CONCENTRATION-DEPENDENT ACOUSTIC AND ELECTRICAL-PROPERTIES OF HIGHLY CONDUCTING BI3.5PB0.5SR3CA3CU4OZ-TYPE GLASSY PRECURSORS FOR HIGH-T-C SUPERCONDUCTORS(XAG(2)O)

We report the concentration-dependent electrical conductivity and acou stic parameters of the (Bi-Pb)(4)Sr3Ca3Cu4Oz + xAg(2)O (x = 0-10 wt%)- type glassy precursors for high T-c superconductors. Unlike (Bi, Pb)(4 )Sr3Ca3Cu4Oz or many other transition-metal oxide glasses, these Ag-co ntaining glasses are; highly conducting. Unlike many other transition- metal oxide glasses, the small-polaron hopping mechanism of conduction is found not to be applicable for these glasses, which might be due t o a partial contribution of the Ag ions to the conductivity. The veloc ities of sound, elastic constants, microhardness, acoustic impedance a nd Debye temperatures are found to decrease monotonically, as does the density, with increasing Ag concentration. On the other hand, the the rmal expansion coefficient, internal friction and Poisson's ratio incr ease with increasing content of Ag2O. The concentration-dependent acou stic parameters and the corresponding derived quantities indicate a so ftening of the glass structure with addition of Ag. All these glasses become high-T-c superconductors in their respective crystalline phases .