Group and phase sound velocities in an Eu1Ba2Cu3O7 superconductor and related perovskite oxides

To measure phase velocity versus frequency, ν(ω), accurately over a large frequency range, a modified amplitude-spectrum pulse-echo method was used. A buffer rod whose elastic impedance differed substantially from that of the specimen was used. Also, very broadband ultrasonic transducers and a broadband receiver with a large dynamic range were employed. The validity of the measurement method was established by measuring BaTiO₃ and SrTiO₃ polycrystals. The method was then used to measure the longitudinal-wave velocities in an Eu₁Ba₂Cu₃O₇ superconductor, at 295 and 76 K. Despite a complicated substructure and a complicated electronic structure, Eu₁Ba₂Cu₃ O₇ fails to show ν(ω) dispersion at megahertz frequencies at temperatures either above or below the normal superconducting phase transition