DETERMINATION OF THE VALENCE OF PR, GD, AND HO IN YBA2CU3O7 BY X-RAY ABSORPTION-SPECTROSCOPY

The L1,2,3 edges of Pr, Gd, and Ho in YBa2Cu3O7 were compared with a variety of reference compounds in an attempt to determine their valence and electronic configuration. A double-differential data analysis technique was used to resolve the multiplet structure of the L1,2,3 edge resonances. Features were observed in the spectra that were specific for each valence. The results showed that Gd and Ho were trivalent while the spectra of Pr in Y-Ba-Cu-O were unique. The most intense L2,3 edge resonances were at the same energy position and nearly the same in appearance as the trivalent Pr reference compounds but with unique, extra features attributable to Pr4+. Their intensity was inversely proportional to Pr concentration. We tentatively identified this structure as substitution of Pr4+ into the Cu2 site. These resonances may have important implications for understanding the electronic structure of Pr in Y-Ba-Cu-O and the effect on superconductivity. © 1990 The American Physical Society.