Metal-Insulator Transition inPrRu4P12with Skutterudite Structure

The low temperature properties of ${\mathrm{PrRu}}_4{\mathrm{P}}_{12}$ and ${\mathrm{PrOs}}_4{\mathrm{P}}_{12}$ have been studied by means of electrical resistivity and magnetic susceptibility measurements. The resistivity of ${\mathrm{PrRu}}_4{\mathrm{P}}_{12}$ decreases with decreasing temperature from room temperature to about 60 K, but increases sharply with decreasing temperature below 60 K. A metal-insulator transition is found at around 60 K. The susceptibility of the phosphide shows no distinct anomaly at this temperature. No significant change in the powder x-ray diffraction pattern of ${\mathrm{PrRu}}_4{\mathrm{P}}_{12}$ is detected down to 10 K. The anomalous behavior may arise from a $4f$ instability of the Pr ion.