The thermal conductivity and diffusivity of U 4O 9−y from 250 to 415 K

Abstract

The thermal conductivity and diffusivity of U 4O 9−y with various O U ratios (2.227, 2.234, 2.254) were measured by means of a scanning temperature method in the temperature range from 250 to 415 K. An anomaly of the second-order phase transition type was revealed by the thermal diffusivity measurements, and the peak temperature for each O U ratio was in good agreement with that previously obtained from heat capacity measurements. The anomaly was not as clearly observed in the thermal conductivity data as in the thermal diffusivity data. The measured values for thermal conductivity of U 4U 9−y, were very low: from 10 −2 to 2 × 10 −2 W K −1 cm −1 over the temperature range investigated, and varied little with temperature. The phonon mean free path values calculated from the thermal conductivity data were very small, and all fell within the range 2 1 2 to 5 1 2 Å, being higher in the specimens with the lower oxygen content. Mean free path values decreased with increase in temperature, and the rate of decrease was greater in the region of the transition.