Study of oxygen-ion conductivity and luminescence in the ZrO2-Nd2O3 system : impact of local heterogeneity

Stabilized fluorites and pyrochlores with different types of substitution in the (Nd2O3 ? ZrO2 system (NdZrO)) have been studied by Raman spectroscopy, X-ray diffraction, and impedance spectroscopy methods. Ionic and proton conductivity maps for 9 compositions in the NdZrO system are presented. Oxygen partial pressure measurements show a typical ionic conductor behavior, with a significantly increase of conductivity for (Nd2?xZrx)Zr2O7+x/2 (x = 1.27) fluorite and (Nd2?xZrx)Zr2O7+x/2 (x = 0.4, 0.2) pyrochlores. For the same compositions the strong luminescence was observed. Strong luminescence and high oxygenion conductivity of these solid solutions can be associated with the presence of phases with the different degree of structural disorder (tetragonal phase, fluorite) in local nanodomains in fluorite or pyrochlore matrix in the ZrO2 ? Nd2Zr2O7 region. Really, Raman spectra of (Nd2?xZrx)Zr2O7+x/2 (x = 0.5 ? 0.2) solid solutions demonstrated the fluorite + pyrochlore structural type in the short-range order. Fluorite nanodomains in pyrochlore matrix (ZrO2 ? Nd2Zr2O7 region) resulting from an order?disorder transition can only be detected at a radiation wavelength comparable to the fluorite nanodomain size. Thus, using Raman spectroscopy the broad isomorphism range in the ZrO2 ? Nd2Zr2O7 system has been shown to be nonuniform.371C-9F16-EBDE | Eduarda GomesN/

Proton Conductivity of La2 (Hf2−x Lax )O7−x/2 “Stuffed” Pyrochlores

The design of new oxygen-and proton-conducting materials is of paramount importance for their possible utilization in solid oxide fuel cells. In the present work, La2 (Hf2–x Lax )O7–x/2 (x = 0, 0.1) ceramics were prepared using ball milling of oxide mixtures (La2 O3 and HfO2 ) followed by high-temperature annealing at 1600◦ C for 10 h in air. La2 Hf2 O7 ceramics exhibit an ordered pyrochlore-type structure, whereas La2 (Hf1.9 La0.1)O6.95 has a defect pyrochlore structure type with oxygen vacancies at the 48f positions. The oxygen ion and proton conductivity of La2 (Hf1.9 La0.1 )O6.95 “stuffed” pyrochlore ceramics was investigated by electrochemical impedance spectroscopy (two-probe AC) and four-probe DC measurements in a dry and a wet atmosphere (air and nitrogen). The use of two distinct conductivity measurement techniques ensured, for the first time, the collection of reliable data on the proton conductivity of the La2 (Hf1.9 La0.1)O6.95 “stuffed” hafnate pyrochlore. La2 Hf2 O7 was found to be a dielectric in the range 400–900◦ C, whereas the La2 (Hf1.9 La0.1 )O6.95 “stuffed” pyrochlore had both oxygen ion and proton conductivities in this temperature range. The proton conductivity level was found to be equal to ~8 × 10−5 S/cm at 700◦ C. Clearly, the proton conductivity of the La2 (Hf1.9 La0.1 )O6.95 “stuffed” hafnate pyrochlore is mainly due to the hydration of oxygen vacancies at 48f positions. © 2022 by the authors. Licensee MDPI, Basel, Switzerland

New data on the basement of Franz Josef Land, Arctic region

We have studied pebbles of igneous rocks from the Lower Jurassic sedimentary succession of Hall Island, Franz Josef Land. Pebbles are represented by felsic intrusive and extrusive rocks, often cataclased and greisenized. The U–Pb age of crystallization for zircons of the studied samples yielded the Latest Devonian–Early Carboniferous and Early–Middle Permian ages. In addition, the studied zircons demonstrate a broad scatter of ages, from Middle Paleozoic to Mesozoic, suggesting repeated thermal reworking and metamorphism of granites. It is shown that coeval Late Paleozoic magmatism indicates the similarity of the geological evolution of the northern Barents Sea and the Severnaya Zemlya archipelago.</p