PHASE TRANSITION OF CeAuGe UNDER PRESSURE. U. Schwarz and R. Pöttgen. MPI für Festkörperforschung, Heisenbergstr. 1, 70569 Stuttgart, Germany.

We have characterized the pressure induced structural phase transition of CeAuGe from a layer type structure at ambient pressure into a high pressure polymorph with a three dimensional anion framework by means of full profile refinement of x-ray powder data.

A large number of binary intermetallic phases REM₂ (RE = rare earth metal; M = Cu, Ag, Au, Ga) crystallize in AlB₂ varieties. Ternary phases like REAuGe (RE = Sc, Ce, Lu) form closely related crystal structures. Substituting the rare-earth metal causes a change of the [AuGe] polyanions from two dimensional fragments in CeAuGe to a three dimensional network in ScAuGe [1]. Hydrostatic pressures induce similar changes of the gallium framework in binary REGa₂ compounds. Thus, the investigation of the ternary intermetallic compound CeAuGe is performed in order to compare the effects of pressure on the chemical bonding in these two classes of compounds.

At ambient pressure CeAuGe crystallizes in the NdPtSb type structure (ordered CaIn₂ variety, P6₃mc, no. 186) [2]. At a pressure of 9(1) GPa we observe a structural phase transition and data sets of the high pressure modification can be indexed and refined assuming an orthorhombic TiNiSi type (Pnma, no. 62) crystal structure. Calculation of the Au-Ge bond lengths reveal that the phase transformation is associated with a change of the anion coordination from trigonal to distorted tetrahedral.

[1] R. Pöttgen et al., J. Alloys Comp., in press.

[2] R. Pöttgen et al., J. Magn. Magn. Mat. 152 (1996) 196.