| AVS 64th International Symposium & Exhibition | |
| Actinides and Rare Earths Focus Topic | Monday Sessions |
| Session AC+MI+SA+SU-MoM |
| Session: | Magnetism, Complexity, and Superconductivity in the Actinides and Rare Earths |
| Presenter: | Silvie Maskova, Charles University, Prague, Czech Republic |
| Authors: | S. Maskova, Charles University, Prague, Czech Republic K. Miliyanchuk, Ivan Franko National University of Lviv, Lviv, Ukraine S. Middleburgh, Westinghouse Electric Sweden AB, Vasteras, Sweden L. Havela, Charles University, Prague, Czech Republic |
| Correspondent: | Click to Email |
U3Si2 (tetragonal structure with the space group of P4/mbm and two different U-positions, U1 and U2, in the unit cell) is considered to be promising material (due to its high density of uranium) as an accident-tolerant nuclear fuel [1] with rather high melting point (1938 K) indicating a high thermodynamic stability. From this point of view, it is very important to study its resistance to oxygen or hydrogen, as it can significantly influence the integrity of the material. U3Si2 was reported to oxidize at elevated temperatures [2].
We studied the H absorption and concomitant changes of basic electronic properties. We found that U3Si2 reversibly absorbs hydrogen (H can be released again by heating up to approx. 700 K) to the level of approximately 1.8 H/f.u., i.e. yielding U3Si2H1.8. The H absorption proceeds at very low H pressures (kPa range) already, resulting in 10 % volume expansion. The temperature-induced desorption experiment showed that the hydrogen atoms are located in one specific position only. The crystal structure arrangement suggests that two different positions should be considered - U3Si tetrahedra (similar to U3T tetrahedra in U2T2X compounds [3] crystallizing in an ordered ternary derivative of the U3Si2 structure) and a split position in the U6 octahedra consisting of 4 U1 and 2 U2 atoms (H atom shifts from the central position into the tetrahedra formed by 2 U1 and 2 U2 atoms. As H generally does not occupy two adjacent tetrahedra, we can assume only two from the 4 tetrahedra occupied). The later was confirmed as more plausible option by ab-initio calculations using Vienna Ab-initio Simulation Package (VASP) with the PBE-GGA exchange correlation.
Magnetic studies of U3Si2 confirmed that it is a Pauli paramagnet, as reported previously [4]. The volume expanded hydride reveals a Curie-Weiss behavior and a weak and inhomogeneous ferromagnetism arising gradually below T = 100 K. The low-temperature specific heat of U3Si2H1.8 shows an upturn and a dramatic enhancement of the Sommerfeld coefficient of electronic specific heat γ, which reaches 440 mJ/mol f.u. K2 (γ = 88 mJ/mol f.u. K2 for U3Si2).
This work was supported by The Czech Science Foundation under the Grant No. 15-01100S.
[1] K.D. Johnson, A.M. Raftery, D.A. Lopes, J. Wallenius, J. Nucl. Mater. 477 (2016) 18-23.
[2] E. Sooby Wood, J.T. White, A.T. Nelson, J. Nucl. Mater. 484 (2017) 245-257.
[3] K. Miliyanchuk, L. Havela, A.V. Kolomiets, A.V. Andreev, Physica B 359–361 (2005) 1042-1044.
[4] T. Miyadai, H. Mori, T. Oguchi, Y. Tazuke, H. Amitsuka, T. Kuwai and Y. Miyako, J. Magn. Magn. Mater. 104-107 (1992) 47-48.