Thermal expansion of the intermediate valence system Sm_1-xY_xS

The thermal expansion, (T), of intermediate valent (IV) Sm1-xYxS single crystals has been measured. For x = 0.7, (T) behaves similar to that published for many other IV systems. For x = 0.28 and x = 0.25, gigantic negative (T) peaks at 172 and 275 K as well as distinct low-T anomalies are observed and ascribed to the vicinity of a first-order valence transition. © 1986.