Ultrasonic Study of the Elastic Behaviour of Zone Refined Single Crystalline Rhodium

Abstract
We report on temperature dependent sound velocity measurements performed below ambient temperature on a rhodium single-crystal of exceptional high purity of about 99.999%. In particular, the excellent acoustic quality of the sample permits a quite accurate determination of the elastic moduli for a sound frequency covering the range between 20 and 150 MHz. Primarily our investigations concentrate on the role of the electrons in single-crysalline rhodium which band structure, as speculated, causes a considerable elastic anisotropy and therefore gives rise also to the peculiar mechanical properties commonly known from the poly-crystalline material. A comparative analysis of al1 stiffness coefficients based on our sound data reveals a strong shear rigidity indicating quite angular dependent crystal forces, which are indeed not reminiscent of ordinary metals. Also the temperature dependence studied in detail equally points out that the electronic band structure of rhodium has to be taken into account for a satisfactory description of the elastic behaviour and cannot be treated properly within the free electron model.