Elastic behaviour of Nd_1.85Ce_0.15CuO_4-yand Nd₂CuO_4-Y

Abstract

Ultrasonic measurements on the electron doped high Tc superconductor Nd1.85Ce0.15CuO4-y and Nd2CuO4-y its nonsuperconducting parent compound are presented. Although the superconductor shows no evidence of acoustic mode softening below room temperature, there is a clear change in the temperature dependence of the longitudinal mode velocity around 220 K. This effect is far less pronounced for the shear mode and is not observed in the parent compound, indicating that the intermediate valence state of the Ce ions plays an important role in the elastic behaviour of the superconductor. The first results for the pressure dependences of the elastic constants are reported.