INTERMEDIATE VALENCE BEHAVIOR OF YB IN YB2NI12(P,AS)(7)

Temperature-dependent specific heat, magnetic susceptibility, and resi stance measurements have been carried out to study the electronic stat e of Yb ion in Yb2Ni12(P,As)(7). All the measurements identify a valen ce fluctuating state for the Yb in both compounds. The electronic cont ributions to the specific heat, gamma, are enhanced compared to those of the corresponding Yttrium compounds. The gamma is temperature depen dent (increasing with lowering temperature) for Yb2Ni12P7 and temperat ure independent for Yb2Ni12As7. The parameters of valence fluctuation for the Yb ion are calculated from magnetic susceptibility using the I CF model and were found to be T-sf approximate to 68 K, E-ex approxima te to 278 K and T-sf approximate to 204 K, E-ex approximate to 1709 K, resulting in the Yb valence of 2.21 and 2.79, for Yb2Ni12(P,As)(7), r espectively. (C) 1998 Elsevier Science B.V. All rights reserved.