HARDNESS ANISOTROPY IN BI-SR-CA-CU-O

Microhardness measurements with a Knoop indenter have been carried out on (001) surfaces of Bi2Sr2CaCu2O8. They show an anisotropy of betwee n 0.8 and 2.5 GPa. Indentations along the hard orientation have long a nd short diagonals in the ideal ratio of 7.11, but for one along a sof t orientation the ratio can drop as low as 4. The log-log plot of long diagonal length against the load is linear, with a slope of 2. These observations indicate extreme ease of plastic flow in the high-T(c) su perconducting material.