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E. Ingier-Stocka et al. / Journal of Alloys and Compounds 450 (2008) 162–166
From preliminary investigations conducted on the CeBr3–KBr
binary system [33], a similar evolution of the activation energy
is foreseen. On the other hand, the concentration evolution of
EA appears to be intermediate (Fig. 7) in the CeBr3–NaBr sys-
the LaBr3 systems with KBr, RbBr and CsBr, is present in the
CeBr3–NaBr, it is clear that the activation energy behaves differ-
ently from CeBr3–LiBr, as it was also observed for the analogous
LaBr3–NaBr mixture [26]. Finally, Fig. 7 clearly illustrates that
the activation energy increases with the alkali cationic radius
particularly in the MBr-rich (M = Li, Na) melts. It is likely that
this is due to an increase of the LnBr63− complex concentration
in the melt. This observation agrees well with mixing enthalpy
measurements[35], thatalsoshowedthattheformationenthalpy,
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3−
attributed to CeBr6 complex ions, increases with the ionic
radius of the alkali metal cation. The alkali bromides provide
additional bromide ions to enable Ce3+ to expand its coordina-
tion shell. But there is competition between M+ and Ce3+ for Br−
in the ionic environment. The result of this competition depends
on the relative attracting power of the alkali metal ion. The radius
of the alkali metal cation will therefore govern the complex ion
formation in the CeBr3–MBr binary systems. Thus, the presence
of NaBr in mixtures with CeBr3 favors complex ion formation
more than LiBr does and results in a larger enthalpy of formation
and larger activation energy for electrical conductivity.
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Kisza Piechowice, Poland, June 20–25, 2004, p. 170.
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Acknowledgement
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Nucl. Mater. 344 (2005) 115.
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Some of us (E.I-S., S.G. and L.R.) wish to thank the Ecole
Polytechnique de Marseille for hospitality and support during
this work.
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