ANOMALOUS BEHAVIOR OF THE COEFFICIENT OF THERMAL-EXPANSION IN INTERMEDIATE VALENCE SYSTEMS

The electronic contribution to the coefficient of thermal expansion alpha for intermediate valence systems is related to the temperature derivative of 4f-level occupancy. Using the Green's function technique, the occupancy of the 4f-level and its temperature derivative have been evaluated self-consistently with the periodic Anderson model in the limit of infinite Coulomb repulsion and upto quadratic terms in hybridization interaction. The influence of the 4f-level position with respect to the conduction band and the strength of hybridization interaction on the temperature dependence of the coefficient of thermal expansion is investigated. It has been noted that alpha displays a peak-like behaviour as a function of temperature and also can be both positive and negative as observed in some experiments.