Effects of Ag, Ag2O and AgNO3 addition on the superconducting properties of Tl2Ba2CaCu2O8

The effects of 5 wt.% Ag additions in the form of Ag powder, Ag2O and AgNO3 on phase formation and superconductivity of Tl-2212 is reported. Samples were prepared using two different solid state synthesis routes: (a) addition of 5 wt.% Ag to presynthesized (PS) Tl-2212 powder and (b) premixing (PM) of 5 wt.% Ag to unreacted powders with starting composition of Tl2Ba2CaCu2O8. For PS samples, addition of Ag showed little effect on Tc values. For PM samples, addition of Ag in the form of Ag powder and AgNO3 showed a lowering of Tc zero to around 70 K. In the case of Ag2O the deterioration is severe and the sample was not superconducting down to 10 K. X-ray diffraction patterns of PM samples showed existence of Tl-2212 phase and a substantial amount of unreacted Tl2O3. We also report results of microstructural investigations using scanning electron microscope and Vickers Microhardness measurements and their variation with the synthesis methods and the different forms of Ag-additives. The different forms of starting silver give rise to varied Tl-2212 properties and the PS AgNO3 sample showed the best improvement in normal state conductivity compared to metallic silver and silver oxide powders.