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Ch. Ladany, E. Gratz, A. Lindbaum, H. Nowotny:
"Thermal Expansion of RCu₂";
Poster: 52. Jahrestagung der ÖPG, Leoben; 23.09.2002 - 26.09.2002.

The intermetallic RCu2 (R=rare earth and Y) compounds crystallize in the orthorhombic CeCu2 type structure.
The thermal expansion of these compounds has been measured using a Siemens D500 diffractometer equipped with a He-flow cryostat. We are presenting the volume thermal expansion (_V/V vs T) and the temperature variation of the normalized lattice parameters (_a/a, _b/b and _c/c) in the range from 4.2 K up to 300 K. Among the compounds selected for the presentation are compounds showing magnetic ordering (GdCu2:TN=42 K and EuCu2:TN=25 K). In these cases it will be shown, that there is a pronounced discontinuity in a(T), b(T), and c(T) at the corresponding TN, whereas in _V/V there is no anomaly visible.
Thermal expansion of two RCu2 compounds are included in the discussion which are known for the intermediate valence state of the R-ions (Eu and Yb), i. e. in both compounds the R-ion is not in the 3+ state as all the other R-ions in RCu2. It has been found, that for these compounds _V/V is much larger than that observed for YCu2 and LuCu2 (nonmagnetic references) where the Y and Lu ions are in the 3+ state. As a general tendency found for all the compounds investigated, we observed _a/a < _c/c < _b/b. Qualitative arguments will be given how this can be understood. These results are closely related to another poster presented at the ÖPG-meeting 2002 which is entitled ?Lattice Dynamics in YCu2?.