NMR study of antiferromagnetic black sodalite Na8(AlSiO4)6

27Al and 29Si NMR spectra and spin–lattice relaxation in heavily sodium-doped sodalite Na8(AlSiO4)6 are presented. The magnetic hyperfine shifts of 27Al and 29Si have Curie–Weiss-type temperature dependences with the same Weiss parameter Θ=−168±5 K. From an abrupt broadening of the resonance lines the transition temperature to the antiferromagnetic phase TN=54±2 K is determined. Above 200 K thermally activated ionic motion (activation energy, EA/kB=2000 K) is found in sodalite cages containing Na43+ ions which is much slower than the motion (EA/kB=750 K) in the cages containing Na33+ ions.