Structural and Electrical Properties of Layered Pervoskite Manganites Nd2 - 2x Sr1+2x Mn2O7 (x = 0.25, 0.3, 0.4)

Tetragonally layered perovskite manganites of Nd2 - 2x Sr1+2x Mn2O7 (x = 0.25, 0.3, 0.4) were fabricated by using solid-state reaction technique. Structural characterization of the compounds was investigated by X-ray diffraction (XRD) and FT-IR absorption spectra. The XRD patterns revealed that all the samples were single phase. X-ray photoemission spectroscopy (XPS) was used to investigate their electronic structures. It was found that manganese was in mixed states of Mn3+ and Mn4+ whereas lattice oxygen and chemical absorbed oxygen were existed in all the samples. The high temperature electrical properties of Nd2 - 2x Sr1+2x Mn2O7 (x = 0.3, 0.4) were measured by standard four-probe technique. The results showed that both compounds had semi-conductivity behavior in the temperature range of 300 ~ 1073 K, and the electrical conduction was dominated by thermally activated behavior above 500 K.