119Sn Mossbauer Spectra Research Articles

Pecularities of antiferroelectric phase transitions in PbZr0.71 Sn0.29 O3 crystal investigated by Mössbauer effect

The Mossbauer spectra of 119Sn in PbZr1−xSnxO3 compound were studied from 30 to 300 °C with particular emphasis on the regions of phase transitions. Some changes of the Mossbauer spectrum near the phase transition temperatures were observed, as expected from the change in the crystal structure. The measurements also showed that the Mossbauer fraction considerably drops near the temperature of the phase displacive transition between two antiferroelectric phases (AFE1–AFE2), whereas this drop is considerably smaller at Curie point. Little difference was found in the center shift of the spectrum, indicating that the bonding character is not affected by the phase transitions. The obtained results were interpreted according to Dvorak's suggestion that in antiferroelectrics the frequency over the entire optical branch may soften at particular phase transitions. According to the theory, the mode softening should manifest as a decrease in the Mossbauer–Lamb recoil-free fraction (f-factor) due to the increasing vibrational amplitude of the soft mode. Such softening was already observed in Raman scattering measurements in the PbZr1−xSnxO3 single crystals.

Local environment of 119Sn4+ probe ions in the bulk and on the surfaces of substituted chromites with perovskite-type structure Y1–x Ca x CrO3

A specific feature of the Mossbauer spectra of 119Sn in Y1–xCaxCrO3 samples containing 0.3 at % Sn4+ in the bulk of crystallites is an extra sextet component corresponding to hyperfine field H(119Sn) = 65 kOe at 4.2 K. This effect is explained by the formation of Sn4+ impurity associates in the chromium sublattice. A drastic weakening in spin polarization is observed for the Sn4+ ions in surface sites, but is found not to be related to the presence of heterovalent Ca2+ ions.

119Sn Mössbauer study of the influence of a gas atmosphere on the valence state and distribution of tin atoms in the MgO structure

Analysis of the Mossbauer spectra of dopant 119Sn in cubic MgO has demonstrated that the Sn2+ ions can be stabilized on the surface of crystallites of an oxide with a structure differing from the corundum structure. The Mossbauer parameters (at 100 K, the isomer shift is δ = 2.50 ± 0.01 mm/s and the quadrupole splitting is Δ = 2.30 ± 0.02 mm/s) point to the stereochemical activity of the lone pair of Sn2+. Being in contact with oxygen at 295 K, tin is rapidly converted to the tetravalent state (δ = 0.08 ± 0.01 mms, Δ = 0.58 ± 0.01 mm/s). The lack of formation of Sn2+ on the surface of another cubic oxide (MnO) can be explained by rapid segregation of tin from the bulk of crystallites as stannate clusters.

The Mössbauer effect observed on tin impurity atoms in liquid gallium

The recoilless absorption of gamma quanta by 119Sn impurity atoms in massive metallic gallium disappears at 292.454 K. However, the dispersion of liquid gallium containing tin impurity in a porous glass with an average pore size of about 70 A allows the Mossbauer spectra of 119Sn to be observed even at 298.15 K, which is explained by increased “rigidity” of the phonon spectrum of finely dispersed gallium.

Mossbauer spectra of tin in binary Si-Sn oxide glasses

The Mossbauer spectra of 119Sn in binary glasses of SnO and SiO2, in varying proportions of between 16.8 and 71.5 mol% SnO, have been obtained at 77 K. From these spectra the tin was found to be predominantly in the 2+ state. The isomer shift and the quadrupole splitting were both significantly greater than those in crystalline SnO and were found to decrease with increasing tin content, which also corresponds to decreasing molar volume. A second series of spectra of two of the samples was taken at temperatures between 10 and 300 K. These spectra show a decrease in shift with temperature which was the same for the two samples and which could only partly be accounted for by the second-order Doppler shift. The remainder was ascribed to the temperature dependence of the isomer shift. By using these data together with the measured expansivity and increase in density with tin content, it was possible to correct the isomer shift for the effects of the change in volume, and it was found that the volume-corrected isomer shift increased with increasing tin content. This showed that there was an increase in s-electron density at the tin nuclei, while the accompanying decrease in quadrupole splitting showed a decrease in the p-electron character, as expected for a decrease in covalency. From the decrease in absorption area with temperature the Debye temperature of tin was estimated to be ~190 K, which is slightly less than that of crystalline SnO, and decreased with increasing tin content. All the data suggest that the Sn-O bonds become progressively less covalent as more tin is added to SnO-SiO2 glasses, and possibly indicate a change from 4-fold to 6-fold co-ordination. A third series of spectra was obtained for the glass containing 40.9 mol% of SnO after a series of heat treatments. The spectra show changes in the oxidation state of the tin which depended upon the different conditions applied.

