Crystal structure and Kondo lattice behavior of CeNi9Si4 -: art. no. 224428

We have studied the crystal chemistry and magnetic, thermodynamic, and transport properties of RNi9Si4 with R=La and Ce. These compounds crystallize in a fully ordered tetragonal (space group I4/mcm) variant of the cubic NaZn13 type. The low-temperature properties characterize CeNi9Si4 as a Kondo lattice with a large Sommerfeld value gamma=155(5) mJ/mol K-2 as compared to gamma=33 mJ/mol K-2 of Pauli paramagnetic LaNi9Si4. The temperature dependencies of the specific heat and susceptibility are well described by the degenerate (J=5/2) Coqblin-Schrieffer model with a characteristic temperature T(0)similar or equal to180 K. The large Ce-Ce spacing in CeNi9Si4 (d(Ce-Ce)approximate to5.6 A) implies very weak Ce-Ce intersite exchange interactions which is corroborated by the thermoelectric power S(T) showing close agreement with theoretical results of the degenerate Anderson lattice without intersite interactions. CeNi9Si4 appears to be a model type Kondo lattice system with T-0>Delta(CEF)>T-RKKY where T-0, Delta(CEF) (crystalline electric field), and T-RKKY (Ruderman-Kittel-Kasuya-Yosida) are the characteristic energy scales of the Kondo interaction, crystal field splitting, and Ce-Ce intersite exchange coupling, respectively. CeNi9Si4 shows a remarkably low ratio A/gamma(2)=0.83 (8)x10(-6) muOmega cm(molK/mJ)(2) which is one order-of-magnitude smaller than the usual Kadowaki-Woods ratio of heavy-fermion systems.