Temperature and pressure dependence of the Yb valence state in YbMn∼0.17Si∼1.89.

Single crystals of the non-stoichiometric YbMn_∼0.17Si_∼1.89 intermetallic compound were investigated by room-temperature x-ray diffraction as well as by temperature and pressure-dependent x-ray absorption experiments at the Yb L₃ edge. The crystal structure can be described in the orthorhombic space group Cmcm or in the non-centrosymmetric P2₁ monoclinic space group. In both cases, the cell comprises two Yb sites of identical multiplicity with close coordination numbers and interatomic distances. The average Yb valence is found independent of temperature ν_av ∼ 2.42. Such a low Yb valence is hardly compatible with the occurrence of local magnetism on Yb inferred from a previous study. The pressure dependence of the Yb valence at 10 K does not reveal any first-order transition. The average Yb valence increases continuously under pressure but remains far from trivalency (ν_av ∼2.63) even under the highest external pressure used of 37 GPa. [ABSTRACT FROM AUTHOR]