A mossbauer study of 119Sn in alloys of iron with Si, Al and Rh: interaction potentials and phase diagrams

Mossbauer spectra of 119Sn at a concentration of 0.2% in alloys of iron with Si, Al and Rh are presented. The strength of some of the interaction potentials between Sn and Si, Al and Rh are obtained, and some details of the iron-rich corner of the ternary phase diagrams elucidated. In alloys of iron with silicon and aluminium, the interaction potentials are found to be large and positive, in agreement with the Miedema-Krolas and size-mismatch theories. The authors find that in both these alloy systems, the presence of tin in concentrations as low as 0.2% strongly lowers the value of the concentration of the alloying element at which order states of Fe3Si and Fe3Al appear. In the iron-rhodium alloys, they find a potential at the first-neighbour distance between Sn and Rh atoms of -32 meV, in fair agreement with the Miedema-Krolas prediction of -84 meV. At the second-neighbour distance the potential cannot be determined. For Rh concentrations greater than 3%, an intermetallic compound is formed in which 119Sn has a positive hyperfine field of 57 kOe and an isomer shift 0.1 mm s-1 less than is found at 119Sn in iron.

The interaction between119Sn atoms and transition element atoms dissolved in iron

Mossbauer spectra of 119Sn introduced at a concentration of 0.2% into alloys of iron with transition metals are used to derive the interaction potentials between tin atoms and the transition metal atoms at first and second neighbour distances. A semi-empirical theory due to Miedema (1977) and Krolas (1981) is a useful predictor of the interaction at first neighbour distances, and a weak correlation is found between the interaction at second neighbour distances and the atomic volume. The spectra also give some information about the interactions between the transition elements themselves, which are found to be generally strongly repulsive at both first and second neighbour distances.

The interaction between119Sn atoms and impurity atoms of s-p elements of the fourth period dissolved in iron

Mossbauer spectra of 119Sn dissolved in binary iron alloys with elements Co, Ni, Cu, Sn, Ga, Ge are used to derive the interaction potentials existing between the tin atom and the atoms of the alloying element. It is shown that the Miedema-Krolas theory successfully predicts the first neighbour potential, while the second neighbour potential correlates well with the atomic volume. Some comments are made on the elastic contribution to the heat of solution.

Mössbauer and X-ray diffraction study of an aluminium-magnesium-silicon alloy containing Pb and Sn

The Mossbauer parameters of tin in aluminium matrix were studied and published in an earlier paper1. The aim of this work was to carry out investigations on tin in an aluminium alloy containing magnesium, silicon and lead beside the Mossbauer active tin. The effect of heat treatments on the formation of intermetallic compounds was studied by X-ray diffraction and by the Mossbauer spectra of119Sn.

Mössbauer Effect in Fluorotrimethyltin(IV)

Abstract The angular dependent Mossbauer spectra of 119Sn in needle crystals of fluorotrimethyltin(IV) were studied at 110 K. The principal axis of the electric-field gradient was observed at about 20° from the a axis. 19F NMR spectra of the solid were also studied. From the temperature dependence of the linewidth, the activation energy for the motion of the F atom was estimated to be 6.7±1.3 kJ mol−1.

57Fe and 119Sn M�ssbauer studies of natural tin-bearing garnets

The Mossbauer spectra of 119Sn and 57Fe in three natural and a synthetic garnet were studied between 20 and 300 K. These spectra reveal the presence of octahedral Sn4+ as well as octahedral Fe3+ and Fe2+. Sn2+ could not be detected. On the basis of these results the following cation substitution can be derived for the tin-bearing Silicate garnets of this study: Sn4+ (oct)+Fe2+ (oct) ⇌ 2 Fe3+ (oct).

M�ssbauer effect in superconducting tin-europium-molybdenum-sulfides

Mossbauer spectra of119Sn in Sn1−zEu z Mo6S8 (z=0, 1/3, 2/3) have been measured in the temperature range 4.9 K≦T≦293 K. The spectra consist of a quadrupole doublett with unequal intensities at all temperatures. The Debye-Waller factor, the isomeric shift and the asymmetry of the intensity of the quadrupole components show irregularities between 50 K and 110 K which are interpreted as arising from a structural phase transition. The temperature dependence of the Debye-Waller factor can be approximated by a simple phonon spectrum. No quantitative explanation can be given for the large values of the asymmetry. Evidence is presented that this behavior is connected with the properties of the librational modes of the Mo6S8-units in the crystal.

M$ouml$ssbauer studies of copper manganese alloys with dilute 119Sn

The Mossbauer spectra of 119Sn in face-centred cubic copper manganese alloys containing from 3 at.% to 97 at.% Mn have been obtained at 300 °K, 77 °K and 42 °K, and the appearance of hyperfine fields at 119Sn nuclei as the temperature was reduced has been used to define ordering temperatures. Long range magnetic ordering has been observed in all alloys, the distributions of hyperfine fields and the ordering temperatures reflecting the change in magnetic structure at 75% Mn. The ordering is discussed. The isomer shifts for 119Sn in copper and gamma manganese with respect to white tin were determined as −083 ± 001 mm s−1 and −0.91 ± 0.02 mm s−1 respectively, and the hyperfine field at 119Sn in pure gamma manganese was found by extrapolation to be 255 ± 5 kOe.