NMR study of antiferromagnetic black sodalite Na8(AlSiO4)6

Al-27 and Si-29 NMR spectra and spin-lattice relaxation in heavily sodium-doped sodalite Na-8(AlSiO4)(6) are presented. The magnetic hyperfine shifts of Al-27 and Si-29 have Curie-Weiss-type temperature dependences with the same Weiss parameter Theta= - 168 +/- 5 K. From an abrupt broadening of the resonance lines the transition temperature to the antiferromagnetic phase T-N= 54 +/- 2 K is determined. Above 200 K thermally activated ionic motion (activation energy, E-A/k(B) = 2000 K) is found in sodalite cages containing Na-4(3+) ions which is much slower than the motion (E-A/k(B) = 750 K) in the cages containing Na-3(3+) ions. (C) 2000 Elsevier Science B.V. All rights reserved.