Low-temperature specific heat and critical magnetic field of alpha-uraniumsingle crystals - art. no. 224510

The current work reports on the specific heat and the electrical resistivit y of alpha -uranium at cryogenic temperatures. Measurements were made on al pha -uranium single crystals that have some unexpected mechanical propertie s. Despite the fact that alpha -uranium normally work hardens and often fai ls in a brittle manner, these crystals bend easily. Presumably, the combina tion of flexibility and strength comes from twinning in response to stress, and these twins can run freely during deformation. Because grain boundarie s are not present, we anticipated that the characteristics of the charge de nsity wave (CDW) might be more prominent in these crystals. For these reaso ns, the specific heat was measured from T approximate to0.5 to 110 K, using semiadiabatic calorimetry in zero field, and the electrical resistivity wa s 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 typi cal of a superconducting transition was observed as the temperature fell be low 0.78 K, a temperature at which the resistance fell to 90% from its orig inal value. A residual resistivity ratio RRR approximate to 115 was measure d from the low-temperature resistivity data. In addition, three phase trans itions were clearly seen in the specific-heat data, located at T= 23, 36, a nd 42 K. These transitions are consistent with the alpha (3), alpha (2), an d alpha (1) CDW structures that have been previously observed in uranium me tal. Analysis of the specific-heat data give an electronic specific heat (g amma) = 9.13 mJ K-2 mol(-1) and a low-temperature limiting Debye temperatur e (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 tha t 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 highli ght the properties of these alpha -uranium single crystals.