Local structure and valence of impurity ions in oxides by TDPAC and Mössbauer emission spectroscopy

The features of time-differential perturbed angular correlation (TDPAC) in studies on local chemical structures around impurity atoms are described in comparison with those of Mössbauer emission spectroscopy with four typical examples of recent applications to metal oxide systems, namely,⁹⁹Rh⁹⁹Ru in -Fe₂O₃ and YBa₂Cu₃O_7– and¹¹⁷Cd¹¹⁷In in MO (M=Mn, Co, Ni) and BaRu_2/3Cd_1/3O₃.     

A study of carbonic anhydrase using Mössbauer spectroscopy

The preparation and characterization of an Fe(II) bovine carbonic and human carbonic anhydrase are presented. Results of Mössbauer spectroscopy measurements indicate that the Fe(II) (low spin) is bound at the enzymatically active site. The results are compared with previous studies which had used the technique of perturbed angular correlations of γ-radiation.     

Emission (57Co) Mössbauer spectroscopy as a tool for probing speciation and metabolic transformations of cobalt(II) in bacterial cells

The emission (⁵⁷Co) variant of Mössbauer spectroscopy, rarely used in biology-related studies, was applied to study binding and possible transformations of ⁵⁷Co^II traces in live and dead (hydrothermally treated) cells of the rhizobacterium Azospirillum brasilense (strain Sp7) at T?=?80 K in frozen aqueous suspensions and as their dried residues. The Mössbauer parameters calculated from the spectra were compared with the similarly obtained data reported earlier for another A. brasilense strain, Sp245 (which differs from strain Sp7 by the ecological niche occupied in the rhizosphere and was found earlier to exhibit different metabolic responses under similar environmental conditions). Similarly to strain Sp245, live cells of strain Sp7, rapidly frozen 2 min and 1 h after their contact with ⁵⁷Co²⁺ (measured in frozen suspensions), showed marked differences in their Mössbauer parameters, reflecting metabolic transformations of ⁵⁷Co²⁺ occurring within an hour. However, the parameters for strains Sp7 (this work) and Sp245 (reported earlier), obtained under similar conditions, were found to significantly differ, implying dissimilarity in their metabolic response to Co²⁺. This is in line with their different metabolic responses to several heavy metals, including Co²⁺, detected earlier using Fourier transform infrared spectroscopy.     

Mössbauer spectroscopy as an analytical tool

Mössbauer spectroscopy is a powerful tool in qualitative and quantitative analysis of solid substances containing Mössbauer-active elements. Information either on the bulk sample or on its surface can be obtained.     

Fe- and Cr-substituted mullites: Mössbauer spectroscopy and rietveld structure refinement

Fe-substituted mullite samples Al_4.5-yFe_ySi_1.5O_9.75 (y = 0.25 and 0.50) have been prepared using a sol-gel route involving Si and Al alkoxides and iron nitrate as precursors. Mössbauer spectroscopy reveals the presence of three different Fe(III) sites but does not allow to conclude concerning the ion environments, tetrahedral or octahedral. Rietveld refinements reveal that Fe ions are distributed between octahedral and tetrahedral positions, the proportion of octahedral iron increasing from y = 0.25 to y = 0.50. On the other hand, for Cr-substituted mullite, Cr ions arc mainly located on octahedral positions. This difference between Fe and Cr has been attributed to the fact that Cr shows a clear trend to occupy octahedral sites compared to Fc and that it is incorporated inside the mullite structure only at high temperature.     

Characterization of iron promoter in tungstated zirconia catalysts by Mössbauer spectroscopy at very low temperatures

A tungstated zirconia (WZ) catalyst with iron promoter used for the conversion of n-pentane into isopentane has been characterized by M?ssbauer spectroscopy. The M?ssbauer spectra have been recorded in zero magnetic field in the temperature range 0.05-295 K and with a magnetic field up to 7 T between 4.2 and 50 K. Both the recording of M?ssbauer spectra with an applied magnetic field and at extremely low temperature allowed for the demonstration that iron is present in the catalysts as (i) hematite (alpha-Fe2O3) particles a few 10 nm in size, (ii) very small oligomeric Fe(III) species, probably in solid solution in zirconia, and (iii) Fe(III) oxide clusters showing magnetic ordering, probably embedded in the first surface layer and thus forming "rafts". These latter clusters form two ensembles with quite different sizes: one with diameters of about 3 nm, the other with diameters larger than 30 nm. These results are in agreement with those recently obtained by X-ray absorption spectroscopy and electron paramagnetic resonance.     

Development and application of parallel-plate avalanche counter for in-beam Mössbauer spectroscopy

For Mössbauer -rays in the in-beam Mössbauer experiments using various beams such as heavy ion, secondary short-lived isotope, and neutron beams, it is important to develop a detector. A parallel-plate avalanche counter (PPAC) is the most suitable gas counter for on-line measurements, because PPAC collects the internal conversion electrons emitted by the Mössbauer effect even under high -background. We evaluated the influences of the pressure and flow rate of the counter gas against the counting efficiency of PPAC, and determined the optimum conditions for use in the in-beam Mössbauer experiments.     

