Abstract
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 (chi < 2.10(-8) m(3)/mol U) with the shortest inter-uranium distances between the U atoms in different sheets (d(U-U) = 332 pm). The volume-expanded (10%) hydride is a spin fiuctuator 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 CIT and a dramatic enhancement of the Sommerfeld coefficient of electronic specific heat gamma, which reaches 500 mJ/mol f.u. K-2.