NO Intercalation Properties of Double-Layered Cuprate, La2-xBaxSrCu₂O₆. Effect of Treatment with Water Vapor

The NO intercalation properties of substituted double-layered cuprates, La 2- x Ba x SrCu 2 O 6, have been studied by means of XRD, ED, HREM, and FT-IR. The NO absorbability was strongly influenced not only by the amount of Ba substitution but also by the pretreatment with saturated water vapor at 60 °C. The Ba substitution leads to √2 a × √2 a and 3 a × 3 a superstructures, which are associated with the ordering of Ba and oxygen vacancies, respectively. The sample with the superstructure showed rapid NO uptake at 250 °C only after water vapor treatment. The XRD measurement demonstrates a two-stage lattice expansion along the c axis after reactions with water vapor and subsequently with NO. The parallel HREM study suggests that the expanded structure is due to the insertion of H 2 O and NO species into interlayers between bottom planes of CuO 5 pyramids. Aging the sample in water vapor leads to the formation of interlayer hydroxyl groups, which are effective in promoting NO intercalation by expanding the interlayer spacing between the CuO 5 sheets.