Electronic and Structural Properties of Ba₂Y_1-X Pr_XCu₃O_7-δ

Abstract

Measurements of the Hall coefficient in the Ba₂Y_1-xPr_xCu₃O_7-δ system show that an increase in Pr concentration reduces the Hall carrier number (1/eR_H). The Cu formal valence, calculated from the Pr valence, which has been determined to be about +3.5 from its magnetic moment, slightly decreases as the Pr concentration increases. The transition temperature shows a stronger dependence on Hall carrier number and Cu-O formal valence than in the oxygen depleted Ba₂YCu₃O_7-δ system. X-ray diffraction measurements show that the structure remains almost unchanged throughout the series. The persistence of the chain structure explains the major difference in Cu-O valence dependence on Tc between the present system and the oxygen depleted Ba₂YCu₃O_7-δ system on the basis of the two band model. Measurements of the magnetoresistance show that the pure Y compound has a large positive magnetoresistance up to 250 K, while the Pr substitution drives it negative. The temperature dependence of the positive magnetoresistance indicates that it is caused by the superconducting fluctuation. The experiment suggests that there is strong correlation between the appearance of the negative magnetoresistance and the suppression of superconductivity. Rietveld analysis reveals that the CuO₂ plane becomes less flat as a result of the oxygen displacements, and the oxygen in the BaO plane moves toward the QuO₂ plane. These displacements also possibly cause the Tc reduction.