Characterization and thermomechanical properties of Ln_2Zr_2O_7 (Ln=La, Pr, Nd, Eu, Gd, Dy) and Nd_2Ce_2O_7

摘要

Pyrochlore type compound Nd_2(Zr,Ce)_2O_7 is considered to precipitate in ThO_2-based fuel, that is not observed in irradiated UO_2. In order to evaluate the influences on fuel properties, thermomechanical properties of the pyrochlore type compounds, Ln_2Zr_2O_7 (Ln=La, Pr, Nd, Eu, Gd, Dy) and Nd_2Ce_2O_7 were investigated. We synthesized the samples by solid-state reaction and pelletized by spark plasma sintering to make high density (≥ 90%T.D.) pellets. The phase states and lattice parameters were examined by using X-ray diffraction and SEM/EDX analysis. The lattice parameters of Ln_2Zr_2O_7 depended on the ionic radii of lanthanide ions. The heat capacity, thermal conductivity, linear thermal expansion coefficient, and elastic constants were also measured. It was confirmed that the thermal conductivities for Ln_2Zr_2O_7 were lower than that for ThO_2 and depended on Ln ionic radii. The values of elastic constants tended to increase with increasing the Ln ionic radii, corresponding to the thermal conductivity.