مطالعات NMR روي M2GA6TE01

NMR Studies on M2Ga6Te10

The phases M2Ga6Te1Q (M. Li, Na) crystallize in space group R32 (No. 155, Z=2) with the lattice constants: a = 1436.9 (2), c =1759.0(4) pm (T = 180 K, Li2Ga6Te1Q) and a = 1458.0(1), c = 1776.0 (4) pm (T=290 K, Na2Ga6Te10). The crystal structures are based on a Beta-Mn like "eutactic" packing of 20 Te^2-in the pseudo-cubic cell with 12 % of the tetrahedral holes filled by Ga^3+ in an ordered way and Liʹ/Na+ in all metaprismatic holes. The pseudo-cubic unit cell (Z=2 for M2Ga6Te1Q) contains 100 tetrahedral and 4 metaprismatic holes. Thus the initial assumption Li+ in Li2Ga6Telo and Na+ in Na2Ga6Te10 might occupy a fraction of the tetrahedral holes in a statistical way (like the highly mobile Ag+ in the optimized Ag+ ionic conductor alpha-RbAg4I5), was not confirmed. Instead, the Li+/Na+ions occupy those positons which correspond to the immobile Rb+ in alpha-RbAg4I5. MAS-NMR measurements, including multiple quantum NMR, allowed the two different crystallographic M+` sites to be distinguished unambiguously by separate ʹLi and 23Na signals, respectively. The assignment of the NMR signals was supported by measurements of samples in which Li+was partly substituted by larger cottons (Sn^2+, Pb^2+). The results in this paper corresponds with the published by L. Kienle, H. J. Deiseroth and M. Hartung.