Spin and Valence States of Iron in Silicate Postperovskite

4 Spin and Valence States of Iron in Silicate Postperovskite 

Fe enters the sites through charge-coupled substitution, which is also suggested by theoretical calculations. Because the ionic radius of the iow-spin Fe is smaller than that of the high-spin Fe. the low-spin Fe is thus more stable in the smaller octahedral site in postperovskite. SMS studies also show an increase in the Fe abundance with the presence of the kinked structures in postperovskite [59,60], Based on a small negative CS with respect to a-Fe and no QS in the SMS spectrum, a metallic iron phase is proposed to coexist with the Fe +-rich postperovskite. The formation of metallic iron 

The notable difference between the Mossbauer parameters of the perovskite and postperovskite phases is that the QS of the low-spin Fe site is much smaller in postperovskite (Tables 2.1 and 2.2 Figs. 2.7 and 2.9). The smaller QS of the low-spin site in postperovskite can be explained by a less distorted octahedral site, since distortion from a cubic environment around the iron nucleus results in an increased QS value [62]. Since postperovskite is the high-pressure polymorph of perovskite, the QS of Fe in postperovskite could be similar or related to that of Fe in perovskite 

TABLE 2.2 List of Experimental Mossbauer Spectroscopic Results on the Spin and Valence States of Iron in Postperovskite  

Composition, Pressure Range Valence State Suggested Spin State QS (mm s ) CS (mm s ) Reference 

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