Photon Factory Activity Report 2005 #23 Part B (2006)
Chemistry

27B/2004G064

XAFS analysis on molten multivalent metal fluorides
Haruaki MATSUURA*1, Sou WATANABE1, Hiroshi AKATSUKA1,Yoshihiro OKAMOTO2, Ashok K. ADYA3
1Res. Lab. for Nucl. Reactors, Tokyo Tech., Ookayama, Meguro-ku, Tokyo, 152-8550, Japan
2Synchr. Rad. Res. Center, JAEA, Tokai-mura, Naka-gun, Ibaraki, 319-1195, Japan
3
Sch. of Contemporary Sci., Univ. Abertay Dundee, DD1 1HG, U. K.

Experimental
Mixtures of chemicals were pre-melted in glassy carbon
crucibles inside a glove box. These reagents were thenmixed with boron nitride matrix powder homogeneously,
and pressed into pellets. A pellet was installed in anelectric furnace located between ionization chambers.
Transmitted XAFS spectra have been collected, using Si(111) double crystal monochromator at Ln-LIII X-ray
absorption edges.
Results and discussion
The inter-ionic distances and coordination numbers
2+3+around MII or MIII ions in pure melts and their mixtureswith alkali metal fluorides are plotted versus the elements
in Figs. 1 (a) and (b), respectively [3]. Figure1 (a)indicates perfectly the “lanthanide contraction”. The2+3+––
nearest-neighbour MII -F and MIII -F distances have
2+values almost similar to the sum of the ionic radii, MII
3+
for 4-coordinated structures, σMII + σF, and MIII for 6coordinated structures, σMIII + σF. Nevertheless, the trends
in the coordination numbers of all the investigatedsystems seem to be much complicated, especially for thelanthanide fluorides and their mixtures (Fig. 1(b)).
Although only heavier rare-earth fluorides’ data for puremelts are available, local minima in the coordination
numbers occur throughout the pure rare-earth fluoride
series. These changes seem to be correlated to the14Users' Reportvariation in crystal structures at high temperatures. In themixtures with alkali metal fluorides, coordination
numbers decrease in mixtures than those in pure melts.
Another observation that can be clearly made is that withdecreasing ionic radius, the coordination number
decreases with the exception of some elements. The
dependencies on the type of alkali metal cannot beobserved clearly in the case of mixtures with MIF. Thus,in the investigated concentration region (0.2 MIF + 0.8MIIIF), the local environment around lanthanide ion isdetermined mainly by their own characteristics, i.e., the3+strong coulombic interactions between MIII and F ,providing an ideal test case to perform MD simulations.
2.6
pure M IIF2 and M IIIF3M IIF2 and M IIIF3 - LiF
M IIF2 and M IIIF3 - NaF
M IIF2 and M IIIF3 - KF

2.5
R2.4
2.3
2.2(a)
Sr Ba Pb La Ce Nd

Sm Eu Gd

Y Dy Ho ErYb Lu876NIntroductionThe available structural data of molten multivalent
metal chlorides along with other relevant information on
thermodynamic,electrochemical,
physico-chemicalproperties, etc. can be used for nuclear engineering
applications based on pyrochemistry. We have alreadysuccessfully evaluated the structures of some molten puremultivalent metal fluorides using X-ray absorption finestructure (XAFS) technique [1], [2]. Following the similar
strategy, local structures of molten multivalent fluorides
in alkali metal fluorides are also expected to be revealedby this technique. In this report, we have summarized thevariation in local structures of molten divalent metal
fluorides MIIF2 (MII = Sr, Ba, Pb), trivalent metal fluorides
MIIIF3 (MIII = Gd, Dy, Ho, Er, Yb, Lu, Y) and their
mixtures with alkali metal fluorides MIF (MI = Li, Na, K;
MII = Sr, Pb; MIII = La, Ce, Nd, Sm, Gd, Dy, Ho, Er, Yb,Lu, Y; the molar ratio MIIF2 or MIIIF3:MIF being 20:80
mole %) around the multivalent metal ions.

5432(b)Sr Ba Pb La Ce Nd Sm Eu Gd

pure M IIF2 and M IIIF3
MII F2 and M IIIF3 - LiF
MII F2 and M IIIF3 - NaF
MII F2 and M IIIF3 - KF
Y Dy Ho ErYb Lu

Fig. 1(a), (b) Interionic distances and coordination
numbers of 1st coordination shell in various molten
fluoride melts.
References[1] S. Watanabe et al., J. Phys. Chem. Solids, 66, 402(2005).
[2] S. Watanabe et al, Electrochemistry, 73, 612 (2005).
[3] S. Watanabe, Ph. D thesis, Tokyo Tech. (2006)*hmatsuur@nr.titech.ac.jp