Microhardness anisotropy of Bi-2212 crystals

The microhardness of a high quality Bi-2212 crystal, grown by using the temperature gradient method, was measured with the direction of the applied force parallel, and perpendicular to the (a,b) crystallographic plane. The measurement was carried out using a technique which is capable to monitor both the applied force, and the displacement of the indenter relative to the sample surface. A maximum force of 10 mN was used, applied in 20 steps in a square root sequence on a diamond pyramid indenter, having a tip radius of 1 mu m From the load-unload cycle, a number of physical parameters of the Bi-2212 phase were deduced: Young's modulus, Poisson's ratio, the yield strength in compression, the elastic recovery rate, and the energy loss during the indentation process. The results show a strong hardness anisotropy between the two directions of the applied force: 3.78 GPa for the applied force perpendicular, and 0.78 GPa for the applied force parallel to the (a,b) crystallographic plane. (C) 1998 Published by Elsevier Science B.V. All rights reserved.