The effects of quenching and lead substitution on the ultrasonic wave velocity and attenuation in bismuth cuprate high Tcsuperconductors

Publisher Website
Google Scholar
Abstract
The velocity and attenuation of longitudinal and shear ultrasonic waves propagated in ceramic specimens of single phase Bi(Pb)2223, Bi(Pb)2212 and lead-free Bi2212 have been measured between 10 and 295 K. The anomalous elastic effects and hysteresis in the range about 190-240 K reported by other workers have been found in samples of Bi(Pb)2223 and lead-free Bi2212. However, for the Bi(Pb)2212 phase, in which some Bi is substituted by Pb, these anomalies and hysteresis are suppressed. Quenching a sample of the Bi2212 phase from 800 degrees C into liquid nitrogen removes these anomalies, which have therefore been shown to be strongly dependent on chemical composition: either oxygen content or lead substitution for bismuth. The elastic stiffnesses of these bismuth cuprates are unusually small due largely to (i) their open microstructure on the macroscopic level but also in part as a result of (ii) their rather open layer-like structure with weak interlayer binding forces and (iii) the intermediate valence state of the copper ions. It is known that quenching the Bi2212 phase from just below the melting temperature (about 880 degrees C) into liquid nitrogen results in the reduction in oxygen content that is necessary to optimize the superconducting properties of this phase. The authors have now established that quenching also results in substantial longitudinal acoustic mode softening whilst enhancing Tc.