Structural and electrical properties of fluorine doped (Bi, Pb)-1212 ceramics

In the aim to test the effect of fluorine doping on structural and electrical properties of semiconducting Bi(Pb)-1212 phase, bulk samples with nominal composition of Bi0.4Pb0.35Sr2Y0.8Ca0.2Cu2.05O (y) F (x) with x=0,0.2,0.4 and 0.6 are prepared in air by solid state reaction method and characterized. Similarly to other Bi-based cuprates, the scanning electron microscopy shows that fluorine doping increases the grain size of the samples. The obtained X-ray diffraction patterns are indexed in P4/mmm space group. A slight increase of cell volume by doping is revealed, a result which is in line with that seen in Y-123 compounds. Even if the resistivity decreases with fluorine content, all compounds exhibit a semiconducting behavior. The conduction mechanism obeys well to the two dimensional variable range hopping (2D-VRH) model from room temperature down to approximately 40 K. The analysis of the fitting results suggests that the improvement of electrical conduction could be due to a delocalization of charge carriers.