Local Distortion Induced Metal-to-Insulator Phase Transition in PrRu$_4$P$_{12}$

TL;DR

This study uses EXAFS experiments to reveal that a Ru atom displacement, rather than Pr displacement, triggers the metal-insulator transition in PrRu$_4$P$_{12}$ at 62 K, likely due to RuP$_6$ octahedra rotation.

Contribution

The paper demonstrates that Ru displacement, not Pr displacement, is responsible for the MI transition in PrRu$_4$P$_{12}$, highlighting the role of RuP$_6$ octahedra rotation.

Findings

Ru displacement correlates with the MI transition.

No Pr displacement observed across the transition.

High Debye temperature indicates rigid RuP$_6$ octahedra.

Abstract

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$_{12}$.