Local distortion induced metal-to-insulator phase transition in PrRu4P12.

Extended x-ray absorption fine structure (EXAFS) experiments have been carried out on PrRu(4)P(12) and PrOs(4)P(12) to study the metal-to-insulator (MI) phase transition in PrRu(4)P(12). No Pr displacement was observed across the MI transition temperature from the EXAFS data. Instead, our EXAFS data clearly show that a Ru displacement is associated with this MI transition. The very high Debye temperature for the Ru-P bond (Theta(D) = 690 K) suggests that a slight rotation/displacement of relatively rigid RuP(6) octahedra leads to this small Ru displacement, which accompanies the MI transition at 62 K in PrRu(4)P(12).