Leonhard Y. Dorsch

The hydrogenation behavior of FeB type CeGe was investigated. Hydrogenation (deuteration) produces mixtures of two modifications, similar to hydrides of other FeB type phases LnTt (Ln = La, Ce, Nd; Tt = Si, Ge). P-CeGeD0.75(2) (Pnma, a = 8.1603(5) Å, b = 4.0938(3) Å, c = 6.2911(4) Å) crystallizes in the LaGeH structure type (filled FeB type), whereas C-CeGeD0.95(3) (Cmcm, a = 4.2958(2) Å, b = 11.9970(7) Å, c = 4.0885(3) Å) crystallizes in the ZrNiH structure type (filled CrB). Similar to CeSiHx the mixtures feature exceptionally high ferromagnetic ordering temperatures of 21.6(1) K for CeGeDx and 22.1(2) K for CeGeHx (x ≤ 1), with the effective magnetic moments of 2.44(1) μB (CeGeDx) and 2.38(1) μB (CeGeHx) being close to the free ion value of 2.54 μB of Ce3+. The hydrides (deuterides) were studied by neutron powder diffraction (NPD), thermal analysis and magnetic susceptibility measurements.

Two new hydrides, respectively deuterides, of the FeB-type CeSi were synthesized, and their reaction as well as magnetic behavior and structures were studied. Hydrogenation leads to two phases, a kinetic product retaining the FeB structure with hydrogen-filled tetrahedra (LaGeH type, Pnma, P-phase: CeSiD0.82(2)) and the thermodynamically preferred hydrogen-filled CrB-type structure (ZrNiH type, Cmcm, C-phase: CeSiD0.96(1)). Both hydrides are ferromagnets and feature Curie temperatures of 22.4(1) K (C-phase) and 24.3(1) K (P-phase), which are exceptionally high for cerium intermetallics. The effective magnetic moments of μ(Ce3+) = 2.53 μB are very close to the free ion value of 2.54 μB. The compounds were studied using in situ neutron powder diffraction and magnetic characterization and by density functional theory and chemical bonding analysis.