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.