COMPARISON OF IR - ACTIVE PHONONS IN YBCO CERAMICS WITH DIFFERENT CARRIER CONCENTRATIONS

We report on a study of temperature dependent far infrared reflectivit y measurements of partly substituted YBCO ceramics with different carr ier concentrations. Reflectivity spectra show, depending on the carrie r concentration, high metallic reflectivity and strong phonon structur es. A comparison of the data of these measurements shows that the temp erature dependent phonon response clearly scales with T(C). A theoreti cal fit based on the two fluid model can be used to describe the phono n behavior. The assumption of a superconducting gap derived from these measurements will be discussed. Below the critical temperatures a cor relation between phonons and superconducting carriers was found. From these data an energy gap in the superconducting states can be estimate d. The assumption of a superconducting BCS-like gap in the range of 3. 2 k(B)T to 4.6 k(B)T is consistent with our data.