An x-ray diffraction and Raman spectroscopy investigation of A-site substituted perovskite compounds: the (Na1-xKx)0.5Bi0.5TiO₃(0lexle1) solid solution

The (Na 1 - x K x ) 0.5 Bi 0.5 TiO 3 perovskite solid solution is investigated using x-ray diffraction (XRD) and Raman spectroscopy in order to follow the structural evolution between the end members Na 0.5 Bi 0.5 TiO 3 (rhombohedral at 300 K) and K 0.5 Bi 0.5 TiO 3 (tetragonal at 300 K). The Raman spectra are analysed with special regard to the hard modes and suggest the existence of nano-sized Bi 3+ TiO 3 and (Na 1 - 2 x K 2 x ) + TiO 3 clusters. The complementary use of XRD and Raman spectroscopy suggests, in contrast to previous reported results, that the rhombohedral tetragonal phase transition goes through an intermediate phase, located at 0.5 x 0.80. The structural character of the intermediate phase is discussed in the light of sub- and super-group relations.