E0345

ELASTIC PROPERTIES OF SELECTED MINERALS AND DECAGONAL QUASICRYSTALS AT HIGH TEMPERATURES APPLICATIONS OF THE RPR-METHOD Jurgen Schreuer & Walter Steurer Laboratory of Crystallography, ETH Zentrum, CH-8092 Zurich, Switzerland.

The elastic constants and their temperature derivatives of orthorhombic cordierite, monoclinic sanidine, triclinic CuSO₄*5H₂O and a decagonal quasicrystal of the Al-Co-Ni-system will be presented. The examples demonstrate the potential of resonant ultrasound spectroscopy.

Due to their close relationship with many physical properties the elastic constants play a key role for the structural interpretation of physical properties. They can be either used to scrutinize and improve existing models for the atomic interaction potentials or, following the quasi inverse way, to obtain information on the bonding system of an unknown crystal. Especially in the case of decagonal quasicrystals where the axial structure allows an anisotropic elasticity tensor in contrast to the situation found in icosahedral quasicrystals [1] the experimental study of their elastic behaviour contributes to the understanding of their atomic configuration.

Furthermore elastic constants represent not only a highly sensitive probe for the detection of phase transitions but their anomalies offer valubale hints on the driving mechanisms of certain phase transitions.

Our experimental setup is based on the RPR-method introduced by Ohno [2], where the elastic constants are derived from an experimentally measured ultrasonic resonance spectrum of a free vibrating crystal prepared as a rectangular parallelepiped. This relatively new powerful technique is particularly suited for the study of elastic properties at elevated temperatures, because no medium is required for transducer-sample coupling. Further advantages are the small sample size and the short data acquisition time.

[1] Spoor, P.S.; Maynard, J.D.; Kortan, A.R.: Phys. Rev. Letters 75 (1995), 3462-3465.

[2] Ohno, I.: J. Phys. Earth 24 (1976), 355-379.