Intermediate valence behavior of Yb in Yb2Ni12(P,As)7

Temperature-dependent specific heat, magnetic susceptibility, and resistance measurements have been carried out to study the electronic state of Yb ion in Yb2Ni12(P,As)(7). All the measurements identify a valence fluctuating state for the Yb in both compounds. The electronic contributions to the specific heat, gamma, are enhanced compared to those of the corresponding Yttrium compounds. The gamma is temperature dependent (increasing with lowering temperature) for Yb2Ni12P7 and temperature independent for Yb2Ni12As7. The parameters of valence fluctuation for the Yb ion are calculated from magnetic susceptibility using the ICF model and were found to be T-sf approximate to 68 K, E-ex approximate 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), respectively. (C) 1998 Elsevier Science B.V. All rights reserved.