Temperature-dependent nuclear quadrupole resonance (NQR) investigations on the 121,123 Sb nuclei in filled skutterudites MFe 4 Sb 12 (M=Na, Ca, La) are reported. These new compounds show a nice interplay of ferromagnetic and antiferromagnetic correlations best seen in the relaxation rate. Substructures observed in the 121,123 Sb NQR spectra give strong evidence for static (or dynamic) disorder on the filler site. Therefore, we performed ab-initio linearized augmented plane wave (LAPW) calculations for the Sb NQR substructure frequencies for various La and Ca displacement along different direction and compared the obtained values with the experimental data.