New Hydrides REScSiH and REScGeH (RE = La, Ce): Structure, Magnetism, and Chemical Bonding

Abstract

The La2Sb type silicides and germanides REScSi and REScGe (RE = La, Ce) were synthesized from the elements by arc-melting and subsequent annealing at 1170 K. The structures of LaScSi and LaScGe were refined on the basis of single-crystal X-ray diffraction data. The structures consist of a stacking of two-dimensional [ScSi] networks with ScSi4/4 rectangles, which are separated by rare earth atoms, which leave RE4/4 tetrahedral voids. The latter can be completely filled by hydrogenation leading to the quaternary hydrides REScSiH and REScGeH (RE = La, Ce). Hydrogenation is accompanied by an anisotropic unit cell expansion, i.e., a decrease in the a lattice parameter and a strong increase in c. The H-insertion into the compounds based on cerium induces for both a quasi-2D structure, a strong decrease of their antiferromagnetic ordering; for instance T N decreases from 26 to 3.0 K in the sequence CeScSi → CeScSiH and the occurrence of the influence of the Kondo effect evidenced by electrical resistivity and specific heat measurements. The electronic structure calculation applied to CeScSi and its hydride reveals strong Ce−H bonding influencing the magnetic properties of CeScSiH.

Hydrogenation studies on NdScSi and NdScGe

“…This result is very similar to that observed previously for CeScGe [16], GdScGe [17] or GdTiGe for which hydrogen insertion completely destroys the long range ferromagnetic order [45]. Density Functional Theory (DFT) calculations would be helpful to explain such a change in the magnetic properties, notably to determine the role of the electronic effect of H-atom insertion versus that of volume cell expansion.…”

“…The Guinier patterns of the NdScSi and NdScGe samples clearly indicated isotypism with the respective cerium compounds [16]. Analyses of the two data sets were in agreement with space group I4/mmm and the positional parameters of CeScSi [16] were taken as starting values.…”

“…Analyses of the two data sets were in agreement with space group I4/mmm and the positional parameters of CeScSi [16] were taken as starting values. Both structures were then refined with SHELXL-97 [23,24] (full matrix least squares on F o 2 ) with anisotropic displacement parameters for all sites.…”

“…The hydrogen insertion has a drastic influence on the magnetic ground state. Recent examples are the pairs CeScSi/CeScSiH [16] and GdScGe/GdScGeH [17].I n both cases hydrogenation leads to a drastic decrease of the magnetic ordering temperature: (i) T N decreases from 26 to 3 K from CeScSi to CeScSiH and (ii) the 350 K ferromagnet GdScGe switch to the 6 K antiferromagnet GdScGeH.…”

The magnetocaloric properties of GdScSi and GdScGe

“…The single crystal data sets both showed body-centred tetragonal lattices and no further systematic extinctions, in agreement with LaScSi [14] and CeScSi [2], space group I4/mmm. The positional parameters of LaScSi [14] were taken as starting values and both structures were refined using the SHELXLe97 code (full-matrix least-squares on F 2 ) [15,16] with anisotropic atomic displacement parameters for all atoms.…”