Variation of the soft modes with composition in the Raman spectra of charge-compensated series of n=2 and 3 Aurivillius phases

Series of charge-compensated solid solutions of n = 2 and 3 Aurivillius phases with structures derived from the Bi(2)A(n-1)B(n)O(3n+3) by fractional substitution in the (Bi2O2)(2+) blocks as well as in the perovskite-type blocks (A(n-1)B(n)O(3n+1))(2-) have been prepared by solid state reaction. Raman spectra of two series Bi2-xPbxSr1-xNdxNb2O9 and Bi4-xPbxTi3-xNbxO12 for 0 less than or equal to x less than or equal to 1 were obtained in the range of 15-200 cm at room temperature. Significant changes with composition are observed only for the low Raman shift features assigned to soft modes and can be related to the ferroelectric to paraelectric phase transition in these materials. (C) 1997 Elsevier Science Ltd.