- Silvie Mašková: Impact of H-absorption on crystal structure and magnetic properties of Nd2T2X-compounds
- 25. 11. 2015, 14:50
- lecture room F2, first floor Ke Karlovu 5
- more information
Abstract:
We have been studying some members of large family of A2T2X (A = Rare-Earth (RE) or actinide, T = transition metal, X = p-metal) compounds crystallizing in the Mo2FeB2 structure type (space group P4/mbm). Several types of reaction of the Rare Earth 221 compounds RE2T2X (T = transition metal, X = p-metal) to hydrogen were found in the past. One type is the expansion of the tetragonal unit cell. In such case the H concentration is restricted to 2 H/f.u. (RE2Pd2In with heavy RE). Another type is amorphization (found at RE2Pd2In for early RE = La, Ce, Nd), yielding > 4 H/f.u. Orthorhombic distortion (RE2Ni2In, RE = Nd, Pr,Ce, La) can accommodate up to 7 H/f.u. The monoclinic structure found for RE2Ni2Mg hydrides can apparently have even higher H concentration approaching 8 H/f.u. We have chosen to prepare several Nd2T2X-compounds (T = Ni,Pd and X = In, Sn, Mg) to show the impact of hydrogen absorption on crystal structure and magnetic properties. We have found that Nd2Pd2Mg is representing a new example of the reaction on hydrogenation. The crystal-structures of all previously studied hydrides of Nd2Pd2Sn, Nd2Pd2In, Nd2Ni2In and Nd2Ni2Mg can be obtained by distortion of the starting Mo2FeB2 structure. Due to the rearrangement of atoms in Nd2Pd2MgH8 the structure of the hydride cannot be regarded as simple derivative of the structure of the initial compound. For all the studied RE2T2X the hydrogen absorption leads to the suppression of magnetic order which can be understood as due to changes in conduction–electron concentration due to H bonding.