Structure, magnetic and electrical properties of CeIrSb and its hydride CeIrSbH0.8

The ternary antimonide CeIrSb absorbs hydrogen under moderate temperature and pressure conditions (4 MPa and 573 K), leading to the hydride CeIrSbH_0.8. The crystal structures of both compounds have been investigated by X-ray diffraction on powders and single crystals: TiNiSi type, space group Pnma, a=735.07(7), b=456.93(4), c=792.8(1) pm, R1/wR2=0.0206/0.0395, 601 F² values for CeIrSb and a=728.16(14), b=460.35(6), c=825.87(2) pm, R1/wR2=0.0322/0.0735, 528 F² values for CeIrSbH_0.8 with 20 variables per refinement. Hydrogenation induces both an increase of the cell volume V (+4%) and a strongly anisotropic expansion of the unit cell with a maximum of 4.3% in the c direction, leading to a significant increase of the Ce-Ir and Ce-Ce distances in this direction. The H-insertion into CeIrSb leads to a magnetic transition from intermediate valence to antiferromagnetic behavior (T_N=7.0 K) evidenced by magnetization, electrical resistivity and specific heat measurements. This transition can be explained on the basis of the Doniach diagram considering the J_cf interaction between the 4f(Ce) and conduction electrons.