The issue of the valence state of praseodymium (Pr) in Pr-containing cuprates is addressed using electron-energy-loss spectrometry (EELS) in a transmission electron microscope (TEM) on (${\mathrm{Eu}}_{1.5\mathrm{-}\mathit{x}}$${\mathrm{Pr}}_{\mathit{x}}$${\mathrm{Ce}}_{0.5}$)${\mathrm{Sr}}_2$${\mathrm{Cu}}_2$${\mathrm{NbO}}_{10}$ compounds. EELS analysis, in reference to Ce ${\mathit{M}}_{4,5}$ edges, clearly indicates that the energy onset, ${\mathit{M}}_5$/${\mathit{M}}_4$ intensity ratio and the fine structure of the ${\mathit{M}}_5$ and ${\mathit{M}}_4$ edges of a Pr are consistent with Pr valence of +3. These results eliminate theoretical descriptions on these compounds based upon a Pr +4 valence state and a suppression of carrier states. Localized holes, magnetic interactions, and f-electron hybridization remain viable candidates to explain the lack of superconductivity in Pr-based cuprates. © 1996 The American Physical Society.

• Received 29 June 1995

DOI:https://doi.org/10.1103/PhysRevB.53.11779