Electronic property and structure of double-doping Y1−2xPrxCaxBa2Cu3O7−δ with 0 ⩽ x ⩽ 0.14

Equal amount Pr and Ca double-doping Y1−2xPrxCaxBa2Cu3O7−δ with 0 ⩽ x ⩽ 0.14 have been investigated by X-ray diffraction, resistivity, and X-ray photoemission spectroscopy (XPS). The deviation of the linearly decreasing of Tc vs. x curve was observed when x < 0.10. The resistivity and the temperature coefficient of resistivity also exhibit abnormal behaviors around x = 0.10. It is revealed that the conductivity behavior of Y1−2xPrxCaxBa2Cu3O7−δ with low Pr content (x < 0.10) is different from that of the relative high Pr content (x > 0.10), which suggests a change of Pr valence with the Pr content. XPS measurement shows that the relative amount of Pr3+ and Pr4+ is closely related to the total Pr content x. The valence of Pr is close to +3 when x < 0.10 and increases towards +4 when x > 0.10, which implies a different mechanism for depression of superconductivity of Pr content x < 0.10 from that of Pr content x > 0.10 in Pr doping Y-123.