CrossRef enabled

PAC Archives

Archive →

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

Defect-fluorite oxides M1-yLnyO2-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 Zr1-yGdyO2-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.