NMR studies of Ce-based filled skutterudites and

We have carried out the 31 P NMR measurements on Ce-based filled skutterudites CeFe 4 P 12 and CeRu 4 P 12 , which display semiconductive behaviors due to the strong hybridization between Ce 4f and conduction electrons. At higher temperatures, the nuclear spin-lattice relaxation rate 1 / T 1 obeys an activation behavior 1 / T 1 ∝ exp [ - E g / k B T ] with an energy gap of E g / k B = 1300 and 1000 K for CeFe 4 P 12 and CeRu 4 P 12 , respectively. These are in good agreement with the values measured by various measurements.