Kondo-lattice formation in cubic-phase YbCu5

The YbCu5 phase with C15b structure has been prepared by a high-pressure technique, and its physical properties have been investigated. The temperature dependence of magnetic susceptibility, electrical resistivity, and specific heat show Kondo-lattice formation. Furthermore, a heavy Fermi-liquid state without magnetic ordering down to 2.0 K is found to evolve below about 6 K. The electronic specific heat coefficient gamma is enhanced to values as large as to 550 mJ/mol K-2. The magnetization measured up to 40 T at 1.6 K has a field dependence which is expected for a Kondo system when the total angular momentum is J>1. All results are in good agreement with the extrapolation of the previous results of YbCu5-xAgx (0.125 less than or equal to x less than or equal to 1.0) for x-->0. The concentration dependence of characteristic temperatures of YbCu5-xAgx can be quantitatively explained by the chemical pressure effect within the compressible Kondo model for the full range of Ag concentration (0.0 less than or equal to x less than or equal to 1.0). The origins of Kondo-lattice formation in YbCu4Ag and the valence transition in YbCu4In are discussed.