter) placed in a ¹⁶⁰Gd₂O₃ crystal lattice at T = 300 K and surrounded by stable ¹⁶¹Dy nuclei in the composition of ¹⁶¹Dy₂O₃ were measured by the method of (β-γ) coincidences in the beta-decay process ¹⁶¹Tb → ¹⁶¹Dy. Nuclei of ^161m1,m2Dy were obtained according to the chain ¹⁶⁰Gd(n, γ)¹⁶¹Gd → ¹⁶¹Tb → ¹⁶¹Dy from ¹⁶⁰Dy₂O₃ weighted portions irradiated at the PWR-M reactor of the Petersburg Nuclear Physics Institute (PNPI, Gatchina, Russia). The T _1/2 value observed for the isomer ^161m1Dy was found to be correlated with the number of surrounding ¹⁶¹Dy nuclei. The presence of this correlation in ^161m1Dy can be explained by the multiple resonance scattering of photons from isomer decay within the sample used. No such correlation was observed for ^161m2Dy. The half-lives measured for the isomers ^161m1Dy and ^161m2Dy in the absence of the above environment are 29.2(1) and 3.50(1) ns, respectively.     

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.     

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%).     

Effect of pressure on the Mössbauer isomer shift and quadrupole splitting in Au(I)-cyanides

The effect of pressure on the Mössbauer isomer shift and quadrupole splitting was studied with the 77 keV resonance of¹⁹⁷Au in the Au(I)-cyanides AuCN and KAu(CN)₂ at 4.2 K under pressures up to 80 kbar. We observe an increase of the electron density and a decrease of the absolute value of the electric field gradient at the Au nuclei in both compounds with pressure. This variation is different from the correlation that has been established for these parameters within the chemical series of Au(I) compounds at ambient pressure. It indicates that the-bonding increases strongly under pressure. X-ray diffraction studies on AuCN under pressures up to 115 kbar together with investigations of the Goldanskii-Karyagin-effect on AuCN at ambient pressure support the previous assumption that the sign of the electric field gradient at the Au(I) sites is negative.     

Experimental search for the effect of resonant environment on the Mössbauer absorption of gamma rays by <Superscript>57</Superscript>Fe

Due to the virtual photon exchange between atomic nuclei and the field of zero-point electromagnetic oscillations, some nuclei of a given sample are in a virtual excited state with the lifetime ～?/E, where E is the energy of nuclear level. For ⁵⁷Fe nuclei, whose first excited state has an energy of 14.4 keV, this time is equal to ～4.6×10^?20 s. If a thin ⁵⁷Fe Mössbauer gamma-ray absorber is surrounded by a thick screen of the same atoms, the number of virtual excited nuclei in the absorber decreases and, at first glance, it should more strongly absorb Mössbauer gamma rays emitted by an external source and passing through the absorber. In this work, the ratio of the intensities of 14.4-keV gamma rays emitted by the ⁵⁷Fe nuclide and passing through the thin resonant absorber is measured in the absence and presence of the resonant screen around the absorber. Comparison shows that these ratios measured for the gamma source at rest and in the oscillating state differ by 0.00123±0.00075. This value should be treated as the upper limit for the desired effect under these experimental conditions.     

Mössbauer effect study of the pseudo-binary system (Ti1−x Nb x )Fe2

Mössbauer spectroscopy and X-ray diffraction measurements have been done on (Ti_1–x Nb _x )Fe₂ compounds in order to investigate the effect of Nb on the magnetic properties of TiFe₂. The experimental results show that Nb enters the lattice by filling Ti sites, thereby forming a continuous phase over the whole range of Nb concentrations. The Mössbauer spectra at 80 K fitted with a magnetic hyperfine field distribution show a continuous decrease of the average magnetic hyperfine field with increasing Nb concentration, as well as several different magnetic configurations forx0.3.     

119Sn Mössbauer characterization of self assembled organotin(IV) complexes with Schiff bases containing amino acetate skeletons

Several organotin(IV) compounds, viz., diorganotin(IV) compounds of the types Ph₂SnLH (monomer), ⁿBu₂SnLH·OH₂ (monomer), [Me₂SnLH·OH₂]₂ (centrosymmetric dimer), [ⁿBu₂SnLH]₃ (cyclic trinuclear), [Ph₂SnLH] _n (polymer), {[ⁿBu₂Sn(LH)]₂O}₂ (centrosymmetric tetranuclear), dinuclear di-/tri-mixed organotin(IV) compounds Ph₂SnLH·Ph₃SnCl (monomer) and triorganotin(IV) compounds of the types [Bz₃SnLH]₂ (centrosymmetric dimer) and [Me₃SnL¹H] _n (Polymer) (LH = Schiff base carboxylate) have been studied in the solid state at liquid nitrogen temperature using ¹¹⁹Sn Mössbauer spectroscopy. The tin coordination geometry of the compounds determined from crystallography was correlated with the ¹¹⁹Sn Mössbauer results.     

Investigation of conductivity in the Sr(Fe1−xTix)Oy system by iron-57 Mössbauer spectroscopy

On the basis of our previous work electrical conductivity in the Sr(Fe_1–xTi_x)O_y system (0.0x0.9,y3) has been further studied by means of Mössbauer spectroscopy. When 0.0x0.6, the concentration of Fe³⁺ (II) doublet relates to the final firing temperature and electrical conductivity of the materials is sensitive to the concentration of Fe³⁺ (II). Atx=0.25, the curve of the resistivity versus Ti contentx shows a local minimum which is observed for the first time. The results indicate that the coexistence of Fe⁴⁺ and Fe³⁺ in the same lattice leads to high conductivity; the conductivity increases when the Fe⁴ concentration approaches to that of the Fe³⁺ one. When the temperature is at 260 K and 230 K, the presence of the intermediate state showing quadrupole splitting has an effect on the conductivity of the materials.     

