Thermal expansion of PrRu4P12

We present the results of thermal expansion measurement (T = 1.5-300K) in p olycrystalline PrRu4P12, which exhibits metal-insulator (M-I) transition at around 60 K. There is no significant change in lattice volume at M-I trans ition In the thermal expansion coefficient alpha(T). however. a slight jump (similar to 5 x 10(-7) K-1) is observed at the transition. Magnetic field has no effect on alpha(T) at around the transition. at least up to 70 kOe. Those facts suggest that this M-I transition is a non-magnetic one of secon d order. Much below M-I transition. we found that a broad peak emerges in a lpha(T) under magnetic field. As magnetic held increases. this peak becomes much broader and shifts toward higher temperature almost proportional to t he field. Surprisingly, a negative magnetostriction is observed in this tem perature region. (C) 2000 Elsevier Science B.V. All rights reserved.