Characterization Mossbauer effect

In conclusion, Mossbauer spectroscopy has matured into one of the classical techniques for catalyst characterization, although its application is limited to a relatively small number of elements which exhibit the Mossbauer effect. The technique is used to identify phases, determine oxidation states, and to follow the... 

Mossbauer spectroscopy of the 57Fe nucleus has been extensively used to investigate aspects of spin equilibria in the solid state and in frozen solutions. A rigid medium is of course required in order to achieve the Mossbauer effect. The dynamics of spin equilibria can be investigated by the Mossbauer experiment because the lifetime of the excited state of the 57Fe nucleus which is involved in the emission and absorption of the y radiation is 1 x 10 7 second. This is just of the order of the lifetimes of the spin states of iron complexes involved in spin equilibria. Furthermore, the Mossbauer spectra of high-spin and low-spin complexes are characterized by different isomer shifts and quad-rupole coupling constants. Consequently, the Mossbauer spectrum can be used to classify the dynamic properties of a spin-equilibrium iron complex. 

Mossbauer spectroscopy has matured into one of the classical techniques for catalyst characterization, although its application is limited to a relatively small number of elements which exhibit the Mossbauer effect. The technique is used to identify phases, determine oxidation states, and to follow the kinetics of bulk reactions. Mossbauer spectra of super-paramagnetic iron particles in applied magnetic fields can be used to determine particle sizes. In favorable cases, the technique also provides information on the structure of catalysts. The great advantage of Mossbauer spectroscopy is that its high-energy photons can visualize the insides of reactors in order to reveal information on catalysts under in-situ conditions. 

Application of the Mossbauer effect, which is essentially a bulk phenomenon, to the study of surfaces has received significant attention in recent years. The usefulness of this technique lies in its ability to determine the electronic environment and symmetry of the surface nucleus, and it offers a method of investigation that is clearly complementary to other physical methods for the characterization of solid surfaces. Mossbauer spectroscopy has the attractive advantage that it may be used at a variety of pressures and can be applied to the study of heterogeneous catalysis and adsorption processes to probe the nature of the solid surface and its electronic modification when holding adsorbed species. 

Mossbauer effect was first reported by Rudolph Mossbauer in 1958. Three years later, he won the Nobel Prize with his discovery. Since then, it is believed that nuclear y-ray emission and absorption process can take place in recoil-free fashion. In reality, of course we have both recoil and recoil-free events. Mossbauer also utilized the Doppler (velocity) shift to modulate the y-ray energy so that Mossbauer effect could be developed into a spectroscope for material characterization. The emission of y-rays with natural or nearly natural line width allows for observing in the y-ray spectra the interaction between the nucleus and its atom in solids and viscous liquids. 

The Mossbauer effect has been used as an analytical tool to characterize the diffrent iron-bearing minerals in coal. It has been pointed out that by the use of low-temperature measurements (in the presence of a large external magnetic field) and treatment of the coal samples, all the iron-bearing minerals can be identified correctly. The use of Mossbauer spectroscopy as a quantitative analytical tool presents several experimental difficulties. It is recommended that this spectroscopy be used as a complement to and not as a substitute for the standard techniques. 

In this article we will discuss the electronic states that are responsible for the features observed in ESR and Mossbauer effect spectroscopy of the iron transport materials. These electronic states are parameterized by a set of coupling constants which also characterize a class of materials, but we then are making comparisons between the electronic states of molecules rather than between the spectral features. If one knows the electronic state, then predictions of other phenomena can be made. If one merely knows the spectral features, then at best one can only classify the compound. 

Various types of physical probes have been employed in our studies of platinum-iridium clusters. The probes include X-ray diffraction, extended X-ray absorption fine structure (EXAFS), and Mossbauer effect spectroscopy. All of the probes have provided useful information for the characterization of the bimetallic clusters. 

Mossbauer Effect Spectroscopy Studies (41). Another physical probe which has been used in the characterization of platinum-iridium catalysts is Mossbauer effect spectroscopy (3,4), 52). It can be applied to catalysts in which virtually all of the metal atoms are surface atoms. In Mossbauer effect spectroscopy one is concerned with a transition between a ground state and an excited state of a nucleus (53). 

For FeTi(S04)s (Fe l Fe3+)(Fe +TitlJ(SO -)3, the studies on a number of naturally occurring silicate materials allow for a determination of the distribution of Fe environments in the material, including the relative proportions of different Fe oxidation states. The naturally occurring glassy silicate materials called tektites are characterized by very low concentrations of Fe + ions and very low water content. Mossbauer effect spectroscopy is a convenient way of observing the Fe states in tektites. Components of the... 

The samples were characterized by X-ray fluorescence spectroscopy (XRFS), X-ray powder dififiaction (XRD), scanning electron microscopy(SEM) and Mossbauer effect spectroscopy(MES). For MES measurements the Co in chromium matrix was served as the source. Isomeric shift values were given in relation to metallic iron. Spectra were computer-fitted and Mossbauer parameters were calculated. 

The fundamentals of SSS are based on the theory of impurity centers in a crystal. The optical spectrum of an organic molecule embedded in a matrix is defined by electron-vibrational interaction with intramolecular vibrations (vibronic coupling) and interaction with vibrations of the solvent (electron-phonon coupling). Each vibronic band consists of a narrow zero-phonon line (ZPL) and a relatively broad phonon wing (PW). ZPL corresponds to a molecular transition with no change in the number of phonons in the matrix (an optical analogy of the resonance -line in the Mossbauer effect). PW is determined by a transition which is accompanied by creation or annihilation of matrix phonons. The relative distribution of the integrated intensity of a band between ZPL and PW is characterized by the Debye-Waller factor ... 

The various hyperfine interactions described in the preceding sections have been considered in relation to the parameters characterizing the steady-state or Mossbauer effect spectra. On the other hand, when the dynamical properties of... 

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