Uranium substitution for tungsten in the Bi2WO6-Bi2UO6 system Formation of a broad high-temperature solid solution

Polythermic studies of Bi2WO6-Bi2UO6 system revealed existence of a broad Bi2W1-xUxO6 solid solution with the Aurivillius-type structure Below 750 degrees C the homogeneity area is narrow (x <= 0 12) but extends significantly at higher temperatures (up to ca 75% Bi2UO6 at 1025 degrees C) The solid solution retains orthorhombic symmetry over the entire compositional range but substitution of U for W results in significant lowering of second harmonic intensity and Curie point suggesting at high substitution degrees a very close approach to the archetypic body-centered tetragonal centrosymmetric structure The known Bi2WO6-based solid solutions are discussed in terms of thermal stability and a general geometrical explanation is suggested Incorporation of large cations into the B perovskitic positions of [Bi2O2][A(n-1)BnO(3n+1)] Aurivillius structures seems yet to be restricted by the n = 1 case (C) 2010 Elsevier Masson SAS All rights reserved