| AVS 65th International Symposium & Exhibition | |
| Actinides and Rare Earths Focus Topic | Wednesday Sessions |
| Session AC+MI+SA-WeM |
| 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 A. Kolomiets, Lviv Polytechnic National University, Lviv, Ukraine L. Havela, Charles University, Prague, Czech Republic |
| Correspondent: | Click to Email |
The sensitivity of the interactions in the intermetallic systems to modification of the crystal structure makes the experimental techniques involving alteration of the atomic arrangement especially important. Various studies under compression are well-known examples of such methods. From this point of view hydrogenation can be treated as a complementary technique that provides „negative“ pressure. Hydrides can be defined as compounds for which the hydrogen absorption leads to the modifications of the crystal structure, such as pure lattice expansion or the formation of a new structure. As a result, the new compounds (hydrides) exhibit qualitatively new physical properties and such modifications provide us with additional information on the peculiarities of interatomic interactions in the initial compounds.
As an example, we will compare the impact of H absorption on U- and RE-compounds using A2T2X (A = Rare-Earth (RE) or actinide, T = transition metal, X = p-metal) compounds crystallizing in the tetragonal Mo2FeB2 structure type (space group P4/mbm). U2T2X interact with H2 only at high pressure (≈ 100 bar) reaching 2 H/f.u. The H absorption produces a lattice expansion (lower than 10 %), while the tetragonal structure is preserved. Higher H concentrations, which can be achieved in some RE2T2X compounds (up to 8 H atoms/f.u), lead to amorphization or structure symmetry changes (with volume expansion exceeding 20 %), imposed by a minimum H-H distance requirement.
Magnetic properties of U-compounds strongly depend on the U-U distances. Hydrogen intrusion modifies the lattice by expanding it without changing the crystal-structure type leading to a 5f band narrowing. As a consequence, doping of U intermetallics by interstitial hydrogen leads to stronger magnetic properties. On the other hand, the hydrogen absorption has opposite effect on magnetic properties of RE2T2X compounds. For RE compounds, hydrogenation affects mainly the inter-site exchange interaction, which is weakened presumably by reducing the concentration of conduction electrons, responsible for the RKKY interaction.