Raman and infrared spectroscopy of YBa₂Cu₃O_7-δ-BaPbO₃ composites

We present results of Raman and infrared spectroscopic studies of the composite system of superconducting YBa₂Cu₃O_7-δ and metallic BaPbO₃, with the BaPbO₃ fraction ranging from 5 to 30 in weight. The Raman spectra of the YBa₂Cu₃O_7-δ grains in the composite system are typical of well-oxygenated YBa₂Cu₃O_7-δ bulk single crystals, even up to the grain boundaries, independent of the BaPbO₃ fraction. We have also performed infrared reflectivity measurements and have identified the major c-axis transverse-optical phonons of YBa₂Cu₃O_7-δ, consistent with the single-crystal data, confirming that the constituent YBa₂Cu₃O_7-δ crystallites are fully oxygenated. The absence of mode splitting suggests that the crystal symmetry of YBa₂Cu₃O_7-δ grains remains the same as that of bulk single crystals. No phonons indicative of other YBa₂Cu₃O₇- or BaPbO₃-related impurity phases, such as YBa₂Cu₃O₆, Y₂BaCuO₅, and Ba₂PbO₄, have been detected in our Raman and infrared spectra. All these optical features clearly indicate that YBa₂Cu₃O_7-δ is well separated from BaPbO₃ and that BaPbO₃ is an excellent additive material for the synthesis of YBa₂Cu₃O_7-δ bulk materials.