Mossbauer temperature coefficients

Mossbauer spectroscopy is the study of recoilless resonant fluorescence " Sn Mossbauer spectroscopy has been found to be a most usefifl method for studying the bonding and stereochemistry of tin compounds in the solid state. The two most important parameters are the isomer shift (5, mm s ) and the quadrupole sphtting (A q, nuns ), although the recoil-free fractions and temperature coefficients can also supply useful structural indications. 

Mossbauer spectroscopy has proved to be of great value in inorganic tin chemistry (Table 6). Particularly useful have been isomer shift (5) and quadrupole splitting (A) data. The recoil-free fraction and its temperature coefficient are other parameters that have found use in structural elucidations variable temperature Mossbauer studies can be used, for example, in gaining information regarding the degree of aggregation in solid tin compounds. 

With the observed temperature shift data for (dSldT)p and calculated (within the framework of the Debye model) numbers for the temperature shift of SOD and with the known thermal expansion coefficient as well as results from Ta Mossbauer experiments under pressure, the authors [191] were able to evaluate the true temperature dependence of the isomer shift, (dSisIdT) as —33 10 " and —26 10 " mm s degree for Ta and W host metal, respectively. 

Oxidation State Formal Valence EPR g Values (Temperature) Mossbauer Isomer Shift, 8 (mm/s) Cx (nm), (Extinction Coefficient, xl0 3, per Fe)... 

In solution, the complexes behave like type II mixed-valence compounds in the Robin-Day scheme (136). At room temperature, a near-IR feature at —1300 nm can be found and assigned as an intervalence change-transfer band. The extinction coefficient of this band varies from 200 to 700 Af" cm depending on the nature of X and may relate to the barrier for valence detrapping. Mossbauer spectra of the BPMP, BIMP, and HXTA complexes indicate valence trapped species at temperatures below 100 K where quad-rupole doublets due to the Fe(III) and the Fe(II) centers are observed. While the BPMP complex remains valence trapped in the crystalline state even at room temperature (134), valence detrapping is observed for the BIMP complex above 100 K (65) such behavior is believed to be related to the solid-state mobility of the counterions. 

Due to the improved statistics, an increase in the linewidth of this single line could be observed for higher target temperatures. This line broadening was analyzed in terms of a diffusional motion of the iron atoms, which are able to make atomic jumps within the lifetime of the excited nuclear state. Diffusion coefficients were derived (Fig. 6.13) from the broadening of the Mossbauer lines, and these were found to be remarkably consistent with the known high- and low-temperature diffusion coefiicients of Fe in Si. 

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