Intermediate Valence Behavior of Yb₂Cu₉Al₈

Intermediate valence behavior is frequently observed in compounds containing Ce, Yb, Eu, Sm, or Tm. In the current talk, I will discuss synthesis and characterization of an intermetallic compound Yb₂Cu₉Al₈ which crystallizes in the Th₂Zn₁₇ structure type. An excitation energy E_ex/k_B of 319 K and a spin fluctuations temperature T_sf of 60 K are characteristic of its intermediate valence behavior, whereas the valence state of Yb is estimated to be close to 2.04 for the low-temperature region. The valence gradually evolves to the value of 2.80 at T = 400 K. The Sommerfeld coefficient of g_exp = 59 mJ/mol_Yb K² indicates a moderate effective mass enhancement, together with a finite density of states at the Fermi level. The latter is also confirmed by the band structure calculations.