Abstract
The Pr L <sub>3</sub> -edge x-ray absorption near edge structure spectra and antiferromagnetic T <sub>N</sub> (Pr) data for the parent system PrBa <sub>2</sub> Cu <sub>3</sub> O <sub>7-y</sub> (0≤y<1) and the oxygenated system Pr <sub>1+x</sub> Ba <sub>2-x</sub> Cu <sub>3</sub> O <sub>7-y</sub> (0≤x≤1;-0.27≤y≤0.05) are reported. The formal Pr valence in the PrO <sub>8</sub> cage decreases from 3.18 for PrBa <sub>2</sub> Cu <sub>3</sub> O <sub>6.95</sub> [T <sub>N</sub> (Pr)=18.5 K], to 3.12 for Pr <sub>1.2</sub> Ba <sub>1.8</sub> Cu <sub>3</sub> O <sub>6.98</sub> (15.5 K), 3.03 for Pr <sub>1.6</sub> Ba <sub>1.4</sub> Cu <sub>3</sub> O <sub>7.16</sub> (8 K), and 3.00 for Pr <sub>2</sub> BaCu <sub>3</sub> O <sub>7.27</sub> [T <sub>N</sub> (Pr) not observed]. The Pr valence depends both on the number of holes available in the PrO <sub>8</sub> cage and the Pr 4f-O 2p <sub>π</sub> hybridization strength. On the other hand, anomalous T <sub>N</sub> (Pr) is a direct result of exchange interaction though Pr-O-Pr hybridization. However, the relative contribution from Pr <sup>IV</sup> -Pr <sup>IV</sup> superexchange via strong Pr-O orbital hybridization and Pr <sup>III</sup> -Pr <sup>III</sup> /Pr <sup>III</sup> -Pr <sup>IV</sup> superexchange paths is unclear. © 2002 American Institute of Physics.