Magnetic and electrical properties of filled skutterudite compound (Sm1-xRx)Ru4P12 (R=La, Y)

Sm-site substitution effect on filled skutterudite compound SmRu4P12, which shows an intriguing metal-insulator (MI) transition, has been studied by electrical resistivity, magnetic susceptibility and specific heat measurements. Single-phase polycrystalline (Sm1-xLax)Ru4P12 (x=0.1, 0.2, 0.3) and (Sm1-xYx)Ru4P12 (x=0.1, 0.2, 0.3) have been prepared at high temperature and high pressure. Both La and Y substitutions cause a large suppression of the semiconductor-like behavior at low temperature. The MI transition temperature (T-MI) shifts to lower temperature with increasing La concentration. This change is qualitatively consistent with external pressure experiments. It could be due to a negative chemical pressure effect induced by La substitution. However, T-MI also shifts to lower temperature with increasing Y concentration, which is expected for a positive chemical pressure effect. The results suggest that introducing a disorder into the periodicity of Sm affects sensitively the MI transition in this system.