Sb NQR study of the filled skutterudite CeFe4Sb12 synthesized under high pressure

We report the results of Sb nuclear quadrupole resonance (NQR) measurements on the filled skutterudite CeFe4Sb12 synthesized under high pressure (HP) and compare them with those for the sample synthesized under ambient pressure (AP) to understand the influence of the Ce-site filling fraction. The NQR spectra for the HP sample are much sharper than those for the AP sample, suggesting that the Ce filling fraction is higher. Also, the nuclear spin-lattice relaxation rate 1/T 1 follows an exponential decrease 1/T 1 ∝ exp(−Δ/k B T), with the gap being Δ/k B = 270 K at temperatures above 100 K, which is larger than that for the AP sample. This result suggests that the c-f hybridization is enhanced by increasing the Ce-site filling fraction.