Neutron diffraction and FT-Raman study of ion-exchangeable layered titanates and niobates

On the basis of the structure refinements of neutron powder diffraction dat a, the Raman bands of A(2)La(2)Ti(3)O(10) (A = Na, K, and Rb) were successf ully assigned. The existence of a linear A-O-Ti linkage along the c axis in this structure resulted in the strong dependence of their Raman bands on t he nature of the A atom. In contrast, the Raman spectra of A(2)La(2)Ti(3)O( 10). xH(2)O, ACa(2)Nb(3)O(10), and ALaNb(2)O(7) (A = Na, K, Rb, and Cs) wit h no linear A-O-Ti or A-O-Nb connection were essentially the same in the 10 00-400 cm(-1) region regardless of a change of the A atom. In particular, t he band around 930 cm(-1) attributed to the terminal Nb-O bond with double- bond character showed no shift even in the Raman spectra of CsB2Nb3O10 (B = Ca, Sr, and Ba despite a remarkable change of lattice volume depending on the B atom. These results indicate that the Raman shift of ion-exchangeable perovskites depends mainly on the way that the interlayer alkali-metal ato ms are connected with the octahedra in perovskite layers.