Vickers microhardness measurements and investigation of some physical properties of lutetium (Lu) doped Bi-2212 superconductor

Lutetium (Lu) added Bi2Sr2CaLuxCu2O8 superconducting samples, with x=0.0, 0.1, 0.3, 0.5, 0.7 and1.0 were prepared by solid state reaction method on a form of rectangular bar, annealed at 840°C for50 hours. Both the heating and cooling rates of the furnace were adjusted to be 5°C/min and 3° C/minrespectively.. To comparison, undoped sample was prepared in the same annealing conditions. Theprepared samples were characterized using X-ray powder diffraction (XRD), scanning electronmicroscope (SEM), energy dispersive spectroscopy (EDS), resistivity measurements (?-T) andmicrohardness measurements (Hv). The volume fraction and lattice parameters were determined fromthe XRD measurements. The microstructure, surface morphology and element composition analysesof the samples were carried out by SEM and EDS measurements, respectively. Moreover, Zeroresistivity transition temperatures (Tc) of the samples were estimated from the dc resistivitymeasurements. Mechanical characterizations of the samples were determined from the roomtemperature microhardness measurements at different loads (0.25?3N). According to results of thesemeasurements; lattice parameter c and volume fraction of Bi-2212 phase decreased with increasing Lucontent. SEM measurements show that the surface morphology and grain connectivity were obtainedto degrade with increasing Lu content. The EDS results reveal that the elements used for thepreparation of samples distribute homogeneously and the Lu atoms enter into the crystal structure byreplacing Sr and small partly Ca atoms. It is found that Tconset values were obtained to decrease from99.5K to 93K with increasing the Lu addition. The microhardness values of the samples were found tobe load dependent. The load dependent microhardness values of the samples increased with increasingLu addition. In addition we calculated the load independent microhardness, elastic modulus, yieldstrength, and fracture toughness of the samples using the different models. The experimentalmicrohardness results were analyzed using Meyer?s law, elastic/plastic deformation model (EPD),proportional specimen resistance model (PSR), modified proportional specimen resistance model(MPSR) and Hays-Kendall approach (HK). As a result, when all the above mentioned models areapplied to the samples, HK approach best explains the indentation size effect (ISE) behavior of oursamples.In this thesis, the possible reasons for the obtained degradation in microstructural, superconductingand mechanical properties were also discussed in detail.