Microhardness studies on BiCaSrCuO (2122) superconducting single crystals and pellets

Microhardness studies are made on single crystal of Bi₂CaSr₂Cu₂O_8+σ (BISCCO) and polycrystalline pellets of BISCCO containing different concentrations of impurity lead (Pb). Optical photomicrographs of single crystals and pellets are taken. The cleavage steps confirm the single crystalline nature of crystals whereas those of pellets show that they contain pores. XRD results confirm that the major phase is (2122). The load vs. hardness data show that the hardness has higher value at lower loads and decreases with increase in load upto 0.04 kg and remains almost the same thereafter. Increase in concentration of Pb also decreases the value of hardness. Temperature measurements indicate that the hardness decreases with increase in temperature (77 to 300 K) with no abnormality near the transition temperature. The results are explained in terms of intrinsic bond strength.