MICROHARDNESS ANISOTROPY OF BI-2212 CRYSTALS

The microhardness of a high quality Bi-2212 crystal, grown by using th e temperature gradient method, was measured with the direction of the applied force parallel, and perpendicular to the (a,b) crystallographi c plane. The measurement was carried out using a technique which is ca pable to monitor both the applied force, and the displacement of the i ndenter relative to the sample surface. A maximum force of 10 mN was u sed, applied in 20 steps in a square root sequence on a diamond pyrami d 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: You ng's modulus, Poisson's ratio, the yield strength in compression, the elastic recovery rate, and the energy loss during the indentation proc ess. The results show a strong hardness anisotropy between the two dir ections of the applied force: 3.78 GPa for the applied force perpendic ular, and 0.78 GPa for the applied force parallel to the (a,b) crystal lographic plane. (C) 1998 Published by Elsevier Science B.V. All right s reserved.