Preparation, characterization, and far-infrared study of ceramic high-Tc superconductors

We report on a study of single-phase (superconducting) YBa2Cu3O7 and (nonconducting) Y2BaCuO5 and mixed phases of these compounds in bulk and film samples and on an investigation of ceramic bulk material of the homologous series Tl2Ba2CanCun+1O2n+6. We describe preparation and structural characterization by x-ray diffraction analyses and further characterization by electric, magnetic, tunnel junction, and Raman scattering studies, and we present results of far-infrared reflectivity measurements. In a theoretical analysis we relate the phonon structure of reflectivity spectra to geometric structure of a metallic network, with holes filled with nonconducting material. The influence of superconductivity on reflectivity is also investigated

Far-infrared reflectivity and dynamical conductivity of YBa2Cu3O7

For a sintered YBa2Cu3O7 sample that shows high far-infrared reflectivity we determined, by a Kramers-Kronig analysis, the dynamical conductivity and extracted contributions by free charge carriers and phonons. The low temperature conductivity, and also results of a tunnel experiment, can be described by a distribution of energy gaps around 2Δ/kTc reverse similar, equals 4.6. Furthermore we present evidence for superconducting fluctuations and we show that the lowest-frequency infrared-active phonon mode is less damped in the superconducting state than in the normal state