Hydrogen absorption in U3Si2 and its impact on electronic properties

U3Si2 reversibly absorbs hydrogen at very low H2 pressures (kPa range), yielding U3Si2H1.8. One characteristic desorption temperature implies that there is only one type of H sites. U3Si2 is a weak Pauli paramagnet (χ < 2·10−8 m3/mol U) with the shortest inter-uranium distances between the U atoms in different sheets (dU-U = 332 pm). The volume-expanded (10%) hydride is a spin fluctuator with temperature dependent magnetic susceptibility and a weak ferromagnetic component gradually arising below T = 100 K. The location of U3Si2H1.8 at the verge of magnetic ordering is evidenced by the low temperature specific heat with an upturn in C/T and a dramatic enhancement of the Sommerfeld coefficient of electronic specific heat γ, which reaches 500 mJ/mol f.u. K2.