Thermal diffusivity and thermal conductivity studies on thorium-lanthanum mixed oxide solid solutions

Abstract

Study of the heat-transport properties of actinide-based mixed oxides is of importance in nuclear technology. This paper describes laser flash technique studies of the thermal diffusivity and thermal conductivity carried out on thorium-lanthanum mixed oxide solid solutions covering a temperature range from 573 to 1573 K and a compositional range from 0 to 30 mol.% LaO_1.5. The thermal diffusivity and thermal conductivity of the solid solutions were found to decrease with increase in lanthanum oxide content or temperature. From the temperature dependence of the thermal conductivity it was noted that heat transport in these materials is by lattice conduction. The variation of the two resistivity terms, namely the defect thermal resistivity and the intrinsic thermal resistivity, as well as their ratio as a function of lanthanum oxide content was examined. Employing the thermal conductivity data, phonon mean-free paths were also obtained as a function of composition and temperature.