Pressure-induced volume anomaly of intermediate valence compound Sm0.9La0.1S

Thermal expansion of intermediate valence compound Sm(0.9)Lao(0.1)S has bee n measured under high pressure up to 21 GPa in the temperature range, 4.2 l ess than or equal to T less than or equal to 300 K. It is found that the th ermal expansion shows a smooth variation below 0.5 GPa but an anomalously l arge expansion, i.e., a large negative thermal expansion coefficient is obs erved at low temperature above 0.5 GPa. These results are related to the pr essure-induced metal-insulator transition. The negative anomaly in the ther mal expansion coefficient is suggested to be due to the negative Gruneisen parameter of the energy gap. (C) 2001 Elsevier Science B.V. All rights rese rved.