Dependence of property, crystal structure and electric conductivity on substitution content and synthetic process of T′-La2−xRExCuO4−δ (RE = Sm and Tb)

We synthesized T′-La2−xRExCuO4−δ (RE = Sm and Tb) by a co-precipitation method and sintering in vacuum at various temperatures, and investigated relationship among the crystal structure, average valence of Cu, oxygen content and electric conductivity. From X-ray diffraction measurements, it was confirmed that a main phase of the product was T′ structure (S. G.: I4/mmm) regardless of the rare earth element and its concentration, although an impurity phase was observed in a part of samples. In the samples with low average valence of Cu, the resistivity showed a metallic behavior and remarkably decreased at low temperature. Rietveld analyses using synchrotron X-ray diffractions suggested that the electric conductivity was improved by decreasing a bond length of Cu-O1 in the case of La2−xSmxCuO4−δ.