ELECTRICAL-RESISTIVITY AND PHASE-TRANSITION BEHAVIOR OF URANIUM UNDER PRESSURE AND TEMPERATURE

In this paper, we report the electrical resistivity of uranium up to 10 GPa and 1300 K. In alpha-uranium. the electrical resistivity shows a nonlinear rise with temperature with a negative curvature towards the temperature axis. The temperature coefficient of the resistivity is found to decrease with pressure. When the temperature is further increased, uranium undergoes alpha-beta and beta-gamma transitions which are accompanied by sharp resistivity drops. At pressures above 3.6 GPa, a direct alpha-gamma transition is observed, The alpha-beta-gamma triple point is determined to be 3.6 +/- 0.2 GPa and 1078 +/- 3 K. Large temperature hystereses are observed during these transitions. The hystereses are found to decrease with pressure across the alpha-beta and alpha-gamma transitions whereas during the beta-gamma transition hysteresis is almost pressure-independent. On the basis of the present experimental observation, of the two possible scattering mechanisms operating in alpha-uranium. namely the interband and the spin-fluctuation scattering. the latter is found to be the dominant mechanism contributing to the resistivity. From the pressure-independent hysteresis behaviour during the beta-gamma transition it is suggested that either the beta-gamma transition is weakly thermal in nature or that the slope of this transition line is zero. If the latter is true, then a careful determination of the beta-gamma boundary line in the P-T phase diagram of uranium is recommended.