EXAFS study of phase transitions in KIO₃

Abstract

The iodine K-edge EXAFS study of KIO3 was performed to clarify local structural changes on the successive phase transitions. The pair-distribution function of three oxygen atoms in an oxygen octahedron is almost independent on temperature like a covalent bond, whereas that of the other three is gradually reduced with increasing temperature like an ionic bond. The result indicates that iodine and oxygen atoms exist as an IO3- molecule in a pseudo-perovskite-type structure. The anomalous behavior in the Debye-Waller factor for the latter pair-distribution function appears around 50 K, which is associated with the orientational glass transition.

Iodine valence and local environments in borosilicate waste glasses using X-ray absorption spectroscopy

“…4a, 5a, and 5b). The structural parameters determined from the fitting (Tables 2 and 3) show close agreement with respect to crystal structure determinations and earlier EXAFS findings for the iodates [13,[16][17][18], reasonably good agreement for I 2 and CaI 2 Á4(H 2 O) [15,23], and not as good agreement for the nearest-neighbor coordination number for KI [21]. The EXAFS signal from I-I second nearest-neighbors in the KI structure was strong enough to be seen near 4.8 Å in the KI RDF (Fig.…”

“…A number of earlier studies used XAS to characterize iodine in a wide variety of samples [4][5][6][7][8][9][10][11][12][13], including iodine sorption in cement materials [4], iodine in LAW borosilicate glass [5], as well as iodine in spent solvent from nuclear fuel reprocessing [10]. The XAS studies of iodide (I À ) and iodate (IO 3 À ) sorption in hardened cement paste (HCP) and calcium silicate hydrate (CSH) materials [4] as well as iodine in borosilicate glass [5] are of particular interest because of the general chemical similarity of those materials to the glasses investigated here.…”

Incorporation Modes of Iodate in Calcite

“…In addition to the EXAFS spectra collected at 8 K for NaIO 3 , Ca­(IO 3 ) 2 , and KIO 3 , data for NaIO 3 and Ca­(IO 3 ) 2 ·H 2 O obtained at 77 K by Laurencin et al . and data for KIO 3 collected at 10, 100, and 200 K by Yagi et al were also included in the comparison (Figure ). Two main discrepancies were observed.…”

“…Experimental and calculated I K-edge EXAFS spectra (left; Δ E 0 = 7 eV) and corresponding Fourier transform magnitudes (right; Hanning window, d k = 1 Å –1 ) for I in NaIO 3 (top; 3.5 Å –1 ≤ k ≤ 14.7 Å –1 ), Ca­(IO 3 ) 2 ·nH 2 O ( n = 0 or 1; middle; 3.5 Å –1 ≤ k ≤ 14.7 Å –1 ), and KIO 3 (bottom; 3.0 Å –1 ≤ k ≤ 14.0 Å –1 ) for temperatures ranging from 8 to 200 K. EXAFS data collected in this work at 8 K were complemented by data from Laurencin et al and Yagi et al …”

“…Simulated EXAFS spectra of four standard iodate compounds at various temperatures were compared to experiment to evaluate the simulation approach, develop an understanding of the effect of temperature on the EXAFS spectra, and determine how the local environment around IO 3 − might influence the EXAFS spectra. In addition to the EXAFS spectra collected at 8 K for NaIO 3 , Ca(IO 3 ) 2 , and KIO 3 , data for NaIO 3 and Ca(IO 3 ) 2 •H 2 O obtained at 77 K by Laurencin et al 36 and data for KIO 3 collected at 10, 100, and 200 K by Yagi et al 37 were also included in the comparison (Figure 4). Two main discrepancies were observed.…”