Local structure around Gd in GdAl3Cl12 glass and supercooled liquid: a Gd L-III-edge EXAFS study

The coordination environment around Gd3+ ions in GdAl3Cl12 glass and superc ooled liquid has been studied using Gd L-III-edge EXAFS spectroscopy. The G d coordination environment in the glass is found to be similar to that in t he GdAl3Cl12 crystal with eight Cl nearest neighbours and four Al next-near est neighbours. The Gd-CI distance in the glass is the same as that in the crystal (similar to 2.8 Angstrom) although the Gd-Al distance in the glass (similar to 3.85 Angstrom) is longer than that in the crystal (similar to 3 .7 Angstrom), indicating a less dense structure with a larger Gd-Cl-Al bond angle in the former. The Gd-CI distance and coordination number are found to remain unchanged in the supercooled liquid at 60 degrees C. However, the absence of any Gd-Al second-neighbour shell in the EXAFS spectrum of the l iquid indicates substantial increase in static disorder in the spatial disp osition of AlCl4 tetrahedra around Gd in the liquid. Such temperature depen dent structural changes are suggested to be responsible for the marked frag ility of this liquid.