Investigation of the processes of iron-ion recharging on surfaces of natural nanoclays (Based on Mössbauer spectroscopy data)

Experimental results on studying charge exchange in iron ions in systems of reduced dimensionality (nanoclays) of natural origin is presented. The conditions for the observation and the effect of different external factors on the reversible transition of the valence change for iron ions (Fe³⁺ ai Fe²⁺) in typical representatives of clays is established using Mössbauer spectroscopy. A technique of the determination of the location of iron complexes on the aluminosilicate surface of clays for Earth group planets is developed.     

Temperature dependence of the Mössbauer effect on the semiconductors Pb0.78Sn0.22Te and Pb0.80Sn0.20Te:In

Crystals of the semiconductors Pb_0.78Sn_0.22Te and Pb_0.80Sn_0.20Te:In were grown by Bridgman method, and investigated by Mössbauer spectroscopy and X-ray diffraction. Mössbauer spectra were taken at temperatures between 80 and 300 K. The absence of the quadrupole splitting shows a cubic symmetry of the environment for the tin atom, which is in accordance with X-ray data. The temperature dependence of the spectral area is discussed and the Debye temperature is estimated.     

Calculation of contact densities and Mössbauer isomer shifts utilising the Dirac-exact two-component normalised elimination of the small component (2c-NESC) method

ABSTRACT

Utilizing the analytic derivative formalism for the Mössbauer isomer shift in connection with the Dirac-exact two-component Normalized Elimination of the Small Component (2c-NESC) method a new approach to the analytic calculation of the contact densities at the nuclei has been developed and implemented in the general purpose NESC programme. The new approach is applied to the calculation of the contact densities as well as contact density differences in several iodine-, gold-, and mercury-containing molecules. Substantial differences between the contact densities obtained by the spin-free 1c-NESC method and the 2c-NESC method are found, which demonstrate the importance of spin-orbit coupling. However, the influence of spin-orbit coupling on the contact density differences between the sample and the reference nuclei is found to be modest. This result suggests that a low-cost determination of accurate contact densities at the nuclei can be achieved by combining the 1c-NESC densities obtained at the correlated wavefunction level of theory with the contact density differences obtained at the 2c-NESC/DFT level.     

Mössbauer study of the ternary system (Fe1−xVx)3 Ge

Three crystallographically different structures of (Fe_1–xV_x)₃ Ge have been studied by⁵⁷Fe Mössbauer spectroscopy. The hexagonal phase, stable for low values ofx, is ferromagnetic with the spins parallel to thec-axis above a critical temperature, where a spin flip to thec-plane takes place. A V/Fe substitution in the near surrounding of an iron atom leads to a decrease in the isomer shift of –0.02 mm/s and an estimated reduction in the magnetic moment of 0.31 _B from 2.07 _B. A result for the intermediate cubic closed packed structure is that V populates only one type of metal sites. Furthermore, from similarities with-Fe the average value of the change in isomer shift is found to be +0.075 mm/s and +0.02 mm/s per Ge/Fe substitution in the 1nn and 2nn shells, respectively. The spin polarization effect on the magnetic hyperfine field for iron is –8.6%, –0.4%, and –0.6% per Ge/Fe (1nn), Ge/Fe (2nn) and V/Fe (3nn) substitutions, respectively. The simple cubic compound (Fe_0.7V_0.3)₃ Ge is non-magnetic down to at least 5 K. Here a decrease in the isomer shift of –0.05 mm/s is found for a V/Fe (1nn) substitution.On leave from the Department of Nuclear Physics, University of Madras, Madras, India.On leave from the Physics Department, Punjabi University, Patiala, India.     

Mössbauer study of the perovskite series Sr(Fe1−xTix)Oy

⁵⁷Fe Mssbauer effect in the perovskite series Sr(Fe_1–xTi_x)O_y (0.0x0.99; y3) at RT and 78K has been analyzed. The influences of the Ti composition on the coexitence of Fe⁴⁺ and Fe³⁺, the ratio of Fe⁴⁺ to the total Fe, and the Y value have been studied. When 0x0.6 the ratio of Fe³⁺ (II) doublet to the total Fe increases as the final firing temperature increases, agreeing with the result obtained from the positron lifetime measurements. When x0.7, the Fe³⁺ (II) doublet disappears. In the range of x=0.9 and x=0.99, there still exists a considerable content of Fe⁴⁺ in samples, disagreeing with the result obtained from the chemical analysis by Clevenger. The relations between the electrical resistivity and the thermistor material constant B of negative temperature characteristic varying with Ti composition have been discussed.     

237Np Mössbauer Investigations of (U1−x Np x )2Rh2Sn

Surprisingly, Np₂Rh₂Sn does not order magnetically whereas the uranium counterpart U₂Rh₂Sn orders antiferromagnetically at 24 K with a 5f moment μ _U ≈0.38μ _B . We have investigated the magnetic and electronic properties of (U_1−x Np _x )₂Rh₂Sn solid solutions. For x=0.25 and 0.5, the ordering temperature decreases to 11 K whereas the Np-rich compound (x=0.75) shows the onset of magnetic order around T≈6 K. The average Np magnetic moment amounts to 0.84 μ _B ,0.83μ _B and 0.25 μ _B respectively. The isomer shift slightly decreases, from −9.6 mm/s to −10.4 mm/s (versus NpAl₂) as x increases. The values of the quadrupole interaction parameter in the ordered and paramagnetic state suggest that Np moments are parallel to c for x=0.25 and then rotate to the basal plane for higher x. This revised version was published online in September 2006 with corrections to the Cover Date.