Junhu Wang

Defect-fluorite oxides M 1-y Ln y O 2-y/2 (Ln = lanthanide; M = Hf, Zr, Ce, U, Th): Structure, property, and applications*

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.

Correlation of crystal structures with electric field gradients in the fluorite- and pyrochlore-type compounds in the Gd2O3–ZrO2 system

Abstract Correlation of crystal structure with electric field gradient (EFG) in the fluorite- and pyrochlore-type compounds in the Gd2O3–ZrO2 system GdxZr1−xO2−x/2 with 0.18⩽x⩽0.62 were investigated by 155Gd Mossbauer spectroscopy, powder X-ray diffraction and point-charge model (PCM) calculation. An intermediate ordered pyrochlore phase forms for 0.45⩽x⩽0.55, sandwiched with a disordered fluorite phase for 0.18⩽x

155Gd Mössbauer spectra of some Gd(III)-b-diketonato complexes

Abstract155Gd Mössbauer spectra of some Gd(III)-b-diketonato complexes are reported. All of their 155Gd Mössbauer isomer shift (d) values fall in a narrow range of +0.55-+0.65 mm.s-1, and are between those of GdF3 and the cubic form of Gd2O3. This indicates that their Gd-O bonds have small covalent character. The value for quadrupole coupling constant (e2qQ) spread out from 1.67 to 7.56 mm.s-1 and reflects the difference well in symmetry of the coordination polyhedron around Gd(III) ions for those Gd(III)-b-diketonato complexes.

Mössbauer Spectroscopic Studies of 237Np in frozen nitric acid solution

We applied Mossbauer spectroscopy to 237Np in nitric acid solutions to study chemical states. Sample solutions were adjusted to 50 mg/ml of Np(V) and Np(VI) concentration in 0.6 M nitric acid solutions. These solutions were put into original designed containers for samples and mounted to sample holders. The values of isomer shift (IS, relative to NpAl2) of Np(V) and Np(VI) in 0.6 M nitric acid were −17.4(1) and −37.2(3) mm/s at about 10 K, respectively. It was found that Np(V) had 7 coordination number and Np(VI) had 8 in nitric acid solutions from values of IS.