The Pr -substituted YBa 2 Cu 3 O 7-δ( Y 123) superconducting systems with the content of 0.0–1.0 have been systematically studied by positron lifetime and infrared absorption experiments. The results show that the short lifetime τ1 decreases as a function of Pr -substitution x below x=0.6, but when above x=0.6, it increases inversely. The long lifetime τ2 decreases as a function of Pr -substituted x. Based on the present results, we discuss that Pr 4+ substitutes on Ba 2+ ion and forms Pr Ba defects. The variation of τ1 is caused by the oxygen vacancies and τ2 is probably affected by the absence of Cu due to Pr Ba defects. The infrared absorption of Pr -substituted Y 123 systems gives three variational modes, located at 560 cm -1( A 1), 1435 cm -1( A 2) and 1631 cm -1( A 3) respectively. Here the A 3 mode shows that with Pr content increasing from x=0.1 to 1.0, the infrared absorption decreases and the peak tends to broaden. So, combining with the results of the positron lifetime spectra, we can argue that there always exists portion of Pr Ba defects in the Pr -substituted systems, and the Pr 4+ substituted into Ba 2+ is also increasing with the Pr content increasing. When the Pr content is 0.6, the systems have a metal-insulator transition and Pr Ba defects begin to domain the samples' microstructure.
Far-infrared absorption in Sb-doped Ge epilayers near the metal–insulator transition