High-Temperature Electrical Property and Defect Analysis of the Quintuple Perovskite Layered Cuprates Eu₂CaBa₂Cu₂Ti₃O₁₄ and LaYCaBa₂Cu_2+xTi_3-xO_14-y

High-temperature electrical conductivity and thermopower measurements have been performed on undoped Eu₂CaBa₂Cu₂Ti₃O₁₄ and doped and undoped LaYCaBa₂Cu_2+xTi_3-xO₁₄. These quintuple perovskites are members of a family of ordered perovskite-type oxides with double Cu-O sheets and have in-plane Cu-O bond lengths comparable to known superconductors. X-ray diffraction data and transmission electron microscopy show clear evidence of layering in both structures. LaYCaBa₂Cu_2+xTi_3-xO₁₄ exhibits a large-small rare earth ordering on the A′/A″ sites, like its quadruple perovskite counterparts. The transport data indicate that these materials behave similarly to the corresponding quadruple perovskites, but have lower carrier concentrations. The La-Y compound exhibits weaker oxygen partial pressure dependencies in the electrical properties, which are suggestive of a decrease in undesirable oxygen intercalation between the CuO₂ sheets. Upon doping with copper on titanium sites, (Cu″_Ti), a concomitant amount of oxygen vacancies, (V^•• _o), are introduced, as evidenced by TGA and in situ electrical property measurements. Possible defect models are presented and discussed in light of data from TGA, electrical property measurements, and quantitative high-resolution TEM.