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We report ultrasonic and thermal expansion measurements on quasi-one-dimensional (TaSe 4 ) 2 I. The elastic constant C 44 exhibits strong anomalies over a wide temperature range around the Peierls transition. Anisotropic behaviour of the slow shear mode C 44 propagating along and perpendicular to the chain direction is observed around T P . Elastic constants, like electrical resistance, are very sensitive to a small Nb content substituted for Ta. Anomalous behaviour of C 44 at low temperatures is reported. We also present measurements of the anisotropic thermal expansion coefficients.

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We present data of the elastic properties of the Laves phase compound CeRu2 in the normal and superconchtcting state obtained from ultrasound measurements. In the temperature range between the superconducting transition temperature of 6.1 K and 300 K we used a deJormation potential coupling approach to describe the temperature dependence oJ" the elastic constants. The elastic anomalies in the superconducting state are characterised with the model of thermally assisted Jlux flow ( TAFF). This enables us to construct a detailed superconducting B-T phase diagram inchtding the vortex dynamics and interpret the peak effect region. Especially the ultrasonic measurements exhibit clearly the connection between the normal state and the superconducting properties. They show that structural fluctuations have strong effects on the superconductivity and on the vortex dynamics.