Vibrational properties of ferroelectric hexagonal tungsten bronzes AB(x)W(3-x)O(9),where A = K, Rb, Cs and B=Nb, Ta, Zr, Cr

Powder x-ray diffraction, Raman and IR studies were performed for a number of ferroelectric hexagonal tungsten bronzes of the formula AB(x)W(3-x)O(9), where A = K, Rb, Cs and B = Nb, Ta, Zr and Cr. The observed vibrational mo des were assigned to the respective motions of atoms in the unit cell. The x-ray data revealed that the partial substitution of W atoms by atoms with lower valence results in shortening of the W - W distances within the xy pl ane and elongation in the z direction. These changes in the crystal structu re were correlated with the vibrational data. The measured spectra indicate d also the presence of some kind of ordering in the potassium-and rubidium- zirconium bronzes, and the presence of a large number of defects for the ch romium bronzes. Copyright (C) 2001 John Wiley & Sons, Ltd.