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

Abstract Thermal expansion of intermediate valence compound Sm 0.9 La 0.1 S has been measured under high pressure up to 2.1 GPa in the temperature range, 4.2⩽ T ⩽300 K. It is found that the thermal expansion shows a smooth variation below 0.5 GPa but an anomalously large expansion, i.e., a large negative thermal expansion coefficient is observed at low temperature above 0.5 GPa. These results are related to the pressure-induced metal–insulator transition. The negative anomaly in the thermal expansion coefficient is suggested to be due to the negative Gruneisen parameter of the energy gap.