Electrical transport and small polaron hopping conduction in Mn-doped Bi3PbSr3Ca3Cu4-mMnmOx glasses: precursors for high temperature superconductors

Multicomponent Bi3PbSr3Ca3Cu4-mMnmOx (m = 0, 0.02, 0.03, 0.04, and 0.06) gl asses, precursors for high temperature superconductors, have been prepared by fast quenching technique from their melts. These are n-type semiconducto rs and follow non-adiabatic small polaron hopping conduction mechanism abov e 1/2 theta (D) (where theta (D) being the Debye temperature). The lower te mperature(below 1/2 theta (D)) conductivity data can be fitted with the var iable range hopping (VRH) model. The estimated Mott parameters are found to be reasonable for the formation of small polaron and comparable with those of some other similar glasses. However, compared to the usual binary or te rnary transition metal oxide glasses, the density of states at the Fermi le vel N(E-F) is found to be one order of magnitude higher which we consider t o be due to the formation of nanocrystalline (5-20 nm) clusters in these gl asses. All the glasses are found to become superconductors in their glass-c eramic phases and the corresponding superconducting transition temperature decreases continuously with increase of Mn content indicating pair-breaking mechanism. (C) 2001 Elsevier Science B.V. All rights reserved.