The Mössbauer effect in hexafluorostannates

Journal of Structural Chemistry -     

Mössbauer effect in dehydrated nitroprussides

Mössbauer spectra were obtained for hydrated and dehydrated sodium, potassium, lithium, cobalt, cadmium, nickel, zinc, manganese and ferrous nitroprussides. All spectra except for ferrous nitroprusside consisted of two dips separated by an amount ranging from about 1.7 to 1.9 mm/sec. In most cases the isomer shift decreased and the quadrupole splitting increased after the compound was dehydrated. The spectrum of ⁵⁷Fe-enriched ferrous nitroprusside contained eight dips. Linear bridging from the nitroprusside anion to the iron cation is a possible explanation for the complicated spectrum.     

Mössbauer spectroscopy of liquid SnCl4 solutions trapped in a rigid microemulsion

A rigid microemulsion was prepared containing submicroscopic droplets of liquid aqueous tin tetrachloride solution. Recoilless-ray resonance absorption (the Mössbauer effect] was achieved in this system, indicating that the organic dispersion medium of the microemulsion behaved as a carrier, enhancing the Debye-Waller factor for the quasiliquid phase of the system. The Mössbauer spectra reflected the presence of two types of tin(IV) in the cavities of the microemulsion: SnCl₄ species situated in the bulk solution and on the cavity wall, respectively.     

M?ssbauer spectroscopy and structural analysis of solids

Mössbauer spectroscopy is reviewed as a method of analysis of hyperfine interactions in the solid state. It is sensitive both to the atomic scale and to phase structures. It utilizes the interactions between the hyperfine fields and nuclei in solids measured by a nuclear technique. The importance of various Mössbauer isotopes is discussed, the ⁵⁷Fe being still the most important. Principles of the qualitative determination of the structure sites and/or phase attachment are explained on the basis of the measurement of hyperfine structure parameters (i.e. the isomer (chemical) shift, the quadrupole and magnetic splittings). The role of the hyperfine field distribution determination is stressed, especially the magnetic hyperfine induction distribution in magnetically ordered solids. Conditions are explained for the feasibility of quantitative estimations of site occupancy and phase abundance. With respect to the predominant role of the magnetic hyperfine structure predestinating Mössbauer spectroscopy to be considered simultaneously as a special magnetic measuring technique, examples are chosen from the field of new magnetic materials. For the substituted hexagonal (M-type) ferrites (aimed, e.g., for the perpendicular magnetic recording), Mössbauer determination of the cation site occupancy is discussed. Structural changes in ion implanted Fe-B-based amorphous alloys detected by the hyperfine field distribution are shown. For the magnetically extremely soft FeCuNbSiB alloys, produced by the controlled crystallization of an amorphous ribbon, the estimation of their rather complicated phase composition by the Mössbauer phase analysis is demonstrated.Common enterprise of the Department of Low Temperature Physics with the Institute of Physics and Institute of Inorganic Chemistry, Czech Academy of Sciences, Prague     

Ti and Fe speciation by X-ray photoelectron spectroscopy(XPS) and Mössbauer spectroscopy for a full crystal chemical characterisation of Ti-garnets from Colli Albani (Italy)

Different analytical and structural methods (Electron Probe Micro-Analysis, Single Crystal X-ray diffraction, X-ray Photoelectron Spectroscopy, M?ssbauer spectroscopy) were combined to fully characterise the crystal chemistry of natural Ti-bearing garnets from Colli Albani (Lazio, Italy). The study of the relevant complex crystal chemistry ( large number of cation substitutions affecting the three independent X(8-fold), Y(6-fold) and Z(4-fold) crystallographic sites and Fe and Ti transition elements exhibiting several oxidation states and coordination environments) benefited from the multi-technique approach. Electron probe microanalysis provided elemental composition of the analysed samples, which have low Ti-content (TiO2 in the range 1.99 - 3.48 wt %) and slightly different Fe/Al ratios. For all samples, two doublets were fitted to room temperature M?ssbauer spectra and assigned to Fe3+(Y) (approximately 95%) and Fe2+(X) (approximately 5%). Up to three doublets (Ti3+(Y), Ti4+(Y), Ti4+(Z)) were fitted to XPS spectra and yielded direct evaluation of Ti site population. XPS technique confirmed its potential for the study of speciation of Ti in minerals.     

Investigation on the magnetic and Mössbauer spectroscopy of 57Fe doped LiMnPO4

Journal of Radioanalytical and Nuclear Chemistry - The 57Fe doped LiMnPO4 cathode with potential applications in Li-ion batteries was prepared by solid-state reaction. The magnetic susceptibility...     

Mössbauer effect in dehydrated sodium nitroprusside

Mössbauer spectra were obtained for hydrated and dehydrated sodium nitroprusside absorbers at room and lower temperatures. Some of the absorbers were heated at temperatures between 82 and 186°C for various lengths of time before the spectra were taken. The largest changes in the isomer shift and quadrupole splitting were noted after the absorbers had been heated to temperatures above 100°C.     

Applications of Mössbauer spectroscopy to the study of electronic materials

A brief introduction to the methodology of the Mössbauer spectroscopy will be given. The main applications to the study of the intrinsic properties of the materials employed in the electronic technology are reviewed.The reported examples prove the effectiveness of this techniques in the study of semiconducting and magnetic materials.Evidence will be given also to the studies of preparation processes of crystalline and amorphous compound.