An x-ray diffraction and Raman spectroscopy investigation of A-site substituted perovskite compounds: the (Na-1-K-x(x))(0.5)Bi0.5TiO3 (0 <= x <= 1) solid solution

The (Na1-xKx)(0.5)Bi0.5TiO3 perovskite solid solution is investigated using x-ray diffraction (XRD) and Raman spectroscopy in order to follow the stru ctural evolution between the end members Na0.5Bi0.5TiO3 (rhombohedral at 30 0 K) and K0.5Bi0.5TiO3 (tetragonal at 300 K). The Raman spectra are analyse d with special regard to the hard modes and suggest the existence of nano-s ized Bi3+TiO3 and (Na1-2xK2x)+TiO3 clusters. The complementary use of XRD a nd Raman spectroscopy suggests, in contrast to previous reported results, t hat the rhombohedral ct tetragonal phase transition goes through an interme diate phase, located at 0.5 less than or equal to x less than or equal to 0 .80. The structural character of the intermediate phase is discussed in the Light of sub- and super-group relations.