Anomalous Thermal Expansion in Intermediate Valence Compound Ce2Ni3Si5

The linear thermal expansion coefficients in the intermediate valence system Ce2Ni3Si5 were determined along the main crystallographic directions by means of neutron diffraction in the temperature range 10-300 K. The anomalous contribution to thermal expansion due to valence instabilities of cerium was estimated by employing the virtual mix approach. The magnitude of the anomalous magnetic contribution to the volume coefficient of thermal expansion in this intermetallic system is about 1.2 x 10(-5) K-1. The observed effect is caused by a strong temperature dependence of the degree of the partial delocalization of the cerium 4f electrons in the intermediate valence regime. The effective Kondo temperature of Ce2Ni3Si5 T-K = 140 K obtained in the present work is in a very good agreement with the earlier estimates based on the temperature dependences of the macroscopic magnetic and thermodynamic properties.