Low-Temperature Specific Heat And Critical Magnetic Field Of Alpha-Uranium Single Crystals

The current work reports on the specific heat and the electrical resistivity of alpha -uranium at cryogenic temperatures. Measurements were made on alpha -uranium single crystals that have some unexpected mechanical properties. Despite the fact that alpha -uranium normally work hardens and often fails in a brittle manner, these crystals bend easily. Presumably, the combination of flexibility and strength comes from twinning in response to stress, and these twins can run freely during deformation. Because grain boundaries are not present, we anticipated that the characteristics of the charge density wave (CDW) might be more prominent in these crystals. For these reasons, the specific heat was measured from T approximate to0.5 to 110 K, using semiadiabatic calorimetry in zero field, and the electrical resistivity was measured from T approximate to0.1 to 0.50 K, in magnetic fields up to 80 mT using a standard four-probe ar technique. An abrupt resistance drop typical of a superconducting transition was observed as the temperature fell below 0.78 K, a temperature at which the resistance fell to 90% from its original value. A residual resistivity ratio RRR approximate to 115 was measured from the low-temperature resistivity data. In addition, three phase transitions were clearly seen in the specific-heat data, located at T= 23, 36, and 42 K. These transitions are consistent with the alpha (3), alpha (2), and alpha (1) CDW structures that have been previously observed in uranium metal. Analysis of the specific-heat data give an electronic specific heat (gamma) = 9.13 mJ K-2 mol(-1) and a low-temperature limiting Debye temperature (Theta (D))= 256 K (+/- 0.25 K). The highest calorimetric value measured previously was 218 K. Our value of 256 K is in favorable agreement with that previously obtained from elastic constants 250 K (+/-2 K). The agreement between calorimetric and elastic OD values, ductility at room temperature, and a RRR that is three times larger than previously reported values highlight the properties of these alpha -uranium single crystals.