Quadrupole splitting temperature variation

As expected for a material with cubic sites, the RT spectrum of stoichiometric wiis-tite consists of a single line. The spectrum of the non-stoichiometric material shows an asymmetrically broadened doublet with contributions from Fe " resonance and from two quadrupole split Fe" doublets. The component peaks which contribute to this spectrum have not been fully resolved owing to the range of Fe" environments in the structure (i. e. the variation in Fe content and vacancy level). At 77 K the Mossbauer spectrum consists of a broad doublet with contributions from Fe" and Fe ". Fe(OH)2 shows a sextet corresponding to a Bhf of 16.6 T at 20 K (Miyamoto, 1976 Genin et al. 1986) and to -20 Tat 4K (Refait et al. 1999). The Tn is at 34 K (Miyamoto et al., 1967). The spectrum of high pressure FeOOH at room temperature consists of a sextet (Peret et al. 1973). 

Doublet 1 may be assigned unambiguous to P4 symmetry, since the hyperfme parameters follow the expected behaviour for Fe in a relatively undistorted tetrahedral site. The high value of quadrupole splitting indicates a high valence contribution, and displays the expected temperature variation for tetrahedral environments bb 1968). The characteristic Mossbauer temperature 0m is in the range expected for Fe (De Grave and Van Alboom 1991). 

Pol shin et al. (1972a,b) were the first to study the temperature variation of quadrupole splitting in biotite, followed by Annersten (1974), Royer (1991) and Christie et al. (1992a,b). Christie et al. (1992a) examined the magnetically ordered ground state of synthetic annite at Tc 58K. Other Mossbauer spectra of trioctahedral micas are reported... 

A more cursory examination of 24 of these tris-(N,N-disubstituted dithiocarbamato)iron(III) complexes showed no significant variation in the chemical isomer shift which was recorded as 0-38 mm s at room temperature [18]. A significant variation was found in the quadrupole splitting despite the distance of the substituent groups from the central iron atom, and correlation with the structural type of ligand was attempted. In general the experimental parameters were similar to those listed in Table 8.2 from other workers, and are therefore not given. 

The results of thermal treatment of FeO to give Fe and Fe304 have been followed in the MSssbauer spectrum [23]. In some cases there was an apparent reduction in the quadrupole splitting of a sample which had been heated, and magnetic splitting appeared above the bulk FeO Curie temperature. The Zeeman lines were generally smeared out into a broad envelope. One possible explanation for this is that the microscopic variations in the site symmetry cause large variations in the orbital and dipolar contributions to the internal... 

Cl and Cl quadrupole splittings. The splitting was found to depend strongly on sample composition, being especially large at the lowest water contents, but to remain unchanged at temperature variations. 

Fig. 6 Temperature variation of the ratio /A of the inner to the outer quadrupole NMR splittings shown in the spectrum of Fig. 5 (9DDA9-d2o in the...

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