tau-NaxV2O5 (x=0.64): A vanadium bronze with an original intergrowth structure

The structure of the new vanadium oxide bronze VOB, tau-Na0.64V2O5, exhibits an intergrowth structure built up by D4 and DZ layer types characteristic of delta-NaxV2O5 and the still unknown zeta-M(x)V(2)O(5) VOB. The tau-Na0.64V2O5 phase, prepared at 650 degrees C, crystallizes in the monoclinic system, space group C2/m, parameters a = 11.674(9) Angstrom, b = 3.650(2)Angstrom, c = 8.905(5), beta = 91.04 degrees, V = 379.65 Angstrom 3(,) Z = 4. The sodium atoms intercalated between the layers favor the cohesion of the network and have the same type of coordination polyhedra between D4-D4 or D4-DZ interspace; this fact explains the original intergrowth structure. Sodium atoms have a different environment in the DZ-DZ interspace. Comparisons with the related structures delta-M(x)V(2)O(5)(M = Ag, Sr, Na), rho-K0.50V2O5, nu-M(x)V(2)O(5)(M = Ca, K, Rb, NH4), epsilon-CuxV2O5, are established and discussed. (C) 1996 Academic Press, Inc.