COMMENSURATE COMPOSITE STRUCTURE OF BETA- YBV4O8

The crystal structure of beta-YbV4O8 has been determined using a twinn ed specimen and refined as a commensurate composite structure includin g V2O4 framework and Yb cations as substructures. The lattice dimensio ns for V2O4 are a(1)=9.030(5) Angstrom, b(1)=10.72(2) Angstrom, c(1) = 2.876(1) Angstrom, alpha = 89.911(3)degrees; those for the Yb substru cture are a(2) = a(1), b(2) = b(1) - c(1), c(2) = 2c(1). Both substruc tures have the space group P2(1)/n11. The three-dimensional framework of V2O4 is isostructural with those of Fe2O4 in CaFe2O4 and Ti2O4 in N aTi2O4. The Yb cations occupy half of the [8]-coordinated sites in the tunnel of the framework running parallel to [001]. alpha- and beta-Yb V4O8 are polytypes in which the Yb cations are differently arranged wh ile the V2O4 frameworks are essentially the same.