Elastic constants of single-phase Bi2Sr2CaCu2O8+y superconductor

The elastic constants of Bi2Sr2CaCu2O8+y ceramic have been determined for the first time from ultrasonic velocity measurements. Near 200 K both longitudinal and transverse wave velocities show noticeable anomalous behaviour, indicating a possible structural change or a phase transition. The strong hysteresis and the bulk modulus softening are also remarkable. A Debye temperature theta D= 250 K is estimated. The derived elastic constants of this material are substantially smaller than those of YBa2Cu3O7-x and BaTiO3, which is attributed to the weakly interacting multilayers along the very large c axis of Bi2Sr2CaCu2O8+y. However, the Poisson ratios of these perovskite ceramics are quite close, suggesting similar interatomic bonding.