Ultrasonic investigation on high-T c superconductor CaLaBaCu 3O 7−y

Abstract

Ultrasonic measurements on a high- T c superconductive CaLaBaCu 3O 7− y polycrystalline sample have been performed. Both the transverse and longitudinal sound velocities in the sample show an anomaly around T c. The Young's Modulus, Debye temperature, Bulk modulus and Poisson's ratio were calculated; they show an anomaly near T c, which is common to high- T c superconducting materials. Poisson's ratio shows an anomaly in a temperature range from below T c to well above it. Below 80 K, which is the maximum possible T c in the CaLaBaCu 3O 7− y system, Poisson's ratio begins to increase with temperature decrease, and shows a kink near T c. The ultrasonic attenuation in the sample shows a sharp peak at T c when T c is 67 K. As T c dropped to 28 K, two attenuation peaks around T c were observed, which is common in high- T c materials. The attenuation peak below T c may be caused by the fluctuation of normal state, which becomes less apparent as hole concentration increases. The attenuation peak above T c may be related to microstructural change.