Superconductor-metal-insulator crossover in Bi1.7Pb0.4Sr2-xCexCa1.1Cu2.1O8+δ (0.2 ≤ x ≤ 0.6) sintered between 845 deg. C ≤ Ts ≤ 865 oC

Systematic substitutional studies in Bi1.7Pb0.4Sr2-xCexCa1.1Cu2.1O8+δ were carried out by varying the Ce content (0.2 ≤ x ≤ 0.6) and sintering temperature (845 deg. C ≤ Ts ≤ 865 deg. C) to determine the effects of rare earth doping and sintering temperature (TS) on their structural and transport properties. Under the preparative conditions employed, X-ray diffraction studies indicate solid solubility of Ce in the (Bi,Pb)-2212 matrix up to x = 0.6 while the resistivity studies show that superconductor to insulator, insulator to metal and metal to insulator transitions can be realized in the (Bi,Pb)-2212 system by a suitable tuning of temperature, Ce content and TS. The analysis reveals that for each TS, the carrier concentration of (Bi,Pb)-2212 changes progressively with Ce content from the overdoped to the underdoped region and the consequent hole filling leads to decrease in TC and suppression in superconductivity. It is identified that disorder leads to localization of existing carriers and the electronic conduction takes place through thermal activation, variable range and multiphonon hopping at various temperature regimes. The related physical parameters have been evaluated and discussed in detail.