Valence behaviour of ytterbium in YbNiGa_4

摘要

The ternary compound YbNiGa_4 was synthesized from the elements by high-frequency induction melting in an argon atmosphere. No evidence for the existence of a homogeneity range was observed from X-ray powder diffraction data. The crystal structure of YbNiGa_4 was refined using X-ray single-crystal diffraction data: YniAl_4 type, space group Cmcm, Pearson symbol oC24, a = 4.0868(1) A, b= 15.2829(5) A, c = 6.5049(2) A, Z = 4, R(F) = 0.044 for 255 symmetry independent reflections. The coordination numbers are 19 for Yb, 12 for Ga and 9 for Ni. At ambient pressure, the electron configuration of ytterbium, as derived from magnetisation/magnetic susceptibility and X-ray absorption spectroscopy (XAS) measurements and confirmed by band structure calculations, is intermediate between 4f~(13) and 4f~(14). With increasing pressure, the 4f~(14) (Yb~(2+)) is continuously converted to 4f~(13) (Yb~(3+)).