Defect-fluorite oxides M1-yLnyO2-y/2(Ln = lanthanide; M = Hf, Zr, Ce, U, Th): Structure, property, and applications

Nakamura, Akio; Masaki, Nobuyuki; Otobe, Haruyoshi; Hinatsu, Yukio; Wang, Junhu; Takeda, Masuo

doi:10.1351/pac200779101691

Pure Appl. Chem., 2007, Vol. 79, No. 10, pp. 1691-1729

http://dx.doi.org/10.1351/pac200779101691

Defect-fluorite oxides M_1-yLn_yO_2-y/2(Ln = lanthanide; M = Hf, Zr, Ce, U, Th): Structure, property, and applications

Akio Nakamura¹, Nobuyuki Masaki², Haruyoshi Otobe², Yukio Hinatsu³, Junhu Wang⁴ and Masuo Takeda⁴

¹ Advanced Science Research Center, Japan Atomic Energy Agency, Tokai, Naka, Ibaraki 319-1195, Japan
² Nuclear Science and Engineering Directorate, Japan Atomic Energy Agency, Tokai, Naka, Ibaraki 319-1195, Japan
³ Department of Chemistry, Hokkaido University, Sapporo 060-0810, Japan
⁴ Department of Chemistry, Toho University, Funabashi, Chiba 274-8510, Japan

Abstract: An up-to-date summary of our coupled macroscopic (lattice parameter, a₀) and microscopic (Mössbauer) studies on the entitled systems is given, shedding new light on the basic phase and structure properties of these technologically important, highly defective oxides. Through these studies, the intermediate-pyrochlore (P)-based local structure nature of the so-called stabilized-zirconia (SZ)- and stabilized-hafnia (SH)-type defect-fluorite (DF) phases in the M⁴⁺ = Zr and Hf systems seems to be almost unambiguously established with different (from the conventional) approaches: These are (1) the presence of a broad lattice parameter (a₀) hump over the extended stabilized cubic DF region (y = ~0.3-~0.7); (2) the microscopic ¹⁵¹Eu-Mössbauer evidence of Eu³⁺ isomer shifts (ISs) showing characteristic V-shaped minima around the ideal-P area (y ~ 0.50) for both the M⁴⁺ = Zr and Hf systems; and (3) rich ¹⁵⁵Gd-Mössbauer data on the Zr_1-yGd_yO_2-y/2 system [IS, quadrupole splitting (QS), line width, peak height, and relative absorption area (RAA)], revealing detailed features of its ordered P-disordered DF phase and structure relationships. These results are discussed with reported basic-property data of these systems.