Reversible Valence Transition Eu 3+ → Eu 2+ → Eu 3+ in Eu_1-x^2 + Eu_x^3 + MO_3 + x/2 ( M = Ti, Zr, Hf): An Analysis of XAFS and XRD Data

— The regularities of completely reversible valence transition Eu 3+ → Eu 2+ → Eu 3+ in complex europium oxides have been investigated using a combination of X-ray diffraction (XRD) and X-ray absorption spectroscopy (XANES + EXAFS) synchrotron methods. The influence of the type of M 4+ cations on the reduction and oxidation, as well as the formation and evolution of the crystalline and local structure of the Eu_1-x^2 + Eu_x^3 + MO_3 + x/2 ( M = Ti, Zr, Hf) compounds is established. It is shown that oxidation of initially reduced Eu 2+ M O 3 samples leads to the formation of mixed-valence (MV) state Eu 2+ /Eu 3+ with inhomogeneous charge distribution, causing a phase transition with formation of partially amophized intermediate metastable phases Eu 3+ M O 3.5 having a monoclinic structure (sp. gr. Р 12 1 1). An increase in the oxidative annealing temperature to 1000°С facilitates further phase transition with the formation of stable cubic phases Eu _2^3 + M 2 O